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ISSN 1451-4117 UDC 33 Papers are indexed by SCOPUS Journal of Applied Engineering Science 11(2013)4

CONTENTS

Dragan Ružić, Borivoj Stepanov ESTIMATION OF HEAT FLUX CAUSED BY SOLAR IRRADIATION ON A 169 - 176 DRIVER OF PASSENGER CAR USING NUMERICAL SIMULATION Dr Tomáš Hanák, Dr Ivan Marović 177 - 184 BENCHMARKING CONCEPT OF SMALL SIZED CONSTRUCTION COMPANY Aleksandar Mićović, Dr Vladimir Popović, Dragoslava Mićović, Snežana Jovanović TESTING THE CHARACTERISTICS OF FREE AND FORCED OSCILLATIONS ON 185 - 190 FAP 2228 OFF-ROAD VEHICLE Dr Mirjana Filipović, Ana Đurić, Ljubinko Kevac THE METHODOLOGY FOR DEVELOPING THE KINEMATIC MODEL OF SELECTED 191 - 200 CPR-A SYSTEM AS A NECESSITY FOR THE DEVELOPMENT OF A DYNAMIC MODEL Minja Marinović, Dragana Makajić-Nikolić, Milan Stanojević 201 - 208 OPTIMIZATION IN DAY-AHEAD PLANNING OF ENERGY TRADING Goran Duduković, Milutin Ogrizović THE ADVANTAGES OF INTELIGENT APPROACH TO MACHINING PRESENTED 209 - 215 THROUGH PROCESSEING TECHNOLOGY DESIGN DEVELOPED BY I-MACHINING Ian Zaczyk 217 - 223 IMPACT OF COSMIC RADIATION ON AVIATION RELIABILITY AND SAFETY EVENTS REVIEW 224 - 225 ANNOUNCEMENT OF EVENTS

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BOOK RECOMMENDATION

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INSTRUCTIONS FOR AUTHORS 228 - 229 EDITORIAL AND ABSTRACTS IN SERBIAN LANGUAGE 230 - 234

Journal of Applied Engineering Science 11(2013)4

EDITORIAL

MAINTENANCE FOR PROFIT

Dr Jezdimir Knežević

Commonly, maintenance is perceived as “fixing broken things”. As such, it is associated with failures and unplanned expenses, both of which negatively impact business plans or customer satisfaction. However, as failures are an inevitability of the life of any technological system, it would be worthwhile to start looking at maintenance as opportunity for positive impact on business plans or customer satisfaction. Consequently, the main objective is to get focused on the way that failures, once understood, could be managed in the way that reduces the number of in-service interruptions and operational costs.

Users and operators of complex Technological Systems would like to be able to accurately predict how likely is that all planes, trains, buses and similar revenue generating machines will be able to deliver functionality out to all of those expected to take place by well prepared and strategically determined business plans. Answers to these types of questions is essential for the prediction of the size of maintenance teams, number of spares parts, location of maintenance and support facilities and many similar considerations, which directly determine the cost of operation, maintenance and support, which are the main contributors to operational revenue, profit, customer satisfaction and similar business drivers. Therefore, high-level decision makers in any organization should understand what could be done by the new approach to maintenance, rather than to show them how it should be done. Members of the organisations with the wider horizons are needed to fully appreciate the challenge that is facing the maintenance community daily, which is the necessity for simultaneous management of maintenance activities related to system failures, on one hand and the continuous provision of revenue generating functions, on the other. For this to be achieved, a full understanding of the impact of maintenance on both functions is essential. However, this is far from the current situation where the “Boards of Directors” in every company in the world are maximising efforts to minimise maintenance costs. Hence, our main objective in the future is to show how the science based quantitative relationship between the Euro paid for maintenance and the Euro earned from the revenue generated function has been established to enable a trade-off that maximises the profit (success). The new approach to maintenance developed by MIRCE Mechanics is giving answers to such questions and it is my firm belief that Maintenance must have a seat in the Boardroom of any public or private organisation committed to high reliability and value for money. Sincerely yours, Dr Jezdimir Knežević

Journal of Applied Engineering Science 11(2013)4

Original Scientific Paper

doi:10.5937/jaes11-4731

Paper number: 11(2013)4, 261, 169 - 176

ESTIMATION OF HEAT FLUX CAUSED BY SOLAR IRRADIATION ON A DRIVER OF PASSENGER CAR USING NUMERICAL SIMULATION Dragan Ružić* Faculty of Technical Sciences, Novi Sad, Serbia Borivoj Stepanov Faculty of Technical Sciences, Novi Sad, Serbia In this paper, the influence of solar radiation direction and intensity on thermal flux on passenger vehicle driver’s body was analysed. The analysis was carried out on a virtual model of a vehicle cabin. The results showed that the highest heat flux caused by solar radiation could occur when the sun is shining in the front of the vehicle, as proposed in standard ISO 14505-2: 2008. Under these conditions, driver’s chest is the segment with the highest heat flux. The unfavourable situation due to highly asymmetric thermal condition is also when the sun is shining on the left side of the cabin. From that reason, paying attention to solar characteristics of glass and to design of air distribution system in such way that air-conditioner vents can be directed to areas with the highest fluxes is an efficient way to reduce the driver’s and passenger’s thermal stress. Key words: Cabin, Solar radiation, Virtual thermal manikin, Automotive glass, Thermal comfort INTRODUCTION Thermal conditions in a vehicle cabin are more adverse in hot than in cold ambient. Higher ambient temperatures, accompanied with solar radiation, cause increase of both interior air and surface temperatures above safety limits. From that reason, even under moderate outside conditions the closed cabin act like green house and its closed interior could become unpleasant, unbearable and even dangerous for the occupants [03]. Vehicle cab ergonomics is a key factor in ensuring driver’s optimum working performance, which could easily become the weakest link in the process of vehicle driving. Consequences of poor ergonomics of driver’s workplace could be the decrease of the traffic safety level [02]. Experimental determination of local heat fluxes on human body surface caused by solar radiation demands the use of complex and expensive measurement equipment and test facilities. The other way is to simulate these processes in virtual experiments, as in other fields of research (e.g. virtual reality in vehicle development, simulation of dynamic mechanical processes etc.) [04, 09, 10, 17]. This paper deals with numerical modelling of effects of the solar radiation transmitted through a vehicle cabin glazing.

Many researches are focused on human body exposure to solar radiation, and this problem is especially interesting in the context of motor vehicles. In the comprehensive project focused on the reduction of vehicle auxiliary load, done by National Renewable Energy Laboratory [12], variety of researching methods were used to investigate and develop innovative techniques and technologies for lowering thermal loads. The aim of the research was to investigate solutions for improvement of fuel economy of air-conditioning system. They concluded that reflecting the solar radiation incident on the vehicle’s glass is the most important factor in making significant reductions in the thermal loads. The use of solarreflective glass can reduce the average air temperature and the seat temperature. Application of reflective shades and electrochromic switchable glazing is also effective techniques for reducing the solar energy entering the passenger compartment. The project presented in the project report by Bohm et al. [01], concerns the thermal effect of glazing in cabs with large glass areas. The effect of different kind of glass and design of the windows as well as the effects of sun protection and insulation glazing have been studied

* Faculty of Technical Sciences, Trg Dositeja Obradovića 6, 21000 Novi Sad; ruzic@uns.ac.rs

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and evaluated, using the thermal manikin called AIMAN. Results showed that neither in severe winter conditions, nor in sunny summer conditions, could acceptable climate be obtained with standard glazing in cabs with large glass areas. Han and Huang [05] performed CFD simulations where the effects of solar radiation were considered in a virtual model of actual vehicle. They used the comfort model that has the ability to predict the local thermal comfort level of an occupant in a highly non-uniform thermal environment, taking into account direct solar flux on each passenger too. Results of investigation of different types of glazing and solar intensities showed importance of the solar radiation on thermal sensation, which can cause highly asymmetric thermal condition. Results of Ružić et al. [14, 15, 16] showed that cabin glazing is the most influencing factor in cabin heat gain. They concluded that the highest heat flux that enters the cabin is caused by solar radiation through the glass, which could be several times higher than the heat transferred by other modes. Therefore, the selection of appropriate glass properties could be the way to reduce heat load on driver. Furthermore, the heat load on the driver is highly dependent from the shape of a cabin and glass solar properties. Lee et al. [08] carried out numerical simulation in order to investigate the influence of spectral effect on airflows and temperature distribution in the passenger car cabin. For the purpose of the investigation, the experimental measurement of glass spectral properties was performed. They concluded that the solar load in the cabin depends on

the glass properties and the solar spectrum. The direct effects of the solar radiation on passengers were not considered in the research. The aim of the paper is to investigate effects of the sun position relative to the vehicle cabin on heat fluxes caused by solar radiation over the driver’s body surface. Although the vehicle changes its relative position to the sun, these situations could be of interest when the vehicle is stationary, slow moving in traffic jam, or during the prolonged driving on straight motorways. In addition, the goal is to identify the worst case regarding the heat gain caused by solar radiation, in order to reduce the risk of thermal discomfort. METHOD Estimation of heat fluxes caused by solar radiation was done using the numerical simulations. The simulations were carried out in STAR CCM+ software. The CAD model of the virtual thermal manikin (VTM) is a simplified humanoid in the sitting posture. The manikin’s body is symmetric, with its posture defined by characteristic points in places where the main body joints are (hips, shoulders, neck, elbows etc). Main body dimensions are adopted from CATIA database for a 50th percentile European male, and the body is divided into 18 segments (Figure 1, left). According to the chosen sizes of the body, the VTM is 1.74 m tall and weighs 68 kg. The area of VTM body surface in sitting position is 1.796 m2. The VTM surface is discretized in around 13,600 surface elements [13] (Figure 1, right).

Figure 1: Left - Virtual thermal manikin with numbered segments. Right - The VTM surface mesh

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Dragan Ružić - Estimation of heat flux caused by solar irradiation on a driver of passenger car using numerical simulation

The cabin interior was modelled after the shape and dimensions of mid-sized passenger hatchback car, with significant simplification of the cabin geometry. The problem was treated as a steady-state threedimensional, with stationary bodies and boundaries. Solar load was calculated using Solar load model incorporated in CFD software STARCCM+. Although the primary purpose of the CFD software is simulation of thermal and flow processes, this software can be used for modelling of the radiation processes as well [21]. The amount of the solar radiation energy that will be absorbed by the body will depend on the effective projected area and on the solar absorptivity of the body surface. Solar absorptivity of the hu¬man skin is around 0.62, while solar absorptivity for clothing depends on the colour [07, 11]. In this research, solar absorptivity of all VTM’s segments was set to 0.62.

The coordinate system for the orientation of the direct solar flux is shown in the Figure 2. In this study, the gray spectrum model is used and the total solar loads represent the full-thermal spectrum, divided in direct and diffuse radiation. Based on the results given in [08], when the spectral solar radiation and optical properties of the materials are considered, the heat fluxes would be in some extent higher than in the cases without considering spectral effect. For comparative purposes regarding the sun positions, the gray spectrum model is chosen as compromise between the accuracy and computational time. The solar load model is defined by the sun direction and solar flux intensity. The sun direction vector in a specified coordinate system is described by azimuth and altitude angles. The solar flux is consisted of the direct and the diffuse solar fluxes [21].

Figure 2: Orientation of the cabin in solar coordinate system: θS – solar altitude (sun elevation), Φ - azimuth angle

Solar irradiation is variable depending on the position of the sun as well as the orientation of the cabin. The sun position varies throughout the day and year due to the earth’s rotation on its own axis and its orbit around the sun. Graph in Figure 3 presents the values of maximum (“clear sky”) intensity of normal irradiation and its variations during the daylight, in a central European region [18]. Vehicle cabin glazing is semi-transparent medium where solar irradiation can be partially reflected, absorbed and transmitted, Figure 4. While the transmitted radiation influences how much shortwave radiation reaches the body, the absorbed part of the solar energy influences the Journal of Applied Engineering Science 11(2013)4, 261

temperature of the glass. The increase of glass temperature causes heat transfer to the cab interior by both convection and longwave radiation [06,14,15]. Consequently, the solar radiation causes discomfort by increasing the interior air and surface temperatures. In this research, only transmitted solar radiation that falls directly on the driver’s body was analyzed, since it causes discomfort due to significant heat gain and radiation asymmetry. Glass performance regarding the impact of solar radiation is determined by the optical properties of the glass. Using available values of glass properties for green tinted automotive glass with 75% transmittance of visible light, the normal 171

Dragan Ružić - Estimation of heat flux caused by solar irradiation on a driver of passenger car using numerical simulation

solar transmissivity was set to 0.5 [08, 20]. The maximum solar transmissivity of the glass is in region of incident angles less than 40°, but de-

creasing of the transmissivity with the increase of the incident angle was not taken into account in this research.

Figure 3: Solar clear-sky irradiation in a central European region on a day in July [18]. Vertical lines present the solar altitudes that were considered in the analysis

Figure 4: Solar energy transmission through the glass

The heat flux on a driver’s body segment caused by the solar radiation is calculated according to [07]: (1) This mode of heat transfer is independent of other boundary conditions parameters, like ambient temperature, air velocity or radiant temperature (i.e. longwave radiation). The direct solar irradiation on the virtual manikin surface (GS•τS) was directly obtained by CFD simulation post-processing.

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VIRTUAL EXPERIMENTS, RESULTS AND DISCUSSION The aim of the research was to investigate influence of the sun position relative to the vehicle cabin on driver’s body heat fluxes caused by solar radiation. The results should indicate the worst case regarding the local heat flux intensity and the radiation asymmetry. Consequently, the areas on the driver’s body that must be cooled by the forced airflow were pointed out. Simulation were performed for four different sun altitudes (θS = 30°, 60°, 75° and 90°) and five Journal of Applied Engineering Science 11(2013)4, 261

Dragan Ružić - Estimation of heat flux caused by solar irradiation on a driver of passenger car using numerical simulation

azimuth angles ( = 0°, ±45° and ±90°). The values of direct and diffuse solar irradiation were changed with the sun altitude, according to the Figure 3. The conditions include solar irradiation intensity defined by standard ISO 14505-2: 2008 for determination of thermal conditions in vehicle cabin during the cool-down regime: solar irradiation of 800 W/m2, at altitude of 60° and azimuth of 0° [19]. Values of the heat flux for the whole body in dependence of solar azimuth and altitudes are shown on Figure 5. According to the trend of the whole body heat flux in dependence of azimuth, the highest value could be expected at azimuth angle of around −15° with solar altitude of 60°. This condition is very close to the conditions defined by the standard ISO 14505-2: 2008.

The largest effective projected radiation area Aeff of unprotected sitting person is with azimuth and altitude angles of 30º and 15º respectively, giving the total surface equal to [11]: (2) The total surface of human body ADu can be calculated from body weight and height (after Dubois [11]). The factor 0.72 in the equation (2) is effective radiation area factor, and the factor 0.33 is projected area factor [11]. However, due to position of opaque cabin surfaces and lower intensity of the solar irradiation when the sun is very low in the sky, this case is not critical in passenger vehicle. Distribution of the heat flux on VTM’s surface is visualized on Figure 6 and the values are given on Figure 7.

Figure 5: Values of the heat flux for the whole body in dependence of solar azimuth and altitude angles

Figure 6: Distribution of the heat flux caused by the solar radiation over the VTM’s surface in the case with the highest heat flux for the whole body Journal of Applied Engineering Science 11(2013)4, 261

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Dragan Ružić - Estimation of heat flux caused by solar irradiation on a driver of passenger car using numerical simulation

Figure 7: Values of the heat flux caused by the solar radiation on VTM’s segments in the case with the highest heat flux for the whole body

The segment with the highest local value of heat flux was the driver’s chest, at solar azimuth 0°, when the sun was lower in the sky, i.e. at altitude 30°, Figure 7. When the sun is high in the sky (around the noon), the driver’s head is protected relatively good by the cabin roof and the upper

part of the body is exposed to the transmitted solar radiation only when the sun is low in the sky, at altitude below 15°. However, under this circumstance solar irradiation is ap¬proximately at one-half of its maximum value.

Figure 8: Values of the heat flux for the driver’s chest in dependence of solar azimuth and altitude angles

Furthermore, the worst case regarding the asymmetry, evaluated using the difference of heat fluxes between the left and the right body segments, was the case when the sun is shining at the left side of the cabin (driver-side), at altitudes between 30° and 60° (Figure 8). In this case, the driver’s body, and especially the face, are exposed to the strong asymmetric thermal condition. If this condition is prolonged, the asymmet174

ric thermal load must be compensated by proper distribution of the air-conditioned air towards the areas exposed to the solar irradiation.

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Dragan Ružić - Estimation of heat flux caused by solar irradiation on a driver of passenger car using numerical simulation

Figure 9: Distribution of the solar irradiation over the VTM’s surface in the case with the high radiation asymmetry (solar altitude 45°, azimuth angle -90°)

CONCLUSION The influence of the solar radiation direction and intensity on thermal flux on passenger vehicle driver’s body surface was analysed using a virtual model of a vehicle cabin. The virtual experiments were carried out in CFD software STARCCM+, using Solar load model. The results showed that the highest heat flux caused by solar irradiation could occur when the sun is shining in the front of the vehicle, under the same conditions as in standard ISO 145052: 2008. The body segment with the highest heat flux is driver’s chest, particularly when the sun is low in the sky. The unfavourable situation for the driver due to highly asymmetric condition is also when the sun is shining on the left side of the cabin, i.e. on the driver’s side. The typical design of passenger car cabin and the position of the driver on the seat do not offer sufficient protection from the solar radiation. The reasons are the shape of car body determined by aerodynamic and visibility requirements as well as by ergonomic position of the driver. In any case, the exposed body surfaces can be protected only by solar properties of glass, unless some kind of shading devices or direct body cooling by airflow from air-conditioner vents are used. In passenger vehicles the shading devices are limited only to the adjustable interior sun visors, capable to cover the upper part of the windshield or side window. Of course, the visors must not restrict the driver’s normal field of vision. From that reason, paying attention to solar characteristics of glass (especially windshield) and to design of air distribution system in such Journal of Applied Engineering Science 11(2013)4, 261

way that air-conditioner vents can be directed to areas with the highest fluxes, are an efficient ways to reduce the driver’s thermal load. The advantages of the simulation method presented in this paper are the simplicity and independence from other modes of heat transfer. Although the gray thermal radiation model was used, the radiation can be modelled as spectrumdependent. In this case, for achieving accurate prediction of transmitted solar irradiation it is crucial to have spectral properties of glass. However, the numerical values obtained from the simulations should be considered for comparison purposes only, and validation of the numerical model must be done by physical experiment. ACKNOWLEDGMENT This research was done as a part of the project TR35041 - “Investigation of the safety of the vehicle as part of cybernetic system: Driver-Vehicle-Environment”, which was supported by the Serbian Ministry of Education, Science and Technological Development. The authors wish to thank Dr Maša Bukurov for enabling the use of the CFD software STAR CCM+. REFERENCES 1) Bohm, M., Holmer, I., Nilsson, H., Noren, O. (2002): Thermal Effects of Glazing in Driver’s Cabs, JTI-rapport, JTI - Swedish Institute of Agricultural and Environmental Engineering, Uppsala, Sweden 2) Daanen, H.A.M., van de Vliert, E., Huang, X. (2005): Driving performance in cold, warm and thermoneutral environments, Applied 175

Dragan Ružić - Estimation of heat flux caused by solar irradiation on a driver of passenger car using numerical simulation

Ergonomics, 34, pp. 597-602. 3) Dadour, I.R., Almanjahie, I., Fowkes, N.D., Keady, G., Vijayan, K. (2011): Temperature Variations in a Parked Vehicle, Forensic Science International, 207, pp. 205-211 4) Glišović, J. Demić, M., Miloradović, M. (2011): Review of Virtual Reality Applications for Reducing Time and Cost of Vehicle Development Cycle, Journal of Applied Engineering Science, 9(3), pp. 361-372 5) Han, T., Huang L. (2005): A Sensitivity Study of Occupant Thermal Comfort in a Cabin Using Virtual Thermal Comfort Engineering, 2005 SAE World Congress, SAE Tech. paper 2005-01-1509, Detroit, USA 6) Huizenga, C., Zhang, H., Mattelaer, P., Yu, T., Arens, E., Lyons, P. (2006): Window Performance for Human Thermal Comfort, Final Report to the National Fenestration Rating Council, Center for the Built Environment, University of California, Berkeley, USA 7) Incropera, F. P., DeWitt, D. P. (1981): Fundamentals of heat and mass transfer, New York: John Wiley & Sons 8) Lee, W.J., Jang, E.Y., Lee, S.H., Ryou, H.S., Choi, S., Kim, Y. (2013): Influence of the spectral solar radiation on the air flow and temperature distributions in a passenger compartment, International Journal of Thermal Sciences, 75, pp. 36-44 9) Mitić, S., Rakićević, B., Stamenković, D., Popović, V. (2011): Advanced theoreticalexperimental method for optimization of dynamic behaviour of firefighting vehicle modular superstructures, Journal of Applied Engineering Science, 9(1), pp. 267-275 10) Ognjanović, M. (2008): Design in Mechanical Engineering - Multidisciplinary Approach, Istraživanja i projektovanja za privredu, 20, pp. 15-22 11) Parsons, K. (2003) Human thermal environments: The effects of hot, moderate and cold environments on human health, comfort and performance, 2nd ed., London: Taylor & Francis 12) Rugh, J. & Farrington, R. (2008): Vehicle Ancillary Load Reduction Project Close-Out Report, Technical Report NREL/TP-540-42454, National Renewable Energy Laboratory, Golden, USA 176

13) Ružić, D., Bikić, S. (2013): An approach to the modeling of a virtual thermal manikin, Thermal Science, DOI:10.2298/TSCI130115115R, OnLine-First, 14) Ružić, D., Časnji, F. (2011): Agricultural tractor cab characteristics relevant for microclimatic conditions, Journal of Applied Engineering Science, 9(2), pp. 323-330 15) Ružić, D., Časnji, F. (2012) Thermal Interaction Between a Human Body and a Vehicle Cabin, Heat Transfer Phenomena and Applications, Rijeka: InTech, pp. 295-318 16) Ružić, D., Časnji F., Muzikravić V. (2007): Karakteristike stakla kao faktor od uticaja na mikroklimu u traktorskoj kabini, Traktori i pogonske mašine, 12(4), pp. 92-97 17) Sekulić, D., Dedović, V. (2011): Intercity bus users vibration comfort analysis through an oscillatory model with seven DOF using ADAMS/VIEW software, Journal of Applied Engineering Science, 9(3), pp. 401-410 18) http://re.jrc.ec.europa.eu/pvgis/apps3/pvest. php, accessed on January 10th, 2013 19) ISO 14505-2: 2008, Ergonomics of the thermal environment – Evaluation of the thermal environment in vehicles, Part 2: Determination of equivalent temperature 20) Saint-Gobain Sekurit, Glazing Manual, http:// www.saint-gobain-sekurit.com/en/downloads, retrieved on January 15th, 2013 21) STAR-CCM+, User Guide, CD-Adapco Paper sent to revision: 24.10.2013. Paper ready for publication: 05.12.2013.

Journal of Applied Engineering Science 11(2013)4, 261

Original Scientific Paper

doi:10.5937/jaes11-4856

Paper number: 11(2013)4, 262, 177 - 184

BENCHMARKING CONCEPT OF SMALL SIZED CONSTRUCTION COMPANY Dr Tomáš Hanák* Faculty of Civil Engineering, Brno, Czech Republic Dr Ivan Marović Faculty of Civil Engineering, Rijeka, Croatia Increasing competition on a global market forces enterprises to increase the efficiency of internal processes in order to retain competitiveness. Performance measurement is becoming one of the main strategic factors of business success, and can be performed also within the frame of benchmarking initiative. The aim of this paper is to draw up the benchmarking concept of small sized construction company, and verify its application on the case study. For this reason it was necessary to identify the set of performance indicators that can be measured and evaluated. It has been found out that firm size is limiting factor for application of benchmarking in the company, as well as unavailability of all necessary data. However, it was concluded that even a limited form of benchmarking provides a valuable information to the company management relevant to strategic decision making ensuring effective firm’s management, and long term financial stability. Key words: Benchmarking, Construction company, Cost, Financial ratio, Performance indicator INTRODUCTION Increasing competition on a global market forces enterprises to increase the efficiency of internal processes in order to retain competitiveness. This issue is even more important in construction industry suffering from the decrement of the volume of public and private tenders. Thus, it is necessary to focus on performance measurement which makes the establishment of feasible goals possible. The concept of measurement is strongly influenced by the industrial sector in which the company operates, and can be realized within the frame of benchmarking initiative. The aim of this paper is to draw up the benchmarking concept of small sized construction company, which will take into account encountered difficulties associated with the implementation of benchmarking, as well as future directions related to the potential creation of warning system. The applicability of the presented concept is subsequently validated on a case study based on one small sized construction company located in North-Moravian region of the Czech Republic. The paper is structured as follows: Firstly, the literature review on the utilization of benchmarking in industry sector is introduced. Secondly, the re-

search method used in this paper is presented. Thirdly, analysis and results are presented. Finally, discussion on applicability of benchmarking for small sized construction company is discussed together with the recommendations for company management, and possibilities of creating warning system. LITERATURE REVIEW Many research papers focus on the application of benchmarking in different industry sectors [03, 07, 17, 34], and thus a definition of term “benchmarking” is not unified.As benchmarking being defined as the art of learning from companies that perform certain tasks better than other companies [20], Išoraité [18] even argues that there is a considerable confusion as to what “benchmarking” actually means. Nevertheless, it is possible to identify the common essence among various definitions since benchmarking is widely understood as tool/process for improvement [04, 09, 14, 20, 29, 31]. The improvement can be achieved if the institution measures its performance [26], furthermore many authors stress the element of “best practice” since they propose to measure processes against best-in-class companies [01, 18, 21].

* Brno University of Technology, Faculty of Civil Engineering, Institute of Structural Economics and Management, Veveří 95, 602 00 Brno, Czech Republic; hanak.t@fce.vutbr.cz

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Dr Tomáš Hanák- Benchmarking concept of small sized construction company

The measurement of organizational or project performance is realized by means of performance indicators. Alarcón et al. [02] emphasize that the improvement of performance cannot be achieved by measurement alone. They argue the importance of analysis of these indicators with the objective to detect the problems and their causes. Just in this way the benchmarking may answer three basic question: “where are we now?”, “where do we want to get?”, and “how to get there?” [03, 29]. Having standard, systems and methodology of measurement is the necessary prerequisite in order to achieve required company’s or project’s efficiency [08, 14, 30]. If there is a willingness to apply benchmarking in the company, it is necessary to select appropriate benchmarking type to be used. Internal, competitive, parallel industry and best practice benchmarking types were introduced by [22]. Internal benchmarking focuses on comparison between different divisions of a company, competitive benchmarking compares firms with similar products within same industry sector, parallel industry benchmarking considers between different sectors, and best practice draws a comparison to a market leader having exemplary process(es). It is obvious that firm size will be limiting factor for application of particular type of benchmarking in analysed company. Since achieving “best practice” is not always a benchmark, authors consider than the most appropriate definition of benchmarking for the purpose of this paper is to be “Benchmarking enables an organization to identify its performance gaps and opportunities and develop continuous improvement programs for all stages of their process” [02]. Construction industry is specific in many ways. Firstly, its end product differs from other industries since construction products have long-term presence. Secondly, construction is a difficult process that has to be planned precisely including the planning of labour, machines, materials or equipment of construction site. Thirdly, building of the object is a long-term activity in comparison with e.g. food or steel industry. And finally, there are many different stakeholders involved in the process with their different needs and expectations during constructions life-cycle. Above-mentioned facts clarify why performance measurement in construction is distinctive on the contrary to other industrial sectors. Performance 178

indicators may be identified from company’s or project’s point of view [02, 10, 12, 25, 28, 30].Since this paper is focused on small sized construction companies, it is necessary to take into account also following facts: firstly, the main interest of construction companies to be involved in benchmarking is to compare their performance to other companies from the same market segment[10]; and secondly, small sized firms suffer from lack of resources [16]. Main difficulties are related especially to the lack of suitable partners, resource constraints and confidentiality of data [15]. RESEARCH METHOD This paper investigates the application of benchmarking in small sized construction company. As seen in the literature review, there are 4 different types of benchmarking that might be used and there are also many different sets of performance indicators that can be measured. Firstly, competitive benchmarking has been selected as the most appropriate for the purpose of this paper. Decision is based on following facts: Internal benchmarking is not applicable since small size construction company is too small and cannot be divided in divisions. Similarly, parallel industry benchmarking is not appropriate since construction sector is very specific and differs from other industry sectors. Best practice benchmarking approach is not relevant as well due to the large disproportion between “best practice” companies with high resources and constrained small sized companies. Secondly, appropriate performance indicators were identified in available literature and discussed with the panel of experts with respect to the small sized character of the company. Thirdly, it was necessary to check up if there are relevant data at disposal for the measurement of particular selected indicators. Fourthly, one construction company has been appointed as the initiator of the project [33]. Consequently, several small sized construction companies were invited to join benchmarking initiative.Unfortunately, it has been encountered that it is very difficult to cope with the lack of suitable partners. There was not any comparable construction company from the same market segment willing to be involved in this benchmarking initiative. This constraint has been partially removed by using publicly available statistical data from Czech Statistical Office [11], InformaJournal of Applied Engineering Science 11(2013)4, 262

Dr Tomáš Hanák- Benchmarking concept of small sized construction company

tion System on Average Wage [24] and Benchmarking Diagnostic System of Financial Indicators INFA [23]. Finally, recommendations and improvements resulting from performed benchmarking initiative were formulated. PERFORMANCE INDICATORS AND AVAILABILITY OF DATA The subject of a case study is small sized construction company located in North-Moravian region of the Czech Republic. Portfolio of clients consists of both natural and legal persons (pri-

vate i.e. business entity or public i.e. government organizations). The most common subjects of firm’s activity are construction and reconstruction of family houses, and implementation of additional thermal insulation on buildings envelope. Company has 10 permanent employees, and for seasonal works firm hires additionalstaff. Based on performed literature review, bellowmentioned performance indicators were selected as appropriate for benchmarking of small sized construction company. List of performance indicators including the information about availability of data can be seen in Table 1.

Table 1: Availability of data for selected performance indicators No.

Name

Formulae

Cost Variation

(Actual cost – budgeted cost) / budgeted cost

Schedule variation

Result

Availability of data Firm

Market

Cost [2, 10, 12, 30]

n/a

(Actual duration – planned duration) / planned duration

Time [2, 10, 30]

n/a

Cost of client claims

Cost of repairing claims / total project costs

Quality [2, 30]

n/a

Accident risk

(No. of accidents * 100%) / total number of workers

Safety [2, 10, 30]

n/a

Efficiency of direct labour

Planned man-hours / actual man hours

Labour [2, 30]

n/a

Administration productivity

Cost of general administration / monthly sales

Company management [2]

n/a

Market share

Companies output / total output in market segment

Market [3, 30]

n/a

Return on equity

Net income / shareholder equity

Profitability [12, 23, 30]

[23]

Net profit margin

(Net profit * 100%) / revenue

Profitability [12, 23, 30]

[23]

Asset turnover

Net sales revenue / total assets

Turnover [23]

[23]

Equity ratio

Total shareholder’s equity / total assets

Capital structure [23]

[23]

Cash ratio

(current assets – inventory – accounts receivable) / current liabilities

Liquidity [23]

[23]

Current ratio

Current assets / current liabilities

Liquidity [23]

[23]

Average month salary of worker

Sum of annual salaries of workers / (no. of worker * 12)

Labour [24]

[24]

Average month salary of technician

Sum of annual salaries of technicians / (no. of technicians * 12)

Labour [24]

[24]

Costs for labour as % of revenue

Total costs for labour / revenues

Labour [33]

[11]

Inventory as % of Revenue

Value of inventory / revenues

Inventory [33]

[11]

Material as % of revenue

Total costs for material / revenues

Material OC

n/a

Note: ID = internal data of examined company, OC = own construction. Journal of Applied Engineering Science 11(2013)4, 262

179

Dr Tomáš Hanák- Benchmarking concept of small sized construction company

The adequacy of indicators was considered especially in relation to the ability and effectiveness to record specific data in a detailed level. Data necessary for evaluation of proposed performance indicators may be obtained from different sources. At subject company level, data recording is partly obligatory, e.g. in the form of balance sheet or profit and loss account. Other important indicators require detailed voluntary evidence in the form of management accounting providing crucial information for proper company’s management. Therefore, management accounting is considered to be primary data source for the purpose of this study. On the other, in particular cases it can be beneficial to use publicly available data, processed and published by statistical offices, authorities or relevant professional associations or chambers. The availability of needed data is given in the last two columns of Table 1. Proposed list of indicators is aimed to monitor key company’s processes which are presented in following paragraph.Based on observations, most common problems related with building orders are those related with time, costs and quality. As the value of planned and actual costs for construction contracts often vary (e.g. due to extra works, changes in the prices of materials, etc.), it is advisable to monitor cost variation (indicator no. 1; I1). Similar differences also arise for schedule; schedule variation is therefore a logical parameter suitable for observation (I2). With regard to the evaluation of the quality of the work performed, it seems to be interesting to observe cost of client claims (as a share of costs of repairing claims on total project costs, I3). Because it is desirable to reduce the number of accidents on construction site, it is necessary to monitor achieved level of safety with respect to the riskiness of execution of construction works by means of indicator no. 5. Administrative costs may significantly affect the company’s competitiveness, thus observation of this aspect is ensured by means of administration productivity indicator (I6). Increasing market share is one of the most important objectives of business. This indicator (I7) partially eliminates the influence of macroeconomic variables such as GDP growth and therefore activities carried out within the frame of marketing analysis should be also directed to this area. Group of indicators I8 – I13 serves to evaluate the financial health of the company from different perspectives such as prosperity, liquidity, 180

turnover or capital structure. Correct setting of wage tariffs for key professions in the company is monitored by indicators no. 14 and 15. Furthermore, because building production is manpower-intensive, it is worth to compare the total labor costs and revenues as well (I16). Another costly activity in building industry is storage, thus the relative value of inventory is a parameter of great importance (I17). And finally, if we want to prevent e.g. wasting of materials, it is essential to observe materials management system e.g. by means of the portion of material costs on total revenues (I18). DISCUSSION It was found that without suitable partners willing to participate in benchmarking initiative it is not possible to completely collect all necessary data for all selected performance indicators, especially those related with cost, time, quality, safety, company management, and material. This fact significantly reduces the value of benchmarking outputs for construction company, because for its proper operation it is crucial to record: • budgeted and real costs of construction orders (consequence: reduced profit or even loss); • actual and planned duration of construction (consequence: contractual penalty); • data on safety at work (consequence: enhanced costs for indemnification, and for construction all risk (CAR) insurance or erection all risk (EAR) insurance); and • client claims (consequence: labour and/or technological weaknesses are not discovered). Cost analysis is a subject of particular interest, no matter if it is about costs for materials (usually forming about 60% of total costs of construction) or machines. Information on costs in management accounting of the company should be detailed, allowing in-depth analysis of e.g. costs of machines for transport, operation, fuels or depreciation [27], oranalysis of relation between contracted price and time overrun[36]. Such data are not covered by statistical services. Unfortunately, data on indicators no. 1 – 5 were not recorder neither by examined construction company. On the other hand, limited form of benchmarking can be applied to other performance indicators related especially to financial ratios allowing evaluation of “financial health” of a subject. Journal of Applied Engineering Science 11(2013)4, 262

Dr Tomáš Hanák- Benchmarking concept of small sized construction company

Required data on the level of the firm has to be stated in balance sheet as well as in profit and loss account. This case study employees 9 financial ratios; if the purpose of assessment is solely financial health of the firm, a larger set of financial ratios might be used. For that purpose authors in [32] suggested 17 ratios whileanother research [35] suggested16 ratios. Average financial data on similar companies operating on the market can be collected from various databases and statistical services, however the availability and details may vary from country to country. Nevertheless, above-mentioned available outputs are not enough to investigate all crucial processes within the company. For the evaluation of indicator no. 7 it is not necessary to have at disposal data from the market, however it might be very interesting to observe the market share of comparable competitors. Notwithstanding, from the long term perspective the indicator itself expresses whether the company rises or not. In this case, the market is geographically limited to the region of South Moravia and Silesia since the company carries out its activities only in this territory. Next financial ratios provide relevant information to the rate of return on the equity (no. 08), profitability of the company by means of net profit as a percentage of the revenue (no. 09), how efficiently the company is utilizing its assets to produce revenue (no. 10), and to relative proportion of equity applied to finance the assets of a company (no. 11). Liquidity is one of the factors sensitive to the economic changes in the country. EminÖcal et al. [13] have proved that continuous analysis of this factor together with capital structure and profitability, activity efficiency, profit margin and growth, as well as assets structure would provide sufficient information related with both the relative state of the industry with respect to time, and the relative state of any construction company with respect to their rivals. Cash ratio (no. 12) is usually used as a measure of company liquidity in the form of most liquid short-term assets usually used to pay off current obligations. The second liquidity indicator, current ratio (no. 13), describes the ability to meet short-term liabilities by means of company’s short-term assets. If the liquidity is considered as an important factor, the third measurement ratio, cash ratio, can be easily added. Comparison of wage indicators (no. 14, 15 and 16) has to be based only on the South Moravian and Silesian region due to the fact that wages Journal of Applied Engineering Science 11(2013)4, 262

in different regions of Czech Republic are considerably different. It is of particular interest to analyse wages according to professions in order to avoid misrepresentation of the results caused by different employment structure; which can be especially important for small companies. Proper material management is of strategic interest due to the large proportion of material costs on total costs as well as inventory management, because storage is expensive activity involving costs for warehouse operations, its management, guarding or insurance. Various measures can be taken in order to improve company’s assessment. Positive effect can be achievede.g. by implementation of safety management programmes, especially if speaking about construction sector. Authors in [05] have reported improvements in project ROI (return on investment) as a benefit of such programmes. Differences in safety climate perception are considerable between firms; study of Blazhevska et al. has discovered such differences even regarding employee’s work position, age and tenure [06]. Therefore, employers must take appropriate activities to provide safe and healthy work conditions and insurance coverage to avoid expenses related with indemnity (to learn more see [19]). Performed case study analysis has detected unsatisfactory data record management on the level of examined company. Thus, it is recommended to start recording data necessary for future evaluation of performance indicators no. 1-5. Later on, when suitable partners will be available to participate in benchmarking initiative, the data for comparison will be at disposal already. It should be noted that, for the correct interpretation of the indicators is essential to carry out the assessment in the long term run. The actual values of just one year are not sufficient, because it is crucial to identify trends of company development. Even though the recorded specific annual value of the indicator is appropriate, in the long term perspective it should indicate a negative development in comparison with previous periods. Therefore, it is recommended to take into account the period of last 5 years, if applicable. The whole benchmarking concept is graphically demonstrated in Figure 1. The concept takes into account encountered difficulties associated with the implementation of benchmarking as well as future directions related to the potential creation of warning system. 181

Dr TomĂĄĹĄ HanĂĄk- Benchmarking concept of small sized construction company

Figure 1: Scheme of benchmarking concept

This study has confirmed findings on benchmarking reported by other studies. Above all, the crucial issue is to cope with the lack of resources [16], the lack of suitable partners and confidentiality of data [15]. It has to be pointed out, that the performance of above mentioned recommendations can require an employment of a new worker resulting in the increment of labour costs and significantly affecting the values of closely related examined indicators (no. 06, 09 and 16). Hereafter, the benefits of benchmarking outputs must be clearly explained in order to strongly motivate suitable partners to join the benchmarking initiative, and to share internal data with others. 182

CONCLUSION Benchmarking is one of the suitable approaches allowing to measure performance of the company. The application of the proposed concept would allow identification of the key processes with significant impact on the company performance and introduction of better practices related to these processes. However, the possibilities of benchmarking application are largely dependent on the limiting factors such as the availability of data and size of the company. Despite all the obstacles, even a limited form of benchmarking provides to company management valuable information relevant to strategic Journal of Applied Engineering Science 11(2013)4, 262

Dr Tomáš Hanák- Benchmarking concept of small sized construction company

decision making and supports ensuring effective firm’s management,as well as long term financial stability. Yet it should be noted that the limited version is particularly useful for evaluating the financial health of the company, while the essence of a comprehensive assessment of the competitiveness of the company cannot be fulfilled in this way. A case study has shown that the critical issue is to find partners willing to participate in benchmarking initiative and therefore have at disposal corporate data allowing comparison of internal processes between companies. It should be noted that the indicators must be evaluated annually from the long term perspective. In such case it is possible to monitor trends and take appropriate remedial measures in a timely manner. Introduced concept of benchmarking is completely feasible only if there are more comparable companies willing to participate in the initiative. Future research should be also directed towards the development of a warning system allowing timely indication of the occurrence of adverse phenomenon such as lack of liquidity, material waste or low labour utilization. For this purpose, detailed data collection is necessary optimally in monthly interval. REFERENCES 1) Acord, T., (2000) Defining benchmarking,FDM: Des Plaines, 72 (15), 34-35. 2) Alarcón, L.F., Grillo, A., Freire, J., Diethelm, S., (2001) Learning from collaborative benchmarking in the construction industry,IGLC-9, Proceeding of the Ninth International Group for Lean Construction Conference.Available at: http://cic.vtt.fi/lean/singapore/Alarconet.pdf 3) Antošová, M., Csikósová, A., Čulková, K., Seňová, A., (2013) Benchmarking research of steel companies in Europe,Metalurgija, 52 (3), 410-412. 4) Bednárová, L., Liberko, I., Weiss, R., (2009) Benchmarking v riadenipodnikov, In: ActaMontanisticaSlovaca, 14 (1), 86-91. 5) Bernstein, H.M., Russo, M.A., (2013) Contractor safety programs yield financial benefits,ENR (Engineering News-Record), 271 (7). (accepted for publication) 6) BlazhevskaStoilkovska, B., ZileskaPancovska, V., Mijoski, G., (2013) Perceptions of Work Safety among Employees in ConstrucJournal of Applied Engineering Science 11(2013)4, 262

tion Sector in Macedonia, In Proceedings of International Conference Safety Engineering in Function of Improvement of the Working Conditions,Ohrid, pp. 249-255. 7) Borgia, C., García-Bolaños, M., Li, T., GómezMacpherson, H., Comas, J., Connor, D., Mateos, L., (2013) Benchmarking for performance assessment of small and large irrigation schemes along the Senegal Valley in Mauritania, Agricultural Water Management, 121, 19-26. 8) Ćetković, J., Knežević, M., Ivanišević, N., Rutešić, S., (2010) Mark of the investment projects in civil engineering with the special retrospection to the economical-financial mark of the project, Terra Spectra - Central European Journal of Spatial and Landscape Planning, 2 (1), 47-55. 9) Clark, A.M., Atkin, B.L., Betts, M.P., Smith, D.A., (1999) Benchmarking the use of IT to support supplier management in construction, Journal of Information Technology in Construction, 4 (1-16), Available from: http:// www.itcon.org/1999/1 10) Costa, B. D., Formoso, C. T., Kagioglou, M., Alarcon, L. F., (2004) Performance Measurement System for Benchmarking in the Construction Industry, Proc. 12th IGLC Conf. LOSchool, Elsinore Denmark, 451-463. 11) Czech Statistical Office, official web page. Available from: http://www.czso.cz/ 12) Egan, J., (1998) Rethinking construction: report of the construction task force on the scope for improving the quality and efficiency of UK construction. HMSO. Available from: http://www.constructingexcellence.org.uk/ pdf/rethinking%20construction/rethinking_ construction_report.pdf 13) EminÖcal, M., Oral, E.L., Erdis, E., Vural, G., (2007) Industry financial ratios-application of factor analysis in Turkish construction industry,Building and Environment, 42 (1), 385-392. 14) Harrington, H.J., Harrington, J.S., (1996) High Performance Benchmarking: 20 steps to success, McGraw-Hill, USA. 15) Holloway, J.A., Hinton, C.M., Mayle, D.T., Francis, G.A.J., (1997) Why benchmark? Understanding the processes of best practice benchmarking, Proceedings of Business, Track, British Academy of Management Conference, London, 271-291. 183

Dr Tomáš Hanák- Benchmarking concept of small sized construction company

16) Hudson, M., Smart, A., Bourne, M., (2001) Theory and practice in SME performance measurement systems. International Journal of Operations and Production Management, 21(8), 1096-1115. 17) Hung, C.-T., (2013) Evaluating and benchmarking productive performance of shipping companies,Applied Mechanics and Materials, 284-287, 3675-3678. 18) Išoraite,M.,(2004) Benchmarking methodology in a transport sector, Transport, 19 (6), 269-275. 19) Klasić, K., Janzetić, M., (2010) Insurance of individuals on construction sites,Sigurnost, 52(1), 35-47. 20) Kotler, P., (1994) Marketing management – Analysis, Planning, Implementation and Control, Prentice Hall, New Jersey. 21) Leibfried, K.H.J., McNair, C.J., (1994) Benchmarking: a tool for continuous improvement, HarperCollins Publishers, London. 22) Lewis, J.C., Naim, M.M., (1995) Benchmarking of aftermarket supply chains,Production Planning and Control, 6 (3), 258-269. 23) Ministry of Industry and Trade of the Czech Republic. Benchmarkingovýdiagnostickýs ystémfinančníchindikátorů INFA. Available from: http://www.mpo.cz/cz/infa.html 24) Ministry of Labour and Social Affairs of the Czech Republic. Informačnísystém o průměrnémvýdělku. Available from: http:// www.mpsv.cz/clanek.php?lg=1&id=1928 25) Mbugua, L.M., Harris, P., Holt, G.D., Olomolaiye, P.O., (1999) A framework for determining critical success factors influencing construction business performance, In: Hughes, W. (ed) Procs. 15Th Annual ARCOM Conference. September 5-7, Reading: ARCOM. 1, 255-264. 26) Morling, P., Tanner, S., (2000) Benchmarking a public service business management system,Total Quality Management, 11 (4-6), 417-426. 27) Petronijevič, P., Ivaniševič, N., Rakočevič, M. Arizanovič, D., (2012) Methods of calculating depreciation expenses of construction machinery,Journal of Applied Engineering Science, 10(1), 43-48.

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28) Pillai, A. S., Joshi, A., Rao, K.S., (2002) Performance measurement of R&D projects in a multiproject, concurrent engineering envir onment,International Journal of Project Management, 20, 165-177. 29) Renko, N., Delić, S.,Škrtić, M., (1999) Benchnmarking u strategijimarketinga, Mate, Zagreb. 30) Takim, R., Akintoye, A., (2002) Performance indicators for successful construction project performance, In: Greenwood, D (Ed.), 18th Annual ARCOM Conference, 2-4 September 2002, University of Northumbria. Association of Researchers in Construction Management, Vol. 2, 545-55. 31) Van Schalkwyk, P.W., Smith, E., Morgan, N.,(1996) Contemporary Issues in Strategic Management,Kagisco Publishers, Pretoria. 32) Varghese, B., Menacere, K., (2012)The financial health of construction companies in Qatar: A case study,International Journal of Engineering Research in Africa, 8, 55-72. 33) Waszek, J., (2013) Optimalizacenákladůves tavebnímpodniku, Final thesis, Brno University of Technology, Faculty of Civil Engineering. 105 p. Mentor 34) Yakovleva, N., Sarkis, J., Sloan, T., (2012) Sustainable benchmarking of supply chains: The case of the food industry,International Journal of Production Research, 50 (5), 1297-1317. 35) Yunus, N.M., Malik, S.A., (2012) Development of financial model using financial ratios in predicting business performance of IBS construction company, ICSSBE 2012 - Proceedings, 2012 International Conference on Statistics in Science, Business and Engineering: “Empowering Decision Making with Statistical Sciences” 2012, 209-214. 36) Žujo, V., Car-Pušić, D., Brkan-Vejzović, A., (2010) Contracted price overrun as contracted construction time overrun function,Tehnic kiVjesnik, 17(1), 23-29. Paper sent to revision: 13.11.2013. Paper ready for publication: 11.12.2013.

Journal of Applied Engineering Science 11(2013)4, 262

Professional Paper

doi:10.5937/jaes11-4984

Paper number: 11(2013)4, 263, 185 - 190

TESTING THE CHARACTERISTICS OF FREE AND FORCED OSCILLATIONS ON FAP 2228 OFF-ROAD VEHICLE Aleksandar Mićović* Technical Test Center, Belgrade, Serbia Dr Vladimir Popović Faculty of Mechanical Engineering, Belgrade, Serbia Dragoslava Mićović Academy of Criminalistic and Police Studies, Belgrade, Serbia Snežana Jovanović Technical Test Center, Belgrade, Serbia The paper presents the testing of free and forced oscillations characteristics on FAP 2228 BS/A-45 off-road vehicle. The testing of free oscillations was conducted according to SORS 9127 (Standard of Defence of the Republic of Serbia) in laboratory conditions. The testing of forced oscillations was conducted in the course of driving on various surface paths - the heath in Deliblatska pescara, gravel at the territory of Fruska gora, on concrete surface at the runway of the Kovin airport, as well as on the asphalt surface of Belgrade-Šid highway. The testing was carried out according to SORS 0318 and ISO 2631 standards, and the results were evaluated according to 2002/44/EC Directive. Key words: FAP 2228 BS/A-45, Forced oscillations, Free oscillations, Testing, Comfort INTRODUCTION The concept of military vehicles refers primarily to engine-driven special purpose off-road vehicles. It covers various military systems driven by internal combustion engines, such as tanks, infantry armoured fighting vehicles, as well as a number of other special superstructures on offroad vehicles. This is exactly the group of vehicles which are not covered by ecological standards in practice.

Figure 1: FAP 2228 BS/A-45 * Technical Test Center, Vojvode Stepe 445, 11000 Belgrade, Serbia; amicovic1@gmail.com

As these vehicles are not used only during war, but also in peace time, it is necessary to establish the standards which must be applied in order to protect the health of their users. A special problem related to military vehicles results from the fact that they are very durable and last long, and therefore they do not fulfil the standards which the automobile industry started applying in the last ten years [05, 07]. Also, due to the special requirements set before the manufacturers regarding dynamic passability, the autonomous movement, the reliability of fitted components, as well as the accommodation of special equipment and weaponry, the price of manufacturing such vehicles is very high. It is a frequent case in practice that during the designing of superstructures to be installed on a basic type of a vehicle the constructors are faced with huge problems how to reduce the level of vibrations and noise inside the cabin to an acceptable level required for uninterrupted operation of the carrier [06, 08]. The main and transversal supports are connected by screws and rivets. The platform is equipped with JOST locks for container connecting. Overall dimensions of the vehicle are (length x width x height) 9,615 x 2,500 x 3,180 mm. 185

Aleksandar MiÄ&#x2021;oviÄ&#x2021; - Testing the characteristics of free and forced oscilations on FAP 2228 of road vehicle

FATIGUE AND VIBRATIONS Military vehicles are primarily used in off-road, or all terrain conditions. When they are tested, the test drivers from Technical Testing Centre usually cover several thousands of kilometres on various surfaces and in various weather conditions, putting them to test by intensive driving. Most of these vehicles are in prototype stage of development where various functional failures are possible. This is why the concentration of a test driver is of great importance for the safety of testing. However, the necessary consequence of intensive driving testing is the fatigue which occurs in operators [01]. According to a definition, fatigue is a phenomenon occurring as a consequence of the activities of a human body as a whole or an organic system in overcoming various types of burden defined by work requirements. Fatigue warns a body to cease the activity due to overburden and possible consequences. The important characteristic of fatigue is reversibility. When they are in drive, all types of vehicles can be a sources of vibrations which are transfered to the whole body of a driver. The risk of health damage increases in people who are exposed to high level of vibrations on a regular basis and over the long term. In order to determine a daily exposure to vibrations (A(8)) or VDV (Vibration Dose Value), it is necessary to know the duration of total daily exposure to vibrations produced by vehicles used during the work process. Only the data referring to the concrete work process should be taken into account at that, i.e. only the time period during which a driver or a crew member was exposed to vibrations. Testing of the human exposure to vibrations which are transferred to the whole body is carried out according to the method defined in ISSO 2631-1:1997, while the detailed instructions on the application of the vibration measuring method are given in the European Standard EN 14253:2003. The level of vibrations expressed as r. m. s. value (root-meansquare) is expressed as acceleration weighted considering frequency measured at the seat of a person sitting in the course of performing their work tasks, i.e. the feet of the person who is standing during the performance of their work tasks, and it is given as m/s2. The level of vibrations expressed as r. m. s. value is equal to average acceleration measured in the interval of measurement conducted. This is the highest of the three values measured in three orthogonal axes (1.4 awx, 1.4 awy or awz) [09]. 186

The alternative measure of the level of exposure to vibrations is Vibration Dose Value (VDV). VDV has been developed as a measure which represents a better risk indicator or exposure to vibrations with shocks. VDV is expressed in meter per second on 1.75th (m/s1.75) and as opposed to the level of vibrations expressed as r. m. s. value it represents a cumulative measuring result, i.e. it increases as the measuring time is prolonged. This is why it is important to know during all VDV measurements in which time period the value was measured. It should be the highest value measured in one of the three orthogonal axes (1,4 VDVwx, 1,4 VDVwy or VDVwz) [04]. Risk assessment must enable to recognize the method which can control the exposure to vibrations. When evaluating the exposure to vibrations, the work processes that cause them must also be taken into account. Understanding of the manner in which the workers are exposed to vibrations will help recognize the method for the reduction or complete elimination of this exposure [02, 03]. VIBRATION (FREE AND FORCED) MEASURING Portable MAESTRO human vibration meter, manufactured by 01dB-Metravib, was used to measure the vibrations on the seats of both the driver and passengers in the vehicle cabin and the superstructure. This meter is intended primarily for human vibration measuring, i.e. measuring and calculating the influence on the human body (measurement of vibrations at the workplace which are transferred to the whole body or to the hands). Alternatively, it is used to measure the level of noise (as four-channel system, the first three channels are intended for three-axis accelerometers, and the fourth channel can be connected to the oneaxis accelerometer or to a preamplifier with a microphone; it is adapted for measuring the efficiency of the seat and as a basic vibration meter).

Figure 2: Maestro Journal of Applied Engineering Science 11(2013)4, 263

Aleksandar Mićović - Testing the characteristics of free and forced oscilations on FAP 2228 of road vehicle

Figure 3: NetdB12

Its integration time ranges between 1 and 200 seconds and it has the possibility of start/stop mode, the memory capacity is 2 MB, as well as analogue output: 4-pin LEMO connector for signal recording or monitoring of all four channels within the range from 0.4 to 1000 Hz. The autonomous operation (when not plugged in mode) depends on the battery life and on an average it is from 8 to 13 hours. Free oscillations were measured by NetdB12 (01dB Metravib) vibroacoustic measuring system manufactured by Areva, as well as NF piezoelectric accelerometers (type STS AS135/1A). FREE OSCILLATIONS MEASURING Testing of free oscillations was carried out in laboratory conditions on a flat concrete surface according to SORS 9127. The vehicle is equipped

with dependent elastic suspension system on the front bridge with leaf springs, additional rubber cushions and telescopic hydraulic shock absorbers (left and right). Measurements were carried out on two points: • M1 – vehicle frame above the middle of the axle, and • M2 – vehicle frame above the centre of the tandem of vehicle back axles. Exciting a vehicle to natural oscillation is performed by stretching, i.e. free fall of the vehicle ends: front end for measuring point M1 and rear end for M2. Out of the recorded signal as evaluating parameters for free oscillations fo natural frequency and relative coefficient of damping Ψ are taken. As SORS 9127 refers to comfort characteristics – the evaluation of fo and Ψ parameters is given according to the criteria for human organism. From the recorded oscillation signals the values of fo and Ψ parameters were calculated in the form of damped sine wave and the results are shown in Table 1. On the front axle (M1) the parameter of natural frequency suggests comfortable drive, while the coefficient of damping lies on the dividing line between comfortable and uncomfortable driving.

Table 1: Natural frequency fo and relative coefficient of damping Ψ

FAP 2228 with container

Vehicle

Measuring points

Parameters

Measured values

Comfort evaluation

2,3 Hz

Comfortable

0,35

Conditionally comfortable

3 Hz

Conditionally comfortable

0,9

Uncomfortable

On the measuring point at the centre of tandem axle (M2) the parameter of natural frequency is within the range of conditionally comfortable driving, and the coefficient of damping suggests extremely uncomfortable driving. Table 2 shows the results of measuring the total weight of the vehicle with the container, as well as the weight distribution on the sides and axles. In addition to the surface on which the vehicle is being driven, one of the most important parameters that have significant influence on measuring results is also the speed of the vehicle. Journal of Applied Engineering Science 11(2013)4, 263

This parameter has been chosen based on more than 20-year-long experience of the researchers of testing vehicles on testing paths in both Deliblatska pescara and Fruska gora. Realistic average speed on this type of surface is 30 km/h, but in order to obtain a more comprehensive insight into the measuring results and their comparison, the testing was also carried out at the speed of 40 km/h. Figures 4 through 6 show the examples of measuring results, while Table 3 shows the general results for all types of surfaces and all vehicle speeds. 187

Aleksandar MiÄ&#x2021;oviÄ&#x2021; - Testing the characteristics of free and forced oscilations on FAP 2228 of road vehicle

Table 2: Weight distribution on axles and sides Vehicle without the container [kg]

Vehicle with the container [kg]

10900

16100

Left wheel, Gfl

2400

2380

Right wheel, Gfr

2670

2620

Total, Gf

5070

5000

Left wheel, Gml

1550

2940

Right wheel, Gmr

1540

2920

Total, Gm

3090

5860

Left wheel, Grl

1360

2630

Right wheel, Grr

1380

2610

Total, Gr

2740

5240

5830

11100

Left side of the vehicle, Gl

5310

7950

Right side of the vehicle, Gr

5590

8150

Total weight, Gtw

WEIGHT DISTRIBUTION

Front axle

Middle axle

Tandem axle Rear axle

Total tandem weight, GT

Table 3: General review of forced oscillations measuring results Path

Measuring point

Driver

Asphalt

Codriver

Crew

Driver Concrete Codriver Driver Heath Codriver

Driver

Gravel

Codriver

Crew

188

Equivalent threeaxle acceleration related to comfort av (m/s2 )

Comfort evaluation

Equivalent threeaxle acceleration related to health av (m/s2 )

Recommended maximum exposure

0.78

somewhat

0.85

22h22m13s

0.74

somewhat

0.81

23h54m28s

0.73

somewhat

0.80

24h34m1s

1.06

uncomfortable

1.13

11h7m22s

1.04

uncomfortable

1.11

11h29m44s

0.98

uncomfortable

1.04

12h55m2s

0.64

somewhat

0.67

28h14m37s

0.80

uncomfortable

0.84

18h17m1s

1.33

very uncomfortable

1.40

6h43m18s

0.88

uncomfortable

0.97

17h36m50s

0.99

uncomfortable

1.08

13h28m10s

1.11

uncomfortable

1.19

10h10m39s

1.05

uncomfortable

1.16

12h42m1s

1.18

uncomfortable

1.36

11h38m31s

1.64

very uncomfortable

1.87

5h38m41s

1.36

very uncomfortable

1.50

7h26m32s

1.57

very uncomfortable

1.73

5h30m06s

1.06

uncomfortable

1.12

10h22m39s

1.46

very uncomfortable

1.63

6h42m55s

1.17

uncomfortable

1.32

10h55m4s

1.40

very uncomfortable

1.50

6h25m16s

1.37

very uncomfortable

1.48

6h50m31s

1.64

very uncomfortable

1.77

4h43m41s

0.99

uncomfortable

1.07

12h43m28s

1.43

very uncomfortable

1.51

5h46m11s

Speed (km/h)

Journal of Applied Engineering Science 11(2013)4, 263

Aleksandar Mićović - Testing the characteristics of free and forced oscilations on FAP 2228 of road vehicle

Figure 5: Driver’s seat, speed 80 km/h, asphalt

Figure 4: Driver’s seat, speed 40 km/h, heath

CONCLUSION In order to obtain more comprehensive results on asphalt and concrete surfaces respectively, the measurements were carried out at constant speeds ranging from 40 to 80 km/h. Tests were made on the Kovin airport runway and on the part of highway near Sremska Mitrovica. ReJournal of Applied Engineering Science 11(2013)4, 263

gardless of a relatively wide speed interval, the results obtained of the equivalent levels of vibrations at the driver’s seat range from 0.9 to 1 m/s2 for the concrete surface and about 0.75 m/s2 for asphalt surface; it can, therefore, be concluded that various speeds on either concrete or asphalt surface do not have any significant influence on the level of vibrations on either driver’s or co-driver’s seat. It can be noticed that at the same speed the vibrations at the co-driver’s seat are about 10% higher on a concrete surface, but also about 30% on the asphalt surface.

189

Aleksandar Mićović - Testing the characteristics of free and forced oscilations on FAP 2228 of road vehicle

results for the co-driver’s seat are more unfavorable. In regard to the criteria of harm to health, the driving in this off-road vehicle on both the heath and macadam surfaces should be limited in time until the stated warning levels of vibrations. REFERENCES

Figure 6. Co-driver’s seat, speed 50 km/h, asphalt

Considering that both seats (the driver’s and codriver’s) are equipped with the same type of seats, it can be concluded that the distribution of burder, as well as the choice of vehicle suspension system have influence on this irregularity. The oscillations measured during driving on the asphalt surface at the driver’s and co-driver’s seat suggest uncomfortable drive, particularly at the speed of 50 km/h. Measuring of forced oscillations in the field following the comfort ability criteria suggests that driving at both the driver’s and co-driver’s seats can be classified as very uncomfortable on the macadam. This conclusion is also valid for the drive at the speed of 40 km/h on the heath. In general, the 190

1) Bester, R.: The ride comfort versus handling decision for off-road vehicles, PhD thesis, Faculty of Engineering, Built environment and Information Technology (EBIT), University of Pretoria, Pretoria, 2006 2) Blagojević I., Ivanović G., Janković S., Popović V. (2012): A model for gear shifting optimization in motor vehicles, Transactions of FAMENA, 36 2, pp.51-66 3) Directive 2002/44/EC of the European Parliament and of the Council on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (vibration), June 2002 4) ISO 2631 Mechanical vibration and shock - Evaluation of human exposure to wholebody vibration, 1997 5) Mikulić, D., Happ Z., Knezović M. (2004): Ecologically military vehicles, Hrvatski vojnik, No 109/110, pp 8-11 6) Mićović, A., Popović, A., Jovanović, S. (2012): Acoustic testing inside cabin and passenger space of off-road vehicle land rover defender 110 soft top, Proceeding of Papers 23th National conference & 4th International conference - Noise and vibration, pp. 233 -235. 7) Popović V., Vasić B., Rakićević B., Vorotović G. (2012): Optimization of maintenance concept choice using risk-decision factor – a case study, International Journal of Systems Science,4310, pp.1913-1926 8) Stamenković D., Popović V., SpasojevićBrkić V., Radivojević J. (2011): Combination free replacement and pro-rata warranty policy optimization model, Journal of Applied Engineering Science, 9 ,pp. 457-464 9) Smith S, (2008): Dynamic characteristics and human perception of vibration aboard a military propeller aircraft Air Force Research Laboratory, AFRL/RHPA, International Journal of Industrial Ergonomics 38, pp 868–879 Paper sent to revision: 27.11.2013. Paper ready for publication: 12.12.2013. Journal of Applied Engineering Science 11(2013)4, 263

Original Scientific Paper

doi:10.5937/jaes11-4581

Paper number: 11(2013)4, 264, 191 - 200

THE METHODOLOGY FOR DEVELOPING THE KINEMATIC MODEL OF SELECTED CPR-A SYSTEM AS A NECESSITY FOR THE DEVELOPMENT OF A DYNAMIC MODEL Dr Mirjana Filipović* Mihajlo Pupin Institute, Belgrade, Serbia Ana Đurić Wayne State University, Detroit, USA Ljubinko Kevac School of Electrical Engineering, Belgrade, Serbia The authentic form or general form of Cable Suspended Parallel Robot type A, CPR-A mathematical model is defined. The proper definition of the system kinematic model which includes trajectory, velocity and acceleration is a prerequisite for the formulation of a dynamic model. These three components represent the basic functional criteria of the real system which is described by the corresponding geometric relations and differential equations. Kinematic model is defined for the CPR-A system via the Jacobian matrix. An adequate choice of generalized coordinates (in this paper, the motor coordinates), provides a mathematical model that illuminates the mapping of motor (resultant forces in the ropes) and camera carrier forces (acting on a camera carrier) over the Jacobian matrix on motion dynamics of each motor. Software packages AIRCAMA (aerial camera system type A) are formed and used for individual and comparative analysis of the CPR-A system from various aspects. The impact of changing any parameter of the system (workspace dimensions, the mass of a camera carrier, change the size and dynamics of power disturbances, the choice of control law, the reference trajectory, and the presence of singularity avoidance system and a number of other characteristics) can be analyzed through these software packages. Different examples of the CPR-A system motion are analyzed and their results are presented. Application possibilities of CPR-A system are certainly much broader than it may be assumed at this moment, especially for sports, cultural, military or police purposes. Key words: Cable-suspended parallel robot, Observation, Workspace, Modeling, Kinematic, Dynamic INTRODUCTION A system for observation of the workspace with moving objects has been developed to some extent and widely analyzed in various research areas as well as for different applications. Similar systems were analyzed and modeled as presented by numerous publications. The kinematic design of a planar three-degreeof-freedom parallel manipulator is considered, in paper [13]. Four optimal different design criteria are established and analyzed. A trajectory planning approach for cable-suspended parallel mechanisms has been presented in [14]. A planar two-degree-of-freedom parallel mechanism has been used in the analysis. Paper [03] studied the kinematics and statics of under-

constrained cable-driven parallel robots with less than six cables, in crane configuration. In those robots, kinematics and statics are intrinsically coupled and they must be dealt with simultaneously. A motion controller for six DOF tendon-based parallel manipulator (driven by seven cables), which moves a platform with high speed is introduced in [08]. The Workspace conditions and the dynamics of the manipulator are described in details. In the paper [01] authors presented algorithms that enable precise trajectory control of the Networked Info Mechanical Systems - NIMS, and under constrained threedimensional -3D cabled robot intended for use in actuated sensing. They provide a brief system overview and then describe methods to determine the range of operation of the robot. Sev-

* University of Belgrade, Mihajlo Pupin Institute, Volgina 15, 11060 Belgrade, Serbia; mira@robot.imp.bg.ac.rs

191

Dr Mirjana FilipoviÄ&#x2021; - The methodology for developing the kinematic model of selected CPR-a system as a necessity for the development of a dynamic model

eral prototypes of the wire-driven parallel robots, with different actuation schemes have been presented in [22]. Two of them have been evaluated through extensive tests and showed unexpected kinematic problems. The wrench-closure workspace of parallel cable-driven mechanisms is the set poses of their mobile platform for which the cables can balance any external wrench. The determination of this workspace is an important issue in [15] since the cables can only pull and not push on the mobile platform. Parallel cabledriven Stewart-Gough platforms consist of an end-effector which is connected to the machine frame by motor driven cables. Since cables can transmit only tension forces, at least m = n + 1 cables are needed to tense a system having n degrees-of-freedom. This will cause a kinematical redundancy and leads to a (m - n)-dimensional solution space for the cable force distribution presented in [02]. The recent result from a newly designed parallel wire robot which is currently under construction is presented in [27]. It has been used for developing a new technique for computation and transfer of its workspace to the available CAD software. An auto-calibration method for over constrained cable-driven parallel robots using internal position sensors located in the motors has been presented in [23]. A calibration workflow is proposed and implemented including pose selection, measurement, and parameter adjustment. The wire-driven parallel robot presented in [18] has attracted the interest of researchers since the very beginning of the study of parallel robots. This type of robot has the advantage of having light mobile mass, simple linear actuators with possibly relatively large stroke and less risk of interference between the legs. On the other hand their major drawback is that wire actuator can only pull and not push. The paper [26] addressed the issue of control design for a redundant 6-DOF cable robot with positive input constraints. The design is based on feedback linearization controller named reference governor - RG. Nonlinear dynamic analysis of the suspended cable system is carried out with some sensible results presented in [07] that could be useful to the real engineering of LSRT (Large Spherical Radio Telescopes). Integrated mechanical, electronic, optic and automatic control technologies are employed to make considerable improvement upon the same system. A multiple cable robotic crane designed in [31] is used to provide improved cargo handling. The 192

equations of motion are derived for the cargo and flexible cable using Lagrangeâ&#x20AC;&#x2122;s equations and assumed modes method. The results are compared against desired cable lengths and results achieved in previous research using a rigid cable model. This is one of a few papers dealing with flexible ropes. For the requirement of the trajectory tracking of the LSRT, a large fine tuning platform based on the Stewart platform is presented in papers [32] and [33]. The mathematical model for kinematic control is developed with coordinate transformation, and dynamic analysis is made using a Jacobian matrix, which, with singularity analysis, built a solid base for the tracking control. Paper [20] addresses the static analysis of the cable-driven robotic manipulators with the non-negligible cable mass. An approach to computing the static displacement of a homogeneous elastic cable is presented. The resulting cable-displacement expression is used to solve the inverse kinematics of general cable-driven robotic manipulators. Cable suspended parallel robot is analyzed in [35], in which cables are utilized to replace links to manipulate objects. It is developed from parallel and serial cable-driven robot. Compared with the parallel robot, this type of robot has more advantages. The cooperative variation of lengths of six cables pulls the feed cabin to track radio source with six degrees of freedom. The cable-driven parallel manipulator can only bear tension, but not compression. Therefore, a cable system with j end-effectors DOFs requires at least (j+1) cables as shown in [19]. For three-translational motions of the feed in the system, a four-cable-driven parallel manipulator has been developed. For the design of the five-hundred-meter aperture spherical radio telescope, a four-cable-driven parallel manipulator, which is long in span and heavy in weight, is adopted as the first-level adjustable feed-support system. The goal of the paper [34] is to optimize dimensions of the four-cable-driven parallel manipulator to meet the workspace requirement of constraint condition in terms of cable tension and stiffness. One of the works that deals with visualization of workspace is presented in [6]. In the current literature survey there is no any mathematical model of the cable-suspendedparallel robots with double parallel ropes and there is no available procedure for generating the Jacobian matrix of the similar systems. Another problem is that the current published models do not include the motors dynamics. The analysis Journal of Applied Engineering Science 11(2013)4, 264

Dr Mirjana Filipović - The methodology for developing the kinematic model of selected CPR-a system as a necessity for the development of a dynamic model

and synthesis of these complex systems cannot be proper without the motor dynamics, because it represents the dominant dynamics for any electro mechanical system. The kinematic formulation of the presented CPR-A system is a key contribution in this paper, which will be used for the system realization. This formulation can be used for determining the Jacobian matrix of any CPR system configuration. This methodology for developing the kinematic model of selected CPR systems is named the KinCPR-Solver (Kinematic Cable Parallel Robot Solver), and it gives a precise direct and inverse kinematic solutions. The dynamic model is generated using the fundamental dynamic theory based on the Lagrange’s principle of virtual work. The mathematical model of the motors is determined using the same equations and expressed with the generalized coordinates. In this paper the camera carrier workspace has the shape of a parallelepiped, such that the camera carrier hangs over the ropes properly connected on the four highest points i.e. the four upper angles of the workspace. The suspension system is defined in these four points. This

paper analyzes the mechanism which involves only the positioning of the camera carrier. The camera motion is controlled by the ropes which are synchronized by three motors. The gyro sensor, which is installed in the camera carrier, is stabilized towards the horizon. In this paper, the real system abstraction will be used for modeling purposes by neglecting the transverse vibrations of the ropes (un-stretchable ropes). Future researches include implementation of the features of elastic ropes (type of nonlinear dynamic elasticity as defined in [09]-[12], [16]-[17], [28]-[30],) in the mathematical model of the CPR. In future research several different CPR models will be unified according to their similarities into one reconfigurable model, using the approaches presented in [04] and [05]. Most of the Section 2 is devoted to the CPR-A kinematic model, which is directly involved in the development of its dynamic model. Several cases of the system responses are analyzed for different conditions in the Section 3. In the Section 4 the concluding remarks are presented.

Figure 1: CPR-A system in the 3D space

MATHEMATICAL MODEL OF THE CABLE SUSPENDED PARALLEL ROBOT In this Section chosen CPR-A system is analyzed in depth, which graphical representation is shown in Figure 1 and Figure 2. The camera carrier of the CPR-A structure is guided through the work area of the parallelepiped shape with two ropes connected with three winches, each powered by the motors. The ropes of the pulley system are run on the Journal of Applied Engineering Science 11(2013)4, 264

winches (reel) 1, 2, 3, powered by the motors. The ropes coil or uncoil on the winches of radius R1, R2, and R3. The motors rotate winches directly and its angular positions are θ1, θ2, and θ3. This motion moves the camera in the x, y, z Cartesian coordinates. To define a dynamic model of the CPR-A for observation of moving objects in workspace depicted in Figure1, it is first necessary to define the camera carrier velocity of change of the coordinates and the velocity of change 193

Dr Mirjana Filipović - The methodology for developing the kinematic model of selected CPR-a system as a necessity for the development of a dynamic model

of the motor coordinates .The geometrical relationship between the lengths k, h, m, n and the Cartesian coordinates position x, y, z of the camera carrier is defined by the following equations: (1)

The third motor is used to wind up the two ropes about the coil 3. Those motion produce winding or unwinding of both ropes at the same time. This can be seen in Figure 2 and 3a). The winch used for winding ropes has radius R3. The relation between the third motor motion changes and the lengths change are expressed in the equations (7) and (8).

(2) (7) (3)

Or it can be expressed as following:

(4) In Figure 3а, the motion of the motor 1 and the motor 2 are depicted. Both motors motion depend on their angular positive directions, which produce winding or unwinding of the ropes. The motor 1 and the motor 2 motions toward the wall anchors (we call this line “before” motor) are expressed with the following equations respectively: (5) (6)

(8) The equation (9) is obtained by substituting (6) into the equation (7) or (5) into the equation (8): (9) If the sampling time is small enough then the equations (5), (6), and (9) can be expressed, respectively, as: (10) (11) (12)

Figure 2: CPR-A system top view.

194

Journal of Applied Engineering Science 11(2013)4, 264

Dr Mirjana Filipović - The methodology for developing the kinematic model of selected CPR-a system as a necessity for the development of a dynamic model

Figure 3. a) The motors (ropes) forces before motor 1, motor 2 and motor 3 and after motor 1 and motor 2, b) The ropes forces which carry a camera

By differentiating equations (1)-(4) and substituting them into the equations (10)-(12), the relationship between velocities of camera carrier coordinates and velocities of motor coordinates can been obtained:

The system has two ropes in the each direction and the motor 3 simultaneously unwind or wind both ropes. The connection between the resultant motor load moment and camera carrier force is established. See equation (16). (16)

(13) The acceleration vector can be defined by using Newton Euler method. Jacobian matrix Ja is a full matrix. The elements of Jacobian matrix that are beyond the diagonal Ja12, Ja13, Ja21, Ja23, Ja31, Ja32, are not equal to zero and show the strong coupling between the velocities of camera carrier coordinates and velocities of motor coordinates. This methodology for developing the kinematic model of selected CPR-A systems is named the KinCPR-Solver (Kinematic Cable Parallel Robot Solver), and it gives a precise direct and inverse kinematic solutions. The mathematical model of the system has the following form: (14) Where: ,Gv=diagGvi, Lv=diagLvi, Sv=diagSvi. Vector equation (14) is given by applying Lagrange’s equation on the generalized coordinates θ1, θ2, θ3 . Lagrange’s principle of virtual work has been used to find the relation between the resultant motor load moment Ma and the camera carrier force . (15) Journal of Applied Engineering Science 11(2013)4, 264

By substituting equation (16) into the equation (14), the dynamic model of the CPR-A system has been generated: (17) The moment mapping matrix Oa indicates that the system is highly coupled. Control law is selected by the local feedback loop for the position and velocity of the motor shaft in the following form: (18) Where is position constant Klpi, and velocity constant Klvi for the motion control. SIMULATION RESULTS AND ANALYSES The CPR-A system presented in Figure 1 and 2 is modeled and analyzed by the software package AIRCAMA. The software package AIRCAMA is used for validation of the applied theoretical contributions. The software package AIRCAMA includes three essential modules, which are the kinematic, dynamic and motion control law solvers for the CPR-A system. The most important element of the CPR-A system is the motor mathematical model which is an integral part of software package AIRCAMA. 195

Dr Mirjana Filipović - The methodology for developing the kinematic model of selected CPR-a system as a necessity for the development of a dynamic model

Through the simulation results it is shown that the dynamic characteristics of the motor significantly affect the response of the system and its stability. The camera carrier motion dynamics directly depends of the mechanism dynamic parameters. The CPR-A model has been analyzed using the trajectory and the selected system parameters. In order to make the results comparable, the simulation is made for the same desired system parameters defined in the Nomenclature. The motors are selected by Heinzman SL100F and the gear boxes are HFUC14-50-2A-GR+belt. The system is coupled on the reference level and its mathematical model is defined by the equations (1)-(17). The camera moves in 3D space ( x, y and z directions). The camera carrier has the starting point p0start=[0.7 1.0 -0.1] (m), and the end point p0end=[1.3 1.6 -0.8] (m) (see Figure 4a)). The camera motion velocity has a trapezoid form and p0max=0.417 (m/s) as shown in Figure 4b).

All three motor’s angular positions θ1, θ2 and θ3, are involved in the coordinated task generation. This clearly represents a proof that all of these motions are mutually coupled. The system responses, for first and second Examples are shown in Fig. 5 and 6, respectively. These results are comparable and therefore are shown in Table 1. Each example has six pictures related to the: a) camera carrier position at the reference and the real frames, b) motor shaft position at the reference and the real frames, c) motors forces, forces in the ropes at the reference and the real frames, d) deviation between the real and the reference trajectory of the camera carrier, e) deviation between the real and the reference trajectory of the motor shaft positions, f) control signals at the reference and the real frames.

Figure 4: The reference trajectory motion of a) position x0, y0, z0 b) velocity p0max=0.417 (m/s) of camera carrier Table 1: Comparison of two selected Examples Example

Figure

p0max (m/s) 0.417

winch radius Ri(m)

motors reach saturation

R1 = R2 = R3=0.15 (m)

R1 = 0.075 (m), R2 = 0.04 (m), R3=0.06 (m)

yes, all 3 motors

A. Example 1 The first Example is analyzing the CPR-A system which parameters are presented in the Nomenclature Section. This system is working under the ideal conditions. See Figure 5. B. Example 2 The second Example shows the response of the CPR-A system, which differs in the radius of all three motorized pulleys in comparison to the Ex196

ample 1. Other system parameters are the same as in Example 1. For the chosen smaller pulleys radii the motors speed must be higher to achieve the desired trajectory of the camera carrier which is predefined to be the same like in the Example 1. See Figure 6. The CPR-A system being developed in the Mihajlo Pupin Institute, which observes space, is a part of a more complex system. Journal of Applied Engineering Science 11(2013)4, 264

Dr Mirjana FilipoviÄ&#x2021; - The methodology for developing the kinematic model of selected CPR-a system as a necessity for the development of a dynamic model

Figure 5: Example 1

Figure 6: Example 2

CONCLUSION The mathematical model of the CPR-A system is defined in the first phase of the study in this paper. It shows the importance of generating the Jacobian matrix that defines the kinematic model of the CPR-A system. The relation between the camera carrier motion and the motors angular positions has been established. This novel proJournal of Applied Engineering Science 11(2013)4, 264

cedure is named KinCPR-Solver which means Kinematic Cable Parallel Robot Solver. The Jacobian matrix plays an important role in developing the CPR-A dynamic model. The Lagrangeâ&#x20AC;&#x2122;s principle of virtual work has been used for solving the complex relation between the resultant motor load moment (acting as a load at the first, second and third motor shaft) and camera carrier forces (acting at the camera carrier). 197

Dr Mirjana Filipović - The methodology for developing the kinematic model of selected CPR-a system as a necessity for the development of a dynamic model

This relation is used for generating the dynamic model of this system. A very important feature of the coupling between the motion of the camera carrier in the space of the Cartesian coordinates and the motion of motors is discovered. The results show how significant it is to know the properties of the coupling and its effects on the accuracy of the camera carrier motion. The selected characteristics of the motors are satisfactory in the considered examples. The AIRCAMA software package can be used for the confirmation of the validity of defined mathematical models and for the analysis and selection of all parameters of the CPR-A system also. Two different examples have been presented to show the CPR-A application and validity. For future research it is planned to design and test few control algorithms based on papers [25] and [21]. Also, the influence of disturbance force on motion of the camera carrier is going to be analyzed in future [24].

Voltage: Electromotive force constant: Rotor current: Constant of the moment proportionality: Coefficient of viscous friction: Moment of inertia for the rotor and the gear box: Motor inertia characteristic:

Motor damping characteristic:

Motor geometric characteristic:

NOMENCLATURE DOF - Degree Of Freedom CPR - Cable-suspended Parallel Robot AIRCAMA - software packages AIRCAMA (aerial camera system type A) t(s) - time dt = 0.0001 (s) - sample time Camera carrier coordinate (position of camera carrier in the Cartesian space): Total number of DOF: Vector of motor coordinates:

Mass of the camera carrier: Moment mapping matrix: Length of the recorded field: Width of the recorded field: Height of the recorded field: Initial deviation of the motor angular position: Positional constant for motion control:

Motor shaft angular position after the gear box:

Velocity constant for motion control:

Motor force, resultant force:

ACKNOWLEDGMENT

Acting force on the camera carrier: Camera carrier force, total force at the camera carrier: Resultant motor load moment: Winch radius: Jacobian matrix: Rotor circuit resistance: 198

This research has been supported by the Ministry of Education, Science and Technological Development, Government of the Republic of Serbia Grant TR-35003 through the following two projects: “Ambientally intelligent service robots of anthropomorphic characteristics”, by Mihajlo Pupin Institute, University of Belgrade, Serbia, Grant OI-174001 and “The dynamics of hybrid systems of complex structure”, by Institute SANU Belgrade and Faculty of Mechanical Engineering University of Nis, Serbia, and partially supported by the project SNSF Care-robotics project no. IZ74Z0-137361/1 by Ecole PolytechJournal of Applied Engineering Science 11(2013)4, 264

Dr Mirjana Filipović - The methodology for developing the kinematic model of selected CPR-a system as a necessity for the development of a dynamic model

nique Federale de Lausanne, Switzerland. We are grateful to Prof. Dr. Katica R. (Stevanovic) Hedrih from Mathematical Institute, Belgrade for helpful consultations during the implementation of this paper. REFERENCES 1) Borgstrom, P., H., Borgstrom, N., P., Stealey, M., J., Jordan, B., Sukhatme, G., Batalin, M., A., Kaiser, W., J., (2007) Discrete Trajectory Control Algorithms for NIMS3D, an Autonomous Underconstrained Three-Dimensional Cabled Robot, Proceedings of the 2007 IEEE/ RSJ International Conference on Intelligent Robots and Systems, San Diego, CA, USA. 2) Bruckmann, T., Mikelsons, L., Schramm, D., Hiller, M., (2007) Continuous workspace analysis for parallel cable-driven StewartGough platforms”, Special Issue: Sixth International Congress on Industrial Applied Mathematics (ICIAM07) and GAMM Annual Meeting, Zürich, 7(1). 3) Carricato, M., (2011) Under-constrained cable-driven parallel robots, part of book Quarta giornata di studio Ettore Funaioli - 16 luglio 2010, Asterisco, 443-454. 4) Đurić, A., Saidi, R., Al, ElMaraghy, W., (2012) Dynamics Solution of n-DOF Global Machinery Model, Robotics and Computer Integrated Manufacturing (CIM) Journal, 28(5), 621-630. 5) Đurić, A., M., Saidi, R., Al, ElMaraghy, W., H., (2010) Global Kinematic Model Generation for n-DOF Reconfigurable Machinery Structure, 6th IEEE Conference on Automation Science and Engineering, CASE 2010, Toronto, Canada. 6) Dondur N., Spasojević-Brkić, V., Brkić, A., (2012) Crane cabins with integrated visual systems for detection and interpretation of environment - economic appraisal, Journal of Applied Engineering Science (Istraživanja i projektovanja za privredu), No. 4, Vol. 10, pp. 191-196. 7) Duan, B.,Y., (1998) A new design project of the line feed structure for large spherical radio telescope and its nonlinear dynamic analysis, Mechatronics, 9, 53-64. 8) Fang, S., Franitza, D., Torlo, M., Bekes, F., Hiller, M., (2004) Motion control of a tendonbased parallel manipulator using optimal tension distribution, IEEE/ASME Trans. Mechatron., 9(3), 561-568. Journal of Applied Engineering Science 11(2013)4, 264

9) Filipovic, M., Potkonjak, V., Vukobratovic, M., (2007) Humanoid robotic system with and without elasticity elements walking on an immobile/mobile platform, J. Intell. Robot. Syst. 48, 157-186. 10) Filipovic, M., Vukobratovic, M., (2008) Complement of Source Equation of Elastic Line, Journal of Intelligent & Robotic Systems, International Journal, 52(2), 233-261. 11) Filipovic, M., Vukobratovic, M., (2008) Expansion of source equation of elastic line, Robotica, Cambridge University Press, 1-13. 12) Filipovic, M., (2012) Relation between EulerBernoulli Equation and Contemporary Knowledge in Robotics, Robotica, 1-13. 13) Gosselin, C., Grenier, M., (2011) On the determination of the force distribution in overconstrained cable-driven parallel mechanisms, Meccanica, An International Journal of Theoretical and Applied Mechanics, Springer, 46 (1), 3-15. 14) Gosselin, C., Ren, P., Foucault, S., (2012) Dynamic Trajectory Planning of a Two–DOF Cable-Suspended Parallel Robot, 2012 International Conference on Robotics and Automation RiverCentre, Saint Paul, Minnesota, USA, May 14-18, 2012. 15) Gouttefarde, M., Merlet, J-P., Daney, D., (2006) Determination of the wrench-closure workspace of 6-DOF parallel cable-driven mechanisms, Advances in Robot Kinematics, 5, 315-322. 16) Hedrih, (Stevanovic), K., (2010) Energy analysis in the hybrid system forced regimes, Proceeding of Institute of Mathematics NANU Ukraine, 7(3), 90-107. 17) Hedrih, (Stevanovic), K., (2012) Energy and Nonlinear Dynamics of Hybrid System, Chapter in Book Dynamical Systems and Methods, Edited by Albert Luo, Springer, 1, 29-83. 18) Higuchi, T., Ming, A., .Jiang-Yu, J., (1988) Application of multi-dimensional wire crane in construction, In 5th Int. Symp. on Robotics in Construction, Tokyo, June, 6-8, 661–668. 19) Hiller, M., Fang, S., Q., (2005) Design, analysis and realization of tendon-base parallel manipulators, Mech. Mach. Theory, 40, 429-445. 20) Kozak, K., Zhou Q., J., Wang, J., (2006) Static Analysis of Cable-Driven Manipulators With Non-Negligible Cable Mass, IEEE Transaction on Robotics, 22(2), 425-433. 199

Dr Mirjana Filipović - The methodology for developing the kinematic model of selected CPR-a system as a necessity for the development of a dynamic model

21) Lazarevska, M., Trombeva-Gavrilovska, A., Knežević, M., Samardžioska, T., Cvetkovska, M. (2012) Neural network prognostic model for rc beams strenghtened with CFRP strips, Journal of Applied Engineering Science (Istraživanja i projektovanja za privredu), No. 1, Vol. 10, pp. 27-30. 22) Merlet, J., P., (2010) MARIONET, A Family of Modular Wire-Driven Parallel Robots, Advances in Robot Kinematics: Motion in Man and Machine, 1, 53-61. 23) Miermeister, P., Pott, A., Verl, A., (2012) AutoCalibration Method for Overconstrained Cable-Driven Parallel Robots, ROBOTIK 2012 - 7th German Conference on Robotics, Munich, Germany. 24) Mijailović, R., (2012) Methodology for estimating the dependence between force and deplacement – a vehicle crash case, Journal of Applied Engineering Science (Istraživanja i projektovanja za privredu), No. 1, Vol. 10, pp. 1-8. 25) Nunes, I., (2012) Fuzzy systems to support industrial engineering management, Journal of Applied Engineering Science (Istraživanja i projektovanja za privredu), No. 3, Vol. 10, pp. 143-146. 26) Oh, S-R., Agrawal, S., K., A., (2005) Reference Governor-Based Controller for a Cable Robot Under Input Constraints, IEEE Transaction on Control Systems Technology, 13(4), 639-645. 27) Pott, A., (2008) Forward Kinematics and Workspace Determination of a Wire Robot for Industrial Applications, Advances in Robot Kinematics: Analysis and Design, 7, 451-458. 28) Raskovic, D., (1965) Theory of oscillations, Scientific book, Belgrade, Serbia.

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29) Rega, G., (2004) Nonlinear vibrations of suspended cables-Part I: modeling and analysis, ASME, APPL MECH REV, 57(6), 443-478. 30) Rega, G., (2004) Nonlinear vibrations of suspended cables-Part II: deterministic phenomena, ASME, APPL MECH REV, 57(6), 479-514. 31) Shiang, W-J., Cannon, D., Gorman, J., (2000) Optimal Force Distribution Applied to a Robotic Crane with Flexible Cables, Proceedings of the 2000 IEEE International Conference on Robotics & Automation, San Francisco, Ca, April 2000, 1948-1954. 32) Su, X., Y., Duan, B., Y., (2000) The Application of the Stewart Platform in Large Spherical Radio Telescopes, Journal of Robotic Systems by John Wiley & Sons, 17(7), 375-383. 33) Su, X., Y., Duan, B., Y., (2000) The mathematical design and kinematics accuracy analysis of a fine tuning stable platform for the large spherical radio telescope, Mechatronics, 10, 819-834. 34) Yao, R., Tang, X., Wang, J., Huang, P., (2010) Dimensional Optimization Design of the Four-Cable Driven Parallel Manipulator in FAST, IEEE/ASME Transaction on Mechatronics, 15(6) 932-941. 35) Zi, B., Duan, B., Y., Du, J., L., Bao H., (2008) Dynamic modeling and active control of a cable-suspended parallel robot, Mechatronics, 18, 1-12. Paper sent to revision: 16.10.2013. Paper ready for publication: 11.12.2013.

Journal of Applied Engineering Science 11(2013)4, 264

Original Scientific Paper

doi:10.5937/jaes11-4604

Paper number: 11(2013)4, 265, 201 - 208

OPTIMIZATION IN DAY-AHEAD PLANNING OF ENERGY TRADING Minja Marinović* Faculty of Organizational Sciences, Belgrade, Serbia Dragana Makajić - Nikolić Faculty of Organizational Sciences, Belgrade, Serbia Milan Stanojević Faculty of Organizational Sciences, Belgrade, Serbia In the twentieth century electricity was produced and transmitted by and between monopolistic public electric power companies. Over the last twenty years, electricity markets have been deregulated allowing customers to choose from a number of competing suppliers and producers. On one hand electricity market participants try to first satisfy their own country’s demand and, on the other hand, to transmit electricity across borders into neighborhood markets. Cross-border transmission is part of a competition where market participants have non-discriminatory access to interconnected transmission lines. This paper examines the problem of day-ahead planning at trading sections of electricity companies. The underlying assumption is that the demand and supply are known in advance. Available transmission capacities are also known as well as additional transmission capacities that can be purchased. The prices and amounts of trading and transmission are subjects of auctions. The problem of day-ahead planning is here disscussed from the perspective of a decision maker of an energy trading company (ETC). Decisions to be made are: where and how much electricity should the ETC buy and sell, and which transmission capacity will be used in order to maximize daily profit. The problem is formulated according to real- life experience of a Serbian ETC which trades in Central and South-East Europe. It is further modeled as a directed multiple-source and multiple-sink network and then represented by linear programming (LP) mathematical model in which the total daily profit is maximized subject to market constraints and flow capacities. The main goal of this model is to provide a useful tool for preparing auction bids. Numerical examples are given in order to illustrate possible applications of the model. Key words: Energy trading, Day-ahead planning, Network flow, LP model INTRODUCTION Single European electricity market provides seamless competition within the electricity supply chain. Energy trading companies (ETCs) buy transmission capacities from transmission system operators (TSOs) [05]. TSOs consistently release actual maximum amounts of a crossborder transmission capacity to the market. ETCs operate in the middle stage of an energy supply chain [20], and, by buying and selling electricity contracts, they try to manage the risk associated with fluctuating prices. Both traders and end-users are prone to apply different financial instruments such as futures contracts, options, and derivatives to protect themselves against price speculations and fluctuations.

There are few ways of producing electricity: nuclear [04], thermo, hydro, solar, wind [03, 10], as well as several ways of trading electricity but the two most common ones are either by the telephone in bilateral transactions (so called “Over The Counter” or OTC, usually through the intermediation of a broker), or through futures markets such as Nordpool or EEX [02]. Some of the key factors to influence energy prices include geopolitical factors, global economic growth, short term weather condition with possible impact on demand, supply disruptions from maintenance or unexpected outages, fuel price fluctuations, and product swapping in response to relative prices [07].

* Faculty of organizational sciences, Jove Ilića 154, 11000 Belgrade, Serbia; marinovic.minja@fon.bg.ac.rs

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Minja MarinoviÄ&#x2021; - Optimization in day-ahead planning of energy trading

The literature on different aspects of energy trading and transmission is extensive. Kristiansen [11] analyses the auction mechanisms at the crossborder annual, monthly or daily transmission capacity auctions in the area of energy trading between Denmark and Germany. Detailed analysis of the perspective for South-East Europe to become a regional wholesale electricity market or electricity exchange zone is given in [12]. Oggioni and Smeers [17] analyse the impact of emission allowance prices on electricity prices and test two different average cost pricing policies, regional and zonal with different effects on electricity markets of Central and Western Europe. Triki et al. [21] consider multiple interrelated electricity markets, and they propose a multi-stage mixed-integer stochastic model for a capacity allocation strategy in a multi-auction competitive market. Quelhas et al. [19] propose a generalized network flow model of the national integrated energy system which incorporates production, transportation of coal, natural gas, and electricity storage with respect to the entire electric energy sector of the U.S. economy. The authors have formulated a multi period generalized flow problem in which the total cost is minimized subject to energy balance constraints. The problem of energy allocation between spot markets and bilateral contracts is formulated as a general portfolio optimization quadratic programming problem by Liu and Wu [13]. Purchala et al. [18] propose a zonal network model, aggregating individual nodes within each zone into virtual equivalent nodes, and all cross-border lines into equivalent border links. Using flow-based modeling, the feasibility of the least granularity zonal model where the price zones are defined by the political borders is analyzed. Hsieh and Chen [08] consider network systems with multiple-source multiple-sink flow such as electrical and power systems. They examine the problem in which resources are transmitted from resource-supplying nodes to resource-demanding nodes through unreliable flow networks. Nowak et al. [16] analysed the simultaneous optimization of power production and day-ahead power trading and formulated it as a stochastic integer programming model. In this paper we proposed an LP mathematical model of total daily profit maximization subject to arranged demand and supply and additional MW and transmission capacity constraints. [15] We present the problem by a directed multiplesource and multiple-sink network and model using linear programming. Since the right to buy and 202

sell energy and utilize transmission capacity is acquired in auction, the proposed model can be also used as a tool to help decision makers to create bids for auctions. We illustrate this approach with an example of a Serbian ETC trading. The paper is structured as follows. Section 2 is dedicated to a description of the main assumptions of the observed problem; Section 3 presents an LP model for day-ahead planning; in Section 4 we report and discuss numerical results to illustrate two different ways of modelâ&#x20AC;&#x2122;s application. First, we present the solution of an LP model with fixed parameters, and then we investigate the impact of prices on trading capacities and amounts in order to create bids for auctions. Conclusions along with perspectives regarding further study are given in Section 5. PROBLEM DESCRIPTION The focus of this paper is on electricity trading from the perspective of an ETC. The main task of a trading section of an ETC is to meet each and every customer requirements regardless of the circumstances. The trading section also enables the ETC to respond to the ever-changing state of the regional transmission grid and production capacities. Besides, this section deals with spot and long term arrangements, creating schedules, cross-border capacity allocations, optimization of the whole portfolio, managing different energy sources, customers in different countries and cross- border energy flows and costs. The efficiency of a trading section of an ETC can be improved by considering at least two optimization problems: long term and short term (dayahead) planning. Long term planning includes assessment of electricity market e.g. buyers and suppliers interested in cooperation, and transmission capacity to be purchased for the next period. Day-ahead planning refers to finding an optimal plan for selling and buying electricity, which will maximize the daily profit considering the available transmission capacities. Day-ahead planning starts from an established network of potential buyers and suppliers and purchased transmission capacities based on long term decisions. The example of a simplified electricity network where all buyers and suppliers from one country are represented by one node is shown in Figure 1. This network will be used in the later numerical example.

Journal of Applied Engineering Science 11(2013)4, 265

Minja Marinović - Optimization in day-ahead planning of energy trading

Figure 1: Simplified Central and South-East Europe electricity market

Daily demand and daily supply of each country (node) are known. Data about energy efficiency [09] and loses caused by transmission are already included in quantities of ordered and offered electricity. Electricity trade is carried out during the whole day. At all times decisions are made based on the information collected earlier that day. As the information about demand or supply arrives, new decisions are made. Some electricity trades are already arranged and they must be fulfilled. All the electricity bought during one day has to be sold the same day. Therefore, if there is a surplus or shortage of arranged supply, it will be traded through the futures markets. The futures markets such as EEX and EXAA [23] are the places where an ETC can buy or sell the electricity at less favorable prices. The amounts of surpluses and shortages are diferent for every day. If an ETC wants to puchase transmission capacities to be at their disposal for a longer period, it is necessary to announce the amount that will be used. This amount is calculated based on assumptions and represents only an approximation of the real-time situation forecasted on the previous day [12]. Only the amounts announced one day before the day-ahead planning are considered available. The transmission capacity which is not announced is subject to a “use it or lose it” principle and will be reoffered at the daily auction [11]. If daily trading exceeds the amount of announced capacity, it is possible to buy additional daily transmission capacities at the auction price.

Journal of Applied Engineering Science 11(2013)4, 265

Each trade is initiated at an auction. Auction items are: • Amounts of electricity that will be bought or sold, and the prices; • Transmission capacity prices for the capacities that will be used in addition of those previously purchased and announced The Serbian ETC in question trades on the electricity market where a uniform price auction type is used. This assumes that each bidder bids a price and amount. The price bid refers to a maximum price they are willing to pay per item, and the amount refers to the number of units they wish to purchase at that price. Typically these bids are sealed - not disclosed to the other buyers until the auction closes. The auctioneer then serves the highest bidder first, giving them the number of units requested, then the second highest bidder and so forth until the supply of the commodity is exhausted. All bidders then pay the unit price equal to the lowest winning bid (the lowest bid out of the buyers who actually received one or more units of the commodity) regardless of their actual bid [22]. In practice, bidders make several bids with different amounts and prices in order to make sure they will buy needed amounts, and at the lowest possible prices. The goal of this paper is to create a useful tool which will help a decision maker in a trading section of an ETC to simulate market and network situations for different amounts and prices of electricity and transmission capacities. Optimization results should provide a decision maker with the information how to make bids at auctions in order to maximize the ETC total profit. MODEL FORMULATION The described problem can be modeled as a directed multiple-source and multiple-sink network [01]. The notation used to define sets, parameters, and decision variables is as follows. • Sets ○ N – set of all nodes; ○ S – set of all nodes representing sellers, ; ○ B – set of all nodes representing buyers, ; ○ A – set of arcs representing transmission capacity between nodes, ;

203

Minja Marinović - Optimization in day-ahead planning of energy trading

•

Parameters ○ suj – upper bound of electricity that can be bought from supplier j, ; ○ slj – lower bound (arranged buying) of electricity that can be bought from supplier j, ; ○ bui – upper bound of electricity that can be sold to buyer i, ; ○ bli – lower bound (arranged sale) of electricity that can be sold to buyer i, ; ○ fij – announced daily transmission capacity of arc (i,j) ; ○ huij – maximal additional daily transmission capacity which is possible to be bought on arc (i,j) ; ○ cj – purchasing price for supplier j, ; ○ di – selling price for buyer i, ;

○ aij – price for additional transmission capacities on arc (i,j) ; ○ tij –taxes for additional transmission capacities on arc (i,j) . • Variables: ○ xj – amount of electricity that should be bought from supplier ; ○ yi – amount of electricity that should be sold to buyer ; ○ hij – amount of additional transmission capacities on arc (i,j) . All electricity amounts and transmission capacities are expressed in MWh. Unit for all prices and taxes is Euro per MWh. Using given notation the LP mathematical model for day-ahead planning can be stated. (MMDAP) (1)

(2)

(3)

(4) (5) (6) Objective function (1) represents the difference between total income and costs of buying electricity and additional transmission capacities. Constraint (2) provides that quantities of electricity that is bought and sold in one day are equal. Since all nodes are transition nodes, a flow conservation constraint (3) must hold. This constraint has four different interpretations depending on a node type. N (S B) is a set of nodes without demand and supply. For each node from N (S B) constraints (3) ensure that the amount of electricity entering the node must be equal to the amount of electricity leaving the node. S B is a set of source nodes in which the amount of electricity entering a node and electricity bought in this node must be equal to the amount of electricity leaving the node while B S is a set of sink nodes in which the amount of electricity entering a node must equal the amount of electricity 204

leaving the node and electricity sold in this node. B S is a set of source-sink nodes. For each node from B S constraints (3) ensure that the amount of electricity entering the node and electricity bought in this node must equal the amount of electricity leaving that node and electricity sold in that node. Optimal amounts of electricity that should be bought and sold lie between their upper and lower boundaries given by constraints (4) and (5). Constraint (6) refers to the maximal additional daily transmission capacity which can be bought on an arc. NUMERICAL EXAMPLES In order to assess the proposed model we consider two different ways of its application. The first one consists of obtaining an optimal dayahead plan where all parameters have fixed valJournal of Applied Engineering Science 11(2013)4, 265

Minja Marinović - Optimization in day-ahead planning of energy trading

ues. The second application is based on a more realistic situation where some parameters may vary within certain boundaries. Such approach can help the ETC decision maker to create bids for an auction. Both applications are shown on a CSEE network consisting of 18 nodes and 62 arcs (Figure 2).

Figure 2: Graph representation of CSEE electricity market

Each country is presented by a node which is characterized by its lower and upper bounds of electricity that can be bought and/or sold in/from that country as well as purchasing and selling prices. All arcs (in Figure 2, both, solid and dashed lines) represent cross-border connections where it is possible to buy additional transmission capacity. Arcs represented by solid lines indicate the existence of announced transmission capacities purchased earlier, while arcs represented by dashed lines represent the unannounced transmission capacities which can be purchased on the daily base. Amounts of announced and maximal additional daily transmission capacities (Table 1) as well as prices and taxes of each arc are also given. Due to confidentiality issues, in this paper we present a slightly modified data which are within the boundaries of common real-life situations. The model has been implemented and solved using GNU Linear Programming Kit software intended for solving linear programming (LP), mixed integer programming (MIP), and other related problems [06]. The optimal solution for one scenario is given in Table 2. Marks “/” mean that there were no suppliers or buyers in the corresponding country.

Table 1: Upper bounds for additional transmission capacities BEL

GER

AUS

SLO

ITA

GRE

CZE

BEL

200

GER

500 360

AUS SLO

ITA

250

HUN CRO

150

CRO

BiH

MNE

POL

SLK

SER

FRM

280

610

UKR

ROM

BUL

200 50

300 180

ALB

430

100

GRE CZE

280

HUN

240

410

200

320

110 300

100

500 200

BiH

210

340

300

320

MNE

140 350 50

120

POL

420

SLK

250 500

SER ALB

FRM

250

200

300

400

100

200

200 460

250

390

UKR

230

ROM BUL

85 300

455

Journal of Applied Engineering Science 11(2013)4, 265

170 49

155 145

450

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Minja Marinović - Optimization in day-ahead planning of energy trading

Table 2: Optimal solution Buying in MWh

Selling in MWh

node

min

Optimal

max

min

Optimal

max

BEL

GER

AUS

SLO

ITA

GRE

CZE

HUN

CRO

BiH

MNE

SLK

SER

ALB

FRM

ROM

BUL

UKR

In addition to optimal trading amounts, the solution determines additional transmission capacities that should be purchased. In this scenario we obtained: 45 MWh on arc BEL-CZE, 5 MWh on arc SLO-ITA, 41 MWh on arc GRE-BUL, etc. Total daily trade is 396 MWh. The total daily income is 34068 €. The cost for buying electricity is 26803 €, while the cost for additional transmission capacities is 3078 €. The total profit based on this optimal solution is 4187 €. In order to obtain this total profit certain corrections of objective function has to be made: - Taxes for announced transmission capacities and costs of long term purchased transmission capacities evaluated on a daily basis should be subtracted; - Unit prices for previously arranged buying and selling (blj and slj) can differ from actual prices. These differences should be taken into account Nevertheless these corrections do not influence the optimality of the obtained solution. In further analysis we will use term “profit” for the value of goal function, although it is just an approximation. The possibility of buying and selling electricity on futures markets, as well as the possibility of 206

buying additional transmission capacities, will provide the feasibility of all solutions. Since we enabled surpluses and shortages the model will always provide an optimal solution. Based on experiments done so far we noticed that the solution may not always be unique, but that there might be more than one; which one will be chosen depends entirely on the decision maker. To demonstrate the second way of using MMDAP we have simulated a situation where a decision maker creates bids at an auction for buying electricity from one supplier. In the presented example we observed a supplier in node CZE which offers the amount of 85 MWh. We analysed the influence of the purchasing price changes on the optimal amount of electricity that should be bought and an optimal solution as a whole. Based on the experience we have supposed that the electricity price for the supplier in node CZE can vary from 75 to 93 €/MWh. A series of optimizations was made for all integer values of prices in the given interval. Table 3 shows the optimal amounts of electricity that should be bought and the corresponding profits for some characteristic prices of electricity, assuming that all other parameters remain the same. Journal of Applied Engineering Science 11(2013)4, 265

Minja Marinović - Optimization in day-ahead planning of energy trading

Table 3: The impact of prices on optimal amount and profit Price

Optimal amounts

Profit

4442

.. .

4272

4187

4126

.. .

3946

3931

The decrease of optimal amount of electricity and profit was expected because the purchasing price increased, but all the solutions were optimal if the corresponding price became the lowest winning bid. In other words, for different prices established by auction competition, different amounts of electricity that should be bought (and corresponding profits) are optimal. Table 4: List of bids derived from optimal solutions Accumulated Guaranteed amount profit

Bids

Amounts of el.

Price

79-91

4187

75-77

4442-4272

4126-3946

On the basis of presented optimal solutions we can suggest the ETC decision maker to make bids shown in the first three columns in Table 4. Depending on the price equal to the lowest winning bid (which will not be known till the end of the auction), the ETC will buy 0, 15, 61 or 85 MWh from node CZE. For prices that are presented as intervals in Table 3, the ETC decision maker can give any price from that interval for which they estimate that it can win. In any case the corresponding amount will be optimal. The profits given in the right column represent the optimal profit if the corresponding bid becomes the lowest winning bid. If any lower bid wins, the profit becomes larger.

Journal of Applied Engineering Science 11(2013)4, 265

CONCLUSIONS This paper considers the optimization problems which appear in a trading section of energy trading companies, and one of them, day-ahead energy planning, was formulated as a linear programming problem. Day-ahead energy planning implies finding the optimal amounts of electricity that should be bought from each supplier and sold to each buyer and the optimal routes which can satisfy the daily demands using the purchased and additional energy transmission capacities. We have formulated LP mathematical model in order to optimize day-ahead energy plan. In adition, the proposed model can be used by an ETC decision maker as a tool for determining optimal bids in auctions for buying or selling electricity as well as for trading transmission capacities. Two hypothetical numerical examples that demonstrate the use of the model were presented in this paper. Since the developed model is linear, it can be used to solve real-life problems of large dimensions. We suggest that trading through futures markets be taken into consideration as a topic of further research. Another interesting and useful topic for future study may be the modeling of a long-term planning strategy of energy trading companies. ACKNOWLEDGMENTS This research was partially supported by the Ministry of Education and Science, Republic of Serbia, Projects numbers TR32013 and TR35045. REFERENCES 1) Bazaraa, M. S., Jarvis, J. J., Sherali, H. D., (2010) Linear Programming and Network Flows, 4th ed, John Wiley & Sons, New Jersey 2) Daskalakis, G, Markellos, R. N., (2009) Are electricity risk premia affected by emission allowance prices? Evidence from the EEX, Nord Pool and Powernext. Energy Policy, 37(7), 2594–2604. 3) Fric, N., Gligić, B., Dobrić, J., Marković, Z., (2012) Wind towers - design of friction connections for asembling sections of tubular steel towers, Journal of Applied Engineering Science, (10)1, 49-52 4) Greenberg, M., (2009) Energy sources, public policy, and public preferences: Analysis of 207

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US national and site-specific data, Energy Policy, 37(8), 3242-3249 5) http://www.efet.org/Position_Papers/Electricity_Market,_Position_Papers,_European_Level_ 5492.aspx?urlID2r=72 . Accessed 15 December 2012 6) http://www.gnu.org/s/glpk/ . Accessed 17 January 2013 7) http://www.harcourt.ch/cms/hauptseite/zeigeBereich/11/gibDatei/1088/26-energypowertrading.pdf. Accessed 14 December 2012 8) Hsieh, C. C, Chen, Y. T., (2005) Resource allocation decisions under various demands and cost requirements in an unreliable flow network, Computers and Operations Research, 32(11), 2771–2784 9) Jovanović, B., Božanić, V., Jovanović, B. (2013) Education in the field of energy efficiency in serbia-survey results and analysis”, Journal of Applied Engineering Science, (11)1, 15-22 10) Komarov, D., Stupar, S., Posteljnik, Z., (2011) Review of the current wind energy technologies and global market, Journal of Applied Engineering Science 9(4), 437-448 11) Kristiansen, T., (2007a) An assessment of the Danish–German cross-border auctions, Energy Policy, 35(6), 3369–3382 12) Kristiansen, T., (2007b) Cross-border transmission capacity allocation mechanisms in South East Europe, Energ Policy, 35(9), 4611–4622 13) Liu, M., Wu, F. F., (2007) Portfolio optimization in electricity markets, Electric Power Systems Research, 77(8), 1000–1009 14) Marchenko, O., (2007) Mathematical modelling of electricity market with renewable energy sources, Renewable Energy, 32(6), 976-990 15) Marinović, M., Stanojević, M., MakajićNikolić, D., (2011) LP Model for Day-ahead Planning in Energy Trading. 11th International Symposium on Operations Research - SOR’11, 75-80

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16) Nowak, M. P., Schultz, R. D., Westphalenm M. A., (2005) Stochastic Integer Programming Model for Incorporating Day-Ahead Trading of Electricity into Hydro-Thermal Unit Commitment, Optimization and Engineering, 6(2), 163–176 17) Oggioni, G., Smeers, Y., (2009) Evaluating the impact of average cost based contracts on the industrial sector in the European emission trading scheme, Central European Journal of Operations Research, 17(2), 181-217 18) Purchala, K., Haesen, E., Meeus, L., Belmans, R., (2005) Zonal network model of European interconnected electricity network, CIGRE/IEEE PES, International Symposium New Orleans, 362 - 369 19) Quelhas, A., Gil, E., McCalley, J. D., Ryan, S. M., (2007) A Multiperiod Generalized Network Flow Model of the U.S. Integrated Energy System: Part I—Model Description, Power Systems, IEEE Transactions, 22(2), 829 – 836 20) Thery, R., Zarate, P., (2009) Energy planning: a multi-level and multicriteria decision making structure proposal, Central European Journal of Operations Research, 17(3), 265-274 21) Triki, C., Beraldi, P., Gross, G., (2005) Optimal capacity allocation in multi-auction electricity markets under uncertainty, Computers and Operations Research, 32(2), 201–217 22) Vijay, K., (2002) Auction theory, Academic Press, San Diego 23) Zachmann, G., (2008) Electricity wholesale market prices in Europe: Convergence?, Energy Economics, 30(4), 1659–1671 Paper sent to revision: 10.10.2013. Paper ready for publication: 11.12.2013.

Journal of Applied Engineering Science 11(2013)4, 265

Professional Paper

doi:10.5937/jaes11-4514

Paper number: 11(2013)4, 266, 209 - 215

THE ADVANTAGES OF INTELIGENT APPROACH TO MACHINING PRESENTED THROUGH PROCESSING TECHNOLOGY DESIGN DEVELOPED BY I-MACHINING Goran Duduković* Solfins DOO, Belgrade, Serbia Milutin Ogrizović Technical school, Stara Pazova, Serbia The modern day efficient machining requires a new approach to designing machining technology, which enables the complete engagement of all technological machining parameters, like cutting speed and cutting feed depending on the work piece material, characteristics of the machine and tools and volume of the material removed from the machined zone. Controlling physical quantities, which appear in the process of cutting, enables us to achieve faster machining processes when compared to current high speed machining technologies (HSM) and at the same it increases productivity. This approach to machining requires the CAM software intelligence to make decisions in real time and optimize tool path, in order to keeping the constant cutting tool force during whole machining process. This type of approach was used while designing machining for “heat exchanger”with the help of imachiningtechnology within SolidCAMsoftware for programing of CNC machines.Where by reduced the machining time for 36% in accordance to conventional machining and made a total savings of 45.33%. Key words: Side step, Constant cutting force, Efficient machining, I-machining technology INTRODUCTION Imachining technology represents an implemented set of experiences and data in SolidCAM software for designing of machining technology, on which the basic algorithm for creating of optimum tool path is based, Figure 1.

Based on the integrated information about tool, workpiece material and geometry and machine capability, imachining technology automatically synchronizes the cutting speed, cutting feed, cutting depth, milling width, chip thickness and chip shape while creating the executiveg codefile for programing of CNC machine. Synchronizing the cutting conditions is present during the total tool path depending of the tool involvement degree, i.e.Side step value, Figure 2.

Figure 2: Example of tool engagement degree through active Side step

Figure 1: Interactive parameter strategy of imachining technology * Solfins DOO, Lazarevačka 1, 11040 Belgrade, Serbia; goran.dudukovic@solfins.com

In this way we can create perfectly smooth and tangential tool path, which avoid the overuse of the tool and eliminate air cutting, implicating productivity increase and tool wear reduction, Figure 3. 209

Goran DudukoviÄ&#x2021; - The advantages of inteligent approach to machining presented through processingt technology design developed by I-machining

Figure 4: Comparable display of tool path HSM and imachining technology

Figure 3: Example of the classic tool path (left) and imachining tool path (right)

DESIGNING MACHINING WITH IMACHINING TECHNOLOGY Imachining technology advantages The research of current designing machining methodology has shown that there is an incomplete and inadequate control of tool path leading to tool overuse and a large number of air cutting in most cases. That is the reason for the development of advanced generation of designing machining for fast material removal with built â&#x20AC;&#x201C;in intelligence, the so called imachining technology which enables the completely automatic tool path control and cuttingconditions based on the machining parameters. The user does not have to have a wide technological knowledge, because it has already been integrated in the technological base it self. It is just necessary to choose the machine andappropriate tool based on workpiece material. Namely, the integrated

algorithm is capable of making decisions in real time during machining and providing multi-criteria optimization: Geometric tool path optimization Comparable display of tool path for end milling cutter Ă&#x2DC;10[mm] obtained by HSM technology on the left, andimachining technology on the right clearly shows the elimination of air cutting and tool overuse, the tool path obtained through imachining technology is clearly visible and adapted to part geometry with changeable Side step, i.e. milling width, Figure 4. The cutting depth is increased from 0.313 [mm] to 3.14 [mm]. Machining time in the first case took 3:31 [min], whileimachining technology reduced the machining time to 2:35 [min], by 28%. Cutting condition optimization Software automatically calculates the values of cutting speed and cutting feed for the projectedtool path, because their values oscillate in every tool path point depending on the Side step. These calculations are necessary for achievement of constant value of cutting force, Figure 5.

Figure 5: Executive G code file and several points on the tool path with different cutting feed

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Goran DudukoviÄ&#x2021; - The advantages of inteligent approach to machining presented through processingt technology design developed by I-machining

Imachining technology disadvantages In order forimachining technology to work properly, we have to input empirical data in the technological base kept in two tables connected with appropriate relations based on which the algorithm optimizes the tool path. It is necessary to

define machine characteristics, like the power of engine drive, efficiency, the max spindle speed and max Side step. The current data on material require only the value of Ultimate tensile material strength Rm[MPa], Figure 6.

Figure 6: Technological base of selected machine and materials

Current algorithm does not take into consideration other machinability parameters, but the user could manually modify other values as necessary in technological material base. The earlier versions used as basic machining parameter the value of unit power necessary to remove 1cm3 material. Because of the complexity of calculating the value of this parameter, todayâ&#x20AC;&#x2122;s program package version was upgraded and requires the

input of Ultimate tensile material strength which is easily found on the material properties site: www.matweb.com. PROPERTIES OF MACHINE, TOOLS AND WORKPIECE MATERIAL The example material we used was titanium alloy Ti6AI4V, with the following properties, Table 1.

Table 1: Mechanical properties of titanium alloy Ti6AI4V MECHANICAL PROPERTIES Arcam Ti6AI4V

Ti6AI4V, Required**

Yield Strength (Rp 0.2)

950 MPa

758 MPa

860 MPa

Ultimate Tensile Strength (Rm)

1020 MPa

860 MPa

930 MPa

Elongation

14%

>8%

>10%

Reduction of Area

40%

>14%

>25%

Fatigue Strength* @ 600 MPa

>10,000,00 cycles

Rockwell Hardness

33 HRC

Modulus of Elasticity

120 GPa

Due to extreme toughness and Ultimate tensile material strength this alloy represents one of the most difficult machining materials. These alloy properties: high strength, corrosion resistance and low specific mass 4430 [kg/m3], have Journal of Applied Engineering Science 11(2013)4, 266

influenced its application in special branches of industry: military, medicine and air, despite its cost. One of the examples is the heat exchanger (Product ID: 681200.12) for which designed machining technology was created. 211

Goran Duduković - The advantages of inteligent approach to machining presented through processingt technology design developed by I-machining

The said heat exchanger has, among other uses, application in military industry, Figure 7. During machining we used End Mill tool manufactured by SECO Tools JABRO SOLID series of universal tool. We used tool diameter Ø10 [mm], number of flutes 4, Ø6 [mm], number of flutes 4, Figure 8. Figure 7: Heat exchanger –681200.12

Figure 8: Geometric parameters of End Mill tool used – SECO-JABRO SOLID

For the machining of this particular example of heat exchanger we used milling machine Mazak FH4800, with the following properties, Table 2: Table 2: Basic data of Milling machine – Mazak FH480 Max spindle speed [rpm]

25 000

Max cutting feed [mm/min]

15 000

Power [kW]

Effeciency [%]

90 Figure 9: Selected machine, workpiece material

PREPARATION OF EXECUTIVE GCODE FILE FOR PROGRAMING OF CNC MACHINES Besides enhancing productivity in machining, imachining technology simplifies the process of defining technological operations and reduces the number of tools required for the production of parts because it enables machining with lower tool diameter. This leads to shorter preparation period for executive g code file for programing of CNC machines. The user is required to choose the machine which would be used in the machining process and workpiecematerial from technological imachining base and the most suitable Tool for the part in specific, Figure 9. 212

Software with the use of suitable automatisms scans and compares the volume of the target part and the stock part, and defines the optimum tool path. When calculating the tool path and cuttingconditions, algorithm takes into consideration the properties of machine and workpiecematerial, as well as all tool parameters. Based on the machine limitation andcapability, tool diameter and number of tool cutting edges the cutting speed and cutting feed are being calculated for a given workpiecematerial, Figure 10.

Journal of Applied Engineering Science 11(2013)4, 266

Goran DudukoviÄ&#x2021; - The advantages of inteligent approach to machining presented through processingt technology design developed by I-machining

Figure 10: Optimum calculated cutting speed and cutting feed

Software automatically calculate the maximum cutting depth based on the length of the tool cutting edge and workpiece geometry, which is later adjusted to final product geometry, by machining, first, the deepest zones, and then tool is lift-

ed higher in accordance with demanded surface roughness(Scallop). This is an inverse process (Step-Up) of geometry scanning procedure considering the previous CAM high speed machining (HSM) processes, Figure 11.

Figure 11: Geometry scanning procedure by imachining technology

The user has the freedom to define machining aggressiveness depending on the clamping conditions and workpiece stability, cooling possibility and tool condition, during which this technology synchronizes all cutting condition in every tool

path point, Figure 12. This enables fast and simple adjustment, as well as fine tuning of the tool path to the current cutting conditions and processing new executive g code files for programing of CNC machines.

Figure 12: Dialog window for selection â&#x20AC;&#x201C; defining machining aggression degree Journal of Applied Engineering Science 11(2013)4, 266

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Goran Duduković - The advantages of inteligent approach to machining presented through processingt technology design developed by I-machining

During this technology testing, we have done machining with several different setups and we have come tofollowing conclusions: Number of the cutting edges:first of all, the cutting tool been used by three with different number of the cutting edges and of the SECOJABRO SOLID series. Apparently, we have used the tool with two, three and four cutting edges. Two cutting edges made good machining but the machining time was too big. Machining with four cutting edges caused high cutting speed, and this is not well demonstrated in the processing of this material because of high temperature in machining zone. We have concluded the three

cutting edges of the tool is the best solution for this case. Number of axial contact points(ACP):We have concluded that the number of contact points of tool spiral and workpiece directly affects the increased vibration occurrence. The integrated algorithm, based on the diameter, number of tool cutting edges and tool helix angle, calculates the number of contact points and warns the user about the possibility of vibrations occurring. This way user could choose a tool of different geometric properties or change cutting depth in order to reduce vibration during machining, Figure 13.

Figure 13: Number of ACP – axial contact points

Machining aggressiveness (machining level): The maximal possible machining level depends of many factor, including: characteristics of the tool and workpiece, capabilities of the machine and the level of clamping and coolant lubricant. For first test we select machining level 4, and this was demonstrated as very well. We have made several tests and conclude that the best machining level for this case is level 8.In this machining level cutting condition was: S = 6468 [rpm] Feedmin = 2877÷4698 [mm/min] Side step = 0.05÷0.1 [mm] TOOL PATH IN IMACHINING TECHNOLOGY Imachining technology is unique in its tool path shape in which are achieved. Integrated algorithm adjusts the tool path to workpiece geometry and create spiral tool path with changeable Side step and separates islands if it is necessary, Figure 14:

214

Figure 14: Example tool movement with spiral tool path, small number of elevation of the tool and island identification

IMACHINING TECHNOLOGY DEVELOPMENT TENDENCIES SolidCAMCompany is working on developing advanced models of this technology for complete automation of machining preparation process, when the user would be able to choose one of three possibilities given to him while creating tool path: Minimum machining cycle time – this option might be used when a certain part is machined with cheaper tool on high performance machine, due to short delivery deadlines, Longest tool working life – users would be able to decide for this option in order to keep the Journal of Applied Engineering Science 11(2013)4, 266

Goran Duduković - The advantages of inteligent approach to machining presented through processingt technology design developed by I-machining

current tool, due to the tool storeroom shortage, up to the date of the delivery of the final part or product, Lowest cost – algorithm would find the right balance between machining time and tool working life by using data fromtechnological base on tool cost and machine working hours. In collaboration with cutting tool manufacturers, ISCAR Company among others, new tool series are being developed with adjusted cutting part tool geometry and increased number cutting tool edges (6-12). These will farther increase productivity and Tool life.

CONCLUSION Imachining technology represents unique and revolutionary machining technology on the market of CAM software; it enables manufacturing cost reduction and increases productivity among materials difficult for machining. Application of SolidCAMimachiningtechnology in machining of the mentioned heat exchanger we have managed to save 36% of machining time, when compared to standard HSM machining, Figure 15.

Figure 15: Comparative tables of achieved results in machining time by applying SolidCAMimachining technology and standard HSM machining

When machining of lighter materials time savings are smaller but not venial. This technology development enables companies dealing with machining services to accept tasks which they were unable to fulfill due inexperience and insufficient knowledge in the material machining area. List of symbols Cutting Speed V [m/min] Spindle Speed S [rpm] Cutting Feed F [mm/min] Side step [mm] Max spindle speed [rpm] Max cutting feed [mm/min] Power – power of the machine motor [kW] Helical Angle – helix angle of the cutting edge of the tool defined by the tool manufacturer [º] ACP – axial contact points of the tool cutting edge and the workpiece which depend of the cutting depth, diameter and number of cutting edges and tool helix angle Efficiency – current condition of the machine [%]

REFERENCE 1) David Pancoast (2013), SolidWorks, Concord, Massachusetts, USA, 2009. 2) Glišović, J., Demić, M., Miloradović, D. (2011): „Review of virtual reality applications for reducing time and cost of vehicle development cycle”, Journal of Applied Engineering Science (Istraživanjaiprojektovanja za privredu), No. 3, Vol. 9, pp. 361-372 3) Ogrizovic M. (2008): Upravljanje CNC masinamaiz ProENGINEER-a Wildfire, Kompjuterbiblioteka, Beograd 4) Ogrizovic M. (2012): Programiranje CNC masina, Kompjuterbiblioteka, Beograd 5) SolidCAM Technical Support, 2013: SolidCAM_2013_FAQ_iMachining,SolidCAM Company 6) Stanisavljev, S., Ćoćkalo, D., Đorđević, D., Minovski, R. (2013): „The production cycle time in serial production: reduction of the duration in metal processing industry case“, Journal of Applied Engineering Science (Ist raživanjaiprojektovanjazaprivredu), No. 3, Vol. 11, pp. 116-122 Paper sent to revision: 21.09.2013. Paper ready for publication: 11.12.2013.

Journal of Applied Engineering Science 11(2013)4, 266

215

Journal of Applied Engineering Science 11(2013)4

Original Scientific Paper

doi:10.5937/jaes11-5060

Paper number: 11(2013)4, 267, 217 - 223

IMPACT OF COSMIC RADIATION ON AVIATION RELIABILITY AND SAFETY Ian Zaczyk* Mirce Akademy, Woodbury Park, Exeter, United Kingdom The main objective of this paper is to argue that the scientific approach to reliability and safety is the only way forward for the reliability community if accurate predictions regarding occurrences of negative functionability events are to be made and subsequently verified during the operational processes of the future man made, managed and maintained systems. For that to happen, a scientific understanding of the mechanisms that cause occurrences of functionability events of the surrounding natural environment are required. Then and only then, can accurate and meaningful reliability and safety predictions become possible, enabling the ultimate goal of reducing the probability of failure event occurrences during the life of man made, managed and maintained systems. This paper focuses on the scientific understandings of the relevant cosmic radiation on aviation reliability and safety. Key words: Aviation, Cosmic radiation, Functions, Predictions, Event, Reliability, Safety INTRODUCTION Due to the rapid advances in electronics technology and the unrelenting demand for increased avionics functionality in the competitive commercial aircraft industry, the complexity of avionics systems has risen exponentially. As a consequence, ever more advanced microprocessor and memory semiconductor devices are being used that exhibit an increased susceptibility to cosmic radiation phenomena. Single Event Effects (SEEs) have been the primary radiation concern for avionics since the late 1980’s when the phenomenon, which had previously only been observed in orbiting satellites, also began to appear in aircraft electronic systems. According to Baumann, “Left unchallenged, soft errors have the potential for inducing the highest failure rate of all other reliability mechanisms combined” [01]. Atmospheric radiation causes daily concerns regarding the reliability and safety of avionics equipment, particularly for those systems that are considered safety. The trend with each new generation of avionics system is to use increasing quantities of semiconductor memories and other complex devices that are susceptible to failures induced by ionising radiation from the following two main sources: cosmic rays from space and alpha particles from radioactive impurities in the device itself. The interaction of this radiation can result in ei* Mirce Akademy, Exeter, EX5 1JJ, United Kingdom; Ian.Zaczyk@agustawestland.com

ther a transient ‘soft error’ effect such as a bit flip in memory or a voltage transient in logic, alternatively a ‘hard error’ can be induced resulting in permanent damage such as the burn out of a transistor. These functionability effects caused by a single radiation event are collectively termed as Single Event Effects (SEEs). If device memory cells used for flight safety or mission critical functions are affected the concern is that the loss of key system functionality due to corrupted data could cause a flight safety or mission critical failure. The ability to predict and quantify the rate of occurrence of erroneous data bits in memories or voltage transients in logic is one of the key objectives in the field of avionics SEEs research. The main challenge of in-service operation of man made and maintained systems, is the true understanding of the impact of the environment that surrounds them. The reliability and safety of their operation is influenced by a multitude of different factors extending from the Earth’s atmosphere to the far reaches of space beyond our own galaxy. In order to determine the probabilities of occurrence and the resultant impact of functionability events on a system a full awareness of the dynamic nature of the environmental phenomena is required. To identify the causes of functionability events the mechanisms that cause those physical phenomena must first be understood [02].

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Ian Zaczyk- Impact of cosmic radiation on aviation reliability and safety

Consequently, the main objective of this paper is to argue that the scientific approach to reliability and safety is the only way forward for all members of the reliability community who wish to make accurate predictions regarding occurrences of negative functionability events, which will be confirmed during the operational processes of the future systems. For that to happen a scientific understanding of functionability phenomena is required. This paper advocates that research of this nature must include the understanding of the cosmic radiation phenomena, in order for the occurrence of functionability events to be understood. Then and only then, can accurate and meaningful reliability and safety predictions become possible, enabling system design and operational changes to be made to reduce the probability of failure event occurrences during the life of man made, managed and maintained systems. SCIENTIFIC PRINCIPLES OF MIRCE MECHANICS Mirce Mechanics is a new scientific theory, developed at the MIRCE Akademy by Dr. J. Knezevic, that aims to scientifically understand the physical causes and human actions that shape the motion of functionability through lives of man made, managed and maintained systems [02]. For years, research studies, international conferences, summer schools and other events have been organised in order to explain and draw attenton to just the physical scale at which failure phenomena should be studied and understood. In order to understand the motion of functionability events it is necessary to understand the physical mechanisms that cause their occurrences. That represented a real challenge, as the answers to the question “what are the discrete physical and chemical processes that lead to the occurrence of given functionability events” have to be determined. Without accurate answers to those questions the prediction of their future occurrences is not possible, and without ability to predict the future, the use of the word science becomes inappropriate. After a numerous discussions, studies and trials, it has been concluded that any serious studies in this direction, from Mirce Mechanics point of view, have to be based between the following two boundaries: • The “bottom end” of the physical world, 218

which is at the level of the atoms and molecules that exists in the region of 10-10 of a metre, • The “top end” of the physical world, which is at the level of the solar system that stretches in the physical scale around 10+10 of a metre. This range is the minimum sufficient “physical scale” which enables scientific understanding of relationships between system life processes and system failure events. One of the interacting factors from the physical world that directly impacts the functionability trajectory of man made systems are cosmic phenomena, as illustrated by the examples given above. This paper therefore considers major causes of cosmic phenomena from the physical world that can influence system functionability from a reliability and safety point of view. To achieve this goal, this paper examines the cosmic phenomena to understand their mechanisms of occurrence; describes the potential negative functionability event processes that can be initiated and their possible impacts on aviation systems reliability and safety. ATMOSPHERIC RADIATION In the natural environment there are two fundamental radiation particles that can cause transient errors in electronic devices, which can be classified into the following three groups: I. High-energy cosmic ray neutrons. II. Thermal or low energy cosmic ray neutrons. III. Low energy alpha particles emitted from within the semiconductor device and packaging materials. Each of these particle categories is different in terms of flux, energy level, charge or composition, but in essence a single particle of any of the above forms could result in a soft error if it deposits sufficient charge within the susceptible volume of a device. COSMIC RAYS Cosmic rays are individual energetic particles that originate from a variety of energetic sources ranging from our Sun to supernovas and other phenomena in distant galaxies all the way out to the edge of the visible universe. The majority of energetic particles however come from our galaxy with only the most energetic particles believed to Journal of Applied Engineering Science 11(2013)4, 267

Ian Zaczyk- Impact of cosmic radiation on aviation reliability and safety

have originated from extra-galactic sources. Although the term cosmic ray is commonly used, this term is misleading because no cohesive ray or beam actually exists. Cosmic rays are in fact independent energetic particles that travel at approximately 87% of the speed of light. Victor Hess first discovered cosmic rays in 1912, when he discovered the fourfold increase in ionisation rates as he ascended to altitude in a balloon. From this experiment he concluded that “the results of my observation are best explained by the assumption that a radiation of very great penetrating power enters our atmosphere from above.” In 1936 he was awarded the Nobel Prize in Physics for this discovery, although the term ‘cosmic rays’ is actually credited to a fellow scientist, R.A Millikan in 1925. The majority of cosmic rays consist of the nuclei of atoms (atoms stripped of their outer electrons) ranging from the lightest elements in the periodic table to the heaviest. In terms of composition about 90% of the nuclei are hydrogen, therefore just single protons, 9% are helium, alpha particles with the remaining 1% a mix of heavier element nuclei, high energy electrons, positrons and other sub-atomic particles. Cosmic rays must not be confused with gamma rays (high energy photons) that constitute the most energetic form of electromagnetic radiation. However there is a component of cosmic rays, < 0.1% which consists of gamma ray photons produced after high energy particle collisions with matter. Within the atmosphere the three most important parameters used to define the variability of the particle flux at a specific location are altitude, latitude and energy. Within the field of cosmic ray physics altitude is expressed in terms of atmospheric depth, which is the mass thickness per unit of area in the Earth’s atmosphere. At sea level this is approximately 1033 g/cm2 of oxygen and nitrogen and reduces as the altitude increases. Atmospheric depth is the key-determining factor in the particle flux for a specific point in the atmosphere. For example at an altitude of 3000m the flux of neutrons within the atmospheric cascade is around 10 times greater than at sea level. Energy is usually shown as the flux per unit of energy called the differential flux, and geographic latitude is expressed in terms of the geomagnetic field strength expressed in units of GeV Journal of Applied Engineering Science 11(2013)4, 267

and also referred to as a locations geomagnetic rigidity or cut-off. Cosmic rays can be broadly divided into two main categories, primary cosmic rays and secondary cosmic rays. Primary cosmic rays are particles accelerated at astrophysical sources and generally do not penetrate the Earth’s atmosphere. Primary cosmic rays are composed from a mixture of different energetic particles that can be categorised based on origin and energy level into the groups listed below in order of descending particle energy: I. Extra galactic cosmic rays, II. Galactic cosmic rays, III. Solar cosmic rays, IV. Anomalous cosmic rays. As cosmic ray particles are charged, magnetic fields in space will bend their motion paths. Due to the impact of magnetic fields, cosmic ray particles are incident on the Earth from all directions and as a consequence it is impossible to retrace their trajectories to determine their point of origin. However, the trajectory of a gamma ray photon is a straight line, due to their neutral charge. This makes it possible to retrace the trajectories of gamma rays to discover their source. Extra galactic and galactic cosmic rays Extra galactic cosmic rays originating from outside our galaxy and galactic cosmic rays from within bombard the top of the Earth’s atmosphere with a low but continuous flux of protons and heavy ions. The majority of energetic particles are accelerated from within our galaxy but external to the solar system. Cosmic ray particles from extra galactic and galactic sources are typically highly energetic and arrive at the Earth with an approximate flux rate of between 2 to 4 cm-2 s-1. Solar cosmic rays Solar cosmic rays, also termed Solar Energetic Particles, SEPs or Solar Proton Events SPEs, are produced by highly energetic processes that occur on or close to the Sun’s surface. Unlike galactic cosmic rays that arrive at the Earth with an almost steady constant flux, the occurrence of solar particles is not only irregular but also highly variable in terms of flux rate. Typically most solar protons arriving from the Sun lack the energy level required to penetrate the Earth’s magnetic field.

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Ian Zaczyk- Impact of cosmic radiation on aviation reliability and safety

Solar cosmic rays consist of heavy ions and protons with a less energetic spectrum than galactic cosmic rays. In comparison to the maximum energy possessed by galactic cosmic ray protons of 1021 eV, the solar proton peak energy of about 20 GeV is many orders of magnitude smaller. In the case of very powerful flux ejections, SPEs manifest as Ground Level Enhancements or Events, GLEs, on the Earth’s surface and typically last between 20 minutes to a few days dependent on the originating solar mechanism. SPEs can therefore be categorised as either an impulsive event linked to solar flares or gradual events linked to coronal mass ejections, CMEs. The main concern however regarding SPEs are the significant neutron flux enhancements generated at aircraft altitudes particularly at high geographic latitudes where the Earth’s level of magnetic shielding is reduced. During the Sun’s eleven year solar cycle the flux of solar particles incident upon the Earth’s upper atmosphere can increase by a million fold during a GLE relative to the level at a quiescent period close to or at the solar minimum. In contrast the difference between the flux rates between solar minimum and solar maximum, whilst still significant, are less dramatic than the sporadic peak flux rates caused by the most energetic SPEs, as shown in Table 1. Table 1: Mean integral solar cosmic ray flux at solar minimum and maximum Energy Range

Solar Maximum (Particles: cm-2s-1)

Solar Minimum (Particles: cm-2s-1)

Above 30 MeV

3 x 102

2 x 10-2

Above 100 MeV

2 x 10-3

GLEs in general occur 1 to 3 years after a solar maximum and to date since 1942 in total 71 of them have been observed. Over a longer period analysis of nitrate spikes obtained from polar ice cores indicate 154 large SPEs have occurred in the last 450 years. These powerful and evidently rare events are believed to be caused by the most energetic solar flares rather than CMEs. In terms of energy levels SPEs typically range from 10 MeV to 100 MeV although protons up to 20 GeV travelling at near relativistic speeds can be discharged from the Sun during extremely energetic events. The proton energy level determines the speed and hence the arrival time of 220

incident protons. At 1 MeV, protons arrive in 2.9 hrs but at 1 GeV the arrival time is reduced to just 9.5 minutes. Anomalous cosmic rays Anomalous cosmic rays are the final component of primary cosmic rays and possess energy levels significantly lower than any other type of cosmic ray, typically less than ~10 MeV. They are created when electrically neutral atoms enter the heliosheath of the Sun’s solar wind, become ionised and are then accelerated by the termination shock. The termination shock region forms the inner edge of the heliosheath where the solar wind becomes subsonic. This region varies between 75 and 100 AU (1 AU is a unit of length approximately equal to the semi-major axis of Earth’s orbit around the Sun) from the Earth. SINGLE EVENT EFFECTS IN AVIONICS Single Event Effects (SEEs) have been the primary radiation concern for avionics since the late 1980’s when the phenomenon, which had previously only been observed in orbiting satellites, also began to appear in aircraft electronic systems. The principal SEE affecting avionic devices is the Single Event Upset (SEU) caused when a sole incident particle creates a charge disturbance of sufficient magnitude in a memory cell, flip-flop, latch or register to reverse or flip its currently stored data state. Alternatively, in logic or support circuitry a transient voltage pulse can be generated that dependent on the right conditions can propagate through the logic of the device and become latched into a memory cell. Voltage spikes on power supply lines and noise can also cause transient errors; however appropriate shielding and filtering design measures can suppress these types of disturbances. The primary sources of radiation are high energy cosmic particles, low energy (thermal) neutrons and low energy alpha particles emitted from device and packaging contaminants. Radiation can affect electronic devices as the consequence of a single energetic particle strike, termed ‘single event’ or as multiple strikes over an extended period of time. The effects due to multiple events, Total Ionisation Dose (TID) and displacement damage manifest gradually in electronic components as damage is accumulated over time. These total dose effects and hard Journal of Applied Engineering Science 11(2013)4, 267

Ian Zaczyk- Impact of cosmic radiation on aviation reliability and safety

SEEs whilst relevant to electronic systems operating in the harsher space environment have a negligible effect on current semiconductor devices used in the terrestrial environment. Whilst each form of SEE is considered in this paper the main focus will be on SEUs which are the dominant device negative functionability event mechanism affecting electronic devices in the avionics environment. The second most prevalent SEE is the Multiple Bit Upset (MBU) that occurs when a single particle causes the upset of two or more memory cells. Fortunately MBUs only form a fraction of the total number of SEUs, hence they have little significance except for memory architectures employing Error Detection and Correction, (EDAC) techniques. In these circumstances, dependent on the type of error correction technique employed, multiple bit errors could have significant consequences if the protected memory is used for flight or mission critical applications. MBUs are generally assumed to attribute 3% of the total upset rate [04] although rates as high as 5% have been reported. Following MBU, Single Event Functional Interrupt (SEFI) and Single Event Latch ups (SEL) account for the majority of the remaining proportion of SEEs affecting avionic devices. SEFIs occur when an upset initiates an IC test mode or reset mode that causes the device to temporary lose functionality. SELs arise when an incident particle creates a charge disruption sufficient enough to effectively short circuit the device resulting in its permanent change of state or in some circumstances permanent damage if excessive current flows as a result of the latch-up. The last SEE of avionics relevance that can generate soft errors in the core logic of microprocessors and microcontrollers is the Single Event Transient (SET). They are transient and non-destructive in nature and are capable of producing a soft error, (i.e. the storage of an erroneous data value in registers, memories or latches) only if it is propagated through the logic pathways of the device. This is dependent on the dynamic state of the logic at the time of the particle induced nodal voltage transition and the configuration of the logic pathways within the device. If a soft error occurs normal system behaviour can be restored by resetting or rewriting the incorrect data. Of all the forms of SEE, SEUs are the most prevalent in avionic electronic devices; Table 2 illusJournal of Applied Engineering Science 11(2013)4, 267

trates the approximate distribution percentage values, between each type of SEE except SETs, for which no reliable data exists. This problem of limited SEE statistical data is an enduring problem in the field as the capturing and recording of SEEs during flight is impeded by: I) Fault tolerant designs and error correction techniques. II) SEEs incorrectly diagnosed as electrical interference or random component negative functionability events. III) Reluctance of semi-conductor manufactures to disclose proprietary information regarding the root cause negative functionability event mechanisms and the historic negative functionability event statistics gathered from devices returned from in-flight usage. Table 2: Main SEE Apportionments â&#x20AC;&#x201C; Avionics Environment Single Effect Event Type

Percentage

Single Event Upset

90 %

Multiple BIT Upset

Single Event Functional Interrupt

Single Event Latchup

The current convention is to discuss the rate of SEU occurrence in terms of soft error rates (SER), which are measured in failures in time, (FIT). One failure in 1 billion device operating hours is defined as 1 FIT. This term is also widely used in the semiconductor industry to state the expected occurrence rate of hard negative functionability event mechanisms. The first efforts to calculate SEU rates were presented in two papers in 1984, Tsao et al. [05] and a companion paper by Silberberg et al. [06]. The Tsao paper detailed methods of calculating SEU rates from primary & secondary cosmic rays reaching down to 40,000ft and the Silberberg paper introduced methods for calculating SEU rates resulting from secondary neutrons in the atmosphere. The reason that semiconductors have become susceptible to SEEs in the terrestrial environment rather than existing solely in space can be partially attributed to the commercial demands for increased functionality and performance, whilst lowering power consumption and cost. To fulfil these requirements component manufactures have continued to reduce the geometry size of

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integrated circuits with each new generation resulting in higher gate speeds, increased feature density and reduced power consumption. Whilst technology scaling enables the demands of system designers to be met the downside of this is an increased sensitivity to radiation. Within a memory device this is caused by a reduction in the capacitance inside a cell and a significant increase in the number of cells that could potentially be upset within each device. Less capacitance in a device due to the shrinking of process technology and reduced supply voltage means that the minimum amount of charge necessary to hold data in a device, either a logic 1 or 0 is also reduced. This quantity of charge, known as the critical charge, is therefore more susceptible to a charge disturbance caused by an incident radiation particle, thus eroding the components resistance to SEUs. The approximate critical charge of a node can be calculated using the expression: (1) where: Qc is Critical Charge, Cnode is Node Capacitance and VDD is Operating Voltage. A lower nodal critical charge is therefore more likely to be â&#x20AC;&#x2DC; upset â&#x20AC;&#x2122; by incident particles with a lower energy, because the flux of energetic particles increases at lower energy levels. The components most susceptible to SEU are therefore devices that contain the largest number and density of potentially volatile bits namely memories and microprocessors. Table 3 contains a list of the devices that are currently considered to be the most susceptible to SEU in aircraft avionics systems and includes the specific regions within the architecture that are most at risk. Table 3: SEU Sensitive Devices Devise Type

Sensitive Areas

SRAMS and DRAMS

Memory cells and control logic

Microprocessors and Microcontrollers

Registers, cache, sequential and combinational control logic

FPGAs and ASICs

Combinatorial logic and sequential logic

Opto-electronics and power switching components are also susceptible, to various forms of hard and soft SEE but are not considered in this 222

paper due to their very low probability of failure in the avionics radiation environment. Each of the factors discussed in this section, increased functionality and performance, lack of specialist devices, lower critical charge and higher cell density all impact upon the SEU tolerance of advancing semiconductor designs. The net effect is an increase in the overall device SER that if not adequately mitigated against using appropriate methods such as error detection and correction (EDAC) and architectural redundancy, will result in an increased system SER, plus potentially an increase in the number of mission or flight safety critical negative functionability events. CONCLUSION The main objective of this paper was to demonstrate the necessity of addressing all physical causes that lead to the transition of a system from positive to negative functionability state during its life. Addressing the reliability and safety characteristics of a system in isolation from the investigation of the impact of the natural environment is not sufficient. Hence, results of the research performed in [04], presented here; have shown the significant impact of cosmic radiation on the occurrence of negative functionability events, and consequently, the necessity for addressing them when considering the reliability and safety characteristics of avionics, at the design stages of a systems development. This paper presents the research results obtained by applying the principles of Mirce Mechanics to the scientific understanding of the physical mechanisms that lead to the occurrence of the Single Event Upset (SEU), which is the principal SEE affecting avionic devices. It is caused when a sole incident particle creates a charge disturbance of sufficient magnitude in a memory cell, flip-flop, latch or register to reverse or flip its currently stored data state. Alternatively, in logic or support circuitry a transient voltage pulse can be generated that dependent on the right conditions can propagate through the logic of the device and become latched into a memory cell. In summary this paper advocates that any system reliability and safety considerations must include the full understanding of the complex interactions between functionability significant processes and to determine the influence of each discrete factor, on the functionability trajectory Journal of Applied Engineering Science 11(2013)4, 267

Ian Zaczyk- Impact of cosmic radiation on aviation reliability and safety

through life of a complete avionics system. Then and only then, can accurate and meaningful reliability and safety predictions become possible, enabling the ultimate goal of reducing the probability of the occurrence of negative functionability events during the life of man made, managed and maintained systems. ACKNOWLEDGEMENT Authors wish that acknowledge the financial support obtained from the Research Fund of the MIRCE Akademy that enabled this research to be performed.

REFERENCES 1) Baumann, R., “ Radiation-induced soft errors in advanced semiconductor technologies, ” IEEE Transactions on Device and Materials Reliability, vol 5, No 3, pp. 305–316, Sept. 2005. 2) Knezevic, J. Time To Choose between Scientific and Administrative Approach to Reliability, Journal of Applied Engineering Science, No 3,. Year 2012, Vol 10. Belgrade, Serbia. 3) Knezevic, J/, Atoms and Molecules in Mirce Mechanics Approach to Reliability, SRESA Journal of Life Cycle Reliability and Safety Engineering, Vol 1, Issue 1, pp 15-25, Mumbai, India, 2012. ISSN-22500820 4) Zaczyk. I, “Analysis of the Influence of Atmospheric Radiation Induced Single Event Effects on Avionics Failures”, Master Dissertation, MIRCE Akademy, Exeter, UK, 2010. 5) C. H. Tsao, R. Silberberg, and J. R. Letaw, “Cosmic ray heavy ions at and above 40,000 feet, ”IEEE Trans. Nucl. Sci., vol. 31, pp. 1066–1068, Dec 1984. 6) R. Silberberg, C. H. Tsao, and J. R Letaw, “Neutron generated single event upsets,” IEEE Trans. Nucl. Sci., vol. 31, pp. 1183– 1185, Dec 1984. Paper sent to revision: 14.11.2013. Paper ready for publication: 11.12.2013.

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EVENTS REVIEW

BALCOR, international conference was great opportunity to gathered together operational researchers with the objective to present the results of theoretical and applied work. One of the benefits of BALCOR was a successful exchanged of ideas and information of interest to operational research and the promotion of international co-operation, particularly among the Balkan countries.

The XL national Operational Research Symposium â&#x20AC;&#x201C; SYM-OP-IS 2013 was also held in the same period as the XI Balkan Conference on Operational Research â&#x20AC;&#x201C; BALCOR 2013 as a Joint International Meeting. This was joint effort of the University of Belgrade, Faculty of Organizational Sciences and the Serbian OR Society.

The conference got togehter OR researchers from 7-11 September, 2013 in the beautiful city of Belgrade, and the mountain tourism centre Zlatibor.

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The Faculty of Organizational Sciences was delighted to host the XL Symposium on Operational Research – SYM-OP-IS 2013. SYM-OP-IS was a national symposium with international participation. It traditionally gathered operational researchers with the objective to review and share theoretical as well as practical research results and exchange information of interest for operations research, in both a formal and informal way. The Symposium Programme were comprised plenary lectures and theme sections which accommodated the exchange of ideas and the review of relevant issues through valuable encounters of the representatives of the academic body and industry, both from Serbia and abroad. In line with the objectives of SYM-OP-IS, the symposium facilitated the exchange of knowledge between scientists and between scientists and representatives of the economy. Submitting papers were strongly encouraged and conducting research which go beyond borders of scientific disciplines. Broad theme sections of the symposium enabled research in numerous aspects of the defined areas. It was our great pleasure to welcomed you to the beautiful mount Zlatibor, to the University Congress centre, 9-12 September, 2013. Main topics were: • Agriculture, Forestry and Hydraulicity • Civil Engineering • Combinatorial Optimization • Data Mining • Ecology • Economic Models and Econometrics • Electronic Commerce • Energetics • Expert Systems – Decision Support • Finance and Banking • Geographic Information Systems (GIS) • Graphs and Networks • Information Systems • Logistics • Management

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• • • • • • • • • • • • • • •

Mathematical Programming Military Defense Applications Mining and Geology Multicriteria Analysis and Optimization Prediction and Planning Production and Stock Management Queuing Theory Reliability and Maintenance Research and Development Risk Management Simulation Soft Computing Statistical Models Stochastic Models and Time Series Traffic, Transportation and Communication

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ANNOUNCEMENT OF EVENTS 9th SYMPOSIUM RESEARCH AND DESIGN FOR COMMERCE & INDUSTRY 20th-21st December 2013 University of Belgrade, Faculty of Mechanical Engineering, Belgrade, Serbia

MAINTENANCE IN THE BOARDROOM Keynote lecture MAINTENANCE IN THE BOARD ROOM will be held by Dr Jezdimir KneĹževiÄ&#x2021;, MIRCE Akademy, Exeter, United Kingdom Editorial board of scientific journal of Applied Engineering Science in cooperation with Faculty of mechanical engineering in Belgrade, organize IX symposium Research and design for industry, which is traditionally held during the month of December. Objective of the Symposium is networking and experience sharing among experts from public companies in transport, energy and mechanical engineering sector with relevant representatives of City and Republic institutions in order to promote, support and implement new technological developments. The areas covered by the symposium are: planning and execution of projects in a wide range of industrial sectors such as transport, energy, construction, telecommunications, maintenance of technical systems, public sector enterprises, financial sector, IT sector etc. . . Symposium primary present the results of initiated or realized projects in domestic economy, as well as the knowledge, methods and techniques, standards and software tools that have contributed or could contribute to their better implementation. The symposium IIPP, as in previous years, will have plenary sessions, invited lectures, software demonstrations, magazines and books promotions... The authors are invited to submit their papers to the Organizing Committee no later then 15/12/2013. (by sending paper to the e-mail: office@iipp.rs) The accepted papers, whose authors timely paid registration fee, will be published in the Proceedings before symposium. Proceedings will be published in the electronic edition and will be distributed to all participants at the Symposium. Details: www.iipp.rs; +38111 6300 750; +38111 6300 751; +38111 3302 450

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BOOK RECOMMENDATION Recommended by Mrs Nada Stanojević KEY PERFORMANCE INDICATORS (KPI): Developing, Implementing and Using Winning KPIs Author: David Parmenter By exploring measures that have transformed businesses, David Parmenter has developed a methodology that is breathtaking in its simplicity and yet profound in its impact. Now in an updated and expanded Second Edition, Key Performance Indicators is a proactive guide representing a significant shift in the way KPIs are developed and used, with an abundance of implementation tools, including: • The four foundation stones that lead the development and use of KPIs • A 12-step model for developing and using KPIs with guidelines • A KPI resource kit including worksheets, workshop programs, and questionnaires • A new and pragmatic approach to finding critical success factors • Over 300 performance measures • Implementation variations for small to medium enterprises and not-for-profit organizations • New implementation short cuts • How to brainstorm performance measures Now including a discussion of critical success factors, as well as new chapters that focus on implementations issues and ‘how to sections’ on finding your CSFs and brainstorming the performance measures that report progress within the CSFs, Key Performance Indicators, Second Edition will help you identify and track your organization’s KPIs to ensure continued and increased success. Format B5; ; 280 pages; ; ISBN 978-0-470-54515-7; Published: 2010.

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INSTRUCTIONS FOR AUTHORS The benefits of publishing in Journal for Applied Engineering Science are: • No page charges • World wide exposure of your work • Accelerate publication times • Online author service • Automatic transfer of metacontent in SCOPUS, SJR, SCIndeks and other bases supporting international protocols for data transfer • Assignment of numerical identifiers DOI • Fair, constructive and able to follow reviewing process • Dedicated team to manage the publication process and to deal with your needs Submission of the papers has to be done online, trough journal e-service at http://aseestant.ceon.rs/index.php/jaes/login For assistance during the process of submission and publication, please contact graphical editor Mr. Darko Stanojevic at dstanojevic@iipp.rs or +381 116300750 Every manuscript submitted to JAES will be considered only if the results contained in the paper were not already published, that are not currently in the process of publishing and not to be published in another journal. Each paper is sent to a review by two independent experts and the authors are obligated to adopt the observations and comments of the reviewers. Articles presented at conferences may also be submitted, provided these articles do not appear in substantially the same form in published conference proceedings. All articles are treated as confidential until they are published. Manuscripts must be in English free of typing errors. The maximum length of contributions is 10 pages. THE FORMAT OF THE MANUSCRIPT The manuscript should be written in the following format: • A Title, which adequately describes the content of the manuscript. • An Abstract should not exceed 250 words. The Abstract should state the principal objectives and the scope of the investigation, as well as the methodology employed. It should summarize the results and state the principal conclusions. • Not more than 10 significant key words should follow the abstract to aid indexing. • An Introduction, which should provide a review of recent literature and sufficient background information to allow the results of the article to be understood and evaluated. • A Theory or experimental methods used. • An Experimental section, which should provide details of the experimental set-up and the methods used for obtaining the results. • A Results section, which should clearly and concisely present the data using figures and tables where appropriate. • A Discussion section, which should describe the relationships and generalizations shown by the results and discuss the significance of the results making comparisons with previously published work. (It may be appropriate to combine the Results and Discussion sections into a single section to improve the clarity). • Conclusions, which should present one or more conclusions that have been drawn from the results and subsequent discussion and do not duplicate the Abstract. • References, which must be cited consecutively in the text using brackets [1] and collected together in a reference list at the end of the manuscript and in alphabetic order.

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INSTRUCTIONS FOR AUTHORS Units - standard SI symbols and abbreviations should be used. Abbreviations should be spelt out in full on first appearance, e.g., variable time geometry (VTG). Meaning of symbols and units belonging to symbols should be explained in each case or quoted in a special table at the end of the manuscript before References. Figures must be cited in a consecutive numerical order in the text and referred to in both the text and the caption as Fig. 1, Fig. 2, etc. Figures should be prepared without borders and on white grounding and should be sent separately in their original formats. Pictures may be saved in resolution good enough for printing in any common format, e.g. BMP, GIF or JPG. Tables should carry separate titles and must be numbered in consecutive numerical order in the text and referred to in both the text and the caption as Table 1, Table 2, etc. The tables should each have a heading. Tables should not duplicate data found elsewhere in the manuscript. Acknowledgement of collaboration or preparation assistance may be included before References. Please note the source of funding for the research. REFERENCES must be written in alphabetical order and in the following form: Journal: /Number/ (must match number in the text), Last name, Initial of the authors name, (Year of publication). Article title: secondary title. Title of the Journal (italic), volume number (number of the journal), page number. /1/ Sekulić, D., Dedović, V. (2008): Simulation of oscillatory behavior of buses with conventional and active suspension systems, Journal of Applied Engineering Science, Vol. 6, No. 20, pp. 23-32 Book: /Number/ (must match number in the text), Last name, Initial of the authors name, (Year of publication) Book title: secondary title, Place of publishing: Publisher. /2/ Vasić, B., Popović, V. (2007) Inženjerske metode menadžmenta, Beograd: Institut za istraživanja i projektovanja u privredi. Book chapter: /Number/ (must match number in the text), Last name, Initial of the authors name, (Year of publication) Chapter title: secondary title, Book title: secondary title, Place of publishing: Publisher, page numbers. /3/ Vasić, B. (2004) Model Hardverskog resursa, Menadžment i inženjering u održavanju, Beograd: Institut za istraživanja i projektovanja u privredi, 95 – 97. Internet source: /Number/ (must match number in the text), link to the page from which the text is taken, retrieved on (state the date) /4/ http://www.autogume.net/veleprodaje/kelena/, retrieved on November 7th, 2010

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SADRŽAJ

OD UREĐIVAČKOG ODBORA Prof. dr Jezdimir Knežević UVODNIK

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REZIMEI RADOVA Dragan Ružić, Borivoj Stepanov NUMERIČKE SIMULACIJE TOPLOTNOG FLUKSA NA TELU VOZAČA MOTORNOG VOZILA PROUZROKOVANOG ZRAČENJEM SUNCA

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Dr Tomáš Hanák, Dr Ivan Marović BENČMARKING KONCEPT MALOG GRAĐEVINSKOG PREDUZEĆA

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Aleksandar Mićović, Dr Vladimir Popović, Dragoslava Mićović, Snežana Jovanović ISPITIVANJE KARAKTERISTIKA SOPSTVENIH I PRINUDNIH OSCILACIJA NA TERENSKOM VOZILU FAP 2228 SA SPECIJALNOM NADGRADNJOM

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Dr Mirjana Filipović, Ana Đurić, Ljubinko Kevac METODOLOGIJA ZA RAZVOJ KINEMATIČKOG MODELA ODABRANOG CPR-A SISTEMA KAO NEOPHODNOST ZA RAZVOJ DINAMIČKOG MODELA

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Minja Marinović, Dragana Makajić-Nikolić, Milan Stanojević

OPTIMIZACIJA DNEVNOG PLANIRANJA TRGOVINE ELEKTRIČNOM ENERGIJOM

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Goran Duduković, Milutin Ogrizović PREDNOSTI INTELIGENTNOG PRISTUPA MAŠINSKOJ OBRADI PREZENTOVANOG PROJEKTOVANJEM TEHNOLOGIJE OBRADE PRIMENOM IMACHINING TEHNOLOGIJE

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Ian Zaczyk UTICAJ KOSMIČKE RADIJACIJE NA POUZDANOST I BEZBEDNOST U VAZDUHOPLOVSTVU

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OD UREĐIVAČKOG ODBORA

ODRŽAVANJEM DO PROFITA Održavanje se najčešće doživljava kao “popravljanje pokvarenih stvari”. Kao takvo, održavanje je povezano sa zastojima i neplaniranim troškovima i smatra se da ima negativan uticaj na poslovne planove ili zadovoljstvo kupaca. Međutim, kako su otkazi neminovnost života svakog tehnološkog sistema, bilo bi korisno da se u održavanju počne tražiti prilika za pozitivnim uticajem na već pomenute poslovne planove ili zadovoljstva kupaca. Shodno tome, glavni cilj je da se nađe način kojim je moguće upravljati, jednom shvaćenim otkazima, tako da se direktno smanjuju operativni troškovi i broj prekida u radu.

Dr Jezdimir Knežević Korisnici i operateri kompleksnih tehnoloških sistema bi voleli da budu u stanju da tačno predvide verovatnoću da će svi avioni, vozovi, autobusi i ostale mašine za generisanje prihoda moći da ostvare svoju funkciju, kako bi se ostvarili dobro pripremljeni i strateški određeni poslovni planovi. Odgovori na ovu vrstu pitanja su od suštinskog značaja za definisanje veličine timova održavanja, broja rezervnih delova, lokacija održavanja, pomoćnih objekata, kao iza druga slična razmatranja, koja direktno određuju cenu rada, održavanja i podrške, koji najviše doprinose operativnim prihodima, profitu, zadovoljstvu kupaca i sličnim pokretačima poslovanja. Dakle, donosioci odluka visokog nivoa u bilo kojoj organizaciji treba da razumeju doprinos drugačijeg pristupa održavanju i šta se njime može postići, mnogo više nego što je potrebno da razumeju sam postupak rada. Potrebno je da članovi organizacija, sa širim poslovnim pogledima, u potpunosti cene izazove sa kojima se zajednica održavanja svakodnevno suočava. To je neophodno za istovremeno upravljanje aktivnostima održavanja koje su vezane za otkaze sistema sa jedne strane i kontinualnim stvaranjem mogućnosti za povećanje prihoda, sa druge strane. Da bi se ovo postiglo, razumevanje uticaja održavanja na obe pomenute funkcije je od suštinskog značaja. Međutim, to je daleko od trenutne situacije u kojoj “Upravni odbori”, u svakoj kompaniji u svetu, maksimiziraju napore da umanje troškove održavanja. Dakle, naš glavni cilj u budućnosti je da se pokaže kako je kvantitativni odnos, zasnovan na nauci, između potrošenog novca za održavanje i novca zarađenog od generisanih funkcija prihoda, osnovan da omogući kompromis koji maksimizira profit (uspeh). Novi pristup održavanju koji je razvijen u okviru MIRCE mehanike, daje odgovore na takva i slična pitanja, pa je moje nepokolebljivo uverenje da održavanje mora da ima sedište u Upravnim odborima, bilo javnih ili privatnih organizacija koje su posvećene visokoj pouzdanosti sistema i cene vrednost novca. S poštovanjem, Dr Jezdimir Knežević

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REZIMEI RADOVA Originalni naučni članak-doi:10.5937/jaes11-4731

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NUMERIČKE SIMULACIJE TOPLOTNOG FLUKSA NA TELU VOZAČA MOTORNOG VOZILA PROUZROKOVANOG ZRAČENJEM SUNCA Dragan Ružić, Univerzitet u Novom Sadu, Fakultet tehničkih nauka, Novi Sad, Srbija Borivoj Steapnov, Univerzitet u Novom Sadu, Fakultet tehničkih nauka, Novi Sad, Srbija U radu je prikazana analiza uticaja pravca i intenziteta sunčevog zračenja na toplotni fluks na površini tela vozača putničkog automobila. Analiza je izvršena na virtuelnom modelu kabine. Rezultati su pokazali da najveće toplotno opterećenje tela usled sunčevog zračenja može nastati kada je sunce sa prednje strane kabine, što su uslovi koji se primenjuju i u standardu ISO 14505-2: 2008. U tom slučaju, grudi vozača su oblast na telu na kojoj je toplotni fluks najveći. Takođe nepovoljna situacija je kada sunce sija sa leve strane kabine, zbog izrazite asimetrije toplotnih uslova. Iz tih razloga, obraćanje pažnje na solarne karakteristike stakala i na konstrukciju sistema za razvođenje vazduha tako da se ventilacioni otvori mogu usmeriti na površine tela sa najvećim toplotnim fluksevima, osnovni su načini za smanjenje toplotnog opterećenja vozača i putnika. Ključne reči: Toplotni komfor, Automobilsko staklo, Virtuelna toplotna lutka, Sunčevo zračenje, Kabina Originalni naučni članak-doi: 10.5937/jaes11-4856

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BENČMARKING KONCEPT MALOG GRAĐEVINSKOG PREDUZEĆA Dr Tomas Hanak, Građevinski fakultet, Brno, Republika Češka Dr Ivan Marović, Građevinski fakultet, Rijeka, Hrvatska Povećanje konkurencije na globalnom tržištu prisiljava preduzeća da povećaju učinkovitost internih procesa s ciljem zadržavanja svoje konkurentnosti. Merenje uspešnosti postaje jedan od glavnih strateških faktora poslovnog uspeha, a može se takođe odvijati u okviru “benchmarking” inicijative. Cilj ovog rada je izraditi benchmarking koncept malih građevinskih firmi te proveriti njegovu primenu na primeru iz prakse. Zbog toga je bilo potrebno identifikovati niz indikatora uspešnosti koji se mogu meriti i vrednovati. Utvrđeno je da je veličina firme ograničavajući faktor prilikom primene benchmarkinga u firmi, kao i nedostupnost svih potrebnih podataka. Međutim, zaključeno je da čak i ograničeni oblik sprovođenja benchmarkinga pruža vriedne informacije menadžmentu poduzeća koje su meerodavne za strateško donošenje odluka osiguravajući pritom delotvornost menadžmenta preduzeća i dugoročnu finansijsku stabilnost. Ključne reči: Indikator uspešnosti, Finansijski pokazatelj, Trošak, Građevinska kompanija, Benčmarking Originalni naučni članak-doi: 10.5937/jaes11-4856

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UTICAJ KOSMIČKE RADIJACIJE NA POUZDANOST I BEZBEDNOST U VAZDUHOPLOVSTVU Ian Zaczyk, Mirce Akademy, Woodbury Park, Exeter, United Kingdom Glavni cilj ovog rada je razmatranje da je za zajednicu koja se bavi pouzdanošću naučni pristup jedini put napred kada su u pitanju pouzdanost i bezbednost ukoliko su istinita predviđanja u vezi sa pojavom negativnih funkcionalnih događaja koji nastaju i koji se kasnije utvrđuju tokom operacionih procesa budućih sistema koji su napravljeni, a kasnije i upravljani i održavani od strane čoveka. Za takva dešavanja, neophodno je naučno razumevanje mehanizama iz okolne prirodne sredine koji uzrokuju pojave funkcionalnih događaja. Tada i samo tada, mogu se utvrditi i u potpunosti shvatiti predviđanja u vezi sa pouzdanošću i bezbednošću, omogućavajući ostvarenje krajnjeg cilja, a to je smanjenje verovatnoće pojave otkaza tokom životnog veka sistema koji su napravljeni, a kasnije i upravljani i održavani od strane čoveka. Ovaj rad se fokusira na naučna razumevanja relevantne kosmičke radijacije na pouzdanost i bezbednost u vazduhoplovstvu. Ključne reči: Bezbednost, Pouzdanost, Predviđanja, Funkcije, Događaj, Kosmička radijacija, Vazduhoplovstvo 232

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REZIMEI RADOVA Stručni članak-doi:10.5937/jaes11-4984

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ISPITIVANJE KARAKTERISTIKA SOPSTVENIH I PRINUDNIH OSCILACIJA NA TERENSKOM VOZILU FAP 2228 SA SPECIJALNOM NADGRADNJOM Aleksandar Mićović, Tehnički opitni centar, Beograd, Srbija Dr Vladimir Popović, Univerzitet u Beogradu, Mašinski fakultet, Beograd, Srbija Dragoslava Mićović, Kriminalističko-policijska akademija, Beograd, Srbija Snežana Jovanović, Tehnički opitni centar, Beograd, Srbija U radu je dat prikaz ispitivanja karakteristika sopstvenih i prinudnih oscilacija terenskog vozila FAP 2228 BS/A-45. Ispitivanje sopstvenih oscilacija vozila obavljeno je prema SORS 9127 u laboratorijskim uslovima. Ispitivanje prinudnih oscilacija vozila obavljeno je vožnjom po stazi - ispresecana ledina, u oblasti Deliblatske peščare, ravničarski makadam u oblasti Fruške gore, po betonskoj podlozi na pisti aerodroma Kovin, kao i po afaltnoj podlozi autoputa Bgd - Šid. Ispitivanja su obavljena prema SORS 0318 i ISO 2631, a rezultati su ocenjeni prema direktivi 2002/44/EC. Ključne reči: Komfornost, Ispitivanje, Sopstvene oscilacije, Prinudne oscilacije, FAP 2228 BS/A-45

Originalni naučni članak-doi:10.5937/jaes11-4581

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METODOLOGIJA ZA RAZVOJ KINEMATIČKOG MODELA ODABRANOG CPR-A SISTEMA KAO NEOPHODNOST ZA RAZVOJ DINAMIČKOG MODELA Dr Mirjana Filipović, Institut “Mihajlo Pupin”, Beograd, Srbija Ana Đurić, Univerzitet “Wayne State”, Sjedinjene Američke Države Ljubinko Kevac, Elektrotehnički fakultet, Beograd, Srbija Definisan je autentičan oblik generalne forme matematičkog modela Cable Suspended Parallel Robot tipa A, CPR-A sistema. Smisao definisanja kinematičkog modela koji uključuje trajektoriju, brzinu i ubrzanje je pretpostavka za formulaciju dinamičkog modela. Te tri komponente predstavljaju osnovni funkcionalni kriterijum realnog sistema koji je opisan sa odgovarajućim geometrijskim vezama i diferencijalnim jednačinama. Kinematićki model CPR-A sistema je definisan preko Jakobijeve matrice. Adekvatan izbor generalisanih koordinata (u ovom radu unutrašnjih koordinata) obezbedjuje matematički model koji osvetljava preslikavanje unutrašnjih (rezultujućih sila u užadima) i spoljašnjih sila (koje deluju na nosač kamere) preko Jakobijeve matrice na dinamiku kretanja svakog motora. Softverski paket AIRCAMA je razvijen i korišćen za individualnu i komparativnu analizu CPR-A sistema sa različitih aspekata. Smisao promene nekih parametara (dimenzije radnog prostora, mase nosača kamere, promena veličine i dinamike poremećajne sile, izbor upravljačkog zakona, referentne trajektorije i izbegavanja prisutnog singulariteta sistema kao i drugih karakteristika) mogu biti analizirane preko ovog softverskog paketa. Različiti primeti kretanja CPR-A sistema su analizirani i njihovi rezultai su predstavljeni. Mogućnost primene CPR-A sistema je zaista mnogo šira nego što to može i da se pretpostavi u ovom momentu, posebno za sportske, kulturne, vojne i policijske svrhe. Ključne reči: Dinamika, Kinematika, Modeliranje, Radni prostor, Observacija, Kablovski vođen paralelni robot

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REZIMEI RADOVA Originalni naučni članak-doi:10.5937/jaes11-4604

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OPTIMIZACIJA DNEVNOG PLANIRANJA TRGOVINE ELEKTRIČNOM ENERGIJOM Minja Marinović, Fakultet organizacionih nauka, Beograd, Srbija Dragana Makajić - Nikolić, Fakultet organizacionih nauka, Beograd, Srbija Milan Stanojević, Fakultet organizacionih nauka, Beograd, Srbija Tokom XX veka proizvodnja i prenos električne enrgije su sprovođeni isključivo preko monopolističkih javnih kompanija za proizvodnju električne energije. Poslednjih dvadeset godina tržište električne energije je postalo otvoreno što je omogućilo potrošačima da biraju svoje dobavljače i proizvođače. Svi učesnici u trgovini pokušavaju najpre da zadovolje potrebe za električnom energijom u svojoj zemlji kao i da snabdevaju električnom energijom okolna tržišta. Međudržavna trgovina i snabdevanje predstavlja deo takmičenja gde svi učesnici imaju nediskriminatorni pristup transmisionim kapacitetima. U ovom radu posmatramo problem dnevnog planiranja trgovine električnom energijom. Pretpostavlja se da su ponuda i potražnja unapred poznate. Poznati su raspoloživi transmisioni kapaciteti kao i dodatni kapaciteti koji se mogu dokupiti. Cene kupovine, prodaje i prenosa električne energije su predmet aukcija. Opisani problem se ovde posmatra iz ugla donosioca odluke kompanije koja se bavi trgovinom električne energije. Odluke koje on donosi su: gde i koliko električne energije treba kupiti i prodati, kao i koji će se transmisioni kapaciteti koristiti u cilju maksimizacije dnevnog profita. Problem je formulisan na osnovu iskustva jedne kompanije za trgovinu električne energije iz Srbije koja posluje na teritoriji centralne i jugoistočne Evrope i modeliran kao orijentisani graf sa više izvora i ušća, a potom predstavljen linearnim modelom u kom se maksimizira dnevni profit pri ograničenjima za tržište i kapacitet protoka. Glavni cilj ovog modela je da omogući koristan alat za pripremu ponude za aukcije. Numerički primeri su prikazani u cilju da ilustruju moguću primenu samog modela. Ključne reči: LP model; Protok na mrežama; Dnevno planiranje; Trgovina električnom energijom Stručni članak-doi:10.5937/jaes11-4514

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PREDNOSTI INTELIGENTNOG PRISTUPA MAŠINSKOJ OBRADI PREZENTOVANOG PROJEKTOVANJEM TEHNOLOGIJE OBRADE PRIMENOM IMACHINING TEHNOLOGIJE Goran Duduković, Solfins DOO, Beograd, Srbija Milutin Ogrizović, Tehička škola, Stara Pazova, Srbija Efikasna mašinska obrada današnjice zahteva potpuno nov pristup projektovanjem tehnologije obrade koja treba da omogući međusobnu spregu svih tehnoloških parametara obrade, kao što su pre svega brzina rezanja i brzina pomoćnog kretanja u zavisnosti od materijala obratka, karakteristika mašine i alata i trenutne zapremine materijala koja se uklanja iz zone obrade.Kontrolom fizičkih veličina koje se javljaju kao posledica međusobnog dejstva alata na obradak prilikom rezanja moguće je ostvariti znatno oštrije režime obrade u odnosu na postojeć etehnologije obrade visokim brzinama rezanja (HSM) i tako ostvariti ekstremno povećanje produktivnosti. Ovakav pristup mašinskoj obradi zahteva inteligenciju CAM softvera da donosi odluke u realnom vremenu i optimizuje putanje alata u cilju održavanja konstante sile rezanja tokom celokupnog procesa obrade.Ovaj pristup korišćenja je pri projektovanju tehnologije obrade„izmenjivača topolote “pomoću tzv. Imachining tehnologije u okviru Solid CAM programskog paketa za upravljanje CNC mašinama. Pri čemu je mašinsko vreme obrade skraćeno za 36% u odnosu na stadardne metode obrade i ostvarene ukupne uštede od 45%. Ključne reči: I-machnining tehnologija, Efikasna mašinska obrada, Konstantna sila rezanja, Ugao rezanja

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