Journal of Mechanical Engineering 2013 7-8 by Darko Svetak

http://www.sv-jme.eu

59 (2013) 7-8

Since 1955

Papers

425

Steven den Dunnen, Gert Kraaij, Christian Biskup, Gino M.M.J. Kerkhoffs, Gabrielle J.M. Tuijthof: Pure Waterjet Drilling of Articular Bone: An in vitro Feasibility Study

433

Ming Xu, Bo Jin, Guojin Chen, Jing Ni: Speed-Control of Energy Regulation Based Variable-Speed Electrohydraulic Drive

443

Sreten Perić, Bogdan Nedić, Dragan Trifković, Mladen Vuruna: An Experimental Study of the Tribological Characteristics of Engine and Gear Transmission Oils

451

Sedat Karabay: Modification of Conductive Material AA6101 of OPGW Conductors against Lightning Strikes

462

Sedat Yayla: Flow Characteristic of Staggered Multiple Slotted Tubes in the Passage of a Fin Tube Heat Exchanger

473

Baoping Cai, Yonghong Liu, Aibaibu Abulimiti, Renjie Ji, Yanzhen Zhang, Xin Dong, Yuming Zhou: Optimal Design Based on Dynamic Characteristics and Experimental Implementation of Submersible Electromagnetic Actuators

Nenad Popovic, Goran D. Putnik, Ondrej Jasko, Jovan Filipovic: 483 A Contribution for a Pragmatics-Based Approach to Concurrent Engineering Implementation

Journal of Mechanical Engineering - Strojniški vestnik

Contents

7-8 year 2013 volume 59 no.

Strojniški vestnik Journal of Mechanical Engineering

Strojniški vestnik – Journal of Mechanical Engineering (SV-JME) Aim and Scope The international journal publishes original and (mini)review articles covering the concepts of materials science, mechanics, kinematics, thermodynamics, energy and environment, mechatronics and robotics, fluid mechanics, tribology, cybernetics, industrial engineering and structural analysis. The journal follows new trends and progress proven practice in the mechanical engineering and also in the closely related sciences as are electrical, civil and process engineering, medicine, microbiology, ecology, agriculture, transport systems, aviation, and others, thus creating a unique forum for interdisciplinary or multidisciplinary dialogue. The international conferences selected papers are welcome for publishing as a special issue of SV-JME with invited co-editor(s). Editor in Chief Vincenc Butala University of Ljubljana Faculty of Mechanical Engineering, Slovenia Technical Editor Pika Škraba University of Ljubljana Faculty of Mechanical Engineering, Slovenia Editorial Office University of Ljubljana (UL) Faculty of Mechanical Engineering SV-JME Aškerčeva 6, SI-1000 Ljubljana, Slovenia Phone: 386-(0)1-4771 137 Fax: 386-(0)1-2518 567 E-mail: info@sv-jme.eu, http://www.sv-jme.eu Print DZS, printed in 450 copies Founders and Publishers University of Ljubljana (UL) Faculty of Mechanical Engineering, Slovenia University of Maribor (UM) Faculty of Mechanical Engineering, Slovenia Association of Mechanical Engineers of Slovenia Chamber of Commerce and Industry of Slovenia Metal Processing Industry Association Cover: The impact of a waterjet on porcine femural bone. Clinical application of waterjet technology for machining of tough human tissues such as bone can be attractive as it offers clean sharp cuts without tissue heating. Additionally, water supply is possible via flexible tubings, which opens possibilities for minimally invasive surgical access.

Image Courtesy: Photo: Sam Rentmeester

International Editorial Board Koshi Adachi, Graduate School of Engineering,Tohoku University, Japan Bikramjit Basu, Indian Institute of Technology, Kanpur, India Anton Bergant, Litostroj Power, Slovenia Franci Čuš, UM, Faculty of Mech. Engineering, Slovenia Narendra B. Dahotre, University of Tennessee, Knoxville, USA Matija Fajdiga, UL, Faculty of Mech. Engineering, Slovenia Imre Felde, Obuda University, Faculty of Informatics, Hungary Jože Flašker, UM, Faculty of Mech. Engineering, Slovenia Bernard Franković, Faculty of Engineering Rijeka, Croatia Janez Grum, UL, Faculty of Mech. Engineering, Slovenia Imre Horvath, Delft University of Technology, Netherlands Julius Kaplunov, Brunel University, West London, UK Milan Kljajin, J.J. Strossmayer University of Osijek, Croatia Janez Kopač, UL, Faculty of Mech. Engineering, Slovenia Franc Kosel, UL, Faculty of Mech. Engineering, Slovenia Thomas Lübben, University of Bremen, Germany Janez Možina, UL, Faculty of Mech. Engineering, Slovenia Miroslav Plančak, University of Novi Sad, Serbia Brian Prasad, California Institute of Technology, Pasadena, USA Bernd Sauer, University of Kaiserlautern, Germany Brane Širok, UL, Faculty of Mech. Engineering, Slovenia Leopold Škerget, UM, Faculty of Mech. Engineering, Slovenia George E. Totten, Portland State University, USA Nikos C. Tsourveloudis, Technical University of Crete, Greece Toma Udiljak, University of Zagreb, Croatia Arkady Voloshin, Lehigh University, Bethlehem, USA President of Publishing Council Jože Duhovnik UL, Faculty of Mechanical Engineering, Slovenia General information Strojniški vestnik – Journal of Mechanical Engineering is published in 11 issues per year (July and August is a double issue). Institutional prices include print & online access: institutional subscription price and foreign subscription €100,00 (the price of a single issue is €10,00); general public subscription and student subscription €50,00 (the price of a single issue is €5,00). Prices are exclusive of tax. Delivery is included in the price. The recipient is responsible for paying any import duties or taxes. Legal title passes to the customer on dispatch by our distributor. Single issues from current and recent volumes are available at the current single-issue price. To order the journal, please complete the form on our website. For submissions, subscriptions and all other information please visit: http://en.sv-jme.eu/. You can advertise on the inner and outer side of the back cover of the magazine. The authors of the published papers are invited to send photos or pictures with short explanation for cover content. We would like to thank the reviewers who have taken part in the peerreview process.

ISSN 0039-2480 © 2013 Strojniški vestnik - Journal of Mechanical Engineering. All rights reserved. SV-JME is indexed / abstracted in: SCI-Expanded, Compendex, Inspec, ProQuest-CSA, SCOPUS, TEMA. The list of the remaining bases, in which SV-JME is indexed, is available on the website.

The journal is subsidized by Slovenian Book Agency. Strojniški vestnik - Journal of Mechanical Engineering is also available on http://www.sv-jme.eu, where you access also to papers’ supplements, such as simulations, etc.

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Strojniški vestnik - Journal of Mechanical Engineering 59(2013)7-8 Contents

Contents Strojniški vestnik - Journal of Mechanical Engineering volume 59, (2013), number 7-8 Ljubljana, July-August 2013 ISSN 0039-2480 Published monthly

Papers Steven den Dunnen, Gert Kraaij, Christian Biskup, Gino M.M.J. Kerkhoffs, Gabrielle J.M. Tuijthof: Pure Waterjet Drilling of Articular Bone: An in vitro Feasibility Study 425 Ming Xu, Bo Jin, Guojin Chen, Jing Ni: Speed-Control of Energy Regulation Based Variable-Speed Electrohydraulic Drive 433 Sreten Perić, Bogdan Nedić, Dragan Trifković, Mladen Vuruna: An Experimental Study of the Tribological Characteristics of Engine and Gear Transmission Oils 443 Sedat Karabay: Modification of Conductive Material AA6101 of OPGW Conductors against Lightning Strikes 451 Sedat Yayla: Flow Characteristic of Staggered Multiple Slotted Tubes in the Passage of a Fin Tube Heat Exchanger 462 Baoping Cai, Yonghong Liu, Aibaibu Abulimiti, Renjie Ji, Yanzhen Zhang, Xin Dong, Yuming Zhou: Optimal Design Based on Dynamic Characteristics and Experimental Implementation of Submersible Electromagnetic Actuators 473 Nenad Popovic, Goran D. Putnik, Ondrej Jasko, Jovan Filipovic: A Contribution for a Pragmatics-Based Approach to Concurrent Engineering Implementation 483

Received for review: 2012-12-21 Received revised form: 2013-02-22 Accepted for publication: 2013-04-09

Pure Waterjet Drilling of Articular Bone: An in vitro Feasibility Study

den Dunnen, S. – Kraaij, G. – Biskup, C. – Kerkhoffs, G.M.M.J. – Tuijthof, G.J.M. Steven den Dunnen1* – Gert Kraaij1,4 – Christian Biskup3 – Gino M.M.J. Kerkhoffs2 – Gabrielle J.M. Tuijthof1,2 1 Delft

University of Technology, Department of Biomechanical Engineering, The Netherlands 2 Academic Medical Center, Department Orthopedic Surgery, The Netherlands 3 (formerly) Leibniz University Hannover, Institute of Materials Science, Germany 4 Leiden University Medical Center, Department Orthopaedics, The Netherlands

The clinical application of waterjet technology for machining tough human tissues, such as articular bone, has advantages, as it produces clean sharp cuts without tissue heating. Additionally, water supply is possible via flexible tubing, which enables minimally invasive surgical access. This pilot study investigates whether drilling bony tissue with pure waterjets is feasible. Water pressures between 20 and 120 MPa with an orifice of 0.6 mm were used to create waterjets to drill blind borings in the talar articular surface of cadaveric calcaneus bones of human, sheep, goats and pigs. A stand-off distance between 2.5 and 5.5 mm and a jet-time of 5 seconds were chosen. The depth of the holes was measured using a custom-adapted dial gauge. At least 30 MPa of water pressure is required to penetrate the human and goat specimens, and 50 MPa for the pig and sheep specimens. Overall, the machined holes were conically shaped and increased in depth with an increase of pressure. Above certain pressure levels, pure waterjets can be used for machining holes in articular bone, thereby opening a window for further research on pure waterjet drilling in orthopedics. Keywords: pure water jet, water jet drilling, drilling articular bone, orthopedic treatment, water pressure

0 INTRODUCTION Since its first successful application in the 1970s by Hashish, waterjet technology has been applied in many industries [1] such as cutting cardboard, metals and frozen food [2] and [3]. For medical applications, differences in the material properties of human organs allow the precise dissection of soft tissue without damaging stronger tissues such as nerves or veins [4] to [6]. The absence of tissue heating [7] and the always sharp and clean cut, in particular, has led to the further exploration of waterjet technology for applications in orthopedic surgery [8] to [13]. Research in this has field primarily involved cutting cortical bone with abrasive (containing small solid particles) waterjets for preparation for arthroplasty [8] to [10] and [13] to [15]. Additionally, using waterjet technology allows for water supply via flexible tubing, which enables minimally invasive surgical access. The focus of this study will be on the latter application, for which it is necessary to investigate the feasibility of pure waterjets to drill holes in articular bone. Drilling holes in bones is frequently performed in, for example, microfracturing treatments and screw fixations [16] and [17]. Knowledge from previous studies cannot be used to determine the feasibility of pure waterjet drilling in articular bone, as this differs entirely from abrasive waterjet cutting. The differences lie in the interaction between the waterjet and the material,

which causes the penetration depth using pure waterjet drilling to be less than for abrasive waterjet cutting. When cutting, the waterjet is moved over the material with a set feed speed (Fig. 1). The waterjet first strikes the edge of the material and exits at the opposite side. When drilling, the waterjet does not continue its path through all the material, but changes its trajectory 180 degrees after reaching the bottom of the hole (Fig. 1) [18] and [19]. Therefore, interference with the incoming waterjet is inevitable [2] and [3]. This leads to a disruption of the integrity of the waterjet and a turbulent flow in the boring, causing the impact pressure and kinetic energy to diminish [2], [18] and [20]. To improve the cutting capacity of water jets, previous research involved the addition of abrasives to the waterjet [21]. Special biocompatible abrasives have been proposed and tested in a lab settings [8] and [15], but thus far no clinical trials have been performed to verify their safe use. Other than that, articular bone toughness is presumably less than that of diaphyseal cortical bone. Therefore, an abrasive suspension might not be necessary in order to penetrate the articular bone. Pure waterjets are investigated in this study, because they contribute to patients’ safety. The aim of this study is to determine the feasibility of pure waterjet drilling in articular bone, and indicate the minimum water pressure required to penetrate articular bone. The sub-goals are: a) determination of the variation in the minimum penetration pressure.

*Corr. Author’s Address: Delft University of Technology, Mekelweg 2, 2628CD, Delft, The Netherlands, s.dendunnen@tudelft.nl

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This variation can also be expected amongst the patients receiving surgical treatment and is therefore of concern for patient safety; b) global analysis of the shape of holes in bone, because specific hole profiles are desired for certain orthopedic treatments.

Fig. 1. The difference in waterjet flow direction between waterjet drilling and cutting

1 MATERIALS AND METHODS A theoretical overview is established regarding a) the main parameters that influence the machining capacity of a pure waterjet, and b) the expected consecutive steps of the waterjet-material interaction when drilling a hole in articular bone. Based on this, starting conditions for the pilot study were chosen, and interpretations of the results were facilitated. In addition to the mechanical properties of the material, the two dominant parameters for the machining capacity of a waterjet are the velocity and the volume of the water that is striking the object [2]. An increase in either one of these parameters will increase the kinetic energy of the waterjet, which is transferred to the material on impact. Assuming water is incompressible, the relation between the waterjet velocity vliquid [m/s] and the water pressure P [N/m2] and density ρ [kg/m3] is given by Bernoulli’s equation:

vliquid = µ v ⋅

2P . (1) ρ

The velocity coefficient μv depends on the waterjet setup that is used, but is usually between 0.86 and 0.97 [22]. As the μv and ρ remain constant, the waterjet velocity is dependent solely on the water pressure. Therefore, varying the pressure was chosen. When drilling in articular bone, the waterjet needs to penetrate cartilage, subchondral bone and 426

trabecular bone, consecutively. Each layer has a specific composition and material properties [23]. The mechanical properties that play a significant role in the effectiveness of waterjet machining are, in order of importance, the tensile strength, compressive strength, modulus of elasticity and hardness [3]. An increase in any of these properties will increase the strength of the material and thus the resistance to a waterjet. The tensile strength at the tissue level for articular cartilage, cortical bone and trabecular bone in human femora are approximately 30 MPa [24], 120 MPa [25] and [26] and 20 MPa [27] and [28], respectively. Even though these numbers alone cannot be used to predict whether a waterjet can penetrate the bone tissue, the subchondral bone layer will most likely offer the highest resistance. The cartilage is expected to be machined the most easily as the modulus of elasticity and the hardness is lower than for trabecular bone [26] and [29]. In summary, the feasibility of drilling articular bone with pure water greatly relies on the ability to penetrate the subchondral plate. Increasing the water pressure will increase the waterjet’s ability to penetrate this bone layer. Waterjet drilling of bony tissue was performed on an industrial waterjet cutting system (Fig. 2a) equipped with a high-pressure intensifier pump DU 400-4/PL. The cutting table was controlled by a Berger Lahr NC control system (Posab 3300), which also regulated the waterjet time. A waterjet nozzle diameter (Fig. 2b) of 0.6 mm and a jet time of five seconds was used in all experiments. The diameter of the machined holes created by this nozzle were most comparable to the 1.3 mm diameter holes that are frequently created in orthopedic microfracturing. Based on the experiments of Honl et al. [10], the water pressure was varied between 20 and 120 MPa. The genuine pressure was measured directly in front of the water jet cutting head at a sample frequency of 50 Hz with a WIKA high pressure transducer (type 891.23.610). Fresh frozen calcanei of four mammals were obtained: five goat, six sheep, four pig and five human bones. The animals were chosen as they are frequently used for orthopedic animal-experiments due to their similar weight, metabolism [30] and [31] and bone volume fraction [32] to [34] as humans. The specimens were removed from frozen storage 30 minutes before the experiment and sprinkled with a 0.9% saline solution, thereby preserving the cartilage tissue and allowing the bone to come to room temperature before waterjet drilling. To prevent collision with the waterjet nozzle, protrusions were sawed off (Fig. 2c).

den Dunnen, S. – Kraaij, G. – Biskup, C. – Kerkhoffs, G.M.M.J. – Tuijthof, G.J.M.

Strojniški vestnik - Journal of Mechanical Engineering 59(2013)7-8, 425-432

Fig. 2. a) overview of the experimental setup, b) potential waterjet settings, c) two bone specimens fixated in a clamp

Holes were drilled in the posterior articular facet of the calcanei, at least 5 mm from the rim of the surface area to prevent drilling in cortical bone (Fig. 2c). A specially adapted clamp allowed for perpendicular alignment of the bone surface and the waterjet. Individually adjustable pins at the sides of the clamp provided a firm grip on the specimens (Fig. 2c). To prevent location-based bias, holes were machined in a random order of sequence per calcaneus. Depending on the size of the articular surface, six to nine holes were drilled at least 4 mm apart in each specimen. As perpendicular drilling enables the deepest cuts in cortical bone drilling [10], an impact angle of 90 degrees was used for all experiments (Fig. 2b). The stand-off distance between the nozzle and the specimen was set at 3 mm, using a spacer. In practice, this led to a stand-off distance between 2.5 and 5.5 mm due to the curved articular surface of the bones. The depth of the machined blind holes was measured with a dial-gauge [18]; the standard 1 mm wide sensory tip was replaced by a 0.3 mm wide tip made out of pivot steel wire. The adaptation increased the measurement depth to 30 mm and decreased the minimum required hole diameter. The 0.3 mm tip was small enough to reach the bottom of the holes, but could not enter natural cavities in the undrilled trabecular bone. To prevent the trabecular bone from being damaged by the wire, the insertion force was kept between 0.2 and 0.3 N by using a spring. Three measurements were performed on each hole, and a re-measurement was performed if the variation was larger than 0.25 mm.

The cartilage thickness was measured by inserting a dial gauge equipped with a sharp pin into an intact cartilage layer. The sharp pin penetrated the layer of cartilage, but was stopped by the harder subchondral bone plate. The distance covered by the pin was assumed to be equal to the thickness of the cartilage. For each mammal tested, this measurement was performed on two bone specimens at three different locations. One specimen of each animal was scanned with a Scanco microCT80 scanner to examine the internal damage caused by the water jet and examine the shape of the drilled holes. This allowed 20 holes to be examined, which was considered sufficient to determine a consistent trend in hole shape. Cartilage tissue damage was examined with a Keyence VHX100 digital microscope equipped with a Keyence VHZ-35 lens. The actual water pressures were calculated with a custom written Matlab routine. The hole-depth and the cartilage thickness measurements were averaged and rounded off to 0.1 mm. As the adapted dial-gauge measured the combined depth of the hole in the bone and the cartilage, the average thickness of the cartilage layer was subtracted to discriminate between pure bone waterjet drilling and cartilage waterjet drilling. For each specimen, the penetration pressure threshold was determined by the lowest pressure with which a hole depth larger than 0 mm was drilled. 2 RESULTS Pure waterjets can be used for machining holes in subchondral bone. The minimum-threshold pressure

Pure Waterjet Drilling of Articular Bone: An in vitro Feasibility Study

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Strojniški vestnik - Journal of Mechanical Engineering 59(2013)7-8, 425-432

for drilling in the subchondral bones of human, goat, sheep and pig calcaneus bone were 37 (SD 10), 36 (SD 5.9), 62 (SD 8.5) and 56 MPa (SD 5.8) respectively (Table 1). In general, the cutting depth increases with pressure (Fig. 3). The gradual rise in depth is most apparent for goat and pig specimens, while sheep and human bone show a more scattered plot. Observations showed that pressures below the minimum-thresholds caused a continuous waterjet reflection at an angle of approximately 30 degrees to the surface. This induced dents in the cartilage, which were approximately 50% larger in diameter (from 2 to 3 mm) compared to holes that penetrated bone. The reflection angle to the surface increased when the waterjet did penetrate bone. Besides exiting at the hole, water escaped at the sawed-off protrusion (Fig. 2a and 4).

For the majority of the specimens, a pressure of 30 MPa was sufficient to penetrate the cartilage up to the subchondral plate (Table 1). The μCT-scans showed consistently that the waterjets create coneshaped holes running from the subchondral plate into trabecular bone (Fig. 4). 3 DISCUSSION The pilot study demonstrated that waterjet drilling with pure waterjets can machine blind holes in articular bone. The minimum water pressure ranged between 36 (average goat) to 62 MPa (average sheep). Variations in minimum water pressure between the animals and between the specimens indicate that one pressure will result in a variance of hole depth. These variations can be caused by differences in bone volume fraction and thicknesses of cartilage, subchondral and trabecular

Table 1. Outcomes of experiment for each mammal calcaneus bone

Goat Sheep Pig Human

Average Cartilage Thickness [mm] 1.0 0.8 1.2 1.8

Total number holes drilled

No holes (depth of 0 mm)

Piercing holes

34 48 32 32

5 19 15 10

10 2 0 0

Immeasurable due to cavity in bone (>30 mm) 0 0 0 5

Average pressure to penetrate subchondral plate ([MPa] (SD)) 36 (SD 5.9) 62 (SD 8.5) 56 (SD 5.8) 37 (SD 10)

Fig. 3. The outcomes of the waterjet pressure versus the depth of the machined hole for four different mammal calcaneus bones

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bone layers. An increase in bone volume fraction or the thickness of the subchondral bone layer results in stronger bone [32] and [35] that is more resilient to waterjets. For waterjet drilling with similar pressures, human and sheep bone show a larger deviation in hole depth compared to goat and pig specimens (Fig. 3). A possible cause for the larger deviation can be the consistency in origin, forage, treatment and age of the animals, which has a significant influence on the mechanical properties of bone [36] and [37]. The goat and pig bone specimens were acquired from animals nurtured under similar circumstances. For human and sheep cadaveric bone specimens, the age and gender were unknown, thereby contributing to the larger difference in depths for similar pressures.

Fig. 4. A slice of a μCT scan with three machined holes; 1) full penetration of the bone, 2) and 3) cone shaped holes, 4) the sawed-off protrusion, and 5) a natural cavity in the bone

Fig. 5. Different stages of waterjet drilling; a) reflection tangential to the surface, b) small cavity changes reflection angle, c) incoming and outgoing waterjets start to interfere, widening the hole beyond the waterjet diameter, and d) hole depth and diameter are further increased (based on [2], [3], [18] and [19])

The results support Eq. (1), which indicates that an increase of hole depth is expected by an increase of water pressure. Impact pressures, frictional drag and shockwaves are all intensified at higher pressures, which also contribute to the forming of a deeper hole [3] and [38]. The larger dents in the cartilage when the subchondral plate was not penetrated can be explained by the difference in material properties between the bone layers in combination with the reflection angle of the waterjet after impact. During the drilling

process, the reflection angle increases with the hole depth (Fig. 5a to d). When the minimal penetration pressure threshold is not met, the energy of the waterjet is insufficient to machine the subchondral plate. Instead of continuing its original path, the water spreads tangentially to the surface (Fig. 5a) [3] and [18], which damages the surrounding cartilage. When the pressure threshold is met, this phenomenon is only present for a split second, thereby leaving a smaller dent. The four μCT scans gave a view of the shapes of 20 holes that were machined by pure waterjets. This does not allow for generalization, but does demonstrate a consistent trend. The holes showed a decrease in diameter with an increase of depth (Fig. 4). The conical shape of the holes can be explained by the variances in the intensity of the interfering incoming and outgoing water jets. At the top of the hole, the incoming jet enters the water-filled cavity, resulting in disturbances in the water flow and a decrease in the waterjet velocity (Fig. 5). The waterjet’s energy is dissipated by pushing the superfluous water towards the circumference and the exit of the hole. This results in a widening of the hole (Figs. 5c and d). At greater hole depths, the waterjets’ energy has been partially dissipated, causing the superfluous water to be pushed out at lower velocities. As a result, the hole diameter at the bottom of a hole increases at a slower pace compared to the shallow depths. This conical shape is potentially useful in orthopedic treatment, such as screw fixation or bone marrow stimulation. The pre-programmed CNC-controlled nozzle caused some holes to be drilled too close to the rim of the bone, where the bone is thinner than 5 mm. This primarily occurred in the goat bones, which had the smallest dimensions compared to the other calcaneal bones. In these cases, the bone was fully penetrated (piercing hole) and could not be measured (Table 1, column piercing hole). The missing values of the piercing holes are not considered to have a significant effect on the outcomes of this study. For human specimens, five holes could not be measured because the holes were deeper than the maximum of the 30mm that the adapted dial-gauge could measure (Table 1). In these cases, the water pressures were considerably higher than the minimum pressure for penetrating articular bone and therefore do not affect the conclusions of this study. Nevertheless, an increase of the sample size and smaller water pressure increments could have contributed to a higher accuracy in determining the minimum pressure threshold. The sawed-off protrusion might have caused an increase in hole depth. When a slug of water reaches

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the bottom of a hole, it moves to the path with the least resistance towards an exit. For waterjet drilling in nonporous materials, the primary exit is the hole itself (Figs. 1 and 5c to d). The open trabecular structure in combination with a sawed-off protrusion allowed the water to leave at a secondary exit, thereby partially removing the interference between the incoming and outgoing jets. Consequently, the drilled holes in this pilot experiment are expected to be deeper than when drilling bone that is complete, which is favorable from the safety point of view. Fluctuations in the water pressure caused by the intermittently reciprocating plungers [12] may have caused variations in the hole depths, but they were considered marginal compared to the variations in the material characteristics of the bone. This experiment showed a range of pressures and a resulting range of in depth, which clearly indicates the influence of bone material properties. These results show that pig bone is the most difficult to be machined, which can be considered for future experiments to investigate waterjet settings that can penetrate any type of articular bone. For clinical safety, controlling the depth of a waterjet machined hole is an issue that needs to be addressed. Solely using pressure to control the depth is insufficient due to the heterogeneous characteristics of the bone tissue. To this extent, an additional safety system that shuts off the waterjet after penetrating the suchondral plate is recommended. Nevertheless, piercing bone is unlikely as the majority of the holes in orthopedics are drilled towards the center of a bone where it is thicker. 4 CONCLUSION Machining blind holes in bone by using waterjet technology without adding abrasives is feasible. A minimum pressure threshold needs to be overcome before any damage is inflicted. This threshold differs for every animal tested. A waterjet pressure of 60 MPa is sufficient to inflict damage to the majority of articular bone tissue and should be considered as a starting point for future research. The conical shape of the holes makes pure waterjet drilling in bone a potentially valuable option for orthopaedic treatments. 5 ACKNOWLEDGEMENTS Prof. Dr.-Ing. Fr.-W. Bach, head of the Institute of Materials Science in Hannover, receives our acknowledgement for the use of the facilities at the Water Jet Laboratory Hannover. We are grateful to A.C. Kok, I.N. Sierevelt and J.R.A. Dukker for 430

their help in the preparations of the experiment, statistics and fabrication of experimental equipment, respectively. Finally, we would like to thank Dr. Ir. B. van Rietbergen and Dr. Ir. L. Mulder (Eindhoven University of Technology) for using the μCT scanner and providing μCT imaging related support. This work was supported by the Technology Foundation Stichting voor de Technologische Wetenschappen (STW), Applied Science Division of NWO, and the technology program of the Ministry of Economic Affairs, The Netherlands (grant number 10851). The sponsor had no involvement in the study design, analysis or interpretation of the data. 6 REFERENCES [1] Hashish, M., Duplessis, M.P. (1978). Theoretical and experimental investigation of continuous jet penetration of solids. Journal of Engineering for Industry-Transactions of the ASME, vol. 100, no. 1, p. 88-94, DOI:10.1115/1.3439351. [2] Summers, D. (1995). Waterjetting Technology. Taylor & Francis, London. [3] Tikhomirov, R.A., Petukhov, E.N., Babanin, V.F., Starikov, I.D., Kovalev, V.A. (1992). High-Pressure Jetcutting. ASME Press, New York. [4] Cadavid, R., Jean, B., Wustenberg, D. (2009). On the selection of the nozzle geometry and other parameters for cutting corneal flaps with waterjets. Biomedizinische Technik, vol. 54, no. 3, p. 134-141, DOI:10.1515/BMT.2009.017. [5] Bibbo, C. (2010). VERSAJET (TM) Hydrosurgery technique for the preparation of full thickness skin grafts and the creation of retrograde split thickness skin grafts. Journal of Foot & Ankle Surgery, vol. 49, no. 4, p. 404-407, DOI:10.1053/j.jfas.2010.04.013. [6] Tschan, C.A., Keiner, D., Muller, H.D., Schwabe, K., Gaab, M.R., Krauss, J.K., Sommer, C., Oertel, J. (2010). Waterjet dissection of peripheral nerves: An experimental study of the sciatic nerve of rats. Neurosurgery, vol. 67, suppl. 2, p. 368-376, DOI:10.1227/NEU.0b013e3181f9b0c8. [7] Schmolke, S., Pude, F., Kirsch, L., Honl, M., Schwieger, K., Kromer, S. (2004). Temperature measurements during abrasive water jet osteotomy. Biomedizinische Technik, vol. 49, no. 1-2, p. 18-21, DOI:10.1515/ BMT.2004.004. [8] Honl, M., Rentzsch, R., Muller, G., Brandt, C., Bluhm, A., Hille, E., Louis, H., Morlock, M., (2000). The use of water-jetting technology in prostheses revision surgery - First results of parameter studies on bone and bone Cement. Journal of Biomedical Materials Research, vol. 53, no. 6, p. 781-790, DOI:10.1002/10974636(2000)53:6<781::AID-JBM20>3.0.CO;2-G. [9] Honl, M., Rentzsch, R., Schwieger, K., Carrero, V., Dierk, O., Dries, S., Louis, H., Pude, F, Bishop, N., Hille, E., Morlock, M., (2003). The water jet as a new

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of the Royal Society of London,vol. 260A, no. 1110, p. 295-308. [21] Hashish, M. (1989). An investigation of milling with abrasive-waterjets. Journal of Engineering for Industry-Transactions of the ASME, vol. 111, no. 2, p. 158-166, DOI:10.1115/1.3188745. [22] Momber, A.W., Kovacevic, R. (1998). Principles of Abrasive Water Jet Machining. Springer, London, DOI:10.1007/978-1-4471-1572-4. [23] An, Y.H., Draughn, R.A. (2000). Mechanical Testing of Bone and the Bone-Implant Interface. CRC Press, Boca Raton. [24] Kempson, G.E. (1982). Relationship between the tensile properties of articular cartilage from the human knee and age. Annals of Rheumatic Disseases, vol. 41, no. 5, p. 508-511, DOI:10.1136/ard.41.5.508. [25] Reilly, D.T., Burstein, A.H. (1975). The elastic and ultimate properties of compact bone tissue. Journal of Biomechanics, vol. 8, no. 6, p. 393-405, DOI:10.1016/0021-9290(75)90075-5. [26] Burstein, A.H., Reilly, D.T., Martens, M. (1976). Aging of bone tissue: mechanical properties. Journal of Bone and Joint Surgery-American Volume, vol. 58, no. 1, p. 82-86. [27] Kuhn, J.L., Goldstein, S.A., Ciarelli, M.J., Matthews, L.S. (1989). The limitations of canine trabecular bone as a model for human: A biomechanical study. Journal of Biomechanics, vol. 22, no. 2, p. 95-107, DOI:10.1016/0021-9290(89)90032-8. [28] Odgaard, A., Hvid, I., Linde, F. (1989). Compressive axial strain distributions in cancellous bone specimens. Journal of Biomechanics, vol. 22, no. 8-9, p. 829-35, DOI:10.1016/0021-9290(89)90066-3. [29] Athanasiou, K.A., Rosenwasser, M.P., Buckwalter, J.A., Malinin, T.I., Mow, V.C. (1991). Interspecies Comparisons of Insitu Intrinsic Mechanical-Properties of Distal Femoral Cartilage. Journal of Orthopaedic Research, vol. 9, no. 3, p. 330-340, DOI:10.1002/ jor.1100090304. [30] Lane, J.G., Massie, J.B., Ball, S.T., Amiel, M.E., Chen, A.C., Bae, W.C., Sah, R.L., Amiel, D. (2004). Follow-up of osteochondral plug transfers in a goat model: A 6-month study. The American Journal of Sports Medicine, vol. 32, no. 6, p. 1440-50, DOI:10.1177/0363546504263945. [31] Newman, E., Turner, A.S., Wark, J.D. (1995). The potential of sheep for the study of osteopenia: current status and comparison with other animal models. Bone, vol. 16, no. 4, suppl. p. 277S-284S. [32] Teo, J.C.M., Si-Hoe, K.M., Keh, J.E.L., Teoh, S.H. (2007). Correlation of cancellous bone microarchitectural parameters from microCT to CT number and bone mechanical properties. Materials Science and Engineering: C, vol. 27, no. 2, p. 333-339, DOI:10.1016/j.msec.2006.05.003. [33] Siu, W., Qin, L., Cheung, W.H., Leung, K. (2004). A study of trabecular bones in ovariectomized goats with micro-computed tomography and peripheral

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quantitative computed tomography. Bone, vol. 35, no. 1, p. 21-26, DOI:10.1016/j.bone.2004.03.014. [34] Hildebrand, T., Laib, A., Muller, R., Dequeker, J., Ruegsegger, P. (1999). Direct three-dimensional morphometric analysis of human cancellous bone: Microstructural data from spine, femur, iliac crest, and calcaneus. Journal of Bone and Mineral Research, vol. 14, no. 7, p. 1167-1174, DOI:10.1359/ jbmr.1999.14.7.1167. [35] Bevill, G., Eswaran, S.K., Gupta, A., Papadopoulos, P., Keaveny, T.M. (2006). Influence of bone volume fraction and architecture on computed large-deformation failure mechanisms in human trabecular bone. Bone, vol. 39, no. 6, p. 1218-1225, DOI:10.1016/j.bone.2006.06.016.

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[36] Crenshaw, T.D., Peo, E.R. Jr., Lewis, A.J., Moser, B.D., Olson, D. (1981). Influence of age, sex and calcium and phosphorus levels on the mechanical properties of various bones in swine. Journal of Animal Science, vol. 52, no. 6, p. 1319-29. [37] Zioupos, P., Currey, J.D. (1998). Changes in the stiffness, strength, and toughness of human cortical bone with age. Bone, vol. 22, no. 1, p. 57-66, DOI:10.1016/S8756-3282(97)00228-7. [38] Chen, L., Siores, E., Wong, W.C.K. (1996). Kerf characteristics in abrasive waterjet cutting of ceramic materials. International Journal of Machine Tools & Manufacture, vol. 36, no. 11, p. 1201-1206, DOI:10.1016/0890-6955(95)00108-5.

den Dunnen, S. – Kraaij, G. – Biskup, C. – Kerkhoffs, G.M.M.J. – Tuijthof, G.J.M.

Received for review: 2012-12-13 Received revised form: 2013-03-13 Accepted for publication: 2013-04-16

Speed-Control of Energy Regulation Based Variable-Speed Electrohydraulic Drive Xu, M. – Jin, B. – Chen, G. – Ni, J. Ming Xu1,* – Bo Jin2 – Guojin Chen1 – Jing Ni1 1 Hangzhou Dianzi University, Department of Mechanical Engineering, China 2 Zhejiang University, State Key Laboratory of Fluid Power Transmission and Control, China

The variable-speed electrohydraulic drive is a promising drive principle due to its high energy efficiency and large speed-range. However, its slow response and poor low-speed behaviour limit its application. To address these disadvantages, a energy regulation based variable-speed electrohydraulic drive is proposed. This novel drive principle is combined with the advantages of variable-speed drive and valve-control drive. The speed-control of the energy regulation based variable-speed electrohydraulic drive is discussed. The speed-control strategy, which is aimed at the multiple-input multiple-output (MIMO) structure of the proposed drive principle, is analysed. The results of simulations and experiments comparing it with three other drive principle systems show that the proposed drive principle has not only a good speed-control accuracy, but also a perfect energy-saving performance. Keywords: variable-speed, speed-control, energy regulation, energy-saving

0 INTRODUCTION With the developments in frequency converters, the variable-speed electrohydraulic drive (a speedcontrolled electric motor in combination with a hydraulic constant pump) has been greatly improved. A review of the literature [1] shows the development of the variable-speed drive. References [2] to [7] discuss the energy-saving performance of variablespeed drive, while references [8] to [11] discuss the control strategy. In addition to the high energy efficiency of the volume drive (a constant-speed electric motor in combination with a hydraulic variable-displacement pump), the variable-speed drive can enhance system reliability and expand the speed-range [12]. However, due to the large inertia of the electric motor and hydraulic pump, the main disadvantages of the variable-speed drive are slow response and poor control precision [13]. To address these disadvantages, a flow valve was added into the variable-speed (AKA variablefrequency) drive system to create a compound drive, in which the frequency converter adjusts the speed of the electric motor to satisfy the actuator’s flow requirement and the flow valve controls the actuator’s position or speed. The compound drive principle can improve control precision and low-speed performance [14]. In the low-speed range, the hydraulic pump maintains a constant speed to gain sufficient flow, while the flow-valve drives the actuator. The compound drive can also improve the deceleration response owing to the fast dynamic response of the flow valve, although it is unable to improve the response when accelerating [13]. Therefore, it

is mainly applied in hydraulic elevators, injection machines, etc., which do not require a fast response. A energy regulation based variable-speed electrohydraulic drive has been proposed in order to improve responsiveness, especially when accelerating [12]. This drive is distinguished from the compound drive by the inclusion of an energy regulation device (ERD). The electric motor-pump cannot always speed up as needed when accelerating, so the ERD releases energy to improve the acceleration response. When decelerating but the electric motor-pump cannot always slow down as needed, so the ERD absorbs redundant hydraulic oil. In other cases, the ERD is turned off. The position-control of the variable-speed drive based on energy regulation has been studied [13], although the speed-control has not. Speed-control is widely used in hydraulic systems, such as hydraulic cutting machine, hydraulic elevators, and so on. The key issues associated with speed-control research for hydraulic systems, in addition to energy savings, are how to deliver high speed-control accuracy and a fast acceleration response. The goal of this research is to develop a novel electrohydraulic drive principle for speed-control, which is useful for practical application. 1 SYSTEM STRUCTURE Fig. 1 shows the cylinder speed-control in a variablespeed drive system based on energy regulation. A hydraulic constant pump is driven by a frequency converter via an asynchronous electric motor. The cylinder is controlled by a proportional directional valve. The position of the cylinder along its stroke

*Corr. Author’s Address: Hangzhou Dianzi University, Department of Mechanical Engineering, Hangzhou, China, xumzju@163.com

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is measured by a position sensor mounted inside the cylinder. The cylinder velocity is calculated by differentiating the position signal, because there is no suitable speed sensor for this system. The pressures ps and pe are measured by two pressure sensors. The flow of the hydraulic pump outlet is measured by a high-pressure flowmeter.

controlled hydraulic constant pump control the cylinder rod together. (4) Variable-speed drive based on energy regulation.

Fig. 2. Energy regulation test-rig

Fig. 1. Cylinder speed-control of a variable-speed drive system based on energy regulation

The ERD, mounted on the hydraulic pump outlet, is composed of a bladder accumulator, a proportional flow valve, and a relief valve. Due to its simple structure and fast response characteristics, the bladder accumulator was chosen for storing hydraulic energy. The flow between the ERD and the main hydraulic circuit is controlled by the proportional flow valve. The relief valve is used as a safety valve. The ERD is a semi-active device because its function depends on the pressure difference between the ERD and the hydraulic pump outlet. Fig. 2 shows a multifunctional test-rig where experiments for four different drive principles can be implemented. (1) Valve control. The ERD is closed. The electric motor speed is 1500 r/min at all times. The proportional directional valve controls the speed of the cylinder rod. (2) Variable-speed drive. The ERD is closed. The speed of the hydraulic constant pump can be adjusted. The proportional directional valve controls the movement direction of the cylinder without throttling. (3) Compound drive. The ERD is closed. The proportional directional valve and the speed434

As shown in Fig. 1, the controller is composed of an industrial computer, an analogue-to-digital converter (ADC), and a digital-to-analogue converter (DAC). The Visual C++ was selected as the programming environment. The control voltage of the proportional directional valve’s amplifier is from –10 to +10 V. For the proportional flow valve of the ERD, it is from 0 to 5 V. The main parameters of the test-rig are shown in Table 1. The control period indicates that the control process is executed per 0.01 s. Table 1. Main parameters of the test-rig Parameters Power of the frequency converter PI [kW] Electric motor nominal power PM [kW] Electric motor nominal speed nm [r/min] Pump displacement sp [cm3/rad] Cross-sectional area of no rod-side Ap1 [dm2] Cross-sectional area of rod-side Ap2 [dm2] Cylinder-rod stroke S [m] Piston mass m [kg] Accumulator volume Va0 [dm3] Accumulator precharge pressure pe0 [MPa] Relief valve cracking pressure pcr [MPa] Nominal flow of the flow valve (Δp = 0.5 MPa) qtnom [dm3/s] Nominal flow of the directional valve (Δp = 0.5 MPa) qdnom [dm3/s] Effective bulk modulus of hydraulic oil Eh [MPa] Density of hydraulic oil ρ [kg·m3] Control period tc [s]

Value 15 15 1 500 3.185 0.313 0.153 0.3 50 6.3 2 4 0.533 0.533 700 850 0.01

The parameters of the ERD (such as accumulator volume, precharge pressure, etc.)

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have been studied [12] and they are very important for energy regulation. However, the aim of this research is to demonstrate the applicability of ERD in cylinder speed-control, not to have a general discussion of ERD.

where u (k ) = k fp e(k ) + λ f k fi ∑ e(i ) + k fd [e(k ) − e(k − 1)],

2 SPEED CONTROL STRATEGY Fig. 3 shows the MIMO scheme of the cylinder speedcontrol system in a variable-speed drive system based on energy regulation. There are four inputs (vin, vp, ps, pe) and three outputs (fin, ud, ut) .

1 e ( k ) ≤ e f λf =  .  0 e( k ) > e f

(2) Proportional directional valve. The proportional directional valve uses a PID control strategy. k

ud = min(max((kdp ⋅ e(k ) + λd kdi ⋅ ∑ e(i ) + i =0

+ kdd ⋅ [e(k ) − e(k − 1)]), −10),10),

(2)

1 e(k ) ≤ ed where λd =  . 0 e(k ) > ed Fig. 3. Speed-control principle of the variable-speed drive system based on energy regulation

The speed-control strategy can be explained as following. (1) If vin > vp, the cylinder needs to accelerate. fin and ud should be increased. If pe > ps, the ERD will be open to release energy. If pe < ps, the ERD is closed. (2) If vin < vp, the cylinder needs to decelerate. fin and Ud should be reduced. If pe > ps, the ERD is closed. If pe < ps, the ERD absorbs energy. (3) If vin = vp, the electric motor maintains the current speed and the proportional directional valve is used for speed-control. If pe > ps, the ERD is closed. If pe < ps, the ERD absorbs energy. (4) If vin is very small, the electric motor maintains the preset minimum speed vm0. The proportional directional valve is used for speed-control. If pe > ps, the ERD is closed. If pe < ps, it absorbs energy. The detailed strategies of the three controlledobjects are discussed as below. (1) Frequency converter. The frequency converter adopts the “InputFeedforward + Proportional-Integral-Differential (PID) control.” The input-feedforward plays a major role in reference tracking. And the PID corrects the error caused by load disturbance. The expression for the frequency converter is shown in Eq. (1).

fin = min[max( K in ⋅ Vin + u (k ) , fin min ), fin max ], (1)

(3) ERD. The ERD uses “PID + Logical judgment.” In Eq. (3), vm0 is the smallest speed of the cylinder rod. It is determined by the allowable minimum-speed of the electric motor. k  k ⋅ e k + k ⋅ e(i ) +ktd ⋅ [e(k ) − e(k − 1)] ( ) λ ∑ tp e ti  i =0  vin > v p , pe > ps  k  ktp ⋅ e(k ) + λe kti ⋅ ∑ e(i ) +ktd ⋅ [e(k ) − e(k − 1)] i =0  vin < v p , pe < ps  k (3) ut =  ( ) + λ ⋅ k ⋅ e k k e(i ) +ktd ⋅ [e(k ) − e(k − 1)] ∑ e ti  tp i =0  vin = v p , pe < ps  k k ⋅ e(k ) + λ k ⋅ e(i ) +k ⋅ [e(k ) − e(k − 1)] ∑ td tp e ti  i =0  vin < vm 0 , pe < ps  0 others 

1 e(k ) ≤ ee . where λe =  0 e(k ) > ee There are a lot of control parameters, shown in Eqs. (1) to (3) and Fig. 4, which need to be determined before simulations and experiments are carried out. Fig. 4 shows the setting order of these parameters.

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The parameter determination method is based on the principle of the Ziegler-Nichols method. This method firstly sets the integral and differential gain to zero, and then gradually increases the proportional gain until system oscillation occurs. At this time, the value of the unstable proportional gain is kmax, and the oscillation frequency is f0. Table 2 shows the ZieglerNichols method. Fig.4. Setting order of control parameters

The setting rules of the control parameters are explained below. (1) In the valve-control drive system, the control parameters are kdp , kdi , kdd and ed. The PID parameters kdp, kdi, kdd were determined by the Ziegler-Nichols method. The parameter ed was obtained by experimentations. (2) In the variable-speed drive system, the control parameters are Kin , kfp , kfi , kfd , ef. The inputfeedforward parameter Kin equals the reciprocal of the actuator’s speed-gain. In a variable-speed drive, the frequency converter controls the speed of the hydraulic cylinder throughout. If the frequency converter has an input frequency of fin, the hydraulic cylinder has a steady-state speed of v, accordingly. The cylinder's speedgain is defined as v/fin. Kin is therefore defined as fin/v. The PID parameters kfp, kfi, kfd, were also determined by the Ziegler-Nichols method, whereas the parameter ef was obtained by experimentations. (3) In the compound drive system, the control parameters of the directional valve kdp , kdi , kdd, ed were the same as those in the valve-control drive system. The control parameters of the frequency converter Kin, kfp, kfi, kfd, ef were the same as those in the variable-speed drive system. (4) In the variable-speed drive system based on energy regulation, the control parameters of the direction valve (kdp , kdi , kdd , ed) and the frequency converter (Kin, kfp, kfi, kfd, ef) were the same as in the compound drive system. The PID parameters of the ERD (ktp , kti , ktd , et) were determined by experimentations. Table. 2. Ziegler-Nichols Method Control Type P PI PID

436

kp 0.5 kmax 0.45 kmax 0.6 kmax

ki 0 1.2 f0 2.0 f0

kd 0 0 0.125 / f0

3 SIMULATION RESULTS To demonstrate the speed-control performance of the variable-speed drive based on energy regulation, some simulations and experiments were carried out. In order to compare the speed-control performance, the simulations and experiments of the valve-control drive, variable-speed drive and compound drive principles are also implemented. AMESim was chosen to carry out the simulations. The components of the model are described using analytical models representing the hydraulic, pneumatic, electric or mechanical behaviour of the system. To create the system simulation model in AMESim, the user can make use of a large set of validated libraries of pre-defined components from different physical domains. The expression of each controlled-object in the above three drive principle systems is the same as it is in the proposed drive principle system. Correspondingly, the conditions of the simulations and experiments are the same, as well as the control parameters. Numbers 1 through 4 represent the valve-control, variable-speed drive, compound drive, and energy regulation drive, respectively, without specification, in the following texts and figures. In simulations, the cylinder stroke is assumed to be 1 meter for convenience. Fig. 5 shows the velocity response of the cylinder using the four drive principles on a rectangular reference signal. Curve 4 coincides with Curve 1 exactly when accelerating because the ERD releases hydraulic oil to accelerate the cylinder response. This clearly shows that the tracking

performance of the proposed drive principle is better than that of the variable-speed drive and compound drive. Curves 2 and 3 are almost the same because their accelerations depend on the electric motor. When decelerating, the proportional directional valve can shut down rapidly, so the four curves are almost the same. The upward and downward curves of each drive principle system are not the same due to the asymmetry of the single-rod hydraulic cylinder.

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Table 3. Average hydraulic power simulations using the four drive principles on a rectangular signal System Average hydraulic power [kW]

1 7.50

2 0.87

3 3.82

4 3.30

Fig. 7 shows the performance of flowrate compensation in a variable-speed drive based on energy regulation. The positive flowrate represents the ERD as it releases oil. The negative flowrate represents the ERD as it absorbs oil. The ERD therefore plays the role of regulating energy consumption according to the system’s requirements. Fig. 5. Velocity simulations of the cylinder using the four drive principles on a rectangular signal

The hydraulic power consumption of the systems using four different drive principles are shown in Fig. 6. They are calculated by:

Ps = ps * Qs .

(4)

The hydraulic power of the valve-control system is always highest. The hydraulic power in the variablespeed drive is the lowest, most of the time. When the direction of the cylinder movement changes, the hydraulic power increases rapidly because of the pressure shock. The hydraulic power of Curve 4 is smaller than that of Curve 3 because the ERD can absorb hydraulic oil so as to keep the hydraulic power from overflowing and throttling when the cylinder decelerates or maintains a constant speed. Table 3 shows the average hydraulic power consumption of each system.

Fig. 7. The flowrate compensation effect in a variable-speed drive based on energy regulation

To analyse the speed-control performance comprehensively, simulations on the sine reference signal were also carried out. Because the cylinder stroke is only 0.3 meter, the four drive principle systems have the smallest work-frequency below the designated speed. If the reference speed of the cylinder is: vin = v A ⋅ sin( wt + θ ), (5)

and θ ＝0,

vin = v A ⋅sin( wt ) (6)

where wt ∈ [2kπ ,(2k + 1)π ] or wt ∈ [(2k + 1)π ,(2k + 2)π ] , (k = 0, 1, 2, ...), then the actual displacement of the piston rod is: Fig. 6. Hydraulic power consumption simulations of the four drives principles on a rectangular signal

s=∫

π /w

vin dt = ∫

and

Speed-Control of Energy Regulation Based Variable-Speed Electrohydraulic Drive

π /w

v A ⋅ sin( wt )dt , (7)

s ≤ l .

(8) 437

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From Eqs. (5) to (8), the lowest work-frequency is where l = 0.3 m and vA = 0.2 m/s: fmin = 0.21 Hz. If the frequency is smaller than 0.21 Hz, the piston rod will collide with the cylinder block. Therefore, the frequency of the sine reference signal can be taken to be 0.25 Hz. Fig. 8 shows the velocity response of the four drive principle systems under the condition of vA = 0.2 m/s and f = 0.25 Hz. Although the simulation results for the tracking performance look similar for all of the four drive principles, there are differences. The total error of tracking performance in a cycle is 2 > 3 > 4 > 1. Table 4 shows the mean square error (MSE) of the four drive principles.

Table 4. MSE of sine simulations using the four different drive principles System MSE [10-4m2/s2]

1 0.551

2 1.283

3 1.148

4 0.847

1 n ∑ (vin (i) − v p (i))2 , n is the n i =0 numerical value of the sampling times. Table 5 shows the average hydraulic power consumption of the four drive principle systems. Because the electric motor has a preset minimum speed in energy regulation drive, the average hydraulic power of the energy regulation drive is a little greater than that of the compound drive. It Table 4 MSE =

Table 5. Average hydraulic power of the sine simulations using four different drive principles System Average hydraulic power [kW]

1 7.50

2 0.26

3 1.79

4 2.26

Fig. 9 shows the spectrums of speed-amplitude simulations using four different drive principles (the speed-amplitude is 0.2 m/s). The bandwidth of Curves 2 and 3 are almost the same. According to common sense, the bandwidth of the energy regulation drive principle system should be the smallest out of all four drive principle systems due to the large volume (6.3 l) of the accumulator. However, Curve 4 still has good bandwidth characteristics, which is attributed to the energy regulation performance. Fig. 10 shows the spectrums for hydraulic power simulations using four different drive principles. The hydraulic power of System 1 is greater than the other three systems. In the high frequency region, the electric motor always maintains a high speed and does not slow down in a timely manner. Therefore Curves 2 to 4 almost coincide. The hydraulic power of Curve 4 438

d) Fig. 8. Sine simulations of the cylinder using four different drive principles; ; a) to d)

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is always bigger than that of Curve 3, because there is a preset minimum-speed in System 4.

four drive principle systems have almost the same responses because their decelerations basically depend on the proportional directional valve.

Fig. 9. Spectrums of speed-amplitude simulations of the cylinder using four different drive principles Fig. 11. Velocity experiments of the cylinder using the four drive principles on a rectangular signal

Fig. 12 shows the ps and pe in the energy regulation drive principle system. When the cylinder accelerates, the ERD releases hydraulic oil. When the cylinder decelerates or maintains a constant speed, the ERD absorbs hydraulic oil.

Fig. 10. Spectrum of hydraulic power simulations of the cylinder using four drive principles

4 EXPERIMENTAL RESULTS Since there are not any suitable speed sensors for this test-rig, the cylinder velocity is calculated by differentiating the position signal. However, this causes high-frequency interference. To calculate the cylinder velocity accurately, a Butterworth filter of order 10, whose cutoff frequency is 150 Hz, was designed by using the Filter Design&Analysis Tool of MATLAB. A moving-average filtering algorithm is also employed to reduce random interference. Since the cylinder stroke is only 0.3 m, the piston can only move in one direction during a signal period. Fig. 11 shows the velocity tracking experiments of the cylinder using the four drive principles on a rectangular signal. Curve 4 coincides with Curve 1 exactly and their responses are obviously faster than those of Curves 2 and 3. When decelerating, the

Fig. 12. pe and ps in the energy regulation drive

Fig. 13 shows the electric motor speed in the energy regulation drive. It can be seen that the acceleration time of the electric motor is long (about 0.2 s from 460 r/min to 900 r/min). Therefore, the flow discharged by the hydraulic pump cannot meet the requirements of the cylinder speed-control in a timely manner. Fig. 14 compares the hydraulic power consumption of four drive principles. The hydraulic power in System 1 is consistently the highest. The other three systems have almost the same power

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consumption. Because the electric motor has the preset minimum-speed in System 4, the hydraulic power in System 4 is a little bigger than that in Systems 2 and 3. Due to the pressure shock caused by the change in direction of the cylinder motion, the four curves have power shocks.

Fig. 13. Speed of the electric motor in the energy regulation drive

Fig. 14. Hydraulic power experiments using four drive principles on a rectangular signal

Fig. 15 shows the velocity experiments on the cylinder using four different drive principles on the sine reference signal. The speed-tracking error is very small in System 4, which is approximately equivalent to Curve 1. Table 6 shows the mean square error of the four drive principles. Table 6. MSE of the sine experiments using the four different drive principles System MSE×10-4 [m2/s2]

440

1 1.672

2 2.157

3 1.996

4 1.743

d) Fig. 15. Velocity experiments on the cylinder using the four drive principles on the sine reference signal; a) to d)

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Fig. 16 shows the spectra of hydraulic power consumption of the cylinder using the four different drive principles on the sine reference signal. The frequency of the sine reference signal ranges from 0.25 to 3 Hz. As shown in Fig. 16, the hydraulic power consumption in System 1 is always the largest. System 2 has the smallest hydraulic power consumption. System 4 consumes a little more hydraulic power than System 3 because the electric motor has little time to slow down at high frequency bandwidths.

Fig. 16. Spectra of hydraulic power experiments of the cylinder using the four different drive principles on the sine reference signal

According to Figs. 15 and 16, it can be seen that the energy regulation drive not only speeds up the response when the cylinder needs to accelerate but also contributes to better speed tracking and improved energy-saving performance. 5 CONCLUSIONS The energy regulation based variable-speed electrohydraulic drive is a good method of improving the response and low-speed performance of the variable-speed drive. However, it is a MIMO control system, coupled with strong nonlinear and structural uncertainties, which make the control strategy complex. A compound PID control strategy, as well as a parameter tuning rule, is proposed to address these issues. The proposed novel drive principle will increase the cost of the system and increase control complexity. However, the simulation and experimental results show that it demonstrates a good comprehensive performance with high speed-control accuracy, a fast response, and a good energy-saving performance, all of which are useful in practical applications.

6 ACKNOWLEDGEMENT This research is supported by the National Natural Science Foundation of China (Grant No. 51205099), the Zhejiang province key science and technology innovation team (Grant No. 2010R50003), and the Zhejiang Open Foundation of Most Important Subjects. 7 NOMENCLATURE ed integral separation threshold of directional valve control [m/s] ef integral separation threshold of frequency converter control [m/s] ee integral separation threshold of ERD control [m/s] fin input frequency of frequency converter [Hz] finmax maximum input frequency of frequency converter [Hz] finmin minimum input frequency of frequency converter [Hz] fmin minimum work-frequency [Hz] Kin feedforward parameter of frequency converter control kfp,kfi,kfd PID control parameters of frequency converter ktp,kti,ktd PID control parameters of ERD kdp,kdi,kdd PID control parameters of proportional directional valve λd integral separation parameter of proportional directional valve control λf integral separation parameter of frequency converter control λe integral separation parameter of ERD control l stroke of the cylinder rod [m] pe pressure of energy regulation device [Pa] ps pressure of hydraulic pump outlet [Pa] Ps hydraulic power consumption [kW] Qs flow of hydraulic pump outlet [m3/s] ud control voltage of proportional directional valve [V] ut control voltage of proportional flow valve in ERD [V] vA maximum velocity of cylinder rod [m/s] vin reference velocity of cylinder rod [m/s] vp actual velocity of cylinder rod [m/s] vm0 preset minimum speed of cylinder [m/s] w frequency [Hz] xp position of cylinder rod [m]

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8 REFERENCE [1] Ristic, M. (2008). Conversant technology – New key aspects: Development of variable speed drives. Proceedings of International Fluid Power Conference, Dresden, p. 93-108. [2] Yutaka, T., Kazuo, N. [1991]. Variable-speed control of hydraulic pump for energy-savings. International Symposium on Fluid Power Transmission and Control, Beijing, p. 10-14. [3] Manasek, R. (2000). Simulation of an electro-hydraulic load-sensing system with AC motor and frequency changer. Proceeding of the 1st FPNI-PhD Symposium, Hamburg , p. 311-324. [4] Helduser, S. (2003). Improved energy efficiency in plastic injection molding machines. The 8th Scandinavian International Conference on Fluid Power, Tampere, Finland, p. 1219-1229. [5] Jelali, M., Kroll, A. (2003). Hydraulic Servo-system: Modeling, Identification and Control. Springer, DOI:10.1007/978-1-4471-0099-7. [6] Berubger, A.G. (1998). The frequency-controlled hydraulic drive. Elevator World, vol. 46, no. 2, p. 9496. [7] Biedermann, O., Engelhardt, J., Geerling, G. (1998). More efficient fluid power systems using variable displacement hydraulic motors. The 21st International Council of the Aeronautical Sciences Congress, Melbourne, Australia. [8] Dahmann, P. (2002). Closed loop speed and position control of a hydraulic manipulator in brick works with a frequency controlled internal gear pump in motor/

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pump operation. The 3st International Fluid Power Conference. Aachen. [9] Detiček, E., Župerl, U. (2011). An intelligent electrohydraulic servo drive positioning. Strojniški vestnik Journal of Mechanical Engineering, vol. 57, no. 5, p. 394-404, DOI:10.5545/sv-jme.2010.081. [10] Lovrec, D., Kastrevc, M., Ulaga, S. (2009). Electrohydraulic load sensing with a speed-controlled hydraulic supply system on forming-machines. International Journal of advanced manufacture technology, vol. 41, no. 11, p. 1066-1075, DOI:10.1007/s00170-0081553-y. [11] Lovrec, D., Kastrevc, M. (2011) Modeling and simulating a controlled press-brake supply system. International Journal of Modeling and Simulation, vol. 10, no. 3, p. 133-144, DOI:10.2507/IJSIMM10(3)3.184. [12] Xu, M., Jin, B., Shen, H.K., Li, W. (2010). Analysis and design of energy regulation device in energy regulation based variable speed electro-hydraulic control system. Chinese Journal of Mechanical Engineering, vol. 46, no. 4, p. 136-142, DOI:10.3901/JME.2010.04.136. [13] Shen, H.K., Jin, B., Chen, Y. (2006). Research on variable-speed electrohydraulic control system based on energy regulating strategy. ASME International Mechanical Engineering Congress and Exposition, Chicago. [14] Xu M., Jin, B., Yu Y.X., Shen H.K., Li W. (2010). Using artificial neural networks for energy regulation based variable-speed electrohydraulic drive. Chinese Journal of Mechanical Engineering, vol. 23, no. 3, p. 327-335, DOI:10.3901/CJME.2010.03.327.

Xu, M. – Jin, B. – Chen, G. – Ni, J.

Received for review: 2012-11-15 Received revised form: 2013-04-04 Accepted for publication: 2013-04-09

An Experimental Study of the Tribological Characteristics of Engine and Gear Transmission Oils Perić, S. – Nedić, B. – Trifković, D. – Vuruna, M. Sreten Perić1,* – Bogdan Nedić2 – Dragan Trifković1 – Mladen Vuruna1 1 University

2 University

of Defence, Military Academy, Serbia of Kragujevac, Faculty of Engineering, Serbia

During the past few decades, special attention has been devoted to developing modern instruments and methods of monitoring the tribomechanical characteristics of technical systems. Today, various physical, chemical and tribological methods are used in tribomechanical systems diagnosis. Scientific experience in technical system exploitation and maintenance has shown that the most effective way to predict failure is based on parameters that are reliable indicators of wear. Analysis of oil samples, which contain particles due to the wear process, enables an evaluation of the tribology condition of the system in the early phases of its use. This paper deals with tribological tests that are part of the oil analysis and are used to access the condition of the system. Furthermore, the results of experimental research on the tribological characteristics of the oil sampled from engines and gear transmissions of the vehicles (Mercedes O 345, PUCH 300GD and PINZGAUER 710M) are shown. All of these road vehicle were in regular use by the Serbian armed forces. The performed research has revealed some significant changes in the tribological characteristics of oil for engine and gear transmission lubrication.. These changes directly depend on the condition of the entire engine and transmission elements, i.e. depend on their functional characteristics. The presented method of oil analysis should contribute to an early detection of failures due to friction and wear processes in vehicle engines and reduce the need for preventive maintenance. Keywords: oil condition monitoring, lubricants, engine oils, dynamic modelling

0 INTRODUCTION The main goal in tribology is to provide a thin layer of low shear strength medium at the surface contact between loaded solids in relative motion. This is to reduce friction and guard against surface wear. The tribochemical behaviour of the surface-lubricant interface is quite important. The goal of lubrication is to provide a layer of a diﬀerent material between the surfaces in contact that reduces the friction force between them, either by being softer than the surfaces, or by being a coherent liquid lubricant trapped between the two surfaces by their relative movement [1] and [2]. Using the model in this paper, it is possible to identify the status of the tribomechanical system and to reduce the need for preventive maintenance by using adequate sampling methods and undertaking tribological studies [3] to [5]. The primary role of the lubricant is to reduce the negative effects of tribological processes related to friction, wear, and increases in temperature in tribomechanical systems, therefore all types of maintenance include lubrication as a very important part of the whole maintenance process. On the other hand, the lubricant is a key constituent of the contact conjuction that carries information about the state of the whole system, from the point of view of tribological and other ageing processes. Therefore, analysis of the lubricant oil, based on a properly defined program, represents a very

effective method for monitoring the state of technical systems, providing early warning signs of potential problems that could lead to failure and breakdown of the technical systems. Like the mechanical components, the lubricant itself can also change and this leads to losses of lubricating properties, such as reduced viscosity, contamination, degradation, loss of load carrying capacity, etc. [6] to [9]. A vehicle as a complex system comprises many load bearing and power transmitting contacts. These are composed of elements that participate in the power and torque transmission from the engine, through the transmission (gearbox, differential and other systems), to the important sub-systems in a vehicle [10]. Since it is a complex tribomechanical system, the transmission gearbox is split into eight main tribological systems. The tribosystems of the transmission gearbox are: tapered roller bearings, spur gears, synchronization elements, splashing, shifting elements, differential gear, sealing elements, and needle bearings [4]. This analysis indicates that the tribological characteristics of a complex tribomechanical system cannot be considered in a simple way. Thus, it is not easy to establish reliable methods, as well as to determine diagnostic parameters, for evaluating the analysed system. There are a variety of reasons for failures of real systems and so far there has been no reliable generic method for predicting the lifetime of complex systems [4] and [11]. Wear, fatigue, and mechanical vibration

*Corr. Author’s Address: University of Defence, Military Academy, Pavla Jurišića Šturma 33, Belgrade, Serbia, sretenperic@yahoo.com

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are some examples of the underlying reasons for contact failures. Gohar and Rahnejat highlight these modes of failure [1]. Fatigue spalling life prediction methods for concentrated contacts are also noted there. There are various underlying mechanisms for failure by wear due to lack of a coherent lubricant film [12]. Vibration is often the cause of failure, as it causes fatigue or wear. There are many examples of this, such as those highlighted for a valve train system by Teodorescu et al. [13] and in rotor and spindle bearings by Aini et al. [14]. Lubricant oil monitoring during use is one of the most important procedures in tribomechanical system diagnostics, due to the importance of the oil’s functions in this system. The advantage of this procedure is that information about the functionality of the system’s components is obtained without stopping and dismantling the vehicle. Modern trends in diagnostics have moved towards an increasing promotion of oil monitoring, which has resulted in an increased interest in oil producers and users. The reasons lie primarily in increasing reliability and effectiveness, as well as in economic considerations and protection of the environment [15] to [18]. There is growing interest in the use of coated contact surfaces in general. Hard wear resistant coatings lead the way, particularly for highly loaded contacts such as cam-follower pairs. This choice is also based on the increased fatigue resistance of coatings [19] to [21]. However, hard wear resistant coatings such as DLC (diamond-like-carbon) can exfoliate through fractures at high shear forces and can also be oleophobic. Due to an ever growing demand to reduce oil consumption and thus the amount of oil in mechanical systems, but also because of the increased severity of the contact conditions, many of systems need to operate under boundary lubrication and starvedlubrication conditions [2] and [22]. 1 TRIBOLOGICAL CHARACTERISTICS OF OIL The development of tribology as an interdisciplinary science based on experimental investigations and the varied experimental equipment and devices (tribometers) needed to carry this out have contributed to creating tribometry as a particular area of experimental research [23] to [25]. Identification of tribological processes, as a precondition to diagnosis of the conditions of real tribomechanical systems, can be carried out by: 444

•

tracking functional behaviour of a real technical system and • model investigations. Tracking the performance of a real tribomechanical system includes a narrow and strictly oriented long-term study without the possibility of varying and examining the influence of input parameters in a wider range. However, using model investigations enables a large range of data to be obtained, indicating the condition of a realistic system and enabling the prediction of its further behaviour with some reliability. In order to conduct these studies it is necessary to take samples from a real system and to simulate the contact conditions as well. In addition, the differences between real tribomechanical systems and studies under model conditions must be taken into account before making conclusions based on tribometric studies. On the other hand, most tribological characteristics are determinated using defined standard tests, as shown in Table 1. For these purposes, some of the standard commercial tribometers such as Falex, Timken, Plint, Koehler, SRV, etc. can be used. Table 1. Lubricant tribological characteristics tests Standard Contact geometry Wear Preventive Characteristics ASTM D2670 Pin and Vee Block ASTM D4172 (Four-Ball) Extreme Pressure Properties ASTM D2782 Block on Ring ASTM D2783 Four Balls Pin and Vee Block ASTM D3233 IP 240 Block on Ring Friction characteristics ASTM D 5183 Four-Ball Tribological behaviour of the lubricant in devices with real mechanical elements ASTM D5182 FZG – Gear Test Rig

A new measurement equipment for tribological studies have been developed and produced over the past few years. A new methodology of investigation is also being developed. The measuring system, applied to determine the tribological characteristics of the tribomechanical system elements is shown in Figs. 1 and 2. It is composed of [11]: • a TPD-93 Tribometer for normal force, frictional force, and frictional coefficient measurements; • thermopairs for temperature measurements of oil and elements in contact; • a PQ-2000 particle quantifier;

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• •

a Microscope for wear parameters measurements (length, width, and depth of worn zone); Talysurf 6, a computerized measuring device for surface topography and wear parameter measurements.

Fig. 1. Model of the investigation procedure of lubricant tribological characteristics during use

It should be pointed out that these investigations imply a previous determination of contact characteristics such as: • contact geometry; • intensity and character of external loads; • type (continual, cyclical, etc.) and velocity of motion; • temperature of elements in contact; • lubrication method. The elements of the contact pair are specified by a detailed analysis of a real tribomechanical system. These elements need to have strictly defined characteristics such as material type, hardness, surface condition, and so on. The examinations were performed using a “block on disc” tribometer with linear contacts typical for elements in a mechanical power transmission system such as gearboxes, gear couplings, rolling bearings, etc. After a certain period of time the linear contact is transformed into a surface contact due to the process of wearing. This type of contact is characteristic for cylindrical mechanical elements such as a strokecylinder pair in an internal combustion engine. As a great number of the elements in contact in the tribomechanical systems of a mechanical power transmission and engine have both linear and surface types of contact, the applied testing model using the “block on disc” tribometer can be used with sufficient accuracy to make a comparison of the tested oils. 2 RESULTS OF THE STUDY OF THE TRIBOLOGICAL CHARACTERISTICS OF OIL

Fig. 2. Measuring system applied for the determination of tribological characteristics

As shown in Fig. 1, the investigation procedure for determining the tribological characteristics of lubricant during use includes: • oil sampling from a real tribomechanical system [26] and [27]; • determination of physical-chemical characteristics; • analysis of wear products in the oil; • measuring tribological characteristics of the tribomechanical system in a model investigation using sampled oil as the lubricant.

Oil was sampled from engines and transmission gearboxes of the vehicles (Mercedes O 345 as vehicle 1, PUCH 300GD as Vehicle 2 and PINZGAUER 710M as Vehicle 3) that were in use. The tribological characteristics of the oil were examined in accordance with standard methods. The analysis was performed using both fresh oil and oil used in the engines and transmission gearboxes of vehicles. Testing of oil samples was carried out in accordance with commonly defined criteria for the quality of used oil. The research was conducted through a periodic oil sampling from the engines and transmission gearboxes of the vehicles listed above. During oil sampling, special attention was paid to the positions of the sampling, which enabled each sample to be a representative one. Each sample was taken from the “live zone,” i.e. the zone closer to the elements in contact. Special attention was also paid to preserving the sample from contamination, both in the sampling phase and in the manipulation phase, according to the prescribed

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procedures. These measures provided a very high level of purity to all elements in the sampling chain as well as for the separation of samples in a way that does not perturb the integrity of the data that the samples carry. Results obtained during the tests contain information about the friction coefficient, friction force, width and depth of the wear track, wear shape of the block's contact surface, change in the friction coefficient and temperature during the time of contact, block's and disc's surface topography parameters before and after the testing, etc. To investigate the dynamics of the contact process, the force and friction coefficient signals were recorded continuously for later processing. Figs. 3 to 5 show the friction coefficient of the engine oil samples against vehicle mileage (distance in traveled kilometres). It can be seen that the mean value of the friction coefficient between the block and the disc is in the 0.0684 to 0.101 range, using the tested engine oil from all vehicles. It can be concluded that increase in vehicle mileage for Vehicle 1 (using SAE 10W-40, API Classification CF engine oil) causes a gradual decrease in the friction coefficient. The increase in vehicle mileage for Vehicle 2 (using SAE 10W-40 API SG/CE engine oil) causes an initial decrease and later increase in the friction coefficient. The engine oil from Vehicle 3 (SAE 30/S3) shows an initial increase and later decrease in the friction coefficient.

sample), used in Vehicle 1, which is higher than the friction coefficient of used engine oil, was measured because of the presence of ZDDP. The ZDDP content of engine oil is different from transmission oil due to the engine conditions.

Fig. 4. Change in the friction coefficient of Vehicle 2 engine oil

Fig. 5. Change in the friction coefficient of Vehicle 3 engine oil

Fig. 3. Change in the friction coefficient of Vehicle 1 engine oil

Zinc dialkyldithophosphate (ZDDP) additives are arguably the most successful lubricant additives ever invented [28]. They were introduced over 60 years ago, have been in continuous use ever since, and are still being employed in practically all engine oils and many transmission oils. The high value of the friction coefficient (μ = 0.101) of fresh engine oil SAE 10W-40, API CF (zero 446

The ZDDP additive has three important functions: it serves as an antioxidant, anti-corrosion, and antiwear additive. At low temperatures (below 100 °C), the ZDDP has an antioxidant function. If applied at higher temperatures, which is the case for engine oils, it thermally decomposes and the resulting products have an antioxidant function. The temperature of this degradation process is dependent on the alkyl groups present (and the metal cation) but usually occurs somewhere between 130 and 230ºC. Three main ways that ZDDP acts as an anti-wear agent have been proposed: (a) by forming a mechanically protective film; (b) by removing corrosive peroxides or peroxyradicals; (c) by “digesting” hard and thus abrasive iron oxide particles [28]. When ZDDPs react with hydroperoxides and peroxy radicals they generate products which themselves act as effective oxidation

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inhibitors [29], making ZDDP a highly efficient inhibitor. Figures 6, 7 and 8 show the changes in wear width of sampled engine oils versus vehicle mileage.

Figs. 9 to 11 show the changes in the friction coefficient of the transmission oil (gearbox oil) samples against vehicle mileage.

Fig. 8. Change in the wear width of Vehicle 3 engine oil versus mileage Fig. 6. Change in the wear width of Vehicle 1 engine oil versus mileage

Fig. 9. Change in the friction coefficient of Vehicle 1 transmission oil Fig. 7. Change in the the wear width of Vehicle 2 engine oil versus mileage

The increase in mileage causes an increase in the disc wear width for the tested engine oils from the all three vehicles. The maximum value of the disc wear width is 0.494 mm (Vehicle 1), 0.645 mm (Vehicle 2) and 0.610 mm (Vehicle 3). An increase in wear width in the initial period can be explained by the wellknown bathtub curve diagram, which corresponds to the initial use of the engine with fresh oil. The approximately constant growth in disc wear width as a function of mileage is caused by the wear products increase in the lubricant and the gradual degradation of the lubricantâ&#x20AC;&#x2122;s characteristics during the test. Surface roughness of the discs and blocks were measured, prior to the experiments, using Talysurf 6.

The mean values of the friction coefficient between the block and the disc, using the tested transmission oils, are in the 0.058 to 0.0987 range. The increase in mileage causes a gradual increase in the friction coefficient of the transmission oil used in Vehicle 1, while the friction coefficient of Vehicle 2 transmission oil gradually decreases. In the case of the transmission oil used in Vehicle 3, the friction coefficient initially decreases and then increases with mileage. Fig. 9 shows that the friction coefficient of the samples of used transmission oil ATF (Automatic transmission fluid) Prista (from Vehicle 1) is higher than the friction coefficient of the zero samples of the same oil. Higher temperatures lead to reactions between the additives from the oil and the lubricated surface,

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thus ZDDP decomposes into free radicals. This slows the oxidation process of transmission oil down. Free radicals were found to be present in the used transmission oil (Prista ATF) and were formed as previously described. The free radicals do not influence the decrease in friction and wear, because of the ZDDP antioxidant function.

function. The layers formed on the contact surfaces cause the high values of the friction coefficient.

Fig. 12. Change in wear width of Vehicle 1 transmission oil versus mileage

Fig. 10. Change in the friction coefficient of Vehicle 2 transmission oil

Fig. 13. Change in wear width of Vehicle 2 transmission oil versus mileage

Fig. 11. Change in the friction coefficient of Vehicle 3 transmission oil

From Fig. 10, it can be seen that the friction coefficient for the zero sample of transmission fluid (Vehicle 2) is higher than that for the used transmission oil samples. This result can be explained by the structure of the lubricant, which contains a sulfur-phosphorous EP (extreme pressure) antiwear additive. During contact between surfaces, the phosphorus in the additive reacts with the metal at 700 °C and forms a metal-phosphide layer, which protects the surface from wear. At the same time, the sulfur in the additive reacts with the metal at 900 °C forming metal sulfides, which have the same anti-wear 448

Fig. 14. Change in wear width of Vehicle 3 transmission oil versus mileage

Used UAMS transmission oil contains polar compounds formed in the oxidation chemical reactions of additives and metals, especially at

Perić, S. – Nedić, B. – Trifković, D. – Vuruna, M.

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elevated operating temperatures. In this way, the polar compounds formed are bonded to the block and disc metal surface, forming a layer of metal soap. A formed lubricating layer prevents the contact of block and disc surfaces, resulting in the transition from an initial boundary lubrication to an elastohydrodynamic lubrication. The results are less friction and wear, as well as more sliding of surfaces. Figs. 12 to 14 show the changes in wear width of the sampled transmission oil versus vehicle mileage. The increase in mileage causes the increase in disc wear width for the tested transmission oils from all three vehicles. The maximum values of the disc wear width are 0.752 mm (Vehicle 1), 0.833 mm (Vehicle 2) and 0.676 mm (Vehicle 3). 3 CONCLUSIONS Based on the experimental investigation, the following conclusions can be summarized: 1. In order to choose the correct lubricant, it is necessary to know its formulation (base oil and additive package), physical-chemical properties, lubrication conditions, and the characteristics of the technical system in which it is used. 2. There are changes in the working and tribological properties of all components of the vehicle during use: the speed and degree of degradation processes depend on the operating conditions. Changes that occur in the components of the vehicle and in the lubricants form under the same conditions and are mutually correlated. 3. An effective program of condition assessment of lubricants includes: testing of the physicalchemical properties of lubricants, testing of the content of contaminants, testing of the content and the types of products, as well as testing of the tribological properties of lubricants. 4. The model tests ensure the repeatability of sampling and testing procedures, comparability of results, and assessment of the same elements under different test conditions. 5. The changes in the physical-chemical and tribological properties of the lubricating oil from the vehicle engine and transmission gearbox are directly dependent on the functional characteristics of all the elements of the tribomechanical system. 6. The method of oil analysis, presented above, should enable an early detection of failure due to the development of friction and wear processes during operation.

7. The presented method for the examination of the tribomechanical characteristics of oils under model conditions, together with testing their physical-chemical characteristics, will be used for the development of a new universal diagnostic model. This diagnostic model will allow the condition of components in the mechanical power transmission systems and vehicle engines to be determined. 4 REFERENCES [1] Gohar, R., Rahnejat, H. (2008). Fundamentals of Tribology. Imperial College Press, London, DOI:10.1142/p553. [2] Bhushan, B. (2013). Introduction to Tribology. John Wiley & Sons, New York, DOI:10.1002/9781118403259. [3] Peric, S., Nedic, B. (2010). Monitoring oil for lubrication of tribomechanical engine assemblies. Journal of the Balkan Tribological Association, vol. 16, no. 2, p. 242-257. [4] Wienecke, D., Bartz, W. (2001). Automobile Transmission Gears as Tribological Systems. Tribology Transactions, vol. 44, no. 3, p. 484-488, DOI:10.1080/10402000108982485. [5] Vähäoja, P., Välimäki, I., Roppola, K., Kuokkanen, T., Lahdelma, S. (2008). Wear Metal Analysis of Oils. Critical Reviews in Analytical Chemistry, vol. 38, no. 2, p. 67-83, DOI:10.1080/10408340701804434. [6] Babic, M. (2004). Lubricants Monitoring. University of Kragujevac, Faculty of Mechanical Engineering, Kragujevac. (in Serbian) [7] Peric, S. (2006). Influence of Tracked Vehicle Transmission Gear Exploitation Method upon Physical and Chemical Characteristics of Lubricants, MSc thesis. University of Belgrade, Faculty of Mechanical Engineering, Belgrade. (in Serbian) [8] Barnes, M. (2002). Oil Viscosity - How It′s Measured and Reported. Practicing Oil Analysis. Magazine, Nov.-Dec. [9] Mang, T. (2000). Future Importance of Base Oils in Lubricants. Proceedings of 12th International Colloquium, Tribology Plus, Esslingen, p. 23-35. [10] Beuf, D. (2001). Used Oil Analysis and Equipment Monitoring. Texaco Training, Chevron-Texaco Technology, Ghent. [11] Peric, S. (2009). The Development of a Method of Diagnosis the Condition from the Aspect of PhysicalChemical and Tribological Characteristics of Lubricating Oils of Vehicles, PhD Thesis. University of Defence, Belgrade. (in Serbian) [12] Archard, J.F., Ernest J.G. (1980). Wear Control Handbook. Amer Society of Mechanical Engineers, New York. [13] Teodorescu, M., Kushwaha, M., Rahnejat, H., Taraza, D. (2005). Elastodynamic transient analysis of a four-

An Experimental Study of the Tribological Characteristics of Engine and Gear Transmission Oils

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cylinder valvetrain system with camshaft flexibility. Journal of Multi-body Dynamics, vol. 219, no. 1, p. 1325, DOI:10.1243/146441905X9962. [14] Aini, R., Rahnejat, H., Gohar, R. (1995). An experimental investigation into bearing-induced spindle vibration. Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, vol. 209, no. 2, p. 107-114, DOI:10.1243/ PIME_PROC_1995_209_130_02. [15] Peric, S., Nedic, B., Vuruna, M. (2009). Monitoring physical and chemical characteristics oil for lubrication. Journal Tribology in Industry, vol. 31, no. 3-4, p. 5966. [16] Liu, C., Nemoto, S., Ogano, S. (2003). Effect of soot properties in diesel engine oils on frictional characteristics. Tribology Transactions, vol. 46, no. 1, p. 12-18, DOI:10.1080/10402000308982593. [17] Markova, V., Myshkin, K., Ossia, V., Kong, H. (2007). Fluorescence sensor for characterization of hydraulic oil degradation. Tribology in Industry, vol. 29, no. 1-2, p. 33-36. [18] Godfrey, D., Herguth, W.R. (1995). Physical and chemical properties of industrial mineral oils affecting lubrication. Lubrication Engineering, vol. 51, no. 5, p. 397. [19] Teodorescu, M., Rahnejat, H. (2007). Mathematical modelling of layered contact mechanics of cam-tappet conjunction. Applied Mathematical Modelling, vol. 31, no. 11, p. 2610-2627, DOI:10.1016/j.apm.2006.10.019. [20] Jaffar, J.M. (1989). Asymptotic behaviour of thin elastic layers bonded and unbonded to a rigid foundation. International Journal of Mechanical Sciences, vol. 31, no. 3, p. 229-235, DOI:10.1016/0020-7403(89)901136. [21] Naghieh, G.R., Rahnejat, H., Jin, Z.,M. (1999). Characteristic of frictionless contact of bonded elastic

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and viscoelastic layered solids. Wear, vol. 232, no. 2, p. 243-249, DOI:10.1016/S0043-1648(99)00152-0. [22] Velkavrh, I., Kalin, M., Vižintin, J. (2008). The performance and mechanisms of DLC-coated surfaces in contact with steel in boundary-lubrication conditions – a review. Strojniški vestnik – Journal of Mechanical Engineering, vol. 54, no. 3, p. 189-206. [23] Rac, A. (1991). Tribology. University of Belgrade, Faculty of Mechanical Engineering, Belgrade. (in Serbian) [24] Ripa, M., Spanu, C., Ciortan, S. (2008). Characterization of hydraulic oils by shear stability and extreme pressure tests. Tribology in Industry, vol. 30, no. 3-4, p. 48-54. [25] Neale, M.J. (2001). The Tribology Handbook. Butterworth-Heinemann publications, Oxford. [26] Lee, M.P., Priest, M., Stark, S.M., Wilkinson, J.J., Lindsay Smith, J.R., Taylor, I.R., Chung, S. (2006). Extraction and tribological investigation of top piston ring zone oil from a gasoline engine. Proc. IMechE, J. Engineering Tribology, vol. 220, no. 3, p. 1-10, DOI:10.1243/13506501JET148. [27] Yatsutomi, S., Maeda, Y., Maeda, T. (1981). Kinetic approach to engine oil: 1–analysis of lubricant transport and degradation in engine system. Industrial and Engineering Chemistry Product Research and Development, vol. 20, no. 3, p. 530-536, DOI:10.1021/ i300003a020. [28] Spikes, H. (2004). The history and mechanisms of ZDDP. Tribology Letters, vol. 17, no. 3, p. 469-489, DOI:10.1023/B:TRIL.0000044495.26882.b5. [29] Al-malaika, S., Coker, M., Scott, G. (1988). Mechanism of antioxidant action: Nature of transformation products of dithiophosphates-Part 1. Their role as antioxidants in polyolefins. Polymer Degradation and Stability, vol. 22, no. 2, p. 147-159, DOI:10.1016/01413910(88)90038-9.

Perić, S. – Nedić, B. – Trifković, D. – Vuruna, M.

Received for review: 2012-09-23 Received revised form: 2013-02-07 Accepted for publication: 2013-05-06

Modification of Conductive Material AA6101 of OPGW Conductors against Lightning Strikes Karabay, S. Sedat Karabay*

Kocaeli University, Faculty of Engineering, Turkey In this article, failure in lightning tests and the overcoming of its destructive effects by improving the new generation of optical grounding wire (OPGW) are presented. The designed composite structure for transmission lines in Turkey is composed of six galvanized steel wires, one stainless steel tube with multiple glass fibres and 12 aluminium alloy AA6101 wires. Test samples from prototype OPGW successfully passed short circuit requirements but failed in tests of lightning strikes. Consequently, a material modification was applied by feeding 3% AlB2 master alloy as a 9.5 mm rod into molten metal in the tundish when the metal flows from the melting furnace to the vertical log casting mould. Logs cast from AA6101 are used to manufacture feedstock by means of extrusion press. Impaired electrical conductivity of the AA6101 due to the presence of heavy metal impurities such as Ti, Cr and V should be increased to pass the tests. Following this, the transition metals were transformed into insoluble borides from solution after inoculation with AlB2. As a result, the conductivity of wires drawn from feedstock produced by extrusion press with the modified AA6101 billets was increased from 52.5 to 57% IACS. Consequently, the modified OPGW with AlB2 satisfied the requirements of international standards related to lightning tests. Keywords: optical ground wire, lightning strike, AlB modification, conductivity, AA6101 feedstock, wire breakage

0 INTRODUCTION The situation of overhead power transmission systems varies from year to year. Currently, the development of more reliable power transmission facilities is a serious subject for electric power utilities. Overhead ground wires (OPGW), installed on the upper portions of overhead transmission lines to protect conductors from lightning, may have their strands broken when struck by extremely powerful lightning bolts [1]. In particular, those lines passing through areas where heavy winter lightning frequently occurs or areas in which the total days on which lightning occurs are comparatively high require upgraded lightning resistant overhead ground wires to increase the reliability of the power transmission systems. Recently, the use of OPGW with a communication function has been increasing, and the roles played by OPGW have been becoming increasingly prominent. Information technology, such as web-net services, is undergoing rapid development, and this is driving demand for optical-fibre products for global optic communication link systems [2]. Two types of OPGW are generally available at present. One is a tight buffer type, in which the optical fibres are housed with tension members. The other is a loose buffer type, in which the optical fibres are loosely housed inside a tube. The representative tight buffer type called “spacer type” has an aluminium spacer inserted in the aluminium tube to suppress fibre movement. It is mainly used by Japanese domestic power companies and has proved extremely reliable in installations. The representative loose buffer type, predominantly produced in Europe

and called the “stainless steel tube type” has fibres with surplus length and a jelly compound inserted into the stainless steel tube. Grease is used to fill the spaces between the tube and aluminium-clad steel or galvanized steel and aluminium alloy wires AA6101 or AA6201 in order to avoid galvanic corrosion due to different metals’ contact with each other [3]. However, if the stranding of the wires is not performed perfectly, the gaps between wires cause the grease to leak during heavy rain. The grease can become hardened by sunlight or a dry atmosphere; prolonged exposure to these environmental conditions causes the grease’s anti-corrosion effect to weaken [4]. This phenomenon is exacerbated in particularly harsh environments. This galvanic corrosion problem has been eliminated recently by cladding the steel fibre tube with EC grade aluminium. Using materials of the OPGW such as steel tubes, aluminium-clad steel tubes, aluminium alloy AA6101, galvanized steel wires, and aluminiumclad steel wires, manufacturing various types of combinations is possible [5]. Although new products are supplied to the conductor market to improve OPGW alternatives to pass lightning tests, the final cost is still a significant factor in selling them in developing countries. 1 PARAMETERS OF DESIGNED AND MANUFACTURED OPGW A versatile loose-buffer-type OPGW has been designed and manufactured by considering the environmental conditions of Turkey and the requirements of the Turkish Electrical Authority (TEK). A cross-sectional

*Corr. Author’s Address: Department of Mechanical Engineering, Umuttepe Campus, Kocaeli, Turkey sedatkarabay58@gmail.com

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view and the stranding of sub-parts are shown in Fig. 1.

balanced extremely close to “perfect”. Experimentally determined values per ASTM A370 for the tube’s axial ultimate strength are in the range from 966 to 1379 N/mm². Some anisotropy is expected to exist due to the axial drawing of the tube. Mechanical and electrical properties of the main conductive aluminium part (unmodified aluminium) are shown in Table 4. The OPGW prototype was manufactured using the feedstock of an extrusion press with the mechanical properties shown in Table 4. Aluminium wires are tested according to IEC 104 standard to measure both mechanical and electrical parameters. Table 1. Spectral analysis of conventional (unmodified) AA6101 sample in % wt Mg

0.55

0.25

0.07

0.08

0.06

0.03

0.028

0.026

Table 2. Optical characteristics of fibres located in the stainless steel tube of OPGW

Fig. 1. a) Cross sectional view of OPGW; b) view of OPGW; (1) AA6101, (2) steel wire, (3) steel tube, (4) fibres

In design, the most important part is the conductive part, which is composed of aluminium alloy AA6101. Spectral analyses of the conductive alloy used in the manufacture of the OPGW are shown in Table 1. The main physical parameters of fibre optics located inside of the stainless steel tube are defined in Table 2. The mechanical properties of the zinc-coated steel wires in the construction given in Fig. 1 are presented in Table 3, taken from IEC 888 and ASTM B498. The zinccoated steel wires are manufactured in three grades, as regular, high strength, and extra-high strength steel wires. In the construction for TEK, high strength steel wires were used [6]. The zinc-coating is required for Class 1 of IEC 888. The optical tube used in the prototype OPGW is made of stainless steel Type 304. The tubes are manufactured by axially drawing and mechanically forming a flat strip of stainless steel around the optical fibres and laser welding the gap between the edges of the formed strip. The resulting seam is imperceptible to the unaided eye, and the resulting cylindrical tube is geometrically uniform and

Fibre type Non-zero Dispersion, Shifted Single Mode Fibre Specification (International ITU-T G.655 Telecommunication Union) Mode field diameter 9.6±0.5(at 1550 nm) µm Cladding diameter 125±1 µm Coating diameter 245±10 µm Wavelength 1550 1530 to 1565 1625 nm Attenuation coefficient 0.22 0.27 dB/km Dispersion 2.0 to 6.0 ps/(nm·km) PMD (polarization 0.5 ps/km1/2 mode dispersion)

1.1 Sensitive Part of OPGW: Fibre Optics An optical fibre is a flexible, transparent fibre made of glass (silica) or plastic, slightly thicker than a human hair. It functions as a waveguide, or “light pipe”, to transmit light between the two ends of the fibre. Fibres are used instead of metal wires because signals travel along them with less loss and are also immune to electromagnetic interference. Optical fibres typically

Table 3. Mechanical properties of extra-high strength steel wires, IEC 888 and ASTM B498 Nominal wire diameter [mm] Up to and over including 2.25 2.75 2.75 3.00 3.00 3.50

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Diameter tolerance [mm] ±0.04 ±0.05 ±0.05

Min. stress at %1 Minimum ultimate extension [MPa] tensile strength [MPa] Minimum ultimate elongation Class 1 [%] zinc coating 1410 1590 2.0 1410 1590 2.5 1380 1550 2.5 Karabay, S.

Mandrel diameter Minimum for wrapping test number of twists [mm] in torsion test 4 5 5

14 12 12

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include a transparent core surrounded by a transparent cladding material with a lower index of refraction. Light is kept in the core by total internal reflection. This causes the fibre to act as a waveguide. Fibres that support many propagation paths or transverse modes are called multi-mode fibres (MMF), while those that only support a single mode are called single-mode fibres (SMF). Multi-mode fibres generally have a wider core diameter, and are used for short-distance communication links and for applications in which high power must be transmitted. Some parameters used in selecting of properties of fibres are indicated in Table 2 [7].

where power is now expressed in units of decibelmilliwatt, and α is known as the attenuation coefficient of the fibre in units of decibel per kilometre [7].

1.1.2 Fibre optic Wavelength

1.1.4 Dispersion

Light is an electromagnetic wave that develops in both time and space. The development of a light wave in time is described by the period it takes for a wave’s two identical points to pass; the development of light wave in space is described by wavelength [7].

Attenuation and dispersion are the main forms of linear degradation. Signal attenuation is mainly due to absorption and scattering, while dispersion can be a result of factors such as the waveguide properties of the fibre or wavelength dependence of the index of refraction. A decisive factor that limits the performance of optical links, especially at higher data rates, is dispersion. In general, dispersion refers to the spreading of the pulses that make up a signal as it travels along the fibre [7].

1.1.3 Attenuation The most common form of signal degradation is attenuation. In fact, it was only after the manufacturing of low loss silica fibre began that the field of fibre optics communication became possible. Attenuation is commonly characterized in units of decibel per kilometre. The rationale behind this choice becomes clear once we recognize that the power of an optical signal attenuates exponentially with distance as given in the Eq. (1). I ( z ) = I 0 eα F z . (1)

Here, z is the distance along the length of the fibre, I(z) is the optical power, I0 is power at z = 0 and αF is the attenuation coefficient. Eq. (1) can alternatively be written as given in Eq. (2):

10 log I ( z ) = 10 log( I 0 ) − 4.343α F z. (2)

The relation between ln(x) and log(x) has been defined as ln(x) = 2.302 log(x). Eq. (1) provides a simple and convenient way of expressing the power loss as a function of distance. If we define α = 4.343 αF . Eq. (2) becomes as given in Eq. (3):

P( z ) dBm = P ( 0 )dBm − α z , (3)

1.1.5 Polarization Mode Dispersion (PMD) Another form of dispersion results from pulse broadening due to polarization of an optical pulse and the bi-refringence of fibres. To be more accurate, a given pulse may consist of different polarization components or states, and fibres do not provide an identical index of refraction for these polarization states. Factors such as stress, fibre bends, variations in the composition or geometry, and non-circularity of the fibre can preferentially cause slight changes in the effective index of refraction of fibre along different polarization directions. When the different polarization

Table 4. Test results of drawn wires from feedstock produced by extrusion of AA6101 conventional (unmodified) billets. Wires were exposed to T8 (billet homogenization 560 ºC, 6 hours, wire drawing from feedstock and heat treatment of wires 175 ºC, 6 hours) condition Diameter [mm] 3.04 3.05 3.06 3.07 3.08

Cross-section [mm2] 7.26 7.31 7.35 7.40 7.45

Resistivity [ohm mm²/m] 0.032445 0.032768 0.032836 0.032200 0.032671

DC resistance at 20°C [ohm/km] 4.470 4.485 4.465 4.350 4.385

Conductivity [% IACS] 53.1 52.6 52.5 53.5 52.8

Breaking load [N] 2305.35 2354.40 2393.64 2403.45 2413.26

Tensile strength [N/mm²] (at 250 mm length) 317.64 322.25 325.49 324.71 323.92

Modification of Conductive Material AA6101 of OPGW Conductors against Lightning Strikes

Elongation at 250 mm [%] 4.6 5.1 4.8 5.2 4.7

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components of an optical signal experience different indices of refraction, they propagate with different speeds, causing pulse broadening and dispersion. This effect is known as polarization mode dispersion (PMD) [7]. Standard feedstock produced with AA6101 by the method of extrusion has 40 to 45 HB (Brinell hardness) and 130 to 150 N/mm² tensile strength. Following the cold drawing of them to the required wire diameter, tensile strength and hardness reach the range of 250 to 260 N/mm² and 50 to 55 HB, respectively. Then, heat treatment is applied at 175 ºC, 6 hours in the furnace. Thus, wires reach hardness level as 66 to 68 HB. 2 EXPERIMENTAL STUDIES In the transmission lines of Turkey, several types OPGW constructions are used. Type 1 is manufactured with an SS (stainless steel) tube, loosely located fibres and AlMgSi wires with a combination of galvanized steel wires. In this construction, there are six galvanized steel wires, one SS tube and 12 aluminium alloy wires. Type 2 is a combination of six aluminiumclad steel wires, one SS tube and 12 AA6101 (AlMgSi) wires. Type 3 consists of one aluminium tube located in the central part and aluminium-clad steel wires helically wound around its surface. However, due to harsh environmental conditions, most of the overhead line projects are performed mainly with Type 1 and Type 2 OPGW constructions. Naturally, when the first and second types compared, the combination with Al clad steel wires is better than galvanized steel wires due to absent of galvanic action between different materials. However, the tensile strength of the conductor (OPGW) with Al-clad steel wire is lower than the conductor reinforced with galvanized high strength steel wires. The reason is due to the decreasing of diameter of steel wires by coating with aluminium. Therefore, it is the most popular design about the ground conductor is related to material combination with extra-high-strength galvanized steel, a loose tube and AA6101 alloy wires in transmission lines of Turkey. Moreover, its economical price also makes it popular. Therefore, according to the preferences of the Turkish Electrical Authority, the Type 1 OPGW has been designed and manufactured. The proposed structure was exposed to electrical tests. The behaviours of materials and their results after applications of electrical tests were presented at every stage. The prototype OPGW passed short circuit tests without damage to the wires. Unfortunately, most of its aluminium wires were damaged in the first 454

trial of lightning tests. To overcome this problem, it was decided that main conductive part should be specifically improved to pass the required articles of type test specification [8]. The application methods of the type test procedure to a new designed OPGW may indicate some changes according to the product properties and specifications of different countries. The satisfaction of test conditions may be extremely demanding. Therefore, improvements are needed on some parts of proposed construction to pass the tests. However, the short-circuit current that circulates during the occurrence of a phase-to-ground fault near the substation is one of the most critical parameters for the specification of the OPGW. For a new conductor product, design and manufacturing studies must generally be performed in two stages. The first stage is to design it, theoretically. Then, having completed the manufacturing process of the prototype, prepared samples should be exposed to several tests in the laboratory by simulating environmental conditions. Among of various tests, two tests are vitally essential. These are the short circuit and lightning tests. Conductors can be damaged in seconds when exposed to these effects [9]. To pass of the type test, a product should be designed using a multi parameter equation due to adverse effects of the conductor components. In the study, two vital tests were considered, explaining how the new OPGW was developed and passed heavy electrical test requirements. 2.1 Short Circuit Test and Results The objective of the short circuit test is to verify that the OPGW can withstand repeated short circuit applications without exceeding optical, physical or thermal requirements. A view of the electrical circuit at the laboratory is shown in Fig. 2. Two samples were used for the test. One sample was used to monitor the performance of the optical fibres and to observe any physical damage that might occur during the test [10]. The other sample was used only to measure the temperature at several points in the cross section of the conductor. The conductors were positioned about 1 m apart and 2 m above the ground. The conductors were electrically connected in a series so that they would be subjected to the same short circuit current. The short circuit current was provided by a high level current transformer. A separate low-level transformer was also connected to the test span. It provided a current of several hundred amperes to maintain the cable temperature at 40 °C between short circuit applications. The length of conductor between the current injection points was 10 m the optical fibres

Karabay, S.

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were terminated beyond each dead–end clamp. A turnbuckle was used to tension the cable to the required value. A dynamometer was used to measure the tension. The optical sample was tensioned to about 1369 daN at 40 °C. This is about 15% of the 9126 daN of the rated tensile strength of the conductor. The temperature in the sample was measured at three locations using three fast-responding thermocouples. They were spaced 1 m apart at the following locations. Thermocouple 1 was located between two aluminium alloy wires in the outer layer. Thermocouple 2 was placed between two galvanized steel wires in the first layer. Finally, Thermocouple 3 was installed to the surface of stainless steel for optical unit. The thermocouples were isolated from the other instrumentation to prevent electrical interference. For power attenuation measurement, all twenty-four fibres were spliced producing a total fibre length under test of 240 m (24 fibres × 10 m). The conductor was first subjected to two low-level calibration shots and then ten “official” shots. The purpose of the calibration shots was to ensure that the current level was correct. For the official shots, the target values for the electrical parameters are given in Table 5. For each shot, the fault current and duration may vary slightly from the target values. The objective was to achieve a minimum energy level for each shot. To ensure the optical signals were stable, the power meters were powered on and operating for at least one hour before the first shot. The optical and temperature data were acquired for one hour after the tenth shot. The conductor was maintained at 40 °C during this hold period. The optical attenuation during the short circuit applications newer increased more than 0.05 dB/km at 1550 nm. The maximum absolute temperature reached was 210 °C (163+47 °C). A section of conductor from the mid-span, and near both

dead ends were dissected after the test and visually examined for damage. The results are presented in Table 6. Table 5. Electrical parameters of target values Parameter Energy Fault current Duration Asymmetry Waveform

Target value 109.5 kA²s 14.8 kA 0.5 s Maximum possible To be symmetrical after 3rd cycle

Table 6. Visual damage results of short circuit test Cable Component Aluminium Alloy Wires Galvanized Steel Wires Stainless Steel Tube Fibres Compound

Dead ends (Fixed ends) No melt and breakage No melt and breakage No melt and collapse No melt and breakage No vaporization

Other surfaces of conductor No melt and No melt and breakage breakage No melt and No melt and breakage breakage No melt and No melt and collapse collapse No melt and No melt and breakage breakage No vaporization No Vaporization Midpoint

Acceptance criteria: a) the temperature rise immediately after the current pulse shall be less than 180 °C inside the optical unit; b) the attenuation increase during the tests shall be less than 1 dB/km. There shall be no change in attenuation after the cable has cooled down to 40 °C; c) there shall be no irreversible birdcaging. The cable and hardware shall be dissected midpoint of the span. Each separable component of the cable shall be inspected. 2.1.1 Discussion of Short Circuit test Results There was no sign of birdcaging, excessive wear, discoloration, deformation or other sign of breakdown.

Fig. 2. Conductor temperature rise during short circuit Modification of Conductive Material AA6101 of OPGW Conductors against Lightning Strikes

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Fig. 3. Variation in optical attenuation during short–circuit

Results related to temperature fluctuation in OPGW and attenuation of fibres can be seen by examining the records given in Figs. 2 and 3, respectively. The maximum temperature rise recorded was measured as 163 °C at the outer layer (Max. 163 < 180 °C). The results of conductor components after test have been summarized in Table 6. Consequently, the design study and type test experiments verified each other. Accordingly, the selected materials and construction type of OPGW satisfied all articles related to the short circuit type tests.

surfaces of the OPGW after application of lightning charge are presented in Fig. 5

2.2 First Lightning Test The samples with lengths of 50 m were clamped into the test stand, as shown in Fig. 4. The OPGW was prepared with a protective spiral and a guy spiral. With a mechanical power drive in connection with a tension meter, the wire tension was adjusted to 20% of the17.9 kN of the calculated breaking load (UTS) of the conductor under test. For the purpose of mechanical damping during the lightning test, two springs were installed at each end of the mechanical system, including the test object. The upper rod electrode is vertically adjustable and placed above the OPGW. It is rounded at the end facing the arc and has a diameter of 25 mm. With a wire (copper, diameter 0.1 mm), the lightning current is ignited. The ground wire under test is symmetrically connected to the power source in order to minimize the magnetic force on the arc. To test the behaviour of the OPGW under the most difficult conditions, five tests were carried out on the test sample at different places. The electrode gap was adjusted to 80 mm. The cable was initially stressed with a mechanical load. The amplitude of the arc current was adjusted to 200 A. The duration of the arc was 500 ms (Total charge100 Coulomb according to IEC 60794-1-2 test procedure H2). Views of the 456

Fig. 4. Schematic illustration of lightning test stand

2.2.1 Discussion of First Lightning Test Results Having completed ignition of lightning charge, the conductor must withstand 75% of the rated tensile stress (RTS). The RTS of the OPGW is 8950 kN. This means that the broken Al wires at each trial never number more than nine wires, owing to restriction on the complete strength of OPGW. However, in the experiments 9 to 10 Al wires were destroyed due to lightning arc. Damaged strands due to spot melting and breaking of OPGW are presented in Figs. 5a and b. Although considerably destroying the wires located on the outer layer of OPGW, as seen in Fig. 5, the conductor (OPGW) can still withstand 75% of the RTS. However, the specification of Turkish Electrical Authority indicates that complete resistance of the conductor must not increase 20% over the initial value after application of the lightning charge. This rule restricts the broken wires in the OPGW conductor to “3 wires” after test. For the elimination of excessive

Karabay, S.

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Fig. 5. View of melted and broken wires after lightning test

wire breaking, either the diameter of the wires or the number of wires or the conductivity of metal must be increased. However, the diameter of the conductor is not increased due to compatibility of available grounding wires in the transmission lines. Therefore, modification of the conductive material to increase conductivity was chosen in order to overcome the destructive effects of lightning charges. 2.3 Modification of Aluminium by Inoculating AlB2 When the OPGW samples are exposed to lightning, as seen in Fig. 5, the breaking of excessive wires owing to spot melts can be detected easily. It is clearly understood that the material needs some improvement in order to withstand the effects if lightning. The first idea for the solution of the problem is to increase the melting point of the material by using some additives into the molten material [11]. However, the conductive metal should also satisfy 52.5% IACS of minimum conductivity level, as presented in Table 7. In other words, Table 5 applies a restriction in the increasing of material strength of the conductive part with high strength alloying elements to resist lightning energy. Table 7. Expected minimum tensile strength and conductivity of AA6101 wires after T8, IEC 104 Diameter of wire ≤ 3.5 mm ≤ 3.5 mm

Conductivity 52.5 % IACS 53.0 % IACS

Tensile strength 325 MPa 295 MPa

Some additives fed into the molten material to increase the melting point adversely affect the material’s electrical properties. It is well known that impurities available in the molten metal bath such as Ti, Cr, V, and Zr decrease conductivity or increase resistance [12]. These impurities act a barrier to the flowing atoms in the material. If the conductivity of the material is high, the current flow will be exceptionally fast, so heating of the material will be lower. It was

determined experimentally by Matthiessen that the increase in the electrical resistivity of a metal due to the presence of a small amount of another metal in the solid solution is independent of the temperature [12]. Accordingly, the total electrical resistivity of an impure metal may, therefore, be separated into additive contributions: ρ0, residual resistivity caused by the scattering of electrons by impurity atoms and lattice defects and is temperature independent but dependent on the impurity concentration (c); and ρi, the temperature-dependent intrinsic resistivity arising from the scattering of electrons by lattice waves or phonons. ρ(c,T) defines the total resistance of the metal. The relation including explained parameters is defined in the Eq. (1) [13]:

ρ (c, T ) = ρ0 (c) + ρi (T ). (4)

Consequently, the electrical conductivity of pure metals is reduced by impurities and structural imperfections. It is extremely important to minimize resistance losses in power transmission applications by removing as many such imperfections as possible. The rule of Nordheim states that in the case of dilution, the residual resistivity is proportional to the impurity concentration [13]. When present in a precipitated rather than solute form, the impurities cause a much smaller reduction in conductivity. AlB2 and AlB12 phases of aluminium boron master alloys show clustering to precipitate impurities, in particular titanium, vanadium, chromium, and zirconium in aluminium (99.6 and 99.7%) and also aluminium alloys such as AA6101 and AA6201 [14]. AlB2 can be added into aluminium as a master alloy. There are two ways to produce feedstock for production of the conductor. In OPGW constructions, the aluminium component is composed of drawn wires from feedstock of AA6101 or AA6201 alloys. Both of the feedstock are manufactured by extrusion or continuous casting and then exposed to T8 heat

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treatment. The AA6101 feedstock of the OPGW presented in the study has been produced by an extrusion process using 1600 ton extrusion press; 3% AlB2 in rod form (9.5 mm dia.) is added to the molten aluminium alloy in the tundish when the alloy is cast as 6 m vertical log. Thus, heavy metals Ti, V, Cr, and Zr are transformed into the fine borides as CrB2, VB2, TiB2, and ZrB2, which no longer influence on conductivity [15]. Moreover, the view of the AA6101 structure exposed to precipitation hardening at 175 °C for six hours is presented in Fig. 6.

and tensile stress combination for 6 h. It also shows combinations of over-aging versus tensile stress at upwards temperatures of 175 °C. Having completed sample testing of the OPGW, it was determined that satisfying of the short circuit criteria was realized without encounters any problems. Moreover, lighting and short circuit tests show some similar effects in the sense of conductive metal. Therefore, to determine the degree of influence of AlB2 on conductive material, we decided to design some theoretical constructions using the base configuration shown in Fig. 1 but changing some material components, such as the clad steel and clad tube. Then, calculations of conductivity increases of the wires inoculated with AlB2 were performed on the complete conductor. Thus, increasing of current carrying capacity of base configurations was determined for several alternatives. As a consequence, if the conductivity of the conductive material is increased, the short circuit capacity of the OPGW is increased radically. In theoretical calculations, Eqs. 2 and 3 were used. In Table 8, mechanical and electrical properties of the wires prepared from the modified feedstock were presented.

Fig. 6. View of AA6101 structure after modification with AlB2 and treated at 175º C / 6 hours

In Fig. 6, the distribution of Mg2Si precipitations is seen to be remarkably uniform after T8 treatment of the wires drawn from the extruded feedstock at 510 °C. Thus, their contribution to the strength of the material is at an acceptable level according to Table 8. Moreover, any detrimental effect of AlB2 on strength, elongation and processing of the modified material were not determined after application of heat treatment. Modified AA6101 was exposed to different temperatures and treatment times in the furnace, and both changes of tensile stress and conductivity were determined. Fig. 7 indicates the optimum temperature

Fig. 7. Precipitation hardening of AA6101 wires and changing of temperature versus to tensile stress and conductivity

From the theoretical analysis, it has been proved that increasing the short circuit capacity by decreasing the internal resistance of the material gives durability to the conductor when affected by lightning arcs.

Table 8. Electrical and mechanical properties of AA6101 wires drawn from the extrusion feedstock produced by billets modified with AlB2 (homogenization of billets 560 ºC, 6 hours). Wires are heat treated at 175 ºC, 6 hours. Tests were performed according to IEC 104 and IEC 1089 standards Diameter [mm] 3.04 3.05 3.06 3.07 3.08

458

Cross-section [mm2] 7.26 7.31 7.35 7.40 7.45

Resistivity [Ohm mm2/m] 0.030231 0.030218 0.030262 0.030201 0.030175

DC resistance at 20°C [ohm/km] 4.165 4.136 4.115 4.080 4.050

Conductivity [% IACS] 57.0 57.1 57.0 57.1 57.1

Karabay, S.

Breaking load [N] 2403.45 2432.88 2403.45 2413.26 2423.07

Tensile strength [N/mm2] 331.08 332.85 326.77 325.98 325.20

Elongation at 250 mm [%] 6.0 6.4 7.0 7.2 7.4

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The calculation of the short-circuit current capacity is based on the assumption that no external heat flow would develop (adiabatic heating process).

I t1/ 2 = K c A. (5)

The parameter A is the minimum cross-sectional area of the protective earth conductor [mm2]. I2 t is the energy of the short circuit. Kc is the adiabatic temperature rise constant. The constant Kc is made up of the material properties and temperature range of the conductor material. IEC 60364-5-54 and BS 7454 give some guidance on the calculation of the constant Kc , according to the following equation:

(°C). Some coefficients used in the equation can be selected from the Table 9. Thus, samples of the second trial for testing of the construction against to lightning were prepared from the material given in Table 8. The minimum lay length was used to increase material contact surfaces so that stranding of wires was performed tightly. Table 9. Physical parameters of the earth conductor (OPGW) materials, IEC 60364 Material Aluminum Steel

β 228 202

Qc 2.5×10-3 3.8×10-3

ρ20 28.264×10-6 138×10-6

1/ 2

 Q ( β + 20)   (θ f − θi )   K c =  c  ⋅ ln 1 +   , (6) ( β − θi )   ρ 20   

where Qc is the volumetric heat capacity of the conductor material at 20 °C (J/°C mm³). β is the reciprocal of the conductor temperature coefficient of resistivity at 0 °C. ρ20 is the electrical resistivity of the conductor material at 20 °C [Ω mm]. θi and θf are the conductor initial and final temperatures respectively

2.4 Second Trial of Lightning Test and Results Having completed the manufacturing of the OPGW with new improved wires, samples were prepared for lighting tests again. The test procedure was applied as explained previously. The test was performed five times and results were tabulated in Table 10. Views of strands of OPGW after application of lightning charge are given in Fig. 8.

b) Fig. 8. a) View of slightly damaged surface of improved OPGW after application of second lightning trial, b) view of limited damage and broken wire due to spot melting of conductor surface of improved OPGW after application of second lightning trial Modification of Conductive Material AA6101 of OPGW Conductors against Lightning Strikes

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2.4.1 Discussion of Secondary Lightning Test Performed with Modified Material AA6101 Analysis of view of Fig. 8 and results summarized in Table 10 show that broken wires owing to the lightning effect decrease sharply to one or two. The main reason this is due to the high conductivity of the modified wires compared to unmodified aluminium alloy AA6101. Naturally, some damage related to individual wires on the outer layer of the OPGW occurred. However, the numbers of the broken wires in the second lightning test are extremely low when compared to that of first lightning tests. Therefore, it satisfied both strength restriction 75% RTS and the restriction related to resistance increases of the initial resistivity of the conductor as 20%. The permissible resistance increasing after application of lightning arc allows a maximum of three wires broken (see the last two lines in Table 10). Table 10. Results related to second trial lighting tests of OPGW manufactured from improved AA6101 alloy with AlB2 Test 1 U [V] 1045 I [A] 172.7 Q [C] 89.4 t [ms] 500.4 I2t [kA2s] 14.4 Temperature [°C] 17.1 Melted wire outer layer 1 Broken wires outer layer 1 Melted wire inner layer 0 Visible damage of the No optical unit Remaining UTS [%] 97.56 Electrical Resistance 8.33 Change

Test 2 1042 220.7 110.2 500.8 24.4 16.8 2 2 0

Test 3 1047 216.1 107.5 497.3 23.2 17.3 2 1 0

Test 4 1041 221.3 110.2 497.9 24.4 16.7 1 1 0

Test 5 1053 226.8 112.9 498.0 25.6 16.3 3 2 0

95.12

97.56

95.12

16.67

8.33

16.67

3 CONCLUSIONS The lightning resistance of the designed overhead ground wire has been considerably improved while maintaining mechanical and electrical properties. The experiments clearly indicate that the aluminium component AA6101 of the composite conductor OPGW can be modified to obtain the best conductivity properties by adding the AlB2 compound into the molten metal in the casting of logs. If the diameter of the OPGW is increased, then the conductive area is increased. As a result, the conductor gains lightning resistance. The strategy developed for improvement with AlB2 is (due to some limitations) related to sagging properties of the available transmission lines 460

in the country. However, the increasing of the diameter of the OPGW causes incompatibility with regards to sagging to available grounding conductor working in transmission line. Therefore, the best way for the solution of broken wires is to increase the conductivity of the material to resist lightning arcs. Inoculation for improving of AA6101 should be applied at the casting stage of logs. A master compound of 3% AlB2 in rod form (9.5 mm dia.) should be fed into the flowing metal stream in the tundish located between melting furnace and vertical casting unit. A reaction time of one to two minutes is adequate for boride precipitation. When AlB2 is added to the melt, the most probable compounds that can be formed are diborides as TiB2, ZrB2, CrB2 and VB2. The risk of inadequate dispersion with a slow-moving metal stream can be avoided by applying local restrictions in the tundish to increase the metal viscosity (increase speed). Thus, the best mixing of AlB2 with AA6101 is obtained. Moreover, the stranding of aluminium wires onto a core consisting of steel wire and SS tube must be performed tightly by decreasing lay length up to 1 to 2 cm to prevent clearance between of the wires. This process was performed by changing the distance between the circular plates of the pre-forming unit. The pre-forming head consists of three circular plates with the rollers mounted on its periphery. The three circular plates are mounted on a screw. The distance between first and third plates indicates the lay length of the conductor. In order to avoid spring back of the wires, 0.6 to 0.7 × lay length is adjusted. Thus, clearances of the alloy wires of OPGW are eliminated. Therefore, electrical arcs occurr between the wires when it is liable to lightning strikes are blocked. Moreover, some authors [4] and [5] propose new constructions. They explain that the conductivity of aluminium part of OPGW should be reinforced with aluminium clad steel wires and clad steel tubes or aluminium extruded tube. The high temperature of the lightning strike is the exterior reason for wire breakage, and the lower melting point of the wire is the interior reason for wire breakage. However, the cladding process is more expensive than a zinc coating applied to steel wires. The usage of clad steels substantially increases the price of the product. This is the most decisive parameter for developing countries, due to increasing of the investment budget. Therefore, developing countries apply some restrictions on the final cost of the product. The market price of Al clad steel wire is around $1900 to 2100 per ton. In contrast, the price of zinc-coated steel wires is $800/ ton. The kilometric weight of the OPGW considered

Karabay, S.

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in the study is about 621 kg/km. If clad steel wires are used in the design of the OPGW to increase the conductivity area, the additional kilometric cost for complete conductor is around $420 per km. However, the modification process explained here by adding a 3% AlB2 compound as 3 kg per ton AA6101 is the cheaper way to increase the conductivity of the OPGW. The price of the 3% AlB2 master alloy is around € 8 to10 per kg. It causes additional cost as $9.65/km for modification of per km OPGW. This cost difference considerably expresses the power of the method described in the study. In conclusion, the modified OPGW conductor with AlB2 passed the lightning test and satisfied all the electrical and mechanical test requirements of international standards. 4 REFERENCES [1] Alvim, M.G. (2004). Improved Performance of OPGW under Lightning Discharges in Brazilian Regions with a High Keraunic Level. CIGRE, 40th Session, Paris, p 1-9. [2] Yokoya, M., Katsuragi, Y, Nagata, Y., Asano, Y. (1994). Development of Lightning Resistant Overhead Ground Wire. IEEE Transaction on Power Delivery, vol. 9, no. 3, p. 1517-1523, DOI:10.1109/61.311216. [3] Criasafulli, C.A.; Spoor, D.J. (2008). A Case Study on the Appropriate Selection of Optical Ground Wire. Australasian Universities Power Engineering Conference, paper 106, p. 1-5. [4] Tsuji, T., Namekawa, Y., Fukasawa, T., Momomota, S. (2001). New OPGW with Aluminum Covered Stainless Steel Tube. Hitachi Cable Review, no. 21. [5] Tiancang, D., Zheng, Y., Xia, W. (2006). Study on the Problem of Lightning Strike OPGW. International Conference on Power System Technologies, p. 1-4. [6] Goda, Y., Shigenu, Y., Watanabe, S. (2004). Melting and Breaking Characteristics of OPGW

Strands by Lightning. IEEE Transaction on Power Delivery, vol. 19, no. 4. p. 1734-1739, DOI:10.1109/ TPWRD.2004.832410. [7] Azadeh, M. (2009). Fiber Optic Engineering. Springer Dordrecht Heidelberg London, p. 125-155, DOI:10.1007/978-1-4419-0304-4. [8] Jakl, F.. Jakl, A. (2000). Effect of Elevated Temperatures on Mechanical Properties of Overhead Conductors Under Steady State and Short–Circuit. IEEE Transaction on Power Delivery, vol. 15, no. 1, DOI:10.1109/61.847258. [9] Torvath, T. (2004). Standardization of Lightning Protection Based on the Physics on the Tradition. Journal of Electrostatics, no. 60, p. 265-275, DOI:10.1016/j.elstat.2004.01.008. [10] Chrisholm, W.A; Levine, J.P., Chowdhuri, P. (2001). Lightning Arc Damage to Optical Fiber Ground Wires (OPGW): Parameters and Test Methods. Proceedings of Power Engineering Society, vol. 1, p. 88-93. [11] Guavac, S.J., Nimrihter, M.D., Geric, Lj. R. (2007). Estimation of Overhead Line Condition. Electrical Power System Research, no. 78, p. 556-583. [12] Karabay, S., Uzman, I. (2005). A Study on the Possible Usage of Continually Cast Aluminium 99.6% Containing High Ti, V, and Cr Impurities as Feedstock for the Manufacturing of Electrical Conductors. Materials and Manufacturing Process, no. 20, p. 231243, DOI:10.1081/AMP-200041884. [13] Kittel, C. (1996). Solid State Physics, 7th ed.. John Wiley & Sons, Inc., New York, p. 161-162. [14] Karabay, S., Uzman, I. (2005). Inoculation of Transition Elements by Addition of AlB2 and AlB12 to Decrease Detrimental Effects on the Conductivity of 99.6% Aluminium for Manufacturing of Conductor. Journal of Material Processing Technology, no. 160, p. 174182, DOI:10.1016/j.jmatprotec.2004.06.015. [15] Setzer, W.C., Boone, G.W. (1992). The use of aluminum boron master alloys to improve electrical conductivity. Light Metals, p. 837-844.

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Received for review: 2012-12-07 Received revised form: 2013-05-07 Accepted for publication: 2013-05-29

Flow Characteristic of Staggered Multiple Slotted Tubes in the Passage of a Fin Tube Heat Exchanger Yayla, S. Sedat Yayla*

Yuzuncu Yil University, Department of Mechanical Engineering, Turkey The flow characteristics of inline and staggered cylinders placed in a fin tube heat exchanger model are experimentally investigated for Reynolds numbers of 1500 and 4000, having a duct height to cylinder diameter ratio of 0.4. In this study, the Reynolds number is calculated based on the cylinder diameter. Particle image velocimetry (PIV) is studied to obtain instantaneous representations of the non-steady flow for a specified flow field. Time-averaged flow data clearly indicates that flow through semi-cylinders has a substantial effect on the turbulent flow characteristics. A variation of time-averaged flow data along a specific line is also presented graphically. The flow interactions in the streamwise and cross-stream bases of the staggered cylinders with a flat plate surface result in a three-dimensional and a complex flow behaviour. Keywords: particle image velocimetry (PIV), tube heat exchanger, turbulent flow, staggered slotted cylinders

0 INTRODUCTION Increasing populations and the economic, social and industrial development of countries have resulted in a huge demand for energy in the developing world; therefore, all countries throughout the world are investigating alternative energy sources. For such a need, a heat exchanger is one of the devices that can be developed further with regard to energy saving. Tube heat exchangers are commonly used in a wide variety of industrial, thermal, commercial and household applications, such as in air conditioning systems, unit heaters and radiators in condensers and evaporators. The heat transfer problem and the efficiency of the heat exchanger are strongly related to the flow structure. The flow structure includes developing velocity and thermal boundary layers over the tubes. In heat exchangers, as the flow approaches the tubes, a horseshoe vortex system forms on the front part of each tube in the stagnation area near the tube and the fin junction region [1]. The occurrence of horseshoe vortices introduces additional mixing of hot and cold fluids in the heat exchanger flow passage and consequently increases the fin heat transfer in that area. Horseshoe vortices around the cylinder surface and a detailed flow structure affecting the heat transfer coefficient in the heat exchanger flow passage are reported in detail by Tutar and Akkoca [2]. There are many important reviews in the literature regarding flow characteristics downstream of the circular cylinder. A detailed review of the wake vortex dynamics for the circular cylinder is given by Williamson [3]. One of the most fundamental problems in fluid mechanics is determining the flow field around the cylinder surface. Horseshoe vortices, vortex shedding, and wake regions of 462

circular cylinders at moderate Reynolds numbers have long been topics of interest for many fluid dynamics researchers. Improvements in theoretical developments and experimental techniques over the previous decade have created a perfect insight into the nature of the flow dynamics in the near wake of circular cylinders. Structural vibrations and acoustic noise or resonance caused by periodic surface loading have led to an increase in the unsteady forces acting on the bluff bodies. However, unsteady behaviour of the vortex shedding downstream of the cylinder enhances the heat transfer. Flow control may be accomplished by controlling the boundary layer separation and/or the structure of shear layer(s) in the wake and various methods like blowing, suction, surface roughness elements, splitter plates, small rods, base bleed, etc., as has been studied by many researchers in the past. Passive control techniques suppress the vortex shedding by modifying the shape of the bluff body or by attaching additional devices in the flow field. Active control techniques utilise external energy to change the flow field. Since it is simpler and easier to implement passive techniques compared to active control techniques [4], these techniques have been widely used for flow control applications. The literature survey partly summarises current research on vortex-bluff body interactions, physical aspects of vortical flow, and control of vortices. Different control techniques can be used to control vortex formation around the staggered arrangements of slotted cylinders. Investigations such as [5] to [8] use passive control techniques in their studies. Passive control of vortex shedding behind a circular cylinder in shallow water flow is studied by Akilli et al. [5]. They obtain a flow structure that is more changed by the

*Corr. Author’s Address: Yuzuncu Yil University, Dept. of Mech. Eng., 65080 Van, Turkey, syayla@yyu.edu.tr

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splitter plate length in the wake region of the circular cylinder. In [6], there are more effects of fin spacing on four-row annular-finned tube bundles in staggered and in-line arrangements for the flow control. They report that the horseshoe vortex effect is quite clear in the largest fin spacing and at high Reynolds numbers. In another study on passive control, flow and heat transfer in a plate fins/circular tube assembly is researched using naphthalene sublimation technique [7]. They use the gap to tube diameter ratio, the Reynolds number and the tube location for a single tube for the researched parameters. They found that the horseshoe vortex formed in front of the tube yields a greater increase in the heat transfer rate. In the case of fin-tubes heat exchanger, the spiraling motion of the horseshoe vortex system results in better mixing and the heat transfer in the juncture location [8]. Prediction of flow characteristics thorough the heat exchangers passage is necessary for efficient design. Xu and Zhou [9] state that the heat and momentum transfer characteristics downstream of heated cylinders are also strongly affected by the interaction of wake flow structures. Onal [10] reports on a number of specially configured tube shapes used in heat exchangers to improve the thermal performance effectively and to significantly reduce the size and weight of the heat exchangers. The shapes of these types of heat exchangers tubes are round, elliptical, flat, oval and rectangular. Many researchers have performed experiments to investigate effects of different geometrical parameters on the heat transfer, and the performance of heat exchangers. Yataghene et al. [11] focus on experimental analysis of the flow patterns inside scraped surface heat exchanger (SSHE) under isothermal and continuous flow conditions. The velocity vectors of these two flows form a helical fluid flow pattern in the middle section of the exchanger. Their results indicate that a significant effective flow under certain experimental flow conditions of rotating velocity and axial flow rate can be attained. Solano et al. [12] investigate a new type of rig, whose rotating shaft is changed by a concentric reciprocating rod. They obtain a satisfactory coherence between PIV measurements and numerical results obtained by FLUENT software. In [13], velocity vectors in a vertical coaxial double-duct heat exchanger for parallel rising flow of water under conditions of laminar mixed convection have been obtained experimentally, using the PIV technique. Sahin et al. [14] report the horseshoe vortex in a rectangular duct with a narrow gap modeled to simulate a fin-tube heat exchanger containing a single circular cylinder by using the

PIV method. Variations in the size and intensity of the vortex structures with Re have been observed. Wen et al. [15] research the flow characteristics in the header of a plate-fin heat exchanger by PIV. They find that yield of fluid mal-distribution in a conventional header is highly significant while the sophisticated header configuration with a punched baffle can effectively increase the uniformity of flow distribution. In this study, the flow control for staggered slotted cylinders in a confined flow and similar to a heat exchanger flow passage is investigated by using the PIV technique. The flow behaviour in the heat exchanger flow passage is extremely complex, three-dimensional and unsteady with flow separation, reattachment, recirculation zones, and vortices in the wake of the slotted cylinders. 1 EXPERIMENTAL STUDY 1.1 Experimental Set-Up and Measurement Technique A water-free channel surface was used to conduct the experimental set-up. The internal dimensions of the water channel test section were 8000 mm long, 1000 mm wide and 750 mm high, and made of a 15 mm thick transparent Plexiglas sheet. The speed control unit driven by a 15 kW centrifugal pump was used to form the water flow. A uniform free-stream velocity distribution was provided with flow passes through a two-to-one channel contraction before reaching the test section adjusted to a 610 mm depth of water. A computer, a synchroniser, a frame grabber with a maximum frame rate of 30 Hz, a CCD camera with a resolution of 1600×1186 pixels, a double-pulsed Nd: YAG Laser source with a wavelength of 532 nm were part of the Dantec Dynamics PIV system. The CCD camera was placed under the water channel in the plan-view plane for the velocity measurements. The camera was compatible with the Scheimpflug condition and hence focused over the centre of the measuring plane by sensitive tilting with respect to the lens axis; 60 mm lenses were used in the two cameras. The Dantec Dynamics PIV system and Flow Manager Software were used to perform the measurements and to process the data. Input buffers were used to read and store the image maps. A highspeed digital frame grabber was utilised to transfer the images from the camera to the computer. With the use of a synchroniser, the correct sequence and timing triggered the laser pulses and camera. The fluid motion was observed by the water seeded with neutrally buoyant silver-coated spherical particles,

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12 μm in diameter. The output of the 120 mJ/pulse of maximum laser energy illuminated the measurement plane. A 1.5 ms time interval between pulses for all measurements was applied. The illuminating measurement plane was approximately as thick as a 1.5 mm laser sheet. The interrogation window was obtained according to the time interval, and the laser sheet’s thickness was selected when the maximum amount of particles were displaced. The CCD camera was used to record the movement of the particles. The row displacement vector was calculated by using frame-to-frame adaptive correlation technique. The time interval between the laser pulses was used to determine the raw velocity vector field from this displacement vector field. Spurious velocity vectors (less than 5%) were removed using the local medianfilter technique and replaced by using a bilinear least square fit technique between surrounding vectors. The Gaussian smoothing technique was used to avoid dramatic changes in the velocity field for the smoothed velocity vector field. From the circulation around the eight neighbouring points, the vorticity value at each grid point was calculated. Generally, the seeding particle size, non-uniform particle distribution, particle overlap, interrogation window’s size and electronic and optical image noise caused

uncertainty in velocity measurements. For each continuous running, an acquisition frequency of 15 Hz, a total of 350 instantaneous velocity vector fields were taken. In order to obtain the averaged time velocity vectors and other flow characteristics, these instantaneous flow images were captured, recorded and stored on a computer. The plan view and side view images of the full frame area are 60×70 mm² and 46×20 mm², respectively. Westerweel [16] uses a similar digital PIV technique in a study calculating the uncertainty in the velocity field with a less than 2% error. Extensive information is reported on these uncertainty factors, which affect the PIV measurements by Gallanzi [17]. Hart [18] perform a two-pass digital PIV by using the Matlab program. He presents a non-post-interrogation method of reducing sub-pixel errors and eliminating spurious vectors from PIV results. Adrian [19] mentions the material below complements expositions of established PIV methods based on image correlation. The laser light propagates easily due to the test geometry of the cylinders and the Plexiglas plates. Cleanvec software was used to detect and remove the spurious vectors before the image processing and then the digital images were improved, and the neighbourhood averaging technique was used for

Fig. 1. Schematic representation of laser sheets, plan and side views of test section (all dimensions are in mm)

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Yayla, S.

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smoothing. Fig. 1 shows the schematic of multiple staggered slotted cylinders in a narrow gapped rectangular duct used in the present experiment. The ratio of the laser sheet height to water height was 0.5, and it was used to determine the velocity field around the surface mounted cylinder in the passage by the PIV technique in this study. Flow between semi-cylinders was allowed by cutting the cylinder in to two pieces with a 5 mm whole cross-section slot. The diameter and the height of the cylinder were 50 to 20 mm. The Red 1500 and 4000 are the Reynolds numbers based on the cylinder diameter. 1.2 Experimental Results and Discussion Understanding the flow characteristics for the staggered cylinders placed in a fin tube heat exchanger flow passage is significant in terms of design and efficiency. Velocity vector maps, patterns of streamline, vorticity contours, Reynolds stress contours and turbulent kinetic energy, spectral analysis and the root mean square of the velocity components are presented to reveal the details of the flow. Timeaveraged flow data are obtained by averaging of 350 PIV images. Fig. 2 illustrates the distributions of stream-wise velocities, <u/U>, and the time-averaged normalised Reynolds stress correlations, <u’v’>/U2, and time-

averaged vorticity contours, <ω>, for Red = 1500 and 4000 across the flow passage. The minimum and incremental values are [/U]min = 0.05, and ∆[/U] = 0.05. The distributions of stream-wise velocities, <u/U> presented in Fig. 2 clearly indicate that the wake flow area is extremely small. This result reveals that the wake flow region has a velocity distribution with high magnitude. A pair of vortices with an opposite sign appears as seen in the last row of Fig. 2. In the field of time-averaged vorticity contours, <ω> patterns of negative vorticity are indicated with dashed lines, while positive vorticity is indicated by solid lines. Positive signed vortices or counter-clockwise rotating vortices occur along the slotted cylinder. As shown in Fig. 2, both negative and positive vorticity layers are observed along the flat plate for Red = 1500 and 4000. Minimum and incremental values of the vorticity are ωmin = ±1 s-1 and Δω = 2 s-1. Stronger vorticity layers are obtained for higher Reynolds numbers. Time-averaged normalised Reynolds stress correlations, u’v’/U2, in the downstream vicinity of the slotted cylinders were observed as shown in the second row of Fig. 2. The minimum and incremental values of normalised Reynolds-stress are [<u′v′>/U2] 2 min = ± 0.002 and Δ[<u′v′>/U ] = 0.002, respectively. The negative and the positive normalised Reynolds stress contours are <u′v′>/U2 represented with dashed and solid lines, respectively. It can be concluded that,

Fig. 2. Pattern of time-averaged component of stream-wise velocity, [/U] normalised Reynolds stress contours, [<u′v′>/U2] and vorticity contours, <ω> in the downstream base of the cylinder in side-view planes for Red = 1500 and 4000 Flow Characteristic of Staggered Multiple Slotted Tubes in the Passage of a Fin Tube Heat Exchanger

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Fig. 3. Time-averaged velocity vector field <V>, corresponding streamline topology <ψ> and vorticity contours <ω> for Red = 1500; minimum and incremental value of vorticity are ωmin = ±1 s-1 and Δω = 2 s-1

Fig. 4. Time-averaged velocity vector field <V>, corresponding streamline topology <ψ>and vorticity contours <ω> for Red = 4000; minimum and incremental value of vorticity are ωmin = ±1 s-1 and Δω = 2 s-1

downstream of the slotted cylinder, the peak values of the normalised Reynolds stress correlations, <u′v′>/U2 decrease as the Reynolds number increases. Flow characteristics downstream of the slotted cylinders are more important in terms of the heat transfer rate in comparison to the forward faces of slotted cylinders, since the occurrence of the wake flow region hydro-dynamically deteriorates the rate of heat transfer. Thus, more attention must be paid for these regions. The time-averaged flow data, which includes the velocity vector map, <V>, the patterns of streamlines, <ψ> and the contours of vorticity, <ω> at an elevation of z/h = 0.5, are presented in Fig. 3 for Reynolds numbers Red = 1500. As seen in the image, three cylinders were included in one frame of an image in order to see the cylinder and flow interactions. In the first frame of images, the averaged velocity vector map <V> indicates that a high rate of velocity occurs on the shoulders of each cylinder. Patterns of time-averaged components of the velocity vector, <V>, indicate that vortex formation occurs immediately adjacent to the

base of the cylinder and as these horseshoe vortices immigrate in the direction of the free-stream flow; they also flap in the lateral direction in an unsteady fashion. In the second line of the images, the time-averaged streamline patterns, <ψ>, show that separated flow regions are more compact, since the water jet flow goes through slots directly into the wake flow region. Streamline patterns, <ψ>, illustrate that fresh flow occurred due to the hydrodynamics of the horseshoe vortex system and from the slot is transported in to the wake flow regions for further extent. The corresponding streamline patterns reveal that symmetrical foci with opposite circulation and saddle points downstream are evident. The centres of the foci and the saddle point are designated as F and S, respectively, as indicated in Fig. 3. There is a saddle point, S, for each focus, F. In the last line of the images of the time-averaged vorticity contour, the <ω> values reveal that the present shear layers emerge from both sides of the slotted cylinders moving downstream in between neighbouring slotted cylinders and interact with the shear layers of other

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cylinders for z/h = 0.5. In Fig. 3, a symmetrically distributed cluster of positive (solid line) and negative (dashed line) vorticity layers beginning around the inlet region of slots evidently extends further downstream around the plane of symmetry of the slotted cylinder. Two pairs of strong positive and negative vorticity of horseshoe vortex systems are detected adjacent to the outer region of the shear layer. It seems that the water jet flow sucks the horseshoe vortex in a way that the primary horseshoe vortex comes extremely close to the inlet region of slots. Images for downstream flow of time-averaged data of the slotted cylinders at an elevation of z/h = 0.5 for Reynolds numbers Red = 4000 are presented in Fig. 4. As it is clearly seen, locations of foci are more or less the same as presented by the time-averaged velocity vector, <V>, distributions and corresponding patterns of streamlines, <Ď&#x2C6;>, as the Reynolds number is increased from 1500 to 4000. The structure of the flow changes as a function the Reynolds number. Wake flow regions in lateral directions thicken slightly with the Reynolds number due to the presence

of the other slotted cylinders. In the last line of the images, more compact, stronger, and symmetrically distributed positive and negative vorticity clusters beginning from the vicinity of the slot in the slottedcylinder surface and convecting further downstream around the plane of symmetry are observed. In addition to time-averaged and instantaneous flow data, phase-averaged data also provide detailed information on the structure of the flow field. The history of development of the flow structure is computed using a sequence of 350 instantaneous images of velocity vectors. The natural frequency of shedding vortices is obtained using Fast Fourier Transformation (FFT) analysis and natural frequency spectrum. The spectra of stream-wise velocity fluctuations obtained using FFT analysis for four selected points in the vertical symmetry plane are presented in Fig. 5. The location of the selected points are near the slot (x/d = 0.36, y/d = 0.05) and (x/d = 0.36, y/d = 1.12), far the slot (x/d = 0.36, y/d = 0.54) and (x/d = 0.36, y/d = 0.64) in the wake region. The dominant frequency of f = 4.8 Hz at four points is

Fig. 5. Comparison of the power spectra calculated at various locations of the flow field for Red = 1500 Flow Characteristic of Staggered Multiple Slotted Tubes in the Passage of a Fin Tube Heat Exchanger

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close to the slotted cylinder for the Reynolds number of Red = 1500. The distance from the slot of the point where the dominant frequency occurs is not the same for Reynolds numbers 1500 and 4000 as indicated in Fig. 6. The dominant frequency in the location of selected points (x/d = 0.36, y/d = 0.54) and (x/d = 0.36, y/d = 0.64) is f = 0.81 Hz and the other two points (x/d = 0.36, y/d = 0.05) and (x/d = 0.36, y/d = 1.12) is f = 1.33 Hz for the Reynolds number Red = 4000. However, the spectra taken locations of near the slot (points 1 and 2) shows a clear and distinct peak at f = 0.81, which is smaller than the natural vortex shedding frequency (points 3 and 4) obtained from the slotted-cylinder case. Fig. 7 illustrates time-averaged normalised Reynolds stress correlations, <u′v′>/U2, distributions stream-wise and transverse velocities, u/U and v/U, for Red = 1500 and 4000 across the flow passage in a vertical plane at the central cross-sections downstream of the slotted cylinder. The minimum and the incremental values of each variable are indicated

in the images. In each image, contours of positive velocity components are indicated by solid lines and dashed lines indicate negative velocity components. In the first line of the images, the high levels of negative pockets of time-averaged stream-wise velocity contours, /U, occur in plain view further downstream as the Reynolds number is increased. A cross comparison of the images shown in the mid-line of Fig. 7 with corresponding patterns of time-averaged streamline shown in Figs. 4 and 3 indicate that concentration of <v>/U occurs in between two foci F and saddle point S. The corresponding normalised Reynolds stress contours (<u′v′>/U2, where u′ and v′ are fluctuations of u and v, respectively) are shown in the last line of the images. The peak values of positive and negative Reynolds stress contours indicate the regions under high fluctuations. However, the peak values of Reynolds stress correlation, <u’v’/U2> occurs along the shear layer. It is clear that for Red = 4000, the momentum of the jet flow has a fairly large magnitude and therefore, locally higher values

Fig. 6. Comparison of the power spectra calculated at various locations of the flow field for Red=4000

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Fig. 7. Patterns of time-averaged components of stream-wise, [/U] transverse, [<v>/U] velocity, normalised Reynolds stress contours, [<u′v′>/U2] and for Red = 1500 and 4000; minimum and incremental values are [/U]min = 0.025, [<v>/U]min = 0.05 and ∆[/U] = 0.025, ∆[<v>/U] = 0.05; for contours of normalised Reynolds-stress, [<u′v′>/U2]min = ±0.01, and ∆[<u′v′>/U2] = 0.02

of <u’v’/U2> that are obtainable in the region of jet formation. The turbulent flow characteristics are provided in terms of root mean square values of stream-wise velocity, u, (urms) and transverse velocity, v, (vrms) in order to identify regions of high fluctuations as shown in Fig. 8. Both urms and vrms are normalised by free stream velocity, U, indicating the peak value of these rms of velocity components gradually increasing as the Reynolds number in between neighbouring slotted cylinders is increased. The location of the maximum value of <urms>/U is kept in the same distance from the slotted-cylinder surface. Contours of vrms/U are

stacked far downstream of the cylinder as well as in the proximity of the upper surface of the cylinder at both sides as seen in the last line of Fig. 8. Peak values of urms/U for Reynolds numbers of 1500 and 4000 are 0.25 and 0.0.35, and also vrms/U are 0.1 and 0.2, respectively. The minimum and incremental values of normalised root mean square of stream-wise and transverse velocity fluctuations are given in the figure captions. The results of the turbulent kinetic energy (TKE) for Reynolds numbers of 1500 and 4000 are shown in Fig. 9. The minimum and incremental values of the contours of time-averaged turbulent kinetic

Flow Characteristic of Staggered Multiple Slotted Tubes in the Passage of a Fin Tube Heat Exchanger

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Fig. 8. Patterns of rms of the stream-wise, transverse velocity fluctuation respectively, urms/U, vrms/U for Red = 1500 and 4000; minimum and incremental values are [urms/U]min = 0.05, [vrms/U]min = 0.05 and ∆[urms/U] = 0.05, ∆[vrms/U] = 0.05

Fig. 9. Turbulent kinetic energy (TKE) distribution downstream of the cylinder for Red = 1500 and 4000

kinetic energy is related to the root mean square of the velocity components. Fig. 8 shows that when the Reynolds number is increased, magnitudes of urms/U and vrms/U are lower in shear layers at both sides of the slotted cylinder than the values of these velocity components close to the slot location of the slotted cylinder.

energy remain same for all cases: [<TKE>]min = 3 and ∆[<TKE>]=4, respectively. For the two graphs, the values of turbulent kinetic energy are extremely high close to the slot location due to the jet-like flow. However, it decreases gradually in shear layers at both sides of the slotted cylinder. The maximum value of the normalised TKE for Reynolds numbers of 1500 and 4000 are 23 and 47, respectively. The turbulent 470

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2 CONCLUSIONS The main purpose of this study was to investigate details of flow structure in the downstream of a circular cylinder mounted on a flat surface for multiple slot-cylinders in deep water channels, using the PIV technique. Slotted cylinders are located at the corners of equilateral triangles. Owing to the denseness of this type of heat exchanger, the distance between cylinders surfaces is 1d. The laser sheet was located parallel to the bottom surface of the water channel at the elevation of z/h = 0.5. Due to the arrangement of the slotted cylinders, the flow structure in a plate fin tube the heat exchanger of the thermal unit is composed of staggered cylinders. In closer parts of the slotted cylinders, horseshoe vortices occurred on both surfaces of the plate. The entrainment process and circulatory motions between the core and the wake flow regions, downstream of the slotted cylinder mounted on the flat plate surface in deep water flow are magnified by these vortices. The absence of biased flow was achieved by the jet flow. Wake-flow regions of the slotted cylinders elongate in the stream-wise direction due to the momentum transfer from the slot of the cylinders. In summary, staggered cylinder arrangements enhance the heat transfer rate hydrodynamically even in wake flow regions. 3 ACKNOWLEDGMENTS The author acknowledges the financial support of the BAPB (Directory of Scientific Research Projects of Yuzuncu Yil University, Turkey) for funding under project No: 2012-MIM-B012. Experimental part of the project was carried out in the Fluid Mechanics Laboratory of Mechanical Engineering Department at Cukurova University in Turkey. 4 NOMENCLATURE d Red u v u’ v’ u’ v’ urms vrms U V

cylinder diameter Reynolds number is calculated based on the cylinder diameter stream-wise velocity component transverse velocity component Reynolds stress fluctuations of u mean fluctuations of v root mean square of u root mean square of v free stream velocity velocity vector

ψ ω TKE < >

streamline vorticity Turbulent Kinetic Energy time-averaged value of quantity 5 REFERENCES

[1] Sahin, B., Akkoca, A., Ozturk, N.A., Akilli, H. (2006). Investigation of flow characteristics in a plate fin and tube heat exchanger model composed of single cylinder. International Journal of Heat and Fluid Flow, vol. 27, no. 3, p. 522-530, DOI:10.1016/j. ijheatfluidflow.2005.11.005. [2] Tutar, M., Akkoca, A. (2004). Numerical analysis of fluid flow and heat transfer characteristics in three dimensional plate fin and tube heat exchangers. Numerical Heat Transfer, vol. 46, no. 3, p. 1-21, DOI:10.1080/10407780490474762. [3] Williamson, C.H.K. (1996). Vortex dynamics in the cylinder wake. Annual Review of Fluid Mechanics, vol. 28, p. 477-526, DOI:10.1146/annurev. fl.28.010196.002401. [4] Lee, S.J., Lee, S.I., Park, C.W. (2004). Reducing the drag on a circular cylinder by upstream installation of a small control rod. Fluid Dynamics Research, vol. 34, no. 4, p. 233-250, DOI:10.1016/j.fluiddyn.2004.01.001. [5] Akilli, H., Karakus, C., Akar, A., Sahin, B., Tumen, N.F. (2008). Control of vortex shedding of circular cylinder in shallow water flow using an attached splitter plate. Journal of Fluids Engineering, vol. 130, no. 3, p. 1-11, DOI: 10.1115/1.2903813, DOI:10.1115/1.2903813. [6] Mon, M.S.R., Gross, U. (2004). Numerical study of finspacing effects in annular finned tube heat exchangers. International Journal of Heat and Mass Transfer, vol. 47, no. 8-9, p. 1953-1964, DOI:10.1016/j. ijheatmasstransfer.2003.09.034. [7] Kim, J.Y., Song, T.H. (2002). Microscopic phenomena and macroscopic evaluation of heat transfer from plate fins/circular tube assembly using naphthalene sublimation technique. International Journal of Heat and Mass Transfer, vol. 45, no. 16, p. 3397-3404, DOI:10.1016/S0017-9310(02)00047-9. [8] Tiwari, S., Biswas, G., Prasad, P.L.N., Basu, S. (2003). Numerical prediction of flow and heat transfer in a rectangular channel with a built-in circular tube. Journal of Heat Transfer, vol. 125, no. 3, p. 413-421, DOI:10.1115/1.1571087. [9] Xu, G., Zhou, Y. (2004). Strouhal numbers in the wake of two inline cylinders. Experiments in Fluids, vol. 37, no. 2, p. 248-256, DOI:10.1007/s00348-004-0808-0. [10] Onal, O. (2010). Investigation of flow characteristics around a Single and staggered slotted-cylinders. Ph.D. thesis, Cukurova University, Adana. [11] Yataghene, M., Francine, F., Jack, L. (2011). Flow patterns analysis using experimental piv technique inside scraped surface heat exchanger in continuous flow condition. Applied Thermal Engineering,

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vol. 31, no. 14-15, p. 2855-2868, DOI:10.1016/j. applthermaleng.2011.05.011. [12] Solano, J.P., García, A., Vicente, P.G., Viedma, A. (2011). Flow pattern assessment in tubes of reciprocating scraped surface heat exchangers. International Journal of Thermal Sciences. vol. 50, no. 5, p. 803-815, DOI:10.1016/j.ijthermalsci.2010.11.019. [13] Maré, T., Galanis, G., Voicu, L., Miriel, J., Sow, O. (2008). Experimental and numerical study of mixed convection with flow reversal in coaxial double-duct heat exchangers. Experimental Thermal and Fluid Science, vol. 32, no. 5, p. 1096-1104, DOI:10.1016/j. expthermflusci.2008.01.002. [14] Sahin, B., Ozturk, N.A., Gurlek, C. (2008). Horseshoe vortex studies in the passage of a model plate-fin-andtube heat exchanger. International Journal of Heat and Fluid Flow, vol. 29, no. 1, p. 340-351, DOI:10.1016/j. ijheatfluidflow.2007.06.005.

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[15] Wen, J., Li, Y., Wang, S., Zhou, A. (2007). Experimental investigation of header configuration improvement in plate–fin heat exchanger. Applied Thermal Engineering, vol. 27, no. 11-12, p. 1761-1770, DOI:10.1016/j.applthermaleng.2007.01.004. [16] Westerweel, J. (1993). Digital Particle Image Velocimetry, Theory and Application. Delft University Press, Delft. [17] Gallanzi, M.F. (1998). High accuracy measurement of unsteady flows using digital particle image velocimetry. Optics & Laser Technology, vol. 30, no. 6-7, p. 349359, DOI:10.1016/S0030-3992(98)00020-6 [18] Hart, D.P. (1993). PIV error correction. Experiments in Fluids, vol. 29, no. 13-22, p. 13-22. [19] Adrian, R.J. (2005). Twenty Years of Particle Image Velocimetry. Experiments in Fluids, vol. 39, no. 1, p. 159-169, DOI:10.1007/s00348-005-0991-7.

Yayla, S.

Prejeto v recenzijo: 2012-11-13 Prejeto popravljeno: 2012-11-13 Odobreno za objavo: 2013-05-13

Optimal Design Based on Dynamic Characteristics and Experimental Implementation of Submersible Electromagnetic Actuators

Cai, B. – Liu, Y. – Abulimiti, A. – Ji, R. – Zhang, Y. – Dong, X. – Zhou, Y. Baoping Cai1 – Yonghong Liu1,* – Aibaibu Abulimiti1 – Renjie Ji1 – Yanzhen Zhang1 – Xin Dong1 – Yuming Zhou2 1 China

University of Petroleum, College of Mechanical and Electronic Engineering, China National Petroleum Corporation, Bureau of Geophysical Prospecting, China

2 China

An optimization procedure based on the dynamic characteristics of a submersible electromagnetic actuator constrained in a specific volume has been developed. In order to achieve the minimum response time and low vibration when the actuator is opened, five radial dimensions are optimized when the main limiting quantity is the maximum allowed temperature. Three models, including a thermal model, an electromagnetic model, and a mechanical model are constructed, and optimization calculation is performed by using Matlab/Simulink software. According to the optimization results, an actuator is manufactured and dynamic experiments are performed. The results show substantial agreement between experimental response times and simulated response times. In order to investigate the vibration when the actuator is opened and closed, vibration experiments of the actuator are also performed. The results show that the measured vertical and horizontal accelerations are near the calculated acceleration of the plunger. Both of the experiments show that the optimization procedure is sufficiently accurate, and the optimal submersible electromagnetic actuator is sufficiently secure to be used in subsea BOP stacks. Keywords: submersible electromagnetic actuator, optimal design, magnetic equivalent circuit, dynamic characteristics

0 INTRODUCTION Hundreds of submersible control valves are used in a subsea blowout preventer (BOP) stack, which is located in 3000 m ultra-deep water region. The control valve is an electro-hydraulic device with two stages. The pilot stage, which is a submersible electromagnetic actuator (SEMA), provides a hydraulic pilot signal to operate a main stage. The main stage is a sub-platemounted (SPM) hydraulic valve, which controls the hydraulic pressure to operate the subsea BOP stack functions [1] and [2]. By minimizing response times, especially the opening time of SEMA, the performance of subsea BOP can be improved significantly. High velocity impacts experienced by the moving plunger of the SEMA create frequent vibrations of the SEMA and SPM valve, which could lead to valve seal failure. Therefore, the velocity impacts and vibrations should be sufficiently low [3] and [4]. Empirically, the vibration acceleration of the SEMA should be lower than 1×10–3 m/s2. Additionally, the size and weight savings of the submersible control valves are of considerable significance in reducing the size of the subsea BOP stack. Due to the complexity of design parameters, the actuators require an optimal design. In recent years, various analytical, semi-analytical and numerical methods have been presented in order to improve the performance of electromagnetic devices. Moses et al. [5] studied the linear electromagnetic actuators using finite element analysis (FEA) method in accelerating the design process and

improving the final design. Wu et al. [6] studied an electromagnetic fast linear actuator, using the FEA method. Yatchev et al. [7] optimized an axisymmetric linear electromagnetic valve actuator, using the FEA method. The method gives a precise determination of the electromagnetic device performance but requires a large amount of computation and time reduction when the method is used for optimization. The FEA method is also problematic for other applications, such as dynamic simulation; therefore, some solutions including opening and closing times could not be obtained. Encica et al. [8] and [9] optimized the electromagnetic actuators using a space-mapping method, and Markovic et al. [10] and [11] analysed an electromechanical actuator, using the Schwarz– Christoffel mapping method. The two methods accelerate the optimization processes by exploiting simplified models; however, they cannot easily solve the dynamic characteristics of electromagnetic devices using Matlab/Simulink. Chung and Gweon [12] developed an electromagnetic linear actuator for a mass flow controller, using magnetic equivalent circuit (MEC) method. Cai et al. [13] optimized the submersible solenoid valves for subsea blowout preventers, using MEC method. Batdorff and Lumkes [14] studied an axisymmetric electromagnetic actuator using high-fidelity MEC methods. The method may have some error when predicting electromagnetic force and magnetic flux; however, it is excellent when they are used to optimize and design electromagnetic devices. The dynamic characteristics could be also

*Corr. Author’s Address: China University of Petroleum, College of Mechanical and Electronic Engineering, Qingdao 266580, China, liuyhupc@163.com

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investigated using the methods with Matlab/Simulink environments [15] to [17]. In this paper, an MEC-based optimization design procedure for SEMA, constrained in a specific small volume, is proposed. The optimal design aims to minimize response time, especially the opening time when the main limiting quantity is the maximum allowed temperature. According to the optimization results, a SEMA is manufactured, and its dynamic characteristics are investigated experimentally in order to verify the proposed optimization procedure.

of numerous turns and layers of conducting copper wire, insulation and bonding material. The geometry of the SEMA is shown in Fig. 2 [13].

1 MATHEMATICAL MODEL The SEMA is designed as a solenoid-operated switching spring return actuator, which is essentially composed of a cover, a spring, a spring pocket, a coil, a coil bobbin, a plunger, a plunger sleeve, and a magnetic ring, as shown in Fig. 1. The plunger-type structure is intended to be produced in a small size [18]. When the coil is energized by DC voltage, the plunger of the SEMA retracts upward and extends downwards by releasing the stored energy from the spring [13] and [19].

Fig. 2. Geometry of the SEMA [13]

1.1 Thermal Model

Fig. 1. Schematic diagrams of the SEMA [13]

The cover of the actuator is made of AISI 316L austenitic stainless steel due to its high corrosion resistance to seawater, high strength, and high durability [20] and [21]. However, AISI 316L stainless steel is nonmagnetic. Therefore, four components (plunger, spring pocket, plunger sleeve, and magnetic ring) are used to form a magnetic circuit. The plunger is made of iron, which is a ferromagnetic material. The three other components are made of AISI 440C martensitic stainless steel, which is strongly magnetic but has lower corrosion resistance to seawater than AISI 316L austenitic stainless steel [22]. All of the gaps within the SEMA, e.g. the gap between the coil and the magnetic ring, are filled with conduction oil in order to transfer heat power and prevent high-pressure seawater from crushing the actuator. The coil conducts the current that provides magnetic flux, and it consists 474

The electrical circuit of an electromagnetic actuator supplies current to the coils. This current flows through wires and produces heat due to the wellknown Joule effect. The magnetic circuit provides the flux and the force, also producing heat due to the magnetic losses in the magnetic circuit [23]. Although some magnetic (demagnetization, saturation and magnetization hysteresis) and mechanical (friction and mechanical stress) effects are significant in electromagnetic actuators, the main limiting quantity considered in this study is the maximum allowed temperature of the SEMA in seawater, which is similar to the precondition of the solenoid actuator designed in [24]. Therefore, to minimize the response time for a specific small volume actuator, a study of the heat transfer phenomenon is to be done. A series of expressions has been developed in order to maintain the temperature of the actuator under the safety threshold. For simplicity of design, this study assumes that the coil bobbin is adiabatic, and the maximum temperature is in the centre of the coil; hence, the heat power, produced in the coil due to the energizing current, transfers from the coil to seawater via the conduction oil, the magnetic ring, and the cover of

Cai, B. – Liu, Y. – Abulimiti, A. – Ji, R. – Zhang, Y. – Dong, X. – Zhou, Y.

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the actuator. For the sake of safety and simplicity, continuous operation (100% duty cycle) has been assumed [25]. The steady-state heating balance can be expressed as follows:

2 imax R=

Tco − Tsea , (1) ζ co + ζ oil + ζ mr + ζ cv

where imax is the maximum allowed current in the coil, R is the resistance of the coil, and it is associated with the dimension, resistivity, resistivity temperature coefficient and number of coil turns of the SEMA [13]. Tco and Tsea are the temperature of the coil and seawater, respectively, and ζco, ζoil, ζmr and ζcv are the thermal resistances of the coil, the conduction oil, the magnetic ring, and the cover, respectively, and they are associated with the dimension, conduction coefficients of the coil, and convection coefficient of the conduction oil [13]. The current factor κ is defined as the ratio of the rated current to the maximum current. Therefore, the rated current can be derived from Eq. (3) and written as follows:

ie = κ imax . (2)

By applying the Ohm law, the assigned coil rated voltage can be written as follows:

U e = ie R. (3)

1.2 Electromagnetic Model The electromagnetic model of the SEMA consists of an electrical circuit and a magnetic circuit. The electrical circuit is the actual coil, and the magnetic circuit consists of the plunger, the plunger sleeve, the spring pocket, and the magnetic ring. By applying Kirchhoff’s voltage law, the magnetic and electrical circuits yields:

U e = i (t ) R + N

dϕ (t ) , (4) dt

where Ue is the input coil rated voltage, i(t) is the electrical current, R is the resistance of the coil, N is the number of turns, and ϕ(t) is the total magnetic flux. According to the magnetic equivalent circuit of the SEMA, The electromotive force can be expressed as follows:

i (t ) N = ϕ (t ) Rtm , (5)

where Rtm is the total magnetic reluctance.

The relationship of i(t), N, ϕ1(t), ϕ2(t) and R can be obtained from an analogy of the electric circuit and the magnetic circuit and can be expressed as follows: ( R + R pl + Rgp ) R ps1 Ni (t ) = ga + ϕ1 (t ) + ϕ 2 (t ) Rga + R pl + Rgp + R ps1

+ Rsp1 + Rsp 2 + Rmr + R ps 2 , (6)

R ps1 ϕ1 (t ) , (7) = ϕ 2 (t ) Rga + R pl + Rgp

where ϕ1(t) and ϕ2(t) are the magnetic flux flowing inside the plunger and the upper plunger sleeve, respectively. Rga, Rpl, Rgp, Rps1, Rps2, Rsp1, Rsp2 and Rmr are the magnetic reluctances of the magnetic flux paths of working gap, plunger, gap between the plunger and plunger sleeve, upper plunger sleeve, lower plunger sleeve, lower spring pocket, upper spring pocket and magnetic ring (see Figs. 1 and 2), respectively. For the ferromagnetic parts, consisting of the plunger, the plunger sleeve, the spring pocket, and the magnetic ring, the empirical curve-fit for the B-H curve is used and expressed as follows [26]:

B pl = µ pl H pl =

Bi = µi H i =

C1 H pl 1 + C2 H pl

+ C3 H pl , (8)

C4 H i + C6 H i , (9) 1 + C5 H i

where i denotes ps1, ps2, sp1, sp2, and mr, B is the magnetic flux density, H is the magnetic field intensity, C1, C2, C3, C4, C5, and C6 are regression parameters, and μpl, μi are the magnetic permeability of iron and AISI 440C stainless steel respectively, which are both variable. Assuming uniform flux density across the crosssectional area of the plunger, the plunger sleeve, the spring pocket, the magnetic ring, and the two gaps, the magnetic flux density can be expressed as follows:

B pl =

ϕ1 (t ) , (10) Apl

B ps1 =

ϕ 2 (t ) , (11) Aps1

Bi =

ϕ (t ) , (12) Ai

where i denotes ps2, sp1, sp2, and mr.

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Substituting Eq. (10) into Eq. (8), and Eqs. (11) and (12) into Eq. (9), the magnetic permeability of μpl, μps1 and μi can be expressed as functions of ϕ1(t), ϕ2(t) and ϕ(t) as follows: µ pl = f pl (ϕ1 (t )) =

(C1 + C3 ) Apl − C2ϕ1 (t ) 2 Apl

{[(C + C ) A + 1

µ ps1 = f ps1 (ϕ 2 (t )) = +

− C2ϕ1 (t )]2 + 4ϕ1 (t )C2C3 Apl 2 Apl 2 Aps1

}

1/ 2

, (13)

{[(C4 + C6 ) Aps1 − C5ϕ 2 (t )]2 + 4ϕ 2 (t )C5C6 Aps1}1/ 2

µi = f i (ϕ (t )) = +

(C4 + C6 ) Aps1 − C5ϕ 2 (t )

2 Aps1

, (14)

(C4 + C6 ) Ai − C5ϕ (t ) + 2 Ai

{[(C4 + C6 ) Ai − C5ϕ (t )]2 + 4ϕ (t )C5C6 Ai }1/ 2 , (15) 2 Ai

where i denotes ps2, sp1, sp2, and mr. Therefore, the relationship of parameters above can be rewritten as follows:   Lga L pl L  Lps1 + + gp     Nie  µ0 Aga f pl (ϕ1 (t )) Apl µ0 Agp  f ps1 (ϕ 2 (t )) Aps1 +  ϕ (t ) + ϕ (t ) = L L pl L Lps1 ga 2  1 + + gp + µ0 Aga f pl (ϕ1 (t )) Apl µ0 Agp f ps1 (ϕ 2 (t )) Aps1   Lsp1 Lsp 2 L ps 2 Lmr  + + + + . (16) f ( ϕ ( t )) A f ( ϕ ( t )) A f ϕ t A f ϕ ( ( )) ( (t )) Aps 2 sp1 sp1 sp 2 sp 2 mr mr ps 2   L ps1  f ps1 (ϕ 2 (t )) Aps1  ϕ1  = L L pl L ga  ϕ2 + + gp  µ0 Aga f pl (ϕ1 (t )) Apl µ0 Agp 

As shown in Eq. (16), the system of equations, consisted of two unknown quantities ϕ1(t) and ϕ2(t), can be solved using an iterative procedure. The electromagnetic force can be expressed as:

Fmag =

ϕ12 (t ) . (17) 2 µ0 Aga

The magnetic flux ϕ1(t) depends on the variation of the length of the working gap according to Eq. (16). Therefore, electromagnetic force also depends on the length of the working gap. 1.3 Mechanical Model For optimal design purposes, a simpler second-order, one-degree of freedom model has been adopted. The 476

mechanical model consists of a mass, spring and damper under the effect of magnetic and pressure forces, which can be represented by Newton’s second law as: d 2 x(t ) dx(t ) +b + k (δ + x(t )) = Fmag (t ) + Fpre , (18) 2 dt dt

where x is the displacement of the plunger (x = 0 when the actuator is opened, and x = 2.7×10–3 m when it is closed), m is the total movable mass, b is the lumped damping coefficient, k is the effective spring coefficient, δ is the spring pre-tension, Fmag are the electromagnetic force, and Fpre are the pressure force. During the optimal design, the pressure force is considered as constant. 2 OPTIMIZATION AND DISCUSSION The SEMA is constrained in a specific small volume with constant length and diameter. The objective is to optimize the designs of the individual components in order to achieve the minimum response time when the actuator is opened. Five radial dimensions including the thickness of the plunger (wpl), the thickness of the upper plunger sleeve (wps), the thickness of the coil (wco), the thickness of the magnetic ring (wmr), and the gap between the plunger and plunger sleeve (wgp) are optimized when the other radial dimensions are constant. The geometric optimization of SEMA is performed by using Matlab/Simulink software. The Simulink model consists of three main parts: the thermal subsystem, the electromagnetic subsystem, and the mechanical subsystem, as shown in Fig. 3. The thermal subsystem solves the number of turns, the resistance of the coil, and the rated voltage based on the five input radial dimensions when the initial main parameters are set as follows: the maximum allowed temperature of the SEMA is 120 °C because the synthetic enamelled copper wire will be burned down and short circuit when the temperature is higher than 120 °C, and the ambient seawater temperature is 4 °C. The three parameters solved by the thermal subsystem with the displacement of the plunger fed back from the mechanical subsystem are then input to the electromagnetic subsystem, and the electrical current and electromagnetic force can be solved. Using the electromagnetic force, the displacement, velocity and acceleration of the plunger are solved in the mechanical subsystem.

Cai, B. – Liu, Y. – Abulimiti, A. – Ji, R. – Zhang, Y. – Dong, X. – Zhou, Y.

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Fig. 3. Simulink model of the SEMA for dynamic characteristics

Fig. 4. Simulated dynamic characteristics of the SEMA; a) current of the coil and displacement of the plunger, and b) velocity and acceleration of the plunger

The simulated dynamic characteristics, including current of the coil, displacement, velocity and acceleration of the plunger for the SEMA with certain radial dimensions are shown in Fig. 4. When the coil is energized, the current increases rapidly until the sum of magnetic force and pressure force exceeds the spring force. This time period is considered to be the plunger delay time (tod). As the plunger starts to move, the inductance of the coil starts to increase due to the decreasing working gap. Therefore, the effective time constant increases, and the current of the coil decreases until the plunger reaches its final position. This time period is considered as plunger travel time

(tot). Therefore, the total opening time of the actuator (topen) is the sum of the plunger delay time and plunger travel time. Similarly, the total closing time of the actuator (tclose) is the sum of the plunger delay time (tcd) and plunger travel time (tct) when the coil is deenergized. It is governed by the force balance between the pressure force, the spring force, and the magnetic holding force. The current and holding force decay in the de-energized magnet are not instantaneous, but they follow a transient state. This retards the beginning of the motion of the plunger depending on the level of holding current [27]. By inputting the combination of different values of wps and wgp, wpl and wmr, and wmr and wco shown in Fig. 3, the response time can be obtained from the dynamic characteristic curves shown in Fig. 4. The response time including opening time and closing time as functions of the five radial dimensions is shown in Fig. 5. As shown in Figs. 5a and b, when the initial two dimensions are set as wpl = 5×10–3 m, and wmr = 2×10–3 m, as the thickness of the upper plunger sleeve (wps) and the gap between the plunger and the plunger sleeve (wgp) decreases, the opening time increases and the closing time decreases. The smaller the magnetic flux flows to the upper plunger sleeve, the bigger it flows to plunger, which is analogous to current of a parallel electric circuit. A big magnetic flux produces a big magnetic force and a short opening time. The big magnetic flux also produces big holding current and subsequent long closing time. For the SEMA used in subsea BOP stack, closing time is secondary to opening time. In order to maximize the opening time, the thickness of the upper plunger sleeve has to be minimized. However, if the thickness is too small, its strength is significantly weakened. Therefore, a suitable thick upper plunger sleeve should be used. Similarly, the small gap between the plunger and plunger sleeve produces small magnetic reluctance, a big magnetic flux, a big magnetic force and a short opening time. However, the small gap also produces major friction between the plunger and the plunger sleeve. Therefore, based on the overall consideration of various factors including opening time, closing time, strength and friction, the two design dimensions are set as wps = 1.8×10–3 m and wgp = 0.2×10–3 m. When the two dimensions are set as wps = 1.8×10–3 m and wgp = 0.2×10–3 m, the opening time and closing time as functions of the thickness of the plunger (wpl), the magnetic ring (wmr) and the coil (wco) are shown in Figs. 5c to f. The three dimensions are dependent on each other due to the fact that the sum of the three values is a constant when the two

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other are constant. With increasing wpl and wmr, the opening time increases and the closing time decreases. When wpl is 6.0×10–3 m, and wmr is 3.0×10–3 m, the opening time reaches the minimum of around 15×10–3 ms, and the closing time is about 36×10–3 s. Therefore,

the optimal resolution of the SEMA is wpl = 6.0×10–3 m, wco = 6.0×10–3 m, and wmr = 3.0×10–3 m, wps = 1.8×10–3 m, wgp = 0.2×10–3 m. For the optimal SEMA, the rated voltage (Ue) is 16 V and the rated current (ie) is 1.3 A.

Fig. 5. Optimization results of the SMEA: a) Opening time as a function of wps and wgp, b) Closing time as a function of wps and wgp, c) Opening time as a function of wpl and wmr , d) Closing time as a function of wpl and wmr , e) Opening time as a function of wmr and wco, f) Closing time as a function of wmr and wco

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3 EXPERIMENTS AND DISCUSSION According to the optimization results, a SEMA was manufactured and its dynamic experiment was also performed, as shown in Fig. 6. The DC power was supplied by a switching power supply (Zhaoxin, RXN3020D, China), which was set to 16 V. The current of the coil was measured by a current transducer (LEM, LTS 6-NP, Switzerland). Because it was very difficult to measure the displacement of the plunger with the hydraulic pressure, the hydraulic pressure was replaced by a long spring under the plunger, which produced a nearly constant force. The displacement was measured with an eddy current displacement sensor (Jingxin, JX70-04-B-M16*1-75-03K, China), which was fixed in an extension rod connected to the plunger. The signals of current and displacement were acquired synchronously by an oscillograph and processed with a computer. In order to acquire accurate vibration acceleration signals, the moment the plunger reached its

Fig. 6. Schematic of the dynamic experiments of the SEMA

final positions, vertical and horizontal vibration experiments of the SEMA were also performed. Two acceleration sensors (Lance, LC0152, China) were fixed on the top cover (or bottom cover) and cylinder cover of the optimal actuator. Because the sensors

Fig. 7. Experimental dynamic characteristics of the SEMA; a) measured current and displacement and b) calculated velocity and acceleration when the actuator is opened; c) Measured current and displacement, and d) calculated velocity and acceleration when the actuator is closed Optimal Design Based on Dynamic Characteristics and Experimental Implementation of Submersible Electromagnetic Actuators

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Fig. 8. The vertical and horizontal vibration accelerations of the SEMA when it is; a) opened and b) closed

were not fixed on the plunger, the acceleration when the plunger was moving could not be measured well. However, the rebound problem when the plunger hit the spring pocket, and the bottom cover was represented accurately. The signals of vertical and horizontal vibration acceleration were acquired synchronously by another oscillograph and also processed by the computer. The experimental dynamic characteristics of the SEMA are shown in Fig. 7. Although it is not obvious that the current decreases to its local minimum when the plunger reaches its final positions (Point a and Point b shown in Figs. 7a and c), the opening time and closing time can also be read clearly. From the measured current and displacement, it can be seen that the opening time and closing time are 15×10–3 s and 35×10–3 s, respectively, which shows good agreement with the optimization results. Figs. 7b and d are the calculated velocity and acceleration according to the displacement of the plunger. They clearly differ from the simulated velocity and acceleration shown in Fig. 4b. This is because during the simulation, the rebound problem of impact when the plunger hits the spring pocket and the bottom cover of the actuator is not considered. In addition, the pressure force is replaced by spring force, which also causes some errors. The vertical and horizontal vibration accelerations when the SEMA is opened and closed are shown in Fig. 8. After comparing Figs. 7b and 8a, it can be seen that when the actuator is opened, the measured maximum vertical acceleration of 0.6×103 m/s2 is higher than the calculated acceleration of the plunger of 0.4×103 m/s2, and the measured maximum horizontal acceleration of 0.3×103 m/s2 is slightly lower than the calculated one. Similarly, as shown in Fig. 7d and Fig. 8b, when the actuator is closed, the measured maximum vertical acceleration of 480

0.4×103 m/s2 is higher than the calculated acceleration of the plunger of 0.3×103 m/s2, and the measured maximum horizontal acceleration of 0.25×103 m/s2 is slightly lower than the calculated one. This is mainly because it may cause some errors when calculating the second-order derivative of the displacement, the calculated accelerations are lower that the measured ones. Although the measured vertical and horizontal vibration accelerations are higher slightly, they are lower than the empirical maximum value of 1×103 m/s2; therefore, the vibrations cannot affect the sealing of the SEMA. 4 CONCLUSIONS An optimization procedure based on dynamic characteristics of the SEMA constrained in a specific volume has been developed. The objective is to optimize the designs of the individual components in order to achieve the minimum response time, especially the opening time, when the actuator is opened. Three models including thermal model, electromagnetic model, and mechanical model have been built, and five radial dimension including wpl, wps, wmr, wgp and wgp have been optimized by using Matlab/Simulink when the other radial dimensions are constant. The optimal parameters of the SEMA are wps = 1.8×10–3 m, wgp = 0.2×10–3 m, wpl = 6×10–3 m, wco = 6×10–3 m, and wmr = 3×10–3 m. An optimal SEMA are manufactured, and a dynamic experiment was performed on it. The results show good agreement between the experimental response time and simulated response time. A vibration experiment of the SEMA was also performed, which shows that the measured vertical and horizontal accelerations are near the calculated acceleration of the plunger. The experiments show that the optimization procedure is

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accurate, and the optimal SEMA is sufficiently secure that it can be used to control subsea BOP stacks. 5 ACKNOWLEDGEMENTS The authors wish to acknowledge the financial support of the National High-Technology Research and Development Program of China (No. 2013AA09A220), National Natural Science Foundation of China (No. 51205411), Program for Changjiang Scholars and Innovative Research Team in University (IRT1086), Taishan Scholar Project of Shandong Province (TS20110823), Science and Technology Development Project of Shandong Province (2011GHY11520) and the Fundamental Research Funds for the Central Universities (No. 13CX02077A). 6 REFERENCES [1] API Specification 16D (2004). Specification for Control Systems for Drilling Well Control Equipment and Control Systems for Diverter Equipment, American Petroleum Institute, Washington. [2] Turner, P.A. (2001). Material compatibility in directional control valve designs. 2001 Offshore Technology Conference, OTC13233, DOI:10.4043/13233-MS. [3] Peterson, K.S., Stefanopoulou, A.G. (2004). Extremum seeking control for soft landing of an electromechanical valve actuator. Automatica, vol. 40, no. 6, p. 10631069, DOI:10.1016/j.automatica.2004.01.027. [4] Eyabi, P., Washington, G. (2006). Modeling and sensorless control of an electromagnetic valve actuator. Mechatronics, vol. 16, no. 3-4, p. 159-175, DOI:10.1016/j.mechatronics.2005.11.008. [5] Moses, A.J, Al-Naemi, F., Hall, J. (2003). Designing and prototyping for production. Practical applications of electromagnetic modeling. Journal of Magnetism and Magnetic Materials, vol. 254-255, p. 228-233, DOI:10.1016/S0304-8853(02)00963-0. [6] Wu, D., Xie, X.D., Zhou, S.Y. (2010). Design of a normal stress electromagnetic fast linear actuator. IEEE Transactions on Magnetics, vol. 46, no. 4, p. 10071014, DOI:10.1109/TMAG.2009.2036606. [7] Yatchev, I., Gueorgiev, V., Hinov, K. (2009). Optimization of an axisymmetric linear electromagnetic valve actuator. COMPEL - The International Journal for Computation and Mathematics in Electrical and Electronic Engineering, vol. 28, no. 5, p. 1249-1256, DOI:10.1108/03321640910969494. [8] Encica, L., Echeverria, D., Lomonova, E.A., Vandenput, A.J.A., Hemker, P.W., Lahaye, D. (2007). Efficient optimal design of electromagnetic actuators using space mapping. Structural and Multidisciplinary Optimization, vol. 33, no. 6, p. 481-491, DOI:10.1007/ s00158-006-0054-6.

[9] Encica, L., Paulides, J.J.H., Lomonova, E.A., Vandenput, A.J.A. (2008). Aggressive output spacemapping optimization for electromagnetic actuators. IEEE Transactions on Magnetics, vol. 44, no. 6, p. 1106–1109, DOI:10.1109/TMAG.2007.916224. [10] Markovic, M., Jufer, M., Perriard, Y. (2004). Analyzing an electromechanical actuator by Schwarz-Christoffel mapping. IEEE Transactions on Magnetics, vol. 40, no. 4, p. 1858-1863, DOI:10.1109/TMAG.2004.828920. [11] Markovic, M., Jufer, M., Perriard, Y. (2008). Analytical force determination in an electromagnetic actuator. IEEE Transactions on Magnetics, vol. 44, no. 9, p. 2181-2185, DOI:10.1109/TMAG.2008.888573. [12] Chung, M.J., Gweon, D.G. (2003). Optimal design and development of electromagnetic linear actuator for mass flow controller. KSME International Journal, vol. 17, no. 1, p. 40-47. [13] Cai, B.P., Liu, Y.H., Tian, X.J., Wang, Z.L., Wang, F., Li, H., Ji, R.J. (2011). Optimization of Submersible Solenoid Valves for Subsea Blowout Preventers. IEEE Transactions on Magnetics, vol. 47, no. 2, p. 451-457, DOI:10.1109/TMAG.2010.2100825. [14] Batdorff, M.A., Lumkes, J.H. (2009). High-fidelity magnetic equivalent circuit model for an axisymmetric electromagnetic actuator. IEEE Transactions on Magnetics, vol. 45, no. 8, p. 3064-3072, DOI:10.1109/ TMAG.2009.2017531. [15] Topcu, E.E., Kamis, Z., Yuksel, I. (2008). Simplified numerical solution of electromechanical systems by look-up tables. Mechatronics, vol. 18, no. 10, p. 559565, DOI:10.1016/j.mechatronics.2008.05.006. [16] Sefkat, G. (2009). The design optimization of the electromechanical actuator. Structural and Multidisciplinary Optimization, vol. 37, no. 6, p. 635644, DOI:10.1007/s00158-008-0254-3. [17] Zhao, J.F., Seethaler, R.J. (2010). Compensating combustion forces for automotive electromagnetic valves. Mechatronics, vol. 20, no. 4, p. 433-441, DOI:10.1016/j.mechatronics.2010.03.003. [18] Lovisolo, A., Roccato, P.E., Zucca, M. (2008). Analysis of a magnetostrictive actuator equipped for the electromagnetic and mechanical dynamic characterization. Journal of Magnetism and Magnetic Materials, vol. 320, no. 10, p. e915-e919, DOI:10.1016/j.jmmm.2008.04.065. [19] Cai, B.P., Liu, Y.H., Ren, C.K., Abulimiti, A., Tian, X.J., Zhang, Y.Z. (2012). Probabilistic Thermal and Electromagnetic Analyses of Subsea Solenoid Valves for Subsea Blowout Preventers. Strojniški vestnik Journal of Mechanical Engineering, vol. 58, no. 11, p. 665-672, DOI:10.5545/sv-jme.2012.681. [20] Cai, B.P., Liu, Y.H., Tian, X.J., Wang, F., Li, H., Ji, R. (2010). An experimental study of crevice corrosion behaviour of 316L stainless steel in artificial seawater. Corrosion Science, vol. 52, p. 3235-3242, DOI:10.1016/j.corsci.2010.05.040. [21] Cai, B.P., Liu, Y.H., Tian, X.J., Li, H., Ji, R., Wang, F., Zhang, Y.Z. (2011). Susceptibility of 316L stainless

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steel to crevice corrosion in submersible solenoid valve. Materials and Corrosion, vol. 62, no. 8, p. 753759, DOI:10.1002/maco.201005917. [22] Tanaka, S., Ueda, K., Mitamura, N., Oohori, M. (2006). The Development of an austenitic stainless steel bearing with high corrosion resistance and high nonmagnetic property. Journal of ASTM International, vol. 3, no. 9, p. 1790-2013, DOI:10.1520/JAI100424. [23] Angadi, S.V., Jackson, R.L., Choe, S.Y., Flower, G.T., Suhling, J.C., Chang, Y.K., Ham, J.K. (2009). Reliability and life study of hydraulic solenoid valve. Part 1 A multi-physics finite element model. Engineering Failure Analysis, vol. 16, no. 3, p. 974887, DOI: 10.1016/j.engfailanal.2008.08.011. [24] Oriol, G.B., Campanile, L.F. (2010). Design Rules for Actuator in Active Mechanical Systems, 1st ed., Springer, London.

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[25] Oriol, G.B., Samuel, G.A., Antoni, S.A., Daniel, M.M., Campanile, L.F. (2007). Linear electromagnetic actuator modeling for optimization of mechatronic and adaptronic systems. Mechatronics, vol. 17, no. 2-3, p. 153-163, DOI:10.1016/j.mechatronics.2006.07.002. [26] Haskara, I., Kokotovic, V.V., Mianzo, L.A. (2004). Control of an electro-mechanical valve actuator for a camless engine. International Journal of Robust and Nonlinear Control, vol. 14, no. 6, p. 561-579, DOI:10.1002/rnc.903. [27] Topcu, E.E., Yuksel, I., Kamis, Z. (2006). Development of electro-pneumatic fast switching valve and investigation of its characteristics. Mechatronics, vol. 16, no. 6, p. 365-378, DOI:10.1016/j. mechatronics.2006.01.005.

Cai, B. – Liu, Y. – Abulimiti, A. – Ji, R. – Zhang, Y. – Dong, X. – Zhou, Y.

Received for review: 2012-10-05 Received revised form: 2013-01-14 Accepted for publication: 2013-01-18

A Contribution for a Pragmatics-Based Approach to Concurrent Engineering Implementation Popovic, N. – Putnik, G.D. – Jasko, O. – Filipovic, J. Nenad Popovic1 – Goran D. Putnik2,* – Ondrej Jasko3 – Jovan Filipovic3

1 ABS Electro, Russia of Minho, Department of Production Engineering and Systems, Portugal 3 University of Belgrade, Faculty of Organizational Sciences, Serbia

2 University

The paper investigates how a pragmatics-based approach may influence Concurrent Engineering (CE) implementation projects. Pragmatics, a field of semiotics, is used as a perspective for analyzing, as an instrument for constructing manufacturing systems and, in this particular research, as an instrument for CE implementation projects. In particular, as a part of the CE implementation methodology, modeling and the effects of different interpretations (as pragmatics aspects) of the assessment of processes’ simultaneity in a manufacturing organization are studied. The underlying thesis is that different interpretations significantly influence the perception of the organization’s reality, which has an impact on the project’s success. As a representation class, the so-called Simultaneity (Concurrency) Matrix (SCM) was used for simultaneity process assessment. The thesis is validated in two manufacturing companies. The results suggest that further improvements of the CE implementation methodologies, when using the pragmatics-based approach, lead to better quality of decisions and provide some assurance for the success of short-time and low-cost CE implementation projects. Keywords: pragmatics, Concurrent Engineering, simultaneity assessment, Concurrent Engineering implementation, Simultaneity (Concurrency) Matrix (SCM)

0 INTRODUCTION This paper investigates how a pragmatics-based approach may influence Concurrent Engineering (CE) implementation projects. Pragmatics, a field of semiotics, is used as a perspective for analyzing and constructing manufacturing systems, i.e. CE implementation projects. Predominantly, as a part of the CE implementation strategy, which also includes CE readiness assessment, modeling and effects of different interpretations of the assessment of processes simultaneity, as pragmatics aspects are studied. This paper follows the theoretical framework of Semioticsbased Manufacturing Systems Integration [1] and [2] and presents its practical implementations, validation and implications in industrial environments. The main research thesis is that the assessment processes (within the CE readiness assessment) are interpretation dependent and, therefore, the application of traditional prescriptive methodologies may lead to failure or serious challenge of the projects. Further, as a second part of the thesis, that the application of a pragmatics-based approach might significantly improve potential for successful implementation of CE is validated. As an approach to a CE implementation strategy, the methodology based on the so-called simultaneity matrices (also called concurrency matrices) is used, for which two different interpretations are compared. The proposed methodology is validated in a reallife environment, i.e. in two SME manufacturing

companies, which have planned to apply CE. The results confirm the expectations that different interpretations may imply different management decisions and, therefore, corrupt the best possible decision. Consequently, in order to assure the best decisions for the case under consideration, an improved methodology for CE implementation strategy (including the CE Readiness Assessment (CERA)), should include multiple interpretations, i.e. should apply the pragmatics-based approach. The relevance of the research is multifold: i) Although the CE concept has existed for over two decades, companies still struggle to implement it to its full capacity. In addition, despite CE developments towards collaborative engineering, no alternative approach that paradigmatically negates or eliminates the CE as obsolete has surfaced yet. In other words, the CE implementation projects have been reaffirmed as currently being valid; ii) In the present market, characterized by high levels of uncertainty, companies are in search of low costs and short implementation times, and trusted technologies. In fact, up to 70% of all new projects fail or are somehow challenged (The percentages are different by different sectors) [3]. Therefore, it is not surprising that companies are reluctant to implement new organizational projects. This implies the need for reliable CE implementation methodologies;

*Corr. Author’s Address: University of Minho, Campus of Azurem, 4800-058 Guimaraes, Portugal, putnikgd@dps.uminho.pt

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iii) While it is evident that use of advanced computer technologies contributes to a reduction of the throughput time of CE implementation processes, providing more efficiency and speed in the processes, the role of technology-oriented approaches to reduce the CE implementation projects failure rate is less obvious, if not detrimental. In reality, the top five factors of project success are not technological [3]. In other words, “Tools by themselves do not promote success; the proper use of the tools does.” [3]. Accordingly, we promote non-technological approaches, such as a pragmatics-(i.e. semiotics)based approach to CE implementation strategy; iv) This paper provides validation of the pragmaticsbased approach to CE implementation methodology, with respect to simultaneity of processes. Therefore, the primary objective of the paper is to investigate the influence of a pragmaticsbased approach on CE implementation projects and particularly evaluation of process simultaneity, as one of the main features of a CE implementation strategy and a CE readiness assessment. In order to facilitate the application of CE in a wider range of companies, the secondary objective of the paper is to contribute to the development and improved methodology of pragmatics-based CE implementation methodology. This paper is organized in nine sections. After the introduction, Section 2 briefly presents pragmatics as the underlying meta-theoretical approach, in the context of the above-mentioned relevance factors. Section 3 summarizes basic requirements for and principles of CE. Section 4 presents an overview of the CERA methodology and the (CE) process simultaneity assessment methodologies (as an integral part of the CE implementation strategy). Therefore, the state-of-the-art is presented throughout the third and fourth section. The new methodology is outlined in Section 5. Section 6 presents two case studies. This section represents a validation of the thesis on the influence of pragmatics-based approaches on the CE implementation project, and specifically of the evaluation of the simultaneity of processes, as well as on the identification of intervention areas for CE implementation. A mold-making company was chosen for the first case study and a manufacturer of energy engineering products and systems for the second. Both companies are SMEs, and have well-developed designs and production. Secondary data, already reported in [4], were used for the first case study. For the second case study, the primary data were used. Section 6 presents research results analysis and 484

Section 7 provides conclusions and recommendations for future research. Finally, Section 8 presents the references. 1 PRAGMATICS In addition to syntax and semantics, pragmatics is field of semiotics, which is the science of signs. Probably the most used definition of the syntax, semantics and pragmatics is by Morris [5]: “[P]ragmatics is that portion of semiotics which deals with the origin, uses and effects of signs within the behavior in which they occur; semantics deals with the signification of signs in all modes of signifying; syntax deals with combination of signs without regard for their specific significations or their relation to the behavior in which they occur.” While the other two fields of semiotics, syntax and semantics, are already well known and widely used in manufacturing, or production systems, pragmatics is a new approach that deals with interpretations and their effects on the analysis and construction (i.e. project, or design) studies. As a means of, among other benefits, overcoming the problems of failing project rates, the assumption is that pragmatics could be used as a perspective for analyzing and constructing manufacturing systems [1] and [2], and consequently also applied to CE issues. Pragmatics/semiotics address non-technological aspects of organization. In the research presented in this paper, pragmatics is used as a perspective for analyzing and constructing manufacturing systems: CE implementation projects, specifically. In particular, as a part of the processes simultaneity and CE readiness, the assessment, modeling and effects of different interpretations, as pragmatic aspects, are studied. 2 CE CHARACTERIZATION CE is characterized, by three basic global characteristics: 1) Simultaneity of processes. Fig. 1a presents the signature structure of the Time-to-Market (TTM), denoted T, in sequentially performed operations, denoted OPi, where T is equal to the sum of time n duration ti of each operation OPi, i.e. T = ∑ i =1 ti. In the case of the maximum simultaneity of operations, the Time-to-Market (TTM), denoted T, is equal to the time duration of the operation with maximum time duration, i.e. T = max (ti) | i = 1, …, n. Fig. 1b presents the signature structure for T for the operations performed with certain

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degree of simultaneity, which is a realistic case, i.e. T value is between the T for sequentially performed operations and T for four operations performed simultaneously (Figs. 1a and b) (max(t1, t2, t3, t4) < T < (t1+t2+t3+t4)). In effect, for the operations performed simultaneously, or with a degree of simultaneity, there is a compression of TTM; 2) Concurrency, through multifunctional teams (teamwork) that concurrently and interactively make decisions on new product development (NPD). Simultaneity of operations (processes) does not assure concurrency per se. In the case of simple simultaneity, there is no interactive communication. The communication is reduced to the communication of the conditions for starting another operation that may be performed simultaneously (in parallel) and at its completion. The true concurrent performance of the two operations implies an interactivity between the two operations in order to make the best decision, i.e. the two operations ‘concur’ simultaneously for the best decision through dynamic interactions (communication), or solutions. This is illustrated in Fig. 2b; 3) The effort of 2) and 3) from or in the early stage of the NPD process, i.e. in the phase of design (Fig. 3). These three basic/primary/global features, called the main CE parameters/characteristics, are used as the basic criteria for evaluation of the level of CE readiness and consequent applicability in a company. Probably the most cited definition of CE is by Winner [6]: “CE is a systematic approach to the integrated, concurrent design of products and their related processes, including manufacture and support. This approach is intended to cause the developers, from the outset, to consider all elements of the product life cycle from conception through disposal, including quality, cost, schedule, and user requirements.” and “CE is a system for the achievement of (or, at least, the engineering approximation of) the best possible combination of these objectives.” Although considered synonyms, Simultaneous Engineering (SE) and CE are qualitatively different (similar situation occurs with collaborative engineering). Both concepts imply simultaneity of the processes, but CE also implies mutual communication among workers from different functional areas. This difference is graphically presented in Fig. 2. An example of SE, i.e. Simultaneous Product

Development, which implements many of the elements from CE, is given in [7]. operations

OP1 OP2 OP3 OP4

a) T = t1 + t2 + t3 + t4 operations

OP1 OP2 OP3 OP4

t1 t2

b) max (t1, t2, t3, t4) < T < (t1 + t2 + t3 + t4) Fig. 1. a) Time-To-Market (TTM or T) of sequentially performed processes, and b) realistic TTM (T) compression by achievable degree of processes simultaneity Process 1

Process 1

Preliminary

Final

Preliminary

Final

Process 2 a)

Process 2 b)

Fig. 2. a) Simultaneous (overlapped) execution of processes; b) Concurrent execution of processes (adapted from [8]) Start of production

“Traditional” sequential engineering Concurent Engineering

Resources

End of project

Fig. 3. Resources function pattern shapes for traditional sequential, or functional, engineering and CE (adapted from [9])

3 CE READINESS AND PROCESS SIMULTANEITY ASSESSMENT 3.1 CE Readiness Assessment Readiness assessment, as a part of a global CE implementation framework, is one of the first phases

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in the CE implementation process. Its significance is in determining the concrete mechanisms and degree of details necessary to deploy it. The CE implementation model, presented in Fig. 4 is adopted as the reference model.

Enterprises), Project Management Process Maturity (PM), CERAMConstruct model. The difference between CERA (Concurrent Engineering Readiness Assessment) and RACE (Readiness Assessment for Concurrent Engineering) is that CERA is a generic name of the methodology while the RACE is the name of the methodology formulated by the Concurrent Engineering Research Center (CERC) at West Virginia University. Therefore, RACE functions as a product name. Both CERA and RACE refer to the same problem. A number of similar methodologies are derived from RACE. In addition to the previous overview see also [12] and [13]. 3.2 Process Simultaneity (Parallelism) Assessment

Fig. 4. CE implementation strategy [10]

RACE (Readiness Assessment for Concurrent Engineering) model, which is almost certainly the most used methodology for this purpose, has been developed within this framework. It consists of assessment in two key areas: firstly, a product development process and practices; secondly, a technology, and corresponding nine and five subareas respectively: “The process component encompasses nine major elements and follows a readiness scale adapted from SEI’s CMM [3]. These elements are customer focus, process focus, strategies for team formation and development, accommodation of teams within the organization, management systems, mechanisms for rapid product assurance, agility, senior leadership commitment, and discipline. The technology component covers five areas, namely, application tools, communication, coordination, information sharing services, and integration” [10]. For each sub-area, the critical elements and the key criteria are defined. A questionnaire (manual or computer-based) is used for data gathering. This method has been used as a source for a number of other methods that adapted or modified the original RACE method. In [11] a good overview is presented, including an analysis of their characteristics, of these methods as well as of some others. [11] cites PMO (The Process Model of Organization), PMO-RACE (A Combination of PMO & RACE), PRODEVO (A Swedish Model Based on RACE), CMM (Capability Maturity Model), SPICE (Standardized Process Improvement for Construction 486

Process simultaneity, or process parallelism, is one of the hallmarks of CE. However, apparently little attention has been paid to measuring it. Usually, measures of the process simultaneity/parallelism are adopted from the network theories, i.e. from the activity network analysis applied to project management models. A study presented in [14], which is virtually the only source that explicitly analyzes process simultaneity/parallelism in the context of CE, also provides a good overview of several relevant methods. The study concludes that the measures (which are analyzed in the study, and which are the methods defined primarily for the analysis of activity networks) are not sufficient and the authors proposed a new measure, named W, and its relative measure w (See Eqs. (1) and (2)), which by the examples analyzed in [14] show much better performance. The results indicate that W is an excellent measure of parallelism, particularly for application in concurrent engineering. [14]. Another measure, based on the so-called Simultaneity (Concurrency) Matrix (SCM), was presented in [15]. This measure is used to evaluate degree of simultaneity through the 3-value function dCE of the degree of the particular unit’s participation in the particular product development phase [15] and [4]. Concerning the proposed pragmatics-based approach to simultaneity assessment, the SCM is probably the most appropriate and easier to use, giving three-value graded evaluations, and providing an easier basis for evaluation of interpretations. Therefore, in this paper, the methodology based on SCM is applied. It is worth noting that the use of the simultaneity/concurrency matrix does not prevent use of other measures of the processes simultaneity.

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w = W / N = (N – L) / N,

(2)

where N is the number of activities in the network; L is the length of the activity network, i.e. maximum number of activities in series, and w is the fraction of the activities that are in parallel. 3.2.2 Process Simultaneity Assessment: SCM and DCE The methodology primarily evaluates the simultaneity of processes, i.e. the above-listed first CE characteristic, and could be also used to evaluate global distribution of the effort, i.e. the third CE characteristic. The analysis is presented through the matrices organizational units × phases (used as a short name for product development phases). They indicate the main functions in the functional organization (the company’s organizational units that participate in the product development phases) and the main phases of the product development life cycle. The matrix cell represents the function of the particular unit’s participation in the particular product development phase or process. For the particular product development phase, the cells are filled by the three-value function dCE = f (org_unit, process) where dCE ∈ {0, 0.5, 1}. The values mean: ‘1’ full and active participation; ‘0.5’ partial participation; and ‘0’ no participation of the particular unit in the particular product development phase. When two or more particular units participate in a particular product development phase, it means that these activities are performed in parallel, i.e. simultaneously. The total degree of simultaneity/ concurrency, DCE, for a company (for all the company’s units that participate in the new product development) is calculated as the sum of all dCE in all columns divided by the number of matrix cells: n

DCE =

∑∑d i =1 j =1

CEi , j

m⋅n

⋅100 [ % ] , (3)

where m is number of organizational units and n number of “new product development” phases.

Phases

Organisational unit 1 Organisational unit 2 ... Organisational unit m Total

...

(1)

Phase n

W = (N – L),

Phase 2

3-value matrix

Phase 1

The W measure and its relative measure w of the process simultaneity/parallelism (in the context of CE), were defined in [14] as:

A relative measure is not necessary to define as the measure DCE is expressed in percentage. An example of the three-value SCM is given in Fig. 5.

Organisational unit

3.2.1 Process Simultaneity Assessment

0.5

0.5 0.5 0

2.0 2.5 1.5 1.5

Fig. 5. An example of the 4 × 4 three-value SCM, with the total degree of simultaneity / concurrency for a company of 47%.

4 PRAGMATICS-BASED METHODOLOGY FOR CE IMPLEMENTATION AND INTERPRETED SCM 4.1 Interpreted SCM Pragmatics-based methodology focuses on interpretations and not on the originally declared values by the examinees. It means that once responses from the examinees are gathered in some form, for example in the form of the SCM (or e.g. in the form of activity network graphs), different possible interpretations of the responses are examined and analyzed. Here, we examine interpretations of the original identifications of the processes simultaneity in the form of SCM. With different interpretations of the original 3-value matrix, new matrices are produced, each one corresponding to one interpretation, with differently defined simultaneity degrees, dCE. In consideration of which scores of the matrix’s cells to interpret and how, the most relevant are those with the scores of dCE equal to 0.5. Scores of 1, and especially 0, due to their nature, describe real life processes with much more certainty, while 0.5 scores involve certain level of uncertainty about quality and quantity, in terms of regularity, frequency, content, extension, volume, etc. Therefore, it is more appropriate to interpret 0.5 scores as having different values in reality. In fact, the real values, or more precisely, the values perceived as real, depend of individual and collective interpretations. In other words, the values perceived as real are the results of interpretations processes and negotiations of interpretations among stakeholders, which is the issue belonging to the field of pragmatics. Therefore, for the purpose of

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(4)

Application of Pragmatics-Based Approach will be demonstrated through creation of ‘Interpreted SCM’, for process simultaneity assessment, in three phases of the Concurrent Engineering implementation methodology. These phases are: 1) identification of the current “As-Is” situation, 2) identification of the company’s goals, i.e. To-Be scenario, regarding the desired future level of the CE application, and 3) identification of the domain where the main actions of further development and application of CE should take place, as the difference between the To-Be and As-Is scenarios. The application procedure can be outlined through the following steps: Procedure outline 1. Identification of the current As-Is situation: creation of 3-value As-Is SCM 488

3-value matrix

Organisational unit 1 Organisational unit 2 ... Organisational unit m Total

...

Phase n

Phase 2

Phase 1

Phases

1 0.5 0 1 2.5

Conservative Interpretation I1

Inclusive Interpretation I2

3-value matrix

Organisational unit 1 Organisational unit 2 ... Organisational unit m Total

1 0 0 1 2.0

Organisational unit 1 Organisational unit 2 ... Organisational unit m Total

...

Phase n

Phase 2

Phases Phase 1

Phases

Organisational unit

4.2 Procedure Outline for Application of the PragmaticsBased Approach

...

The first interpretation, I1, a conservative interpretation, because it considers only regular interactions, and neglects the irregular, sporadic, minor and incomplete processes, which is more rigorous interpretation of the processes. The second interpretation, I2, an inclusive interpretation, because it considers (or includes) all interactions as valuable, whether regular or irregular, which is a looser, i.e. a more inclusive interpretation of the processes. Applying interpretations I1 and I2, the original 3-value matrix yields two new matrices, whose cells are filled by the 2-value function: dCE = f (org_unit, process) where dCE Î {0, 1}. The new matrix created by the conservative interpretation I1 is called the conservative matrix and the new matrix created by the inclusive interpretation I2 is called the inclusive matrix. To distinguish 2-value (conservative and inclusive) matrices from the 3-value matrices (called SCM), they are called interpreted SCM. Fig. 6 schematically presents an interpretation of the initial 3-value matrix and its transformation in two 2-value interpreted (Conservative and Inclusive) matrices, where scores 0.5, associated with irregular participation, are interpreted.

Phase n

0.5 → 1.

Organisational unit

and I2:

Phase 1

0.5 → 0

Organisational unit

I1:

→ creation of 3-value As-Is. 2. Identification of the company’s goals, i.e. ToBe scenario, regarding the desired future level of the CE application: creation of 3-value To-Be SCM → creation of 3-value To-Be SCM. 3. Identification of the domain where the main actions of further development and application of CE should take place, i.e. identification of intervention areas for CE implementation, as the difference between the matrices To-Be and As –Is → creation of 3-value “Difference” “SCM”.

Phase 2

our research, we would suggest two interpretations (probably the most appropriate ones):

1 1 0 1 3.0

Fig. 6. Interpretation of the 3-value matrix and its transformation in two 2-value interpreted (conservative and inclusive) matrices

4 Interpretations I1 and I2 of the current “As-Is” situation: 4.1 Interpretation I1 of the current “As-Is” situation → creation of 2-value “As-Is” conservative interpreted SCM. 4.2 Interpretation I2 of the current “As-Is” situation → creation of 2-value “As-Is” inclusive interpreted SCM. 5. Interpretations I1 and I2 of the company’s goals, i.e. “To-Be” scenario:

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Strojniški vestnik - Journal of Mechanical Engineering 59(2013)7-8, 483-494

5.1 Interpretation I1 of the company’s goals, i.e. “To-Be” scenario, regarding future level of the CE application, → creation of 2-value “To-Be” conservative interpreted SCM. 5.2 Interpretation I2 of the company’s goals, i.e. “To-Be” scenario, regarding future level of the CE application, → creation of 2-value “To-Be” inclusive interpreted SCM. 6. Identification of the domain where the main actions of further development and application of CE should take place, i.e. identification of intervention areas for CE implementation based on Interpretations I1 and I2: 6.1 Identification of the domain where the main actions of further development and application of CE should take place, as the difference between the interpreted matrices “To-Be” and “As–Is” based on Interpretation I1 → creation of 2-value “Difference” SCM conservative interpreted. 6.2 Identification of the domain where the main actions of further development and application of CE should take place, as the difference between the interpreted matrices “To-Be” and “As–Is” based on Interpretation I2 → creation of 2-value “Difference” SCM inclusive interpreted. 7. Analysis and negotiation of the values to adopt for consideration in the next phases of the CE implementation. Phase 3 could be circumvented as it is not relevant for the pragmatics-based approach, because it is created over non-interpreted SMC and, therefore, generates incorrect results; the relevant results are only the differences of the interpreted matrices. The analysis implies calculation of the simultaneity degrees of each of the scenarios in order to provide the base for the “negotiation” of the values to be adopted. In order to compare the results, two measures of the processes simultaneity evaluation will be applied: 1) DCE, measure, and 2) Omega measures W and w. 5 CASE STUDIES 5.1 Companies Presentation and Business Requirements Two case studies were conducted in two companies. Company A, in Case Study 1, is an SME mold producer, located in Portugal. Company B, in Case Study 2, located in a transition country, is an energy

equipment manufacturer SME. Both companies integrate typical functions and new product development phases inherent to the CE domain definition, i.e. from marketing through design and production to shipping. For both companies, the question under consideration is what the engineering / manufacturing strategy that would improve the company’s performance be, and how to identify the company’s internal functional domains and organizational units as domains for implementation of that strategy? The engineering/manufacturing strategy, or concept, needed to adopt and implement, should be capable of achieving the following outcomes: Qualitative: 1) providing maximal customer satisfaction and the maximum quality of products in accordance with the customer’s specifications / requirements; 2) enhancing the company’s competitiveness on the market; Quantitative: 3a) reducing the product time to market (for Company A); 3b) reducing the percentage of redesign and customer complaints for 40% in the following 3 years (for Company B). From among different strategies considered, CE has been selected as the candidate strategy. All three requirements suggest the use of CE. 5.2 Organization of the assessment process Questionnaires were used for data collection in both cases. The questionnaire’s content was the empty table of Simultaneity (Concurrency) Matrix (SCM). The respondents had to fill in the organizational units (the “Functions” column) and the new product development phases (the “Phase” row) in their company, as well as to attribute values for dCE ∈ {0, 0.5, 1} for each matrix cell. As the two companies have slightly different organization as well as new product development phases, the tables from the two companies slightly differ. The respondents were representatives from all the organizational units that participate in the product development process chain. They have responded to two questionnaires, one of which collected data for the As-Is situation and the second for the To-Be scenario. The second questionnaire was designed to capture information about desired degrees of simultaneity and collaboration along the product development life-cycle, in accordance with the principle of multifunctional CE approach to the product development and multifunctional CE teams.

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Function

Preliminary project

Project

Project details

Manufacturing

Project approval

These data pertain to the simultaneity of the processes among the organizational units along the product development line.

Quotation

Table 1. As-Is and To-Be (in ( )) – 2 values matrices by conservative interpretation I1

5.3 Case Study 1 – Company A Data for Process Simultaneity Assessment: SCMs for the Company A

Client Techn.-Commerc. Design-CAD Planning Purchase Suppliers Programming - CAM Production Finishing-Assembly Try outs Quality Control

1(1) 1(1) 1(1) 0(0) 0(0) 0(0) 0(0) 0(0) 0(0) 0(0) 0(0)

1(1) 1(1) 1(1) 0(1) 1(1) 0(1) 0(1) 0(1) 0(1) 0(1) 0(1)

1(1) 1(1) 1(1) 1(1) 0(1) 1(1) 0(1) 0(1) 0(1) 1(1) 1(1)

0(1) 0(1) 1(1) 0(1) 1(1) 1(1) 0(1) 0(1) 0(1) 0(1) 0(1)

0(0) 0(0) 0(0) 1(1) 1(1) 0(0) 1(1) 1(1) 1(1) 1(1) 1(1)

1(1) 1(1) 0(0) 0(0) 0(0) 0(0) 0(0) 0(0) 1(1) 1(1) 1(1)

The assessment results for Company A are summarized in Tables 1 and 2, which are of the organizational units × phases matrix type. They are created in the 4th and 5th steps of the procedure outlined in Section 5.2, and present the interpreted matrices for conservative and inclusive interpretations of the As-Is situation and ToBe scenario, respectively. Table 3, created in the 6th step, presents the Difference matrix, i.e. presents the differences between the To-Be and As-Is matrices by conservative and inclusive interpretations.

Phase

Function

Quotation

Preliminary project

Project

Project details

Manufacturing

Project approval

Table 2. As-Is and To-Be (in ( )) – 2 values matrices by inclusive interpretation I2

Client

1(1)

0(1)

0(0)

1(1)

Techn.-Commerc. Design-CAD Planning Purchase Suppliers Programming - CAM Production Finishing-Assembly Try outs Quality Control

1(1) 1(1) 1(1) 1(1) 1(1) 0(0) 1(1) 0(0) 0(0) 0(0)

1(1) 1(1) 1(1) 1(1) 1(1) 0(1) 1(1) 0(1) 0(1) 0(1)

1(1) 1(1) 1(1) 1(1) 1(1) 1(1) 1(1) 0(1) 1(1) 1(1)

0(1) 1(1) 1(1) 1(1) 1(1) 1(1) 1(1) 1(1) 0(1) 1(1)

1(1) 0(0) 1(1) 1(1) 0(0) 1(1) 1(1) 1(1) 1(1) 1(1)

1(1) 0(0) 0(0) 0(0) 0(0) 0(0) 0(0) 1(1) 1(1) 1(1)

Phase

Function

Quotation

Preliminary project

Project

Project details

Manufacturing

Project approval

Table 3. Difference 2 values matrices between To-Be and As-Is matrices (conservative interpretation and inclusive interpretation)

Client Techn.-Commerc. Design-CAD Planning Purchase Suppliers Programming - CAM Production Finishing-Assembly Try outs Quality Control

0(0) 0(0) 0(0) 0(0) 0(0) 0(0) 0(0) 0(0) 0(0) 0(0) 0(0)

0(0) 0(0) 0(0) 1(0) 0(0) 1(0) 1(1) 1(0) 1(1) 1(1) 1(1)

0(0) 0(0) 0(0) 0(0) 1(0) 0(0) 1(0) 1(0) 1(1) 0(0) 0(0)

1(1) 1(1) 0(0) 1(0) 0(0) 0(0) 1(0) 1(0) 1(0) 1(1) 1(0)

0(0) 0(0) 0(0) 0(0) 0(0) 0(0) 0(0) 0(0) 0(0) 0(0) 0(0)

Phase

490

5.4 Case Study 2 – Company B Data for Process Simultaneity Assessment: SCMs for the Company B The assessment results for Company B are summarized in Tables 4 and 5, which are of the organizational units × phases matrix type. They are conservative and inclusive interpretations of the As-Is situation and To-Be scenario, respectively. Table 6 presents the differences between these matrices. The same procedure is used as in Case Study 1 (Section 6.2). 6 RESULTS ANALYSIS Through the analysis of the interpreted data we can make the assessment of: 1) Simultaneity of the processes – CE parameter 1 (Section 2) and 2) Differences in simultaneity assessment between two interpretations (the primary research thesis). The influence of interpretations, as the intrinsic feature of the pragmatics-based assessment of the simultaneity of processes, is highly significant. The results of quantitative evaluation are presented in Table 7. The influence evaluation/quantification process proceeded in the following way: The simultaneity of the processes was assessed for both case studies and two interpretations I1 and I2, (conservative and inclusive), by calculating simultaneity measures DCE, W, and w. The results for the As-Is situation and To-Be scenario and their difference are summarized in columns 3 and 4 of Table 7. Subsequently, differences in simultaneity assessment between two interpretations, for each

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Table 4. As-Is and To-Be (in ( )) – 2 values matrices by conservative interpretation I1 Phase Preliminary Org. Unit project Marketing & selling 1(1) Design commercial 1(1) Process planning 0(1) Product planning 0(1) Purchasing 0(1) Finance 0(1) Human resources 1(1) Logistics 0(0) Production 0(0) Maintenance 0(0) Quality control (Inspection) 0(0) Laboratory testing 0(1) Transport 0(0) Total 3(8)

Quotation

Contracting

Project

1(1) 0(1) 0(1) 0(0) 0(1) 0(1) 1(1) 0(1) 0(0) 0(0) 0(0) 0(1) 0(0) 2(8)

1(1) 0(1) 0(0) 0(0) 0(1) 0(1) 1(1) 0(1) 0(0) 0(0) 0(0) 0(1) 0(0) 2(7)

0(1) 1(1) 0(1) 0(1) 0(1) 0(1) 1(1) 0(0) 0(1) 0(0) 0(1) 0(1) 0(1) 2(12)

Product plann 0(1) 0(1) 0(1) 1(1) 1(1) 1(1) 0(1) 1(1) 0(1) 0(1) 0(1) 0(1) 0(1) 4(13)

Product launch 0(1) 0(1) 0(1) 1(1) 0(1) 0(1) 0(1) 1(1) 0(1) 0(1) 0(1) 0(1) 0(1) 2(13)

Product plann 1(1) 1(1) 1(1) 1(1) 1(1) 1(1) 1(1) 1(1) 1(1) 0(1) 1(1) 0(1) 0(1) 10(13)

Product launch 1(1) 0(1) 0(1) 1(1) 0(1) 1(1) 1(1) 1(1) 1(1) 0(1) 1(1) 0(1) 0(1) 7(13)

Production

Testing

Shipping

0(1) 0(1) 0(1) 1(1) 1(1) 0(1) 1(1) 0(1) 1(1) 1(1) 1(1) 0(1) 1(1) 7(13)

0(1) 0(1) 0(1) 0(0) 0(0) 0(1) 0(1) 0(1) 0(1) 0(1) 0(1) 1(1) 1(1) 2(11)

1(1) 0(0) 0(0) 0(1) 0(0) 0(1) 0(1) 1(1) 0(1) 0(1) 0(1) 0(1) 1(1) 3(10)

Production

Testing

Shipping

1(1) 1(1) 1(1) 1(1) 1(1) 1(1) 1(1) 1(1) 1(1) 1(1) 1(1) 0(1) 1(1) 13(13)

0(1) 1(1) 0(1) 0(1) 0(1) 0(1) 1(1) 0(1) 1(1) 1(1) 1(1) 1(1) 1(1) 7(13)

1(1) 0(1) 0(1) 0(1) 0(1) 0(1) 1(1) 1(1) 1(1) 1(1) 1(1) 1(1) 1(1) 8(13)

Table 5. As-Is and To-Be (in ( )) – 2 values matrices by inclusive interpretation I2 Phase Preliminary Org. Unit project Marketing & selling 1(1) Design commercial 1(1) Process planning 1(1) Product planning 0(1) Purchasing 1(1) Finance 1(1) Human resources 1(1) Logistics 0(1) Production 0(1) Maintenance 0(1) Quality control (Inspection) 0(1) Laboratory testing 0(1) Transport 0(0) Total 6(12)

Quotation

Contracting

Project

1(1) 1(1) 1(1) 0(1) 1(1) 1(1) 1(1) 0(1) 0(1) 0(1) 0(1) 0(1) 0(1) 6(13)

1(1) 1(1) 0(1) 0(1) 0(1) 1(1) 1(1) 0(1) 0(1) 0(1) 0(1) 0(1) 0(1) 4(13)

1(1) 1(1) 1(1) 0(1) 1(1) 1(1) 1(1) 0(1) 0(1) 0(0) 0(1) 0(1) 0(1) 6(13)

Table 6. Difference 2-value matrices between To-Be and As-Is matrices (conservative interpretation and inclusive interpretation) Phase Preliminary Org. Unit project Marketing & selling 0(0) Design commercial 0(0) Process planning 1(0) Product planning 1(1) Purchasing 1(0) Finance 1(0) Human resources 0(0) Logistics 0(1) Production 0(1) Maintenance 0(1) Quality control (Inspection) 0(1) Laboratory testing 1(1) Transport 0(0) Total 5(6)

Quotation

Contracting

Project

0(0) 1(0) 1(0) 0(1) 1(0) 1(0) 0(0) 1(1) 0(1) 0(1) 0(1) 1(1) 0(1) 6(7)

0(0) 1(0) 0(1) 0(1) 1(1) 1(0) 0(0) 1(1) 0(1) 0(1) 0(1) 1(1) 0(1) 5(9)

1(0) 0(0) 1(0) 1(1) 1(0) 1(0) 0(0) 1(1) 1(1) 0(1) 1(1) 1(1) 1(1) 10(7)

Product plann 1(0) 1(0) 1(0) 0(0) 0(0) 0(0) 1(0) 0(0) 1(0) 1(1) 1(0) 1(1) 1(1) 9(3)

Product launch 1(0) 1(1) 1(1) 0(0) 1(1) 1(0) 1(0) 0(0) 1(0) 1(1) 1(0) 1(1) 1(1) 11(6)

A Contribution for a Pragmatics-Based Approach to Concurrent Engineering Implementation

Production

Testing

Shipping

1(0) 1(0) 1(0) 0(0) 0(0) 1(0) 0(0) 1(0) 0(0) 0(0) 0(0) 1(0) 0(0) 6(0)

1(1) 1(0) 1(1) 0(1) 0(1) 1(1) 1(0) 1(1) 1(0) 1(0) 0(0) 0(0) 1(0) 9(6)

0(0) 0(1) 0(1) 1(1) 0(1) 1(1) 1(0) 0(0) 1(0) 1(0) 1(0) 1(0) 0(0) 7(5)

491

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one of the main objectives of the CE implementation methodology. Numerically, the results are: i) DCE between 27.94 and 137.54% with a mean of 65.54%, ii) W between 32.20 and 550.00% with a mean of 178.58%, and iii) w between 5.75 and 172.00% with a mean of 61.77%. The practical importance of these data is exceptionally high, or critical. In practice, it would mean that the CE implementation managers, applying traditional, and not the pragmatics-based approach, could be faced with large under- or over-estimations. The consequences are well known: challenged or failed projects. On the basis of the analysis and evidence provided, we can conclude that the main research thesis of the paper has been confirmed, i.e. the interpretations significantly influence the assessment and that, consequently, the communication, negotiation and similar pragmatics instruments, should take place within the CE implementation methodology.

of the case studies, was calculated and presented in columns 5 and 6 of Table 7. The highlighted results in columns 5 and 6 of Table 7 are the most important, because they quantitatively reveal the differences in assessment of the simultaneity of processes under different interpretation, which constitutes the base for the research thesis validation. Simultaneity degrees results show variations of: i) DCE between 9.43 and 148.09%, with a mean of 51.73%; ii) W between 10.64 and 550.00% with a mean of 98.56%; and iii) w between 1.09 and 172.00%, with a mean of 26.97%. The results clearly demonstrate the superiority of the interpretation-based approach versus a traditional approach. Specifically, depending on the measure applied and the case analyzed, the errors of the assessment might be between 9.43 and 550.00%. If means are considered, the errors might be between 26.97 and 98.56%. Special attention should be paid to the matrix difference that represents the assessment of the intervention areas in which it would be necessary to act for the CE implementation, and which is actually

7 CONCLUSIONS We draw a two-pronged conclusion with respect to CE implementation:

Table 7. Simultaneity evaluation and difference in simultaneity evaluation between two interpretations Matrix

Measure

Inclusive interpretation I2

As-Is

DCE Ω ω

To-Be

DCE Ω ω

Difference

DCE Ω ω

As-Is

DCE Ω ω

To-Be

DCE Ω ω

Difference

DCE Ω ω

43.94 23 0.79 72.73 42 0.88 28.79 13 0.68 23.08 18 0.67 81.20 86 0.91 58.12 59 0.87

68.18 39 0.87 80.3 47 0.89 12.12 2 0.25 57.26 58 0.87 99.15 107 0.92 41.88 40 0.82

CASE 2 Company B

492

Difference in simultaneity assessment between two interpretations

Conservative interpretation I1

CASE

CASE 1 Company A

Simultaneity assessment

Popovic, N. – Putnik, G.D. – Jasko, O. – Filipovic, J.

in relation to I1

in relation to I2

5 6 (|(3-4)| /3) × 100% [%] (|(3-4)| / 4) × 100% [%] 55.17 35.55 69.57 41.03 10.13 9.20 10.41 9.43 11.90 10.64 1.14 1.12 57.90 137.54 84.62 550.00 63.24 172.00 148.09 59.69 222.22 68.97 29.85 22.99 22.11 18.10 24.42 19.63 1.10 1.09 27.94 38.78 32.20 47.50 5.75 6.10

StrojniĹĄki vestnik - Journal of Mechanical Engineering 59(2013)7-8, 483-494

1. The pragmatics-based approach, which implies evaluation of different interpretations of the data, has been proven to be relevant for the CE implementation methodology (simultaneity of the processes assessment, and identification of intervention areas for CE implementation has been addressed). It has been proven that the assessment results are interpretation dependent and, therefore, the application of traditional methodologies may lead to failure or serious challenges of projects. Therefore, it has been demonstrated that application of a pragmaticsbased approach might significantly improve the potential for the successful implementation of CE, which leads towards validation of the primary research thesis of the relevance of the pragmaticsbased approach for CE implementation methodology. 2. The case studies demonstrate the utility and effectiveness of the applied methodology which, although simple, exhibits the sensitivity and capability of identification of phenomenologically highly salient features of the company organization in terms of the CE paradigm. The proposed methodology, with a higher level of certainty than the traditional approaches, clearly identifies areas of primary attention and needs for intervention in the company of concern. The case studies also demonstrated the simplicity of the methodology, which also implies its efficiency, which is one of the business requirements for this stage of evaluation of strategy applied in the companies. Recommendations for future research are as follows: 1. to investigate additional types of interpretations and their applications; 2. to further improve the methodology and to develop a computer-based tool for its application; 3. to assure better perception of the existing measures implications, to improve their definitions, as well as to develop a new, superior, set of measures; 4. the pragmatics-based approach should be applied to other methodologies, particularly the RACEbased methodologies, i.e. to embed an analysis of different possible interpretations of the evaluation of different factors of the CE readiness assessments as well as on the evaluation of the results achieved, and further to apply the pragmatics-based approach throughout the CE implementation methodologies. In other words,

the traditional methodologies should be upgraded with the pragmatics perspective Finally, 1. pragmatics might be considered within the CE practice itself, not only within the CE implementation; 2. application of a pragmatics-based approach means, in fact, the implementation of the concept of co-design, co-creation, co-development (see [16] and [17]), which is fully in accordance with the paradigm of communication as an instrument for organization building, especially as co-design, co-creation, co-development are inherent for CE as it is paradigmatically based on teamwork (e.g. see [7]); 3. the experiments presented demonstrate the importance of the emergent manufacturing systems, such as Ubiquitous Manufacturing Systems (UMS) [2] with embedded (human) communication functionalities as a regular instrument permanently available for manufacturing system organization creation, i.e. co-creation. 8 ACRONYMS CE Concurrent Engineering CERA Concurrent Engineering Readiness Assessment NPD New Product Development SCM Simultaneity (Concurrency) Matrix 9 ACKNOWLEDGEMENTS The authors wish to acknowledge for providing support and assistance in performing research and data gathering: the Foundation for Science and Technology â&#x20AC;&#x201C; FCT, Project PTDC/EME-GIN/102143/2008, Ubiquitous-oriented embedded systems for globally distributed factories of manufacturing enterprises, and EUREKA, Project E! 4177-Pro-Factory UES. 10 REFERENCES [1] Putnik, G.D. (2010), Semiotics-based manufacturing system integration. International Journal of Computer Integrated Manufacturing, vol. 23, no. 8-9, p. 687-690, DOI:10.1080/0951192X.2010.513809. [2] Putnik, G.D., Putnik, Z. (2010), A semiotic framework for manufacturing systems integration â&#x20AC;&#x201C; Part I: Generative integration model. International Journal of Computer Integrated Manufacturing, vol. 23, no. 8-9, p. 691-709, DOI:10.1080/0951192X.2010.510292.

A Contribution for a Pragmatics-Based Approach to Concurrent Engineering Implementation

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[3] The Standish Group Int. (2005). Chaos Rising: A Chaos Executive Commentary, Report. The Standish Group Int., West Yarmouth. [4] Putnik, G.D., Lima, M., Lima, P. (2002). Implementing and improving the concurrent engineering applications: the case of a mould making company. Proceedings of the 18th International Conference on CAD/CAM, Robotics and Factories of the Future, Porto, p. 117125. [5] Morris, C. (1971). Writtings on the General Theory of Signs. Mouton, Hague, Paris. [6] Winner, R.I., Pennell, J.P., Bertrand, H.E., Slusarzuk, M.M.G. (1988). The Role of Concurrent Engineering in Weapon Systems Acquisition. Institute of Defense Analyses Report R-338, Alexandria. [7] Rihar, L., Kušar, J., Gorenc, S., Starbek, M. (2012). Teamwork in the simultaneous product realisation, Strojniški vestnik – Journal of Mechanical Engineering, vol. 58 no. 9, p. 534-544. [8] Yassine, A.A., Chelst, K.R., Falkenburg, D.R. (1999). A decision analytic framework for evaluating concurrent engineering. IEEE Transactions on Engineering Management, vol. 46, no. 2, p. 144-157, DOI:10.1109/17.759142. [9] Hartley, J.R. (1992). Concurrent Engineering: Shortening Lead Times, Raising Quality and Lowering Costs. Productivity Press, Cambridge. [10] Karandikar, H.M., Fotta, M.E., Lawson, M., Wood, R.T. (1993). Assessing organizational readiness for implementing concurrent engineering practices and collaborative technologies. Proceedings of the 2nd Workshop on Enabling Technologies: Infrastructure for Collaborative Enterprises, Los Alamitos, p. 83-93.

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[11] Khalfan, M.M.A., Anumba, C.J., Siemieniuch, C.E., Sinclair, M.A. (2001). Readiness Assessment of the construction supply chain for concurrent engineering. European Journal of Purchasing & Supply Management, vol. 7, no. 2, p. 141-153, DOI:10.1016/ S0969-7012(00)00023-X. [12] Villa, C., Romero, F., Contero, M. (2004). Implementing collaborative engineering environments through reference model-based assessment, Luo, Y. (ed.): Cooperative Design, Visualisation, and Engineering, Springer, Berlin. Heidelberg, p. 79-86. [13] Žargi, U., Kušar, J., Berlec, T., Starbek, M. (2009). A company’s readiness for concurrent product and process development. Strojniški vestnik – Journal of Mechanical Engineering, vol. 55, no. 7-8, p. 427-437. [14] Haberle, K.R., Burke, R.J., Graves, R.J. (2000). A note on measuring parallelism in concurrent engineering. International Journal of Production Research, vol. 38, no. 8, p 1947-1952, DOI:10.1080/002075400188672. [15] Goldense, B.L. (1994). Predictive metrics for concurrent engineering. Electro International Conference Proceedings. Combined Volumes. Boston, p. 485-504. [16] Ueda, K., Markus, A. Monostori, L., Kals H.J.J., Arai, T. (2001). Emergent synthesis methodologies for manufacturing original research article. CIRP Annals Manufacturing Technology, vol. 50, no. 2, p. 535-551. [17] Kito, T., Fujii, N., Ueda, K. (2004). Co-creative decision making in artifactual systems in consideration of bounded rationality. Proccedings of EES: Experiments in Economic Sciences - New Approaches to Solving Real-world Problems, p. 303-317.

Popovic, N. – Putnik, G.D. – Jasko, O. – Filipovic, J.

Strojniški vestnik - Journal of Mechanical Engineering 59(2013)7-8 Vsebina

Vsebina Strojniški vestnik - Journal of Mechanical Engineering letnik 59, (2013), številka 7-8 Ljubljana, julij-avgust 2013 ISSN 0039-2480 Izhaja mesečno

Razširjeni povzetki člankov Steven den Dunnen, Gert Kraaij, Christian Biskup, Gino M.M.J. Kerkhoffs, Gabrielle J.M. Tuijthof: Vrtanje v sklepni del kosti s čistim vodnim curkom: študija izvedljivosti in vitro Ming Xu, Bo Jin, Guojin Chen, Jing Ni: Krmiljenje variabilne hitrosti elektrohidravličnega pogona na osnovi regulacije energije Sreten Perić, Bogdan Nedić, Dragan Trifković, Mladen Vuruna: Eksperimentalna raziskava triboloških lastnosti motornih olj in olj za zobniške prenosnike Sedat Karabay: Modifikacija prevodnega materiala AA6101 kablov OPGW za zaščito pred udari strele Sedat Yayla: Tokovne razmere ob zamaknjenih ceveh z več zarezami v prehodu prenosnika toplote z orebrenimi cevmi Baoping Cai, Yonghong Liu, Aibaibu Abulimiti, Renjie Ji, Yanzhen Zhang, Xin Dong, Yuming Zhou: Optimalna zasnova potopnih elektromagnetnih aktuatorjev na osnovi dinamičnih karakteristik ter eksperimentalna implementacija Nenad Popovic, Goran D. Putnik, Ondrej Jasko, Jovan Filipovic: Prispevek k pragmatičnemu pristopu do uvajanja sočasnega inženirstva Osebne vesti Doktorske disertacije, znanstvena magistrska dela, specialistična dela, diplomske naloge

SI 81 SI 82 SI 83 SI 84 SI 85 SI 86 SI 87

SI 88

Prejeto v recenzijo: 2012-12-21 Prejeto popravljeno: 2013-02-22 Odobreno za objavo: 2013-04-09

Vrtanje v sklepni del kosti s čistim vodnim curkom: študija izvedljivosti in vitro

univerza v Delftu, Oddelek za biomehanski inženiring, Nizozemska medicinski center, Amsterdam, Oddelek za ortopedsko kirurgijo, Nizozemska 3 (prej) Leibnizova univerza v Hannovru, Institut za materiale, Nemčija 4 Univerzitetni medicinski center Leiden, Oddelek za ortopedijo, Nizozemska

2 Akademski

Tehnologija vodnega curka bi lahko postala zanimiva za klinično uporabo pri obdelavi žilavih človeških tkiv, kot je sklepni del kosti, saj zagotavlja čiste in ostre reze brez pregrevanja tkiva. Poleg tega je možen tudi dovod vode prek gibkih cevi, s čimer se odpirajo možnosti za minimalno invaziven kirurški dostop. Za vrtanje v trde industrijske materiale se vodi dodajajo abrazivi (trdi togi delci), ki izboljšajo zmogljivost vrtanja, ki pa lahko povzročijo težave z biozdružljivostjo v kliničnem okolju. Cilj te študije je zato ugotoviti izvedljivost vrtanja s čistim vodnim curkom v sklepni del kosti. Podrejeni cilj je ugotavljanje variabilnosti minimalnega tlaka penetracije zaradi heterogenosti kosti ter globalna analiza oblike lukenj v kosteh. Glavni parameter, ki določa zmogljivost obdelave z vodnim curkom, je hitrost vode ob trku z obdelovancem. Zveza med hitrostjo vodnega curka vtekočine (m/s), vodnim tlakom P (N/m2) in gostoto ρ (kg/m3) je podana z Bernoullijevo enačbo, En. (1). Vrednost ρ je konstantna, zato je hitrost vodnega curka odvisna samo od tlaka vode. Izbrali smo torej spreminjanje tlaka. Na rezultate vrtanja razen hitrosti vodnega curka v veliki meri vplivajo tudi mehanske lastnosti materiala. Kostno tkivo je heterogen material, katerega mehanske lastnosti se spreminjajo znotraj kosti in med kostmi, zato so bili preizkušeni vzorci štirih različnih vrst za preučitev možnosti uporabe tehnologije vodnega curka pri različnih kostnih tkivih. Vodni curek z razponom tlaka med 20 in 120 MPa v korakih po 10 MPa je bil uporabljen za vrtanje slepih lukenj v posteriorno sklepno površino petnice petih človeških, šestih ovčjih, petih kozjih in štirih prašičjih kadavrskih kosti. Uporabljen je bil premer šobe 0,6 mm, čas curka 5 sekund in oddaljenost od 2,5 do 5,5 mm. Odvisno od velikosti sklepne površine je bilo v vsak vzorec pravokotno na površino kosti izvrtanih od 6 do 9 lukenj v razmaku vsaj 4 mm. Globina luknje je bila izmerjena z 0,3-milimetrsko merilno uro. Po en vzorec od vsake vrste je bil preiskan z μCT skenerjem, pri čemer je bila ugotovljena oblika izvrtanih lukenj. Čisti vodni curek je uporaben za vrtanje lukenj v subhondralno kost. Minimalni tlak za vrtanje v subhondralno kost človeške, kozje, ovčje in prašičje petnice je bil 37 (SD 10), 36 (SD 5,9), 62 (SD 8,5) in 56 MPa (SD 5,8). Globina rezanja se v splošnem povečuje s tlakom. Postopno povečevanje globine je najbolj očitno pri kozjih in človeških vzorcih, medtem ko pa je večji raztros pri ovčji in človeški kosti. μCT skeni so dosledno pokazali, da vodni curek ustvarja luknje konične oblike od subhondralne ploskve v trabekularno kost. Študija je pokazala, da je možno vrtanje slepih lukenj v sklepni del kosti s čistim vodnim curkom. Minimalni vodni tlak je bil med 36 (povprečna kozja kost) in 62 MPa (povprečna ovčja kost). Variabilnost minimalnega vodnega tlaka med vrstami ter med primerki iste vrste kaže, da se pri istem tlaku pojavljajo različne globine lukenj. Odstopanja so lahko posledica razlik v volumskem deležu kosti ter v debelini hrustanca, subhondralnih in trabekularnih slojev kosti. Rezultati so skladni z En. 1, ki napoveduje povečanje globine luknje ob povečanju vodnega tlaka. Premer lukenj se zmanjšuje z naraščajočo globino, kar je mogoče pojasniti z zmanjšano hitrostjo vodnega curka na večji globini zaradi trka z vodo, ki se vrača iz izvrtine. Konična oblika bi bila lahko uporabna pri ortopedskem zdravljenju, npr. za pritrjevanje vijakov ali stimulacijo kostnega mozga. Na rezultate so morda vplivali tudi omejevalni dejavniki: povečanje velikosti vzorca in manjši koraki spreminjanja vodnega tlaka so lahko prispevali k večji natančnosti določanja minimalnega tlaka. Eksperimenti so pokazali različne globine lukenj pri istem tlaku, kar dokazuje vpliv materialnih lastnosti kosti. Nadzor nad globino luknje, izvrtane z vodnim curkom, je nujen zaradi klinične varnosti. Zato je priporočljiv dodaten varnostni sistem, ki ob dosegu vnaprej opredeljene globine izklopi vodni curek. Ključne besede: čisti vodni curek; vrtanje z vodnim curkom, sklepni del kosti pri sesalcih, vodni tlak, ortopedska kirurgija

*Naslov avtorja za dopisovanje: Tehniška univerza v Delftu, Oddelek za biomehanski inženiring, Mekelweg 2, 2628CD, Delft, Nizozemska, s.dendunnen@tudelft.nl

SI 81

Prejeto v recenzijo: 2012-12-13 Prejeto popravljeno: 2013-03-13 Odobreno za objavo: 2013-04-16

Krmiljenje variabilne hitrosti elektrohidravličnega pogona na osnovi regulacije energije Xu, M. – Jin, B. – Chen, G. – Ni, J. Ming Xu1,* – Bo Jin2 – Guojin Chen1 – Jing Ni1

1 Univerza

2 Univerza

Hangzhou Dianzi, Oddelek za strojništvo, Kitajska v Zhejiangu, Državni laboratorij za fluidno tehniko, Kitajska

Elektrohidravlični pogoni z variabilno hitrostjo (elektromotor s krmiljenjem hitrosti v kombinaciji s konstantno hidravlično črpalko) so obetavni, saj poleg višje energijske učinkovitosti kot pogoni z elektromotorjem konstantne hitrosti v kombinaciji s hidravlično črpalko spremenljive delovne prostornine zagotavljajo tudi boljšo zanesljivost sistema in širši razpon hitrosti. Glavna slabost pogonov z variabilno hitrostjo je v počasnem odzivu in pomanjkljivi natančnosti krmiljenja zaradi velike vztrajnosti elektromotorja in hidravlične črpalke. Prav natančnost krmiljenja pa je nujna pri hidravličnih rezalnih sistemih, elevatorjih itd. Cilj raziskave je razvoj nove rešitve krmiljenja hitrosti elektrohidravličnega pogona, ki odpravlja pomanjkljivosti pogona z variabilno hitrostjo in je primerna za praktično rabo. Predlagan je elektrohidravlični pogon z variabilno hitrostjo, ki uporablja načelo regulacije energije. Članek obravnava krmiljenje hitrosti valja, s čimer je ponazorjena zmogljivost pogona. Pri pogonu variabilne hitrosti z regulacijo energije uravnava konstantno hidravlično črpalko frekvenčni pretvornik prek asinhronskega električnega motorja, valj pa krmili proporcionalni razvodnik. Regulator energije (ERD), ki je nameščen na izhodu hidravlične črpalke, je sestavljen iz mehastega akumulatorja, proporcionalnega pretočnega ventila in razbremenilnega ventila. Mehasti akumulator za shranjevanje hidravlične energije je bil izbran zaradi enostavne zgradbe in hitrega odziva. Pretok med napravo ERD in glavnim hidravličnim krožnim tokom krmili proporcionalni pretočni ventil. Razbremenilni ventil deluje kot varnostni ventil. ERD je polaktivna naprava, katere delovanje je odvisno od tlačne razlike med ERD in izhodom hidravlične črpalke. Gib valja meri tipalo položaja v valju, hitrost valja pa se izračunava kot odvod položajnega signala. Tlak na izhodu iz črpalke in ERD merita dva tlačna senzorja, pretok na izhodu iz hidravlične črpalke pa meri visokotlačni merilnik pretoka. Nova rešitev pogona združuje prednosti pogona z variabilno hitrostjo in pogona s krmilnim ventilom (elektromotor s konstantno hitrostjo v kombinaciji s konstantno hidravlično črpalko, kjer premik aktuatorja krmili ventil). Razlika v primerjavi s sestavljenim pogonom (pogon variabilne hitrosti v kombinaciji z aktuatorjem s krmilnim ventilom) je v napravi ERD. Če mora aktuator pospešiti, vendar elektromotor in črpalka ne moreta držati koraka, ERD sprosti energijo za hitrejši odziv. Če elektromotor in črpalka ne moreta slediti zahtevi po upočasnitvi aktuatorja, ERD prevzame odvečno hidravlično olje. Naprava ERD v vseh ostalih situacijah ostane zaprta. Analizirana je rešitev krmiljenja variabilne hitrosti pogona na osnovi regulacije energije. Predlagana rešitev krmilnega sistema pogona je tipa MIMO. Sistem ima štiri vhode (referenčna hitrost, dejanska hitrost, izhodni tlak iz črpalke in tlak ERD) in tri objekte krmiljenja (frekvenčni pretvornik, proporcionalni razvodnik in pretočni ventil), močne nelinearnosti in strukturne negotovosti pa še povečujejo zahtevnost strategije krmiljenja. Izpeljana je podrobna strategija krmiljenja treh objektov. Pred simulacijo in eksperimenti je treba določiti več parametrov krmiljenja in članek obravnava vrstni red nastavljanja teh parametrov po Ziegler-Nicholsovi metodi. Za prikaz zmogljivosti krmiljenja hitrosti pogona z variabilno hitrostjo na osnovi regulacije energije je bilo opravljenih več simulacij in eksperimentov. Za primerjavo zmogljivosti krmiljenja hitrosti so bile opravljene simulacije in eksperimenti za pogon s krmilnim ventilom, pogon z variabilno hitrostjo in sestavljeni pogon. Predlagana rešitev pogona sicer prinaša večje stroške sistema in zahtevnejše krmiljenje, rezultati simulacij in eksperimentov pa kažejo dobro celotno zmogljivost sistema: visoko natančnost krmiljenja hitrosti, hiter odziv in prihranek energije. Sistem je zato primeren za praktično uporabo. Ključne besede: variabilna hitrost, krmiljenje hitrosti, regulacija energije, varčevanje z energijo, odziv, MIMO

SI 82

*Naslov avtorja za dopisovanje: Univerza Hangzhou Dianzi, Oddelek za strojništvo, Kitajska, xumzju@163.com

Prejeto v recenzijo: 2012-11-15 Prejeto popravljeno: 2013-04-04 Odobreno za objavo: 2013-04-09

Eksperimentalna raziskava triboloških lastnosti motornih olj in olj za zobniške prenosnike Perić, S. – Nedić, B. – Trifković, D. – Vuruna, M. Sreten Perić1,* – Bogdan Nedić2 – Dragan Trifković1 – Mladen Vuruna1 1

Univerza za obrambo, Vojaška akademija, Srbija v Kragujevcu, Tehniška fakulteta, Srbija

2 Univerza

Sodobni trendi na področju diagnostične obravnave motorjev vozil so v zadnjih letih vse bolj usmerjeni v nadzor mazalnih olj, to pa je pritegnilo pozornost tako proizvajalcev olj kakor tudi uporabnikov. Razlogi so predvsem v pomenu funkcij, ki jih olja opravljajo v vozilih, kakor tudi v povečanju zanesljivosti, učinkovitosti, gospodarnosti in zaščite okolja. Članek obravnava tribološke preskuse kot del analize za vrednotenje stanja olja. Cilj predstavljenega dela je preučitev nekaterih triboloških sprememb pri oljih, ki se uporabljajo v različnih cestnih vozilih. V ta namen so bili v rednih intervalih odvzeti vzorci olja iz motorjev in menjalnikov vozil Mercedes O345, PUCH 300GD in PINZGAUER 710M, ki jih redno uporablja srbska vojska. Vzorci olja so bili poslani v Laboratorij za tribologijo na Tehniški fakulteti v Kragujevcu, kjer je bila nedavno razvita in izdelana nova merilna oprema za določanje triboloških lastnosti elementov tribomehanskih sistemov. Glavna dela te opreme sta Tribometer TPD-93 in računalniška merilna naprava Talysurf 6 za določanje topografije površine in parametrov obrabe. Rezultati, dobljeni v eksperimentih, vključujejo podatke o koeficientu trenja, torni sili, širini in globini obrabne sledi, obliki obrabe kontaktne površine bloka, spremembi koeficienta trenja in temperature v času stika, ter parametre površine bloka in diska pred in po preskušanju. Spremembe koeficienta trenja in širine obrabne sledi za vzorce motornega olja in olja za prenosnike so prikazane kot funkcija števila prevoženih kilometrov. Te spremembe so neposredno odvisne od stanja celotnega motorja in elementov transmisije oz. od obratovalnih značilnosti. Koeficient trenja med blokom in diskom je bil pri preskušenih motornih oljih iz vseh vozil v območju od 0,0684 do 0,101. Srednja vrednost koeficienta trenja med blokom in diskom pri preskušenih oljih iz menjalnikov je bila v območju od 0,058 do 0,0987. Ob povečanju števila prevoženih kilometrov se je povečala tudi širina obrabne sledi na disku za motorna olja in olja iz menjalnikov vseh treh vozil. Največja širina obrabne sledi na disku je 0,833 mm za olje iz menjalnika in 0,645 mm za motorno olje (PUCH 300GD). Preskusi so bili opravljeni s tribometrom vrste »blok na disku« z linearnim stikom, ki je značilen za elemente v mehanskih sistemih prenosa moči kot so menjalniki, zobniške sklopke, valjčni ležaji itd. Linearni kontakt se zaradi obrabe sčasoma spremeni v površinski kontakt, značilen za cilindrične mehanske elemente, kot so pari batov in valjev v motorjih z notranjim zgorevanjem. Postopek analize olja, predstavljen v članku, lahko pomaga pri zgodnjem zaznavanju odpovedi mehanskih sistemov prenosa moči in motorjev vozil zaradi procesov trenja in obrabe med obratovanjem. Prihodnje raziskave bodo usmerjene v razvoj novega univerzalnega diagnostičnega modela, ki bo omogočal določitev stanja elementov tribomehanskih sistemov. Ključne besede: nadzor stanja olja, maziva, motorna olja, dinamično modeliranje

*Naslov avtorja za dopisovanje: Univerza za obrambo, Vojaška akademija, Pavla Jurišića Šturma 33, Beograd, Srbija, sretenperic@yahoo.com

SI 83

Prejeto v recenzijo: 2012-09-23 Prejeto popravljeno: 2013-02-07 Odobreno za objavo: 2013-05-06

Modifikacija prevodnega materiala AA6101 kablov OPGW za zaščito pred udari strele Sedat Karabay* Univerza Kocaeli, Tehniška fakulteta, Oddelek za strojništvo, Turčija

V članku so opisane faze preizkušanja in izboljševanja samonosilnih optičnih kablov (OPGW) z namenom izpolnjevanja zahtev glede lastnosti v primeru kratkega stika in udara strele. Kompozitna konstrukcija kablov, ki se uporabljajo v turškem prenosnem elektroenergetskem sistemu, vključuje 6 pocinkanih jeklenih žic, 1 cevko iz nerjavnega jekla z več optičnimi vlakni ter 12 žic iz aluminijeve zlitine AA6101. Testni vzorci prototipa kabla OPGW so sicer uspešno prestali kratkostični preizkus, ne dosegajo pa zahtevanih lastnosti v primeru udara strele. Material je bil zato modificiran z dodatkom predzlitine 3% AlB2 v obliki 9,5-milimetrske palice v talino v vmesnem koritu med pečjo in vertikalno enoto za litje palic za ekstruzijsko stiskalnico. Vzrok za slabšo električno prevodnost zlitine AA6101 je prisotnost težkih kovin kot so Ti, Cr in V, ki se po modifikaciji z AlB2 izločijo kot netopni boridi. Zasnova kabla OPGW za turški elektroenergetski prenosni sistem, ki bo imel nizke proizvodne stroške in bo izpolnjeval vse zahteve tipskega preskusa ter opravil kratkostični preskus in preskus zaščite proti udaru strele. Z ozirom na značilnosti terena v državi je bil zasnovan in izdelan vsestranski kabel OPGW s prostoležečimi optičnimi vlakni v cevki po zahtevah nacionalnega operaterja električnega omrežja. Pri zasnovi je najpomembnejši električno prevodni del iz aluminijeve zlitine AA6101. Številni fizikalni parametri optičnih vlaken v cevki iz nerjavnega jekla so opredeljeni v priporočilu ITU-T G.655. Mehanske lastnosti pocinkanih jeklenih žic v konstrukciji so določene v IEC888 in ASTM B498. Pocinkane jeklene žice se izdelujejo v treh kvalitetah: kot navadne, visoko trdne in ekstra trdne. Za konstrukcijo so bile izbrane visokotrdne jeklene žice. Cinkova prevleka je skladna z razredom 1 po IEC888. Optična cevka v prototipnem kablu OPGW je bila izdelana iz nerjavnega jekla za cevi 304. Najzahtevnejši vidik zasnove je izbira kombinacije materialov, ki vključuje ekstra trdno pocinkano jeklo, cevko za prosta optična vlakna in žice iz zlitine AA6101. Po izdelavi prototipa so bili pripravljeni vzorci podvrženi več laboratorijskim preskusom s simulacijo okoljskih pogojev. Med različnimi preskusi sta še posebej pomembna dva: kratkostični in preskus na strelo. Vodniki se lahko pod vplivom teh zunanjih dejavnikov poškodujejo že v nekaj sekundah. Kabel OPGW je bil zasnovan in izdelan skladno z nacionalnimi in mednarodnimi standardi ter specifikacijami, temu pa je sledilo več preskusov. V eksperimentih je električni oblok uničil 9-10 aluminijastih žic. Turški operater elektroenergetskega omrežja TEIAS zahteva, da se celotna upornost vodnika po obremenitvi s strelo poveča za največ 20%. Število pretrganih žic v kablu OPGW je tako omejeno na 3. Sledila je odločitev o izboljšavi materiala, saj uporaba alternativnih materialov zaradi večjih stroškov izdelka ni prišla v poštev. Material AA6101 je bil izboljšan v vertikalni liniji za litje palic. Vhodni surovec AA6101 je bil izdelan z ekstruzijsko stiskalnico. V talino za 6-metrske palice so bili dodani 3 kg AlB2 na tono aluminijeve taline za povečanje električne prevodnosti. AlB2 v obliki 9,5-milimetrskih palic je bil dodan v vmesno korito za raztaljeni aluminij. Po vlečenju surovca na zahtevani premer žice je bila uporabljena toplotna obdelava T8 pri temperaturi 175 °C in v trajanju 6 h. Rezultati kažejo, da se je nemodificirana prevodnost žice AA6101 52,5% IACS izboljšala na 57% IACS. Nato je bil izdelan nov kabel OPGW z modificirano žico in preskušen na udar strele. Kabel OPGW je tokrat izpolnil vse zahteve. Glavni razlog za zmanjšanje poškodb žice je v visoki električni prevodnosti modificirane žice v primerjavi z nemodificirano aluminijevo zlitino AA6101. Nekaj škode so seveda utrpele posamezne žice na zunanji strani vodnika, število pretrganih žic v drugem preskusu s strelo pa je bilo zelo majhno – 1 ali 2. Visoka električna prevodnost zmanjšuje izgube energije v prenosnih vodih. Kabli morajo imeti zaradi varčevanja z električno energijo maksimalno električno prevodnost. Ceneni aluminij ima veliko nečistoč v obliki težkih kovin in talino je zato treba v fazi litja modificirati z AlB2 za zmanjšanje upornosti surovca in vlečenih žic, iz katerih je izdelan kabel. Ceneni aluminij je torej uporaben pod pogojem, da se modificira z AlB2 v fazi kontinuirnega litja oz. litja palic. Spojina AlB2 je primerna za povečanje električne prevodnosti aluminija z 99,6-odstotno čistočo. Študija je tudi dokazala, da je AlB2 primeren za povečanje električne prevodnosti zlitin Al-Mg-Si. Kabli OPGW se uporabljajo za prenos podatkov in komunikacijo in države v razvoju lahko predstavljene rezultate uporabijo pri svojih naložbah, ki vključujejo kable OPGW. Predstavljena je cenena metoda za proizvodnjo kablov OPGW za elektroenergetske prenosne vode. Ključne besede: samonosni optični kabel OPGW, udar strele, modifikacija z AlB2, električna prevodnost, surovec iz AA6101, pretrganje žice, kratek stik, izločevalno utrjanje SI 84

*Naslov avtorja za dopisovanje: Univerza Kocaeli, Tehniška fakulteta, Oddelek za strojništvo, Umuttepe Campus, Kocaeli, Turčija, sedatkarabay58@gmail.com

Prejeto v recenzijo: 2012-12-07 Prejeto popravljeno: 2013-05-07 Odobreno za objavo: 2013-05-29

Tokovne razmere ob zamaknjenih ceveh z več zarezami v prehodu prenosnika toplote z orebrenimi cevmi Yayla, S. Sedat Yayla*

Univerza Yuzuncu Yil, Oddelek za strojništvo, Turčija

Za poravnane in zamaknjene valje v modelu prenosnika toplote z orebrenimi cevmi so bile eksperimentalno raziskane tokovne razmere za Reynoldsova števila od 1500 do 4000 pri razmerju med višino kanala in premerom valja 0,4. Reynoldsovo število je bilo izračunano na osnovi premera valja. Trenutna slika nestacionarnega toka za omenjeno tokovno polje je bila zajeta po postopku meritve hitrosti z odslikavo delcev (PIV). Časovno povprečeni podatki o toku jasno kažejo, da ima pretok skozi polvalje pomemben vpliv na značilnosti turbulentnega toka. Spremembe časovno povprečenega toka ob tokovnicah so prikazane tudi v grafični obliki. Interakcije toka vzdolž tokovnic in prečno na tokovnice pri zamaknjenih cilindrih s površino ravne plošče dajejo kompleksen trodimenzionalen tok. Glavni namen študije je uporaba metode PIV za preučitev strukture toka za krožnimi valji z več režami, nameščenimi na ravni površini, v globokem vodnem kanalu. Eksperimentalna oprema je bila postavljena na brezvodni strani kanala. Preskusni del vodnega kanala je bil dolg 8000 mm, širok 1000 mm, visok 750 mm ter izdelan iz 15 mm debelega prozornega pleksi stekla. PIV-sistem Dantec Dynamics je bil sestavljen iz računalnika, sinhronizatorja, digitalizatorja slike z največjo hitrostjo zajema 30 Hz, CCD-kamere ločljivosti 1600×1186 slikovnih točk in impulznega laserskega vira Nd:YAG valovne dolžine 532 mm. CCD-kamera je bila za meritve hitrosti postavljena v ravnino pod vodni kanal. Kamera izpolnjuje Scheimpflugov pogoj in zato ostri nad središčem merilne ravnine z natančnim naklonom glede na os objektiva. Na dveh kamerah je bil uporabljen 60-milimetrski objektiv. Za prenos slike iz kamere v računalnik je skrbel visokohitrostni digitalizator slike. Sinhronizator je skrbel za pravilen vrstni red in časovno usklajevanje laserskih impulzov s kamero. Gibanje tekočine je bilo opazovano z dodatkom posrebrenih sferičnih lebdečih delcev premera 12 μm v vodo. Merilna ravnina je bila osvetljevana z laserskimi impulzi maksimalne moči 120 mJ. Interval med impulzi je bil pri vseh meritvah 1,5 ms. Debelina osvetljene merilne ravnine je bila približno 1,5 mm. Valji z režami so bili nameščeni v ogliščih enakostraničnega trikotnika. Razdalja med površinami valjev je bila zaradi gostote tipa prenosnika toplote 1 d. Lasersko osvetljena ravnina je bila vzporedna s spodnjo površino vodnega kanala, in sicer na višini z/h = 0,5. Prikazana je struktura toka ob valjih z režami v prenosniku toplote z orebrenimi cevmi. V bližini valjev z režami se na obeh površinah plošče pojavljajo podkvasti vrtinci. Ti vrtinci krepijo proces zajemanja ter krožno gibanje med jedrom in območji vrtinčnega toka za valjem z režami na ravni površini plošče v globoki vodi. Odsotnost pristranskega toka je bila dosežena s curkovnim tokom. Območja vrtinčnega toka valjev z zarezami se širijo v smeri tokovnic zaradi prenosa momenta na režah valjev. Zamaknjeni valji z zarezami hidrodinamično izboljšujejo prenos toplote tudi v območjih vrtinčnega toka. Ključne besede: PIV, cevni prenosnik toplote, turbulentni tok, zamaknjeni valji z režami, pasivno krmiljenje, nadzor vrtincev

*Naslov avtorja za dopisovanje: Univerza Yuzuncu Yil, Oddelek za strojništvo, 65080 Van, Turčija, syayla@yyu.edu.tr

SI 85

Prejeto v recenzijo: 2012-11-13 Prejeto popravljeno: 2012-11-13 Odobreno za objavo: 2013-05-13

Optimalna zasnova potopnih elektromagnetnih aktuatorjev na osnovi dinamičnih karakteristik ter eksperimentalna implementacija

Cai, B. – Liu, Y. – Abulimiti, A. – Ji, R. – Zhang, Y. – Dong, X. – Zhou, Y. Baoping Cai1 – Yonghong Liu1,* – Aibaibu Abulimiti1 – Renjie Ji1 – Yanzhen Zhang1 – Xin Dong1 – Yuming Zhou2 1 Kitajska

2 Kitajska

univerza za nafto, Kolidž za strojništvo in elektrotehniko, Kitajska nacionalna naftna družba, Urad za geofizikalne raziskave, Kitajska

Razvit je bil postopek optimizacije potopnega elektromagnetnega aktuatorja (SEMA) omejenih dimenzij na osnovi dinamičnih karakteristik. SEMA je zasnovan kot preklopni vzmeteni aktuator z elektromagnetom, sestavljen pa je iz pokrova, vzmeti, žepa za vzmet, tuljave, jedra tuljave, bata, batne puše in magnetnega obroča. Za najkrajši odzivni čas in čim manj vibracij pri odprtem aktuatorju je treba optimizirati pet radialnih dimenzij: debelino bata (wpl), debelino zgornje batne puše (wps), debelino tuljave (wco), debelino magnetnega obroča (wmr) ter režo med batom in batno pušo (wgp). Glavni omejitveni dejavnik je najvišja dovoljena temperatura. Zasnovani so bili trije modeli: toplotni, elektromagnetni in mehanski, optimizacijski preračun pa je bil izveden s programsko opremo Matlab/Simulink. Za skrajšanje odzivnega časa aktuatorja z značilno majhno prostornino je treba preučiti prenos toplote. Za ohranitev temperature aktuatorja pod varnostno mejo je bila razvita vrsta modelov. Elektromagnetni model SEMA vsebuje električni tokokrog in magnetni tokokrog. Za namen določitve optimalne zasnove je bil prevzet enostavnejši model drugega reda z eno prostostno stopnjo. Mehanski model vključuje maso, vzmet in dušilko pod vplivom magnetnih in tlačnih sil, ki so popisane z drugim Newtonovim zakonom. Model v Simulinku je sestavljen iz treh glavnih delov: toplotnega podsistema, elektromagnetnega subsistema in mehanskega podsistema. Optimalni parametri modela SEMA so wps = 1,8×10-3 m, wgp = 0,2×10-3 m, wpl = 6,0×10-3 m, wco = 6,0×10-3 m in wmr = 3,0×10-3 m. Nato je bil izdelan aktuator z izračunanimi optimalnimi parametri in opravljeni so bili dinamični eksperimenti. Napajanje z enosmerno napetostjo 16 V je zagotavljal stikalni napajalnik. Tok v tuljavi je meril tokovni pretvornik. Ker bi bil premik bata le težko merljiv s hidravličnim tlakom, je bil hidravlični tlak nadomeščen z dolgo vzmetjo pod batom, ki ustvarja praktično konstantno silo. Premik je bil merjen s tipalom na vrtinčne tokove, pritrjenim na podaljšek bata. Signala toka in premika je sočasno zajemal oscilograf, obdeloval pa ju je računalnik. Rezultati kažejo dobro ujemanje med odzivnim časom, določenim z eksperimentom in s simulacijo. Za določitev točnega signala pospeška vibracij v trenutku, ko bat doseže končni položaj, je bila izvedena tudi analiza vertikalnih in horizontalnih vibracij aktuatorja SEMA. Signala pospeška vertikalnih in horizontalnih vibracij je sočasno zajemal drug oscilograf, obdeloval pa ju je računalnik. Rezultati kažejo, da se izmerjeni vertikalni in horizontalni pospešek ujemata z izračunanim pospeškom bata. Eksperimenti so pokazali, da je bil postopek optimizacije dovolj natančen in da je optimalni potopni elektromagnetni aktuator varen za uporabo v podmorskih napravah vrste blowout preventer. Ključne besede: potopni elektromagnetni aktuator, optimalna zasnova, magnetni ekvivalentni tokokrog, dinamične karakteristike

SI 86

*Naslov avtorja za dopisovanje: Kitajska univerza za nafto, Kolidž za strojništvo in elektrotehniko, Qingdao 266580, Kitajska, liuyhupc@163.com

Prejeto v recenzijo: 2012-10-05 Prejeto popravljeno: 2013-01-14 Odobreno za objavo: 2013-01-18

Prispevek k pragmatičnemu pristopu do uvajanja sočasnega inženirstva Nenad Popović1 – Goran D. Putnik2,* – Ondrej Jasko3 – Jovan Filipović3 1 ABS Electro, Rusija v Minhu, Oddelek za proizvodno inženirstvo in sisteme, Portugalska 3 Univerza v Beogradu, Fakulteta za organizacijske vede, Srbija

2 Univerza

Članek obravnava vpliv pragmatičnega pristopa pri projektih uvajanja sočasnega inženirstva (SI). Pragmatika kot področje semiotike je bila uporabljena za izhodišče analize in snovanja proizvodnih sistemov, natančneje pri projektih uvajanja SI. Kot del strategije uvajanja SI, ki vključuje tudi vrednotenje pripravljenosti SI, so preučeni modeliranje ter vplivi različnih interpretacij pri vrednotenju sočasnosti procesov kot orodja pragmatike. Članek sledi teoretičnemu okvirju integracije proizvodnih sistemov na osnovi semiotike ter predstavlja njegovo praktično uporabo, validacijo in implikacije v industrijskem okolju. Procesi vrednotenja (v okviru vrednotenja pripravljenosti SI) so odvisni od interpretacije, zato lahko uporaba tradicionalnih normativnih metodologij pripelje do neuspeha projektov ali pa vsaj do resnih težav. Uporaba pragmatičnega pristopa lahko tudi bistveno izboljša priložnosti za uspešno implementacijo SI. Kot pristop k strategiji uvajanja SI je uporabljena metodologija na osnovi matrik sočasnosti s primerjavo dveh različnih interpretacij. Predlagana metodologija je preverjena v realnem okolju, t.j. v dveh malih oz. srednje velikih proizvodnih podjetjih, ki načrtujeta uvedbo SI. Rezultati potrjujejo napoved, da lahko različne interpretacije pripeljejo do različnih odločitev vodstva ter tako onemogočijo izbiro najboljše možne odločitve. Da bi torej vedno lahko sprejeli najboljše rešitve v danem primeru, mora izboljšana metodologija za strategijo uvajanja SI (vključno z vrednotenjem pripravljenosti SI (CERA)) vključevati več interpretacij oz. pristop na osnovi pragmatike. Glavni cilj tega članka je preučitev vpliva pragmatičnega pristopa na projekte uvajanja SI ter še zlasti na vrednotenje sočasnosti procesov kot eno od glavnih značilnosti strategije uvajanja SI in vrednotenja pripravljenosti SI. Sekundarni cilj članka je prispevek k razvoju in izboljšanju metodologije uvajanja SI na osnovi pragmatike, ki bo olajšal uvajanje SI v različnih podjetjih. Potrjena je teza o vplivu pragmatičnega pristopa na projekte uvajanja SI, še posebej na vrednotenje sočasnosti procesov, kakor tudi na identifikacijo potrebnih področij ukrepanja za uvajanje SI. Za prvo študijo primera je bilo izbrano orodjarsko podjetje, za drugo pa proizvajalec opreme za energetiko. Obe družbi spadata v skupino malih in srednjih podjetij ter imata dobro razvito konstrukcijo in proizvodnjo. Pri prvi študiji primera so bili uporabljeni sekundarni podatki, pri drugi študiji primera pa primarni podatki. Eden najpomembnejših zaključkov raziskave je, da lahko pragmatični pristop bistveno izboljša verjetnost uspešne uvedbe SI, zato je treba tradicionalne metodologije nadgraditi s pragmatiko kot novim orodjem. Omejitve raziskave bodo odpravljene v prihodnjih raziskavah: 1) Preučene bodo dodatne vrste interpretacij in njihova uporaba; 2) Izboljšana bo metodologija in razvita bodo računalniška orodja za njeno uporabo; 3) Zagotovljeno bo boljše dojemanje posledic obstoječih ukrepov, ukrepi bodo bolje opredeljeni, razviti pa bodo tudi novi in boljši ukrepi; 4) Pragmatični pristop bo uporabljen tudi pri drugih metodologijah, zlasti pri tistih na osnovi RACE. Prispevek raziskave je predvsem v potrjevanju koncepta uporabe pragmatike pri sočasnem inženirstvu v realnem okolju, in sicer v funkciji orodja za boljše odločanje. Eksperimenti so tudi potrdili enostavno uporabo koncepta v podjetjih. Raziskava je po znanstveni plati empirično potrdila, da je pragmatika instrument nove paradigme odločanja v tehniki, ki je uporaben pri so-snovanju, so-ustvarjanju in so-razvoju. Ključne besede: pragmatika, sočasno inženirstvo, vrednotenje sočasnosti, uvajanje sočasnega inženirstva, matrika sočasnosti (SCM), vrednotenje pripravljenosti sočasnega inženirstva, odločanje

*Naslov avtorja za dopisovanje: Univerza v Minhu, Oddelek za proizvodno inženirstvo in sisteme, Campus of Azurem, 4800-058 Guimaraes, Portugalska, putnikgd@dps.uminho.pt

SI 87

Strojniški vestnik - Journal of Mechanical Engineering 59(2013)7-8, SI 88-93 Osebne objave

Doktorske disertacije, znanstvena magistrska dela, specialistična dela, diplomske naloge

DOKTORSKE DISERTACIJE Na Fakulteti za strojništvo Univerze v Ljubljani so obranili svojo doktorsko disertacijo: ● dne 17. junija 2013 Jani KENDA z naslovom: »Karakterizacija in napovedovanje učinka poliranja orodnega jekla z dvosmernim abrazivnim tokom« (mentor: prof.dr. Janez Kopač, somentor: doc.dr. Franci Pušavec); Doktorsko delo obravnava proces poliranja z dvosmernim abrazivnim tokom (PDAT). Na področju poliranja največji delež zavzema ročno poliranje, katerega je zaradi različnih zahtev, kot so: krajši čas obdelave, nadzor procesa in možnost napovedovanja učinka, želja zamenjati s strojnimi obdelavami. Alternativo predstavlja PDAT. Časi in posredno učinkovitost obdelave so lahko v primerjavi z ročnim poliranjem tudi do več desetkrat krajši. Doktorsko delo tako zajema karakterizacijo temeljnih parametrov, napovedovanje učinka procesa na podlagi analize z metodo končnih elementov in postavljenega modela. Kot doprinos je bila razvita tudi inovacija preko novega izboljšanega principa PDAT (t.i. poliranje z abrazivnim tokom na principu gibljivega trna); ● dne 19. junija 2013 Simon KULOVEC z naslovom: »Optimiranje prostih površin strešnih konstrukcij s hibridnimi mrežami« (mentor: prof.dr. Jožef Duhovnik); V arhitekturi zaznavamo trend izdelovanja konstrukcij prostih oblik, ki arhitektov ne omejujejo več na izbiro regularnih oblik konstrukcij. Pri prostih oblikah konstrukcij pa so možne težave pri geometrijskem obvladovanju, saj mora posamezna struktura ustrezati različnim omejitvam, ki nam omogočijo fizično izvedbo konstrukcije. Proste oblike konstrukcij lahko predstavimo z različnimi tipi mrež in planarnih mrežnih elementov. Obstoječe mreže prostih oblik so sestavljene iz trikotnih elementov, saj je tako zagotovljena planarnost posameznega mrežnega elementa. V pričujoči doktorski disertaciji se želimo osredotočiti na štirikotne mreže, predvsem zaradi stroškovne ugodnosti in lažje izdelave posameznega vozliščnega elementa. Vendar pa so štirikotne mreže zahtevnejše z vidika geometrijskega obvladovanja. Prvi cilj doktorske naloge je raziskava in zagotavljanje pogoja planarnosti in koničnosti mrežnih elementov z uporabo sekvenčne kvadratične optimizacije (angl. Sequential Quadratic Optimization). Konstrukcije prostih oblik so sestavljene iz tankih pokrivnih panelov in nosilne konstrukcije. Ker so za konstrukcije prostih oblik značilne poljubne oblike, se pojavi težava pri SI 88

naleganju nosilcev v vozliščnem elementu, kar se kaže v različnih višinskih oddaljenostih posameznega nosilca od vozlišča. Zato je drugi cilj naloge raziskati in razviti algoritem, ki bi globalno zmanjšal višinske oddaljenosti posameznih nosilcev v vozliščnih elementih; ● dne 21. junija 2013 Jurij SODJA z naslovom: »Aeroelastična optimizacija propelerskih krakov« (mentor: izr.prof.dr. Tadej Kosel); Aerodinamske lastnosti propelerskih lopatic se določijo po segmentno-momentnem modelu propelerske akcije. Upogibne in torzijske lastnosti lopatic se modelira s pomočjo Euler-Bernoullijeve teorije upogiba tankih nosilcev ter Saint-Venanteve teorije torzije. Na osnovi predlaganega matematičnega modela se je izvedla aeroelastična optimizacija in analiza geometrije lopatic. Validacija matematičnega modela je podana preko primerjave modelnih ter eksperimentalnih rezultatov. * Na Fakulteti za strojništvo Univerze v Mariboru so obranili svojo doktorsko disertacijo: ● dne 24. junija 2013 Teodor ŠTIMEC z naslovom: »Numerični model adsorpcijskega procesa pri toku v kanalu« (mentor: prof. dr. Matjaž Hriberšek); V doktorski disertaciji je predstavljen numerični model za simulacijo adsorpcijskega procesa v kanalu, ki ima na svojih stenah nameščeno plast adsorbenta. V kanalu teče tok nosilne tekočine z zelo nizko koncentracijo adsorbata, ki se zaradi medmolekularnih sil adsorbira v plast adsorbenta. Zaradi nizke koncentracije adsorbata v nosilnem mediju le ta ne vpliva na tokovne razmere v kanalu, ampak je vključen le v adsorpcijski proces. Simulacija toka tekočine v kanalu je izvedena z reševanjem sistema Navier-Stokesovih ohranitvenih enačb, ki so diskretizirane z metodo robnih elementov. Adsorpcijski prenos snovi adsorbata iz glavnine tekočine v plast adsorbenta je modeliran s prilaganjem vrednosti robne koncentracije. Koncentracija adsorbata se ob medfazni površini v tekočini in nad plastjo adsorbenta namreč zaradi adsorpcijskih procesov znižuje, kar povzroči nastanek koncentracijskega gradienta v smeti proti plasti adsorbenta in z njim povezan snovni tok. Vrednost robne koncentracije je odvisna od porazdelitvenega koeficienta, oziroma razmerja med akumulirano ter ravnotežno množino adsorbata v plasti adsorbenta. Ravnotežna množina adsorbata v plasti adsorbenta je določena s primernim ravnotežnim

Strojniški vestnik - Journal of Mechanical Engineering 59(2013)7-8, SI 88-93

modelom, ki podaja omenjene vrednosti na podlagi temperature in koncentracije adsorbata ter snovnih lastnosti dostopnih v literaturi. V numerični shemi so sicer bili uporabljani štirje različni ravnotežni modeli in sicer Freundlichov, Dubinin-Radushkevichev ter SLD ravnotežna modela na osnovi Van der Waalsove ter Peng-Robinsonove enačbe stanja. Z izdelanim numeričnim modelom je bila nato izvedena vrsta simulacij toka revne mešanice zraka ter butana v kanalu, ki je imel na stenah nameščeno plast aktivnega oglja. Na podlagi rezultatov simulacij so bile izvedene: analiza primernosti računske mreže, analiza primernosti časovnega koraka ter primerjava rezultatov z referenčnimi rezultati drugih avtorjev. Primerjava rezultatov kaže, da izdelana numerična rutina omogoča natančno simuliranje adsorpcijskih procesov v kanalu. V zaključku sta bili izvedeni še parametrični analizi vpliva hitrosti ter temperature na adsorpcijski proces v kanal ter podane smernice za nadaljnjo raziskovalno delo; ● dne 26. junija 2013 Blaž VAJDA z naslovom: »Vpliv biogoriv na tokovne pojave v vbrizgalni šobi dizelskega motorja« (mentorica: prof. dr. Breda Kegl); Vbrizgavanje curka goriva spada na področje dvofaznih tokov, ki obravnava karakteristike curka goriva v odvisnosti od fizikalnih lastnosti, s poudarkom na vbrizgavanju različnih goriv, pod različnimi delovnimi pogoji. Poleg ocene kvalitete tvorbe zmesi je raziskovanje karakteristik curka goriva pomembno tudi za oceno izkoriščenosti zraka v zgorevalni komori in zaradi morebitnega nezaželenega stika goriva s stenami zgorevalne komore. Obstoječi fizikalno-matematični modeli lahko v splošnem relativno natančno popišejo razmere dvofaznega toka. V samih podmodelih so prisotne empirične konstante (vplivni parametri), s pomočjo katerih se uravnavajo karakteristike vbrizganega curka in ki so v osnovi odvisne od lastnosti samega vbrizgalnega sistema, predvsem od geometrije vbrizgalne šobe. V okviru naloge bo vpeljan model, ki bo omogočal obravnavanje karakteristik različnih biogoriv, razmer v šobi in posledice vpliva karakteristik na razvoj, obliko in strukturo curka, kjer bo omogočeno natančnejše analiziranje dvofaznih tokov. Model bo zajemal prenosne enačbe za številsko gostoto parnih mehurčkov, z upoštevanjem fizikalnih procesov nastajanja in izginjanja posameznih mehurčkov, pri različnih oblikah kavitacijskih tokov, hkrati pa bo omogočal še raziskavo vpliva med kapljicami goriva ter obravnavo sil trka z vpeljavo velikostne porazdelitve kapljic goriva. Naloga je razdeljena na eksperimentalni in numerični del. V eksperimentalnem delu so določene in analizirane fizikalne lastnosti uporabljenih goriv, karakteristike procesa vbrizgavanja, s pomočjo hitre kamere pa je bil posnet

razvoj curka goriva. V numeričnem delu je prikazan osnovni poenostavljeni fizikalno-matematični model. V disertaciji je pokazano, da je mogoče s spremembo fizikalno-matematičnega modela, ob upoštevanju fizikalnih lastnosti goriva, delovnega režima in karakteristik procesa vbrizgavanja, določiti konstante, ki pri izračunu uravnavajo karakteristike curka goriva. S pomočjo ustreznih izrazov je tako mogoče izraziti empirične vrednosti parametrov in vnaprej napovedati probleme, ki bi se lahko pojavili v dizelskih motorjih z uporabo biogoriv; ● dne 27. junija 2013 Vito TIČ z naslovom: »Inteligentni sistem za oddaljeno spremljanje stanja mineralnih hidravličnih olj« (mentor: doc. dr. Darko Lovrec); Doktorska naloga obravnava široko področje spremljanja stanja hidravličnih tekočin skozi njihov delovni življenjski cikel, pri čemer izpostavlja in podrobneje obravnava problem kvantitativnega ocenjevanja stanja mineralnih hidravličnih olj ter njihove preostale uporabne dobe. Pri uveljavljanju različnih metod in sistemov spremljanja stanja v industrijskem okolju je ključnega pomena njihova praktičnost in uporabnost, zato se doktorska naloga osredotoča na aplikativni razvoj inteligentnega sistema oz. modela za oceno stanja olja in njegove preostale življenjske oz. uporabne dobe, ki zmore samostojno, brez pomoči izkušenega strokovnjaka, preučiti fizikalno-kemične lastnosti hidravlične tekočine in podati informacijo o stopnji njene ustreznosti. Za oceno stanja olja, in njegove preostale uporabne dobe, je v disertaciji predlagan hibridni matematični model, zasnovan na osnovi predhodno pridobljenih podatkov pospešenega staranja olja. Ustreznost izdelanega hibridnega modela je najprej potrjena na bazi podatkov pospešenega staranja hidravlične tekočine, na podlagi katere je bil model tudi izdelan. V nadaljevanju prikazana implementacija modela na realnem industrijskem sistem pa prikazuje praktično uporabnost razvitega sistema, saj je izdelan model sposoben uspešno in dovolj natančno oceniti stanje in preostalo uporabno dobo olja že po prvi tretjini njegove življenjske dobe; ZNANSTVENA MAGISTRSKA DELA Na Fakulteti za strojništvo Univerze v Mariboru je z uspehom zagovarjal svoje magistrsko delo: ● dne 17. junija 2013 Andrejka ZVER z naslovom: »Topologija delovnih prostorov industrijskih robotov« (mentor: izr. prof. dr. Karl Gotlih). SI 89

Strojniški vestnik - Journal of Mechanical Engineering 59(2013)7-8, SI 88-93

SPECIALISTIČNA DELA Na Fakulteti za strojništvo Univerze v Mariboru je z uspehom zagovarjal svoje specialistično delo: ● dne 17. junija 2013 Ervin KOŠTOMAJ z naslovom: »Dimenzioniranje nosilcev motorja letališkega avtobusa MB 1431 LF« (mentor: prof. dr. Srečko Glodež). DIPLOMSKE NALOGE Na Fakulteti za strojništvo Univerze v Ljubljani so pridobili naziv univerzitetni diplomirani inženir strojništva: dne 18. junija 2013: Andrej DOLENEC z naslovom: »Model izračuna rabe električne energije za mehansko prezračevanje za različne tesnosti stavb« (mentor: prof. dr. Vincenc Butala); Miha JERŠIN z naslovom: »Razvoj merilnika 3D oblike teles za pozicioniranje lopatic Francisove turbine« (mentor: prof. dr. Alojz Sluga, somentor: doc. dr. Drago Bračun); Gašper LAVRIČ z naslovom: »Numerična in eksperimentalna analiza protitočne naprave za posredno hlapilno hlajenje zraka« (mentor: prof. dr. Vincenc Butala, somentor: doc. dr. Matjaž Prek); Gašper SLADIČ z naslovom: »Baza znanja za čistilne tehnologije v industrijski obnovi proizvodov« (mentor: prof. dr. Peter Butala); Blaž ŽIBERT z naslovom: »Razvoj sistema za spremljanje ekološkega pretoka vode« (mentor: prof. dr. Alojz Sluga); dne 19. junija 2013: Blaž BORŠNAK z naslovom: »Zasnova eksperimentalne naprave za statično in dinamično obremenjevanje železniških tirov« (mentor: prof. dr. Igor Emri); dne 21. junija 2013: Jan ČOTAR z naslovom: »Tehnično-ekonomska primerjava zvezno in stopenjsko delujoče toplotne črpalke zrak/voda« (mentor: prof. dr. Alojz Poredoš); Gašper HREN z naslovom: »Ekonomska analiza proizvodnje električne energije iz lesne biomase« (mentor: izr. prof. dr. Mihael Sekavčnik); Marko JAGER z naslovom: »Kavitacijski generator za čiščenje komunalne odpadne vode« (mentor: prof. dr. Branko Širok); Borut PELJHAN z naslovom: »Vpliv pulzne širinske modulacije na hrup in vibracije izmeničnih elektromotorjev« (mentor: prof. dr. Miha Boltežar); Jorge RODRIGUEZ LARRAD z naslovom: »Termoekonomska analiza sistema sočasne proizvodnje toplote in električne energije z motorjem z SI 90

notranjim zgorevanjem / Thermo-Economic Analysis of Internal Combustion Engine based Combined Heat and Power Generation« (mentor: izr. prof. dr. Mihael Sekavčnik); Adrian FERNANDEZ GARCIA z naslovom: »Termoekonomska analiza sistema sočasne proizvodnje toplote in električne energije s plinskim postrojem / Thermo-Economic Analysis of Gas Turbine based Combined Heat and Power Generation« (mentor: izr. prof. dr. Mihael Sekavčnik); dne 26. junija 2013: Miha KLOPČIČ z naslovom: »Varjenje bakra z nerjavnim jeklom« (mentor: prof. dr. Janez Tušek); Tomaž POLAJNAR z naslovom: »Analiza vpliva parametrov brizganja termoplasta na izdelovalne tolerance izdelka« (mentor: doc. dr. Tomaž Pepelnjak); Darko SLEMENIK z naslovom: »Predhodno vrtanje posebnih materialov na stroju za rezanje z abrazivnim vodnim curkom« (mentor: doc. dr. Joško Valentinčič, somentor: doc. dr. Henri Orbanić); Janez ŠOTL z naslovom: »Rotacijska obdelava z abrazivnim vodnim curkom« (mentor: doc. dr. Joško Valentinčič, somentor: doc. dr. Henri Orbanić); Leon TOMŠIČ z naslovom: »Hidravlična stiskalnica za ravnanje pločevine« (mentor: prof. dr. Jožef Duhovnik); dne 27. junija 2013: Rok CEGLAR z naslovom: »Zasnova, izdelava in določitev zmogljivosti prototipnega električnega vozila« (mentor: izr. prof. dr. Tomaž Katrašnik); Martin DEBEVC z naslovom: »Simulacija naravne konvekcije v zadrževalnem hramu jedrskega reaktorja« (mentor: izr. prof. dr. Mihael Sekavčnik, somentor: doc. dr. Ivo Kljenak); David GORKIČ z naslovom: »Numerična simulacija toplotnih obremenitev krmilnika za elektromotorje« (mentor: izr. prof. dr. Mihael Sekavčnik); Matej KERIN z naslovom: »Eksperimentalno določanje prenosnih funkcij elektrolizerja v napredni energijski oskrbi« (mentor: izr. prof. dr. Mihael Sekavčnik); Mitja TREFALT z naslovom: »Razvoj modela gorivne celice za sistemske simulacije vozil« (mentor: izr. prof. dr. Tomaž Katrašnik); Alen ZAVOLOVŠEK z naslovom: »Prototipna izdelava ohišja za RASPBERRY PI« (mentor: prof. dr. Janez Kopač); dne 28. junija 2013: Jernej HOČEVAR z naslovom: »Razvoj odsesovalne komore za natančno tehtanje farmacevtskih sestavin« (mentor: izr. prof. dr. Jernej Klemenc, somentor: prof. dr. Branko Širok);

Strojniški vestnik - Journal of Mechanical Engineering 59(2013)7-8, SI 88-93

Ivan MATIJEVIĆ z naslovom: »Numerične simulacije pomešanja vode v mešalni posodi z različnimi mešali« (mentor: doc. dr. Andrej Bombač); Aljoša OREŠEK z naslovom: »Razvoj drobilnika žetvenih ostankov« (mentor: izr. prof. dr. Jernej Klemenc, somentor: prof. dr. Jožef Duhovnik); Jernej PIRNAR z naslovom: »Računalniška FSI simulacija toka zraka z zgornji dihalni poti človeka« (mentor: prof. dr. Iztok Žun). * Na Fakulteti za strojništvo Univerze v Mariboru so pridobili naziv univerzitetni diplomirani inženir strojništva: dne 13. junija 2013: Robert GAČNIKAR z naslovom: »Izdelava orodja za brizganje umetnih mas za nosilec konzole absorberja« (mentor: izr. prof. dr. Borut Buchmeister, somentor: doc. dr. Leo Gusel); dne 27. junija 2013: Tjaša BOSIO z naslovom: »Čiščenje plinov pri uplinjanju trdnih goriv v krožeči lebdeči plasti« (mentor: prof. dr. Niko Samec); Tilen MAR z naslovom: »Ogrevanje stanovanjske hiše z lesno biomaso kot virom iz lastnega gozda« (mentor: izr. prof. dr. Jure Marn). * Na Fakulteti za strojništvo Univerze v Mariboru je pridobil naziv univerzitetni diplomirani gospodarski inženir: dne 13. junija 2013: Tomaž VALAND z naslovom: »Uporaba standarda SIST EN ISO 13485:2012 pri izdelavi individualnih medicinskih vsadkov« (mentor: izr. prof. dr. Igor Drstvenšek, somentor: doc. dr. Andreja Lutar Skerbinjek). * Na Fakulteti za strojništvo Univerze v Ljubljani sta pridobila naziv magister inženir strojništva: dne 19. junija 2013: Bruno De NYS z naslovom: »Nadgradnja tehničnega informacijskega sistema za upravljanje projektne dokumentacije / Configuration of Product Life Cycle (PLC) management system for project documentation« (mentor: izr. prof. dr. Jože Tavčar, somentor: doc.dr. Leon Kos). Jesús GIL CANO z naslovom: »Metoda merjenja premera vodnega curka / Method of Measuring the Water Jet Diameter« (mentor: prof. dr. Mihael Junkar, somentor: doc. dr. Andrej Lebar);

* Na Fakulteti za strojništvo Univerze v Mariboru sta pridobila naziv magister inženir strojništva: dne 28. junija 2013: David JAVORNIK z naslovom: »Uvedba sistema kanban za proizvodnjo odtočnih ventilov tipa 230 v podjetju Geberit - Sanitarna tehnika, d.o.o.« (mentor: izr. prof. dr. Borut Buchmeister, somentor: doc. dr. Iztok Palčič); Maja MAJERIČ BERLOŽNIK z naslovom: »Uvajanje krmiljenja glede na porabo v oskrbni verigi avtomobilskega dobavitelja« (mentor: izr. prof. dr. Borut Buchmeister); * Na Fakulteti za strojništvo Univerze v Mariboru je pridobil naziv magister gospodarski inženir: dne 26. junija 2013: Rok KARAŽINEC z naslovom: »Zasnova proizvodnje in organizacijska oblika podjetja za izdelavo individualizirane opreme« (mentor: izr. prof. dr. Igor Drstvenšek, somentorja: asist. mag. Tomaž Brajlih, doc. dr. Dušan Jovanovič). * Na Fakulteti za strojništvo Univerze v Mariboru je pridobila naziv magister inženir tehniškega varstva okolja: dne 27. junija 2013: Katja POLANEC z naslovom: »Vpliv sodobnega ravnanja z odpadki na zmanjševanje emisij CO2« (mentor: prof. dr. Niko Samec, somentor: viš. pred. dr. Filip Kokalj). * Na Fakulteti za strojništvo Univerze v Ljubljani so pridobili naziv diplomirani inženir strojništva: dne 4. junija 2013: Beno GOLJA z naslovom: »Karakterizacija napak materiala pri izdelavi ogrevalne čepne svečke« (mentor: izr. prof. dr. Roman Šturm); Marko TRAVNIKAR z naslovom: »Načrtovanje preizkuševališča za umerjanje merilnikov pretoka zraka« (mentor: izr. prof. dr. Ivan Bajsić); dne 6. junija 2013: Janez FLORJANČIČ z naslovom: »Razvoj zložljivega drobilca Triplex 800« (mentor: prof. dr. Marko Nagode); Tadej LIPOVŠEK z naslovom: »Sodobno načrtovanje ogrevalnih sistemov« (mentor: prof. dr. Vincenc Butala); SI 91

Strojniški vestnik - Journal of Mechanical Engineering 59(2013)7-8, SI 88-93

Janez MULEJ z naslovom: »Zasnova in vrednotenje gonila vrtalnika za vrtanje s kronskimi svedri« (mentor: prof. dr. Marko Nagode); dne 7. junija 2013: Nejc MAZEJ z naslovom: »Razvoj naprave za trajnostno testiranje tečajev vrat pečice« (mentor: izr. prof. dr. Niko Herakovič); Andrej PAKIŽ z naslovom: »Tehnologija izdelave velikih izdelkov s poudarkom na postopkih frezanja« (mentor: prof. dr. Janez Kopač). dne 18. junija 2013: Miha JAKLIČ z naslovom: »Eksperimentalna analiza dinamičnih lastnosti naprednega hidravličnega preklopnega ventila« (mentor: izr. prof. dr. Niko Herakovič); Matjaž SMERAJEC z naslovom: »Prilagodljiva vpenjalna naprava za vrtanje« (mentor: prof. dr. Janez Kopač, somentor: izr. prof. dr. Niko Herakovič); Aleš ŠVAB z naslovom: »Zasnova in izdelava 3D orodja za brizganje plastike« (mentor: prof. dr. Janez Kopač); dne 19. junija 2013: Tadej GRAČNAR z naslovom: »Program šolanja za gorsko letenje v helikopterskem bataljonu Slovenske vojske« (mentor: izr. prof. dr. Tadej Kosel, somentor: pred. mag. Borut Horvat); Jan HRIBAR z naslovom: »Sistem za avtomatsko spajkanje« (mentor: prof. dr. Jožef Duhovnik, somentor: doc. dr. Leon Kos); Anej LIČEN z naslovom: »Razvoj sestava cestne svetilke« (mentor: prof. dr. Jožef Duhovnik); Matej REJC z naslovom: »Ustreznost malih kurilnih naprav na lesno biomaso glede na emisije trdnih delcev« (mentor: prof. dr. Vincenc Butala); Tomaž ŽGAJNER z naslovom: »Letna energijska učinkovitost klimatske naprave v bolnišnici« (mentor: prof. dr. Vincenc Butala); Darjan PODBEVŠEK z naslovom: »Odstranjevanje vodnega kamna z ultrazvočno kavitacijo« (mentor: prof. dr. Branko Širok, somentor: izr. prof. dr. Marko Hočevar); dne 27. junija 2013: Domen GROZDE z naslovom: »Izračun odprtega navpičnega vetrovnika za padalce« (mentor: doc. dr. Viktor Šajn); Rok JAZBEC z naslovom: »Raziskave učinkovitosti zgorevanja biogoriv, pridobljenih z utekočinjanjem lignoceluloznih materialov v poliolih« (mentor: izr. prof. dr. Tomaž Katrašnik); Nejc LOJEVEC z naslovom: »Termodinamska raziskava sreženja v okolju z nizkimi temperaturami« (mentor: prof. dr. Iztok Žun). SI 92

* Na Fakulteti za strojništvo Univerze v Ljubljani so pridobila naziv diplomirani inženir strojništva (UN): dne 6. junija 2013: Matej JANEŽ; dne 10. junija 2013: Jan ZRELEC; dne 11. junija 2013: Jure KOŠIR; dne 12. junija 2013: Tadej KOČEVAR. * Na Fakulteti za strojništvo Univerze v Mariboru so pridobili naziv diplomirani inženir strojništva: dne 27. junija 2013: Miha FRAS z naslovom: »Metodologija za določitev najšibkejše vlečne naprave v postopku homologacije« (mentor: doc. dr. Janez Kramberger); Nejc HOSTINGER z naslovom: »Razvoj namiznega CNC rezkalnega stroja« (mentor: izr. prof. dr. Ivan Pahole, somentor: dr. Simon Klančnik); Boštjan KOPRIVNIKAR z naslovom: »Optimizacija vrstnega reda montažnih del v sistemu prenosa digitalnega signala« (mentor: izr. prof. dr. Borut Buchmeister, somentor:doc. dr. Marjan Leber); Damijan KRAJNC z naslovom: »Uporaba in vgradnja hidravličnih akumulatorjev« (mentor: doc. dr. Darko Lovrec). * Na Fakulteti za strojništvo Univerze v Mariboru sta pridobila naziv diplomirani inženir strojništva (UN): dne 27. junija 2013: Dino FLORJANČIČ z naslovom: »Konstruiranje podvozja Formula student dirkalnika« (mentor: doc. dr. Matej Vesenjak); Denis SLODNJAK z naslovom: »Tehnologija obnove starodobnih vozil« (mentor: izr. prof. dr. Ivan Pahole, somentor: prof. dr. Jože Balič). * Na Fakulteti za strojništvo Univerze v Ljubljani so pridobili naziv diplomirani inženir strojništva (VS): dne 4. junija 2013: Matic FRANKO z naslovom: »Hidravlična naprava za zvezno pozicioniranje vertikalnega bremena« (mentor: prof. dr. Mitjan Kalin, somentor: doc. dr. Franc Majdič); dne 6. junija 2013: Sebastjan OVNIČ z naslovom: »Vpliv aditiva na delovanje termoelektrarniškega kotla s premogovo prašno kurjavo« (mentor: izr. prof. dr. Andrej Senegačnik);

Strojniški vestnik - Journal of Mechanical Engineering 59(2013)7-8, SI 88-93

dne 7. junija 2013: Robert BOLARIĆ z naslovom: »Dodajni materiali za reparaturno varjenje orodnih jekel in orodij po postopku TIG in z laserjem« (mentor: prof. dr. Janez Tušek); David LOKAR z naslovom: »Primerjava peskanja in rotofiniša na tlačnih aluminijevih ulitkih« (mentor: prof. dr. Janez Kopač); dne 19. junija 2013: Gregor JARABEK z naslovom: »Razvoj merilnika za merjenje 3D geometrije ulitkov večjih dimenzij« (mentor: prof. dr. Alojz Sluga, somentor: doc. dr. Drago Bračun);

dne 27. junija 2013: Gašper HABJANIČ z naslovom: »Nastanek, odkrivanje in posledice nevihtnih pišev« (mentor: prof. dr. Jože Rakovec, somentor: izr. prof. dr. Tadej Kosel). * Na Fakulteti za strojništvo Univerze v Mariboru so pridobili naziv diplomirani inženir strojništva (VS): dne 4. junija 2013: Sebastijan ČIRIĆ z naslovom: »Snovanje in konstruiranje nadstreška za lahka gospodarska vozila« (mentor: prof. dr. Srečko Glodež, somentor: doc. dr. Janez Kramberger).

SI 93

Image Courtesy: Photo: Sam Rentmeester

http://www.sv-jme.eu

59 (2013) 7-8

Since 1955

Papers

425

Steven den Dunnen, Gert Kraaij, Christian Biskup, Gino M.M.J. Kerkhoffs, Gabrielle J.M. Tuijthof: Pure Waterjet Drilling of Articular Bone: An in vitro Feasibility Study

433

Ming Xu, Bo Jin, Guojin Chen, Jing Ni: Speed-Control of Energy Regulation Based Variable-Speed Electrohydraulic Drive

443

Sreten Perić, Bogdan Nedić, Dragan Trifković, Mladen Vuruna: An Experimental Study of the Tribological Characteristics of Engine and Gear Transmission Oils

451

Sedat Karabay: Modification of Conductive Material AA6101 of OPGW Conductors against Lightning Strikes

462

Sedat Yayla: Flow Characteristic of Staggered Multiple Slotted Tubes in the Passage of a Fin Tube Heat Exchanger

473

Nenad Popovic, Goran D. Putnik, Ondrej Jasko, Jovan Filipovic: 483 A Contribution for a Pragmatics-Based Approach to Concurrent Engineering Implementation

Journal of Mechanical Engineering - Strojniški vestnik

Contents

7-8 year 2013 volume 59 no.

Strojniški vestnik Journal of Mechanical Engineering