MSC SHIP AND OFFSHORE STRUCTURES
Simplified Analysis of a Bulk Carrier
Submitted by: Aditya Prakash Bodhe Registration Number: 201272421 8/30/2013
Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
Declaration I hereby declare that this thesis is my own work and effort and that it has not been submitted anywhere for any award. Where other sources of information have been used, they have been acknowledged. All the references used for the study purposes are mentioned under the Bibliography section.
.............. Signature Aditya Bodhe 201272421
Date Aug 30, 2013
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
CONTENTS Acknowledgement ........................................................................................................................ 4 Abstract ......................................................................................................................................... 5 Introduction .................................................................................................................................. 6 Objectives of the Project............................................................................................................. 10 Typical Cross Section of a Handymax Bulk Carrier (Rhinoceros 4.0) .................................... 12 Literature Review ........................................................................................................................ 13 DNV Common Structural Rules ............................................................................................... 13 General principles: .............................................................................................................. 13 Yielding CSR:............................................................................................................................ 14 Torsional CSR and load calculations: ...................................................................................... 15 FT1 and FT2 are distribution factors which are again defined as; ................................................. 15 Direct strength method: ......................................................................................................... 16 Saint Venant’s Principle, Introduction and Stress Concentration theory: .............................. 18 Derivative of angle alpha with respect to z, is rate of twist ........................................................ 19 Techniques and Approaches Used .............................................................................................. 21 Modelling and Boundary Restrictions......................................................................................... 22 Analyses& Results ....................................................................................................................... 24 The Material properties: ......................................................................................................... 24 Elasticity coefficients: ............................................................................................................. 24 Complete Cargo Hold Torsional Loading................................................................................. 25 The Entire model’s Geometry. (imported in ansyswokbench from Rhinoceros 4.0): ........ 25 Meshing of the entire cargo hold: ...................................................................................... 25 Boundary Conditions:.......................................................................................................... 26 Torsional Loading: ............................................................................................................... 27 Results: ................................................................................................................................ 28 Substructure Torsional Loading .............................................................................................. 30 Longitudinal Strength By Cargo Load ...................................................................................... 34 Transverse Hydrostatic Pressure Effect: ................................................................................. 37 Conclusions ................................................................................................................................. 40 Further studies ............................................................................................................................ 41 Bibliography ................................................................................................................................ 42
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
ACKNOWLEDGEMENT I would like to express my heartfelt thanks to Professor Nigel Barltrop for his invaluable guidance during the course of the project that opened the doors of new ways to learn things and revealed professional approachability to technical issues. He took out his precious time whenever possible and showed many ways to find analytical solutions to a ship structural analysis. In addition, I would like to thank Mr Gurpreet Grewal, and many other PhD students who gave me a lot of precious guidance that made it possible for me to go about smooth modelling and approaching appropriate results... I would like to thank the Naval Architecture and Marine Engineering department for providing the facilities required in completion of the project. Last but not the least, I am extremely grateful to my parents overseas who gave me a chance to study further and supported me during my studies. I would like to dedicate this report and my studies to them. I also want to thank all the professors and teachers from the University of Strathclyde who helped me generously. I extend my sincere thanks to my friends at the University of Strathclyde who not only gave me generous help at the software understanding, but also encouraged my efforts whenever I faced difficulties. Moreover, during the course of the studies, the university administration availed the services of the computer laboratory and kindly helped us through many formalities as and when required. I extend my sincere thanks to the respectable staff members of the University of Strathclyde‌
Thank you, all!
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
ABSTRACT Offshore Industry encompasses types of formidable structures which have been helping humanity access deep water oil and gas reservoirs and carry large amount of goods and cargo (oil and gas) in bulk across the seas with incredible efficiency for over one a half century now. A structure serving at sea is subject to various loadings, such as wave loads, selfweight, bending due to lateral loading caused by ballasting and de-ballasting, too. Therefore, it is of utmost importance that we identify the structural strength of the design beforehand we launch the structure at sea, or at an offshore field. The various loading formats and effects are of prime importance in the design of a structure. The complex designs of modern ships demand for greater reliability, efficiency and an economical and powerful method of design and analysis. Unlike the earlier empirical approaches of analysing structural strength, new 'design codes' and rules have been developed by ship classification societies. The design must be approved by these classification societies before the actual service of the structure. It has reduced the amount of time required to design scantlings and design parameters as the classification societies provide easy-to-use formulae. A thorough design of a ship includes all fraternities of science and mathematics, which makes it a joint venture of engineering miracles. In this thesis, we would be dealing with a simplified analysis of a bulk carrier taking its longitudinal ultimate strength calculations and warping and response to torsional loading capacity including St. Venant's Principle into consideration. According to the the 'International Convention for the safety of Life at sea' defines a bulk carrier as "a ship constructed with a single deck, top side tanks and hopper side tanks in cargo spaces and intended to primarily carry dry cargo in bulk; an ore carrier; or a combination carrier." From the earlier studies in the structural analysis, people have done 2D design checks of the ships calculating longitudinal and transverse stability of a floating ship, both in still water and wave loading. Ship as a beam and ship in wave loading is studied thoroughly for decades now. In this paperwork, we will be throwing light on the torsional analysis on a bulk carrier. When a lateral loading on a fully loaded bulk carrier causes when a wave hits the hull at an oblique angle, ship undergoes a torsional loading.
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
INTRODUCTION
"A ship constructed with a single deck, top side tanks and hopper side tanks in cargo spaces and intended to primarily carry dry cargo in bulk; an ore carrier; or a combination carrier."
The types of the bulk carrier are a big topic of discussion as there are various types of bulk carriers taking their purpose and routes and sizes into consideration. The major classification goes according to their sizes as below:
OBO Ships: The ships, which are designed for the carriage of solid and liquid bulk cargoes. They were designed to reduce number of ballast voyages, avoiding their empty voyages.
ConBulkers: The ships, which are capable of carrying containers and dry cargo in bulk that are provided with wider hatches and lifting gears on top of them.
Ore Carriers: Bulk carriers designed to carry Iron ore, grains and cement in bulk. This type of cargo is unpacked and Ore carriers have stowage factors 0.34-0.51m3/ tonne.
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
Great Lakes: The bulk carriers that operate in the region of Great lakes between the EUA and Canada, that are limited by the maximum width of the St. Lawrence canal (22.8m). The great lakes are equipped with self-unloaders (buckets or conveyors). Their designs are intricate compared to the other bulkers as they have many hatches, cargo holds and their deadweight ranges from 26000-38000t
Now, the most important classification of the bulkers is according to their sizes: Bulk carriers are majorly segregated into six types, according to the sizes. Small, handysize, handymax, panamax, capesize, and very large. Ore carriers and VOBC are actually fall under the category of Capesize, but they are considered separately.
Type
Deadweight
Length
Draft
(Ton)
Overall
(m)
(m) Handysize
10000-35000
130-150
10
Handymax
35000-59000
150-200
12
Panamax
60000-80000
200-230
15
Capesize
80000 and over
230-270
18
Important definitions and terms of structural components of a bulk carrier structure are mentioned below which are vital in the design and analysis of a bulk carrier.
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
1. Bulkhead: This element defines the separation of the different compartments on the ship. They are purposefully used to increase the rigidity of the ship, to divide the area Into different zones for usage of machinery and cargo storage, to provide watertight integrity in the case of breach of hull or collision or grounding. The last but not the least is to provide fire resistant walls.
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
Types of the bulkheads are: (Bureau Veritas)
Type
Density
Stiffener Spacing
Insulation Thickness
(kg/m3)
(mm)
(mm)
A15 U MPN 24
24
300
50
A30 U MPN 36
36
250
60
A30 U MPN 66
66
250
30
A60 U MPN 36
36
250
30
Longitudinal Stiffeners: Secondary Structural components which support longitudinally to the structure of the hull starting from Engine-room forward bulkhead to the forward collision bulkhead. these are hull strengthening members of the structure. the profile of the standard Double bottom stiffeners is as follows:
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
OBJECTIVES OF THE PROJECT
A ship is susceptible to the gamut of loading forms such as longitudinal loadings when a ship acts a beam and transverse loading due to lateral wave loading. We need to analyse the effect of this combined format of loading. Hydrostatic pressure, wave loading, fatigue because of the same, longitudinal stress and transverse stresses due to cargo and waves. The loads on the structure consist of its own weight, inertia forces, fuel, cargo weight. Steel and Cargo loads are well defined. Geometric properties of a structure and its orientation easily give us its weight in tonnes. Fuel loads are distributed along the tank bottoms or maybe its bottom nodes in the Numerical model. Inertia loads are found by mass distribution of the loads along the length of the ship, and are applied so as to place the vessel in the dynamic equilibrium. although this static calculation is highly idealized, a comparison has been made of the longitudinal strength calculations for the vessel fully loaded by the static and dynamic methods. In this paper, we will be discussing response and structural strength of a bulker which undergoes torsional loading due to laterally applied wave loading. for that a half wave height is given by the following equation. where is the wavelength in meters This also is used to calculate longitudinal bending moments.
Hw 1.01
0.4
In this paper, we will be discussing the both methods of calculation indicated the same critical loading condition. If a bulk carrier heads a wave at an angle of 60o to a wave of one-half the ship length (wave crest amidships) produced the critical loading. such as follows:
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
Angular dimension: 60o
wave length:
L
0.7
The structural strength is calculated with the help of elasticity theories according to which if yield stress happens to be exceeded by the structure, deformation in the plastic mode happens and other theories based on plastic deformation and plasticity have to be employed in order to assess the strength of structures. Young’s Modulus and shear modulus are the three parameters or the elastic constants that describe the elastic nature in case of an isotropic material. The St. Venant’s principle is also verified in this module by carrying out structural analysis on a software called ANSYS Workbench 14.0 .
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
In this paper, we will go about finding out the resultant response of the structure to the combination of lateral and longitudinal loading, including torsional load on a single compartment of a bulk carrier.
The geometry of a bulk carrier is vital element in carrying out the structural response of the structure. We will consider a Handymax sized bulk carrier for finding out results on Ansys. The ship under analysis is a merchant vessel named MV Maple Creek, whose parameters are as below: Length Overall
190
Beam
32
Draft
11
Deadweight
53474
Gross Tonnage
30002
No. of Cargo Holds
5
Typical Cross Section of a Handymax Bulk Carrier (Rhinoceros 4.0)
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
LITERATURE REVIEW DNV Common Structural Rules DNV’s expertise derived results parameters and number of methods to carry out effect of stresses on the structure with the help of FEA for the static loading conditions. The results are found for; 1. Stresses in the primary and secondary (supporting structural elements) 2. Buckling capability of primary structural elements such as bulkheads 3. last but not the least, the deflections in the structural members. Finite element model is generated to do wave induced loading effects on the structure. and the wave induced loading is highly unsymmetrical. So the structural model formed is the entire cargo hold representing one bulkhead. The model includes all the structural components from supporting members and transverse frames, too.
Modelling a ship structure and presenting it in a real format has been a challenge and an interesting thing for a structural engineer, there are multiple ways to go about the modelling and carrying out analyses for the torsional loading on a bulk carrier. A good software and modelling and application and estimation of loading is a critical selection choice for a designer. DNV with the help of their state of the art Nautics Hull Software, have developed a guidelines for new bulk carriers which are as follows:
General principles:
These set of rules apply to the hull structures of single side skin and double side skin bulk carriers with unrestricted worldwide navigation, having length of 90 m or above. We can use direct calculations for the evaluations of the following: a. Longitudinal Strength b. global strength c. beams and grillages d. detailed strength of hull We will mention a few CSR by the DNV: The schematic shows us an algorithm to follow while going about the entire structural analysis of the bulk carrier.
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
Yielding CSR: DNV defines yielding of steel structure with the help of equivalent stresses; Von Mises Stresses exceeding yield stress of the steel. Von Mises Stress at a node are calculated with the help of following formula:
eq
x 2 y 2 x y 3 xy 2
The von Mises Stresses should not exceed, in case of an isotropic material, yield stress of the structural steel.
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
Torsional CSR and load calculations: To calculate the torsion at any cross section of the bulk carrier is a challenging task for a designer, DNV provides a complex ideology for bringing practical loading conditions to the bulker as follows:
Mwt f p Mwt1 Mwt2
where
L 2 B DCBFT1 T
Mwt1 0.4 C &
2
Mwt2 0.22CLB CBFT2 FT1 and FT2 are distribution factors which are again defined as;
2 x L
FT1 sin
FT2 sin 2
x L
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
Direct strength method:
Hull Girder Effect
Considered
Still water
Wave
MSW
Cwv x Mwv
Centre of midhold
0
0
Centre of midhold
-
CWH x MWH
Centre of Midhold
-
0
Centre of Midhold
Vertical Bending Moment Vertical Shear Force Horizontal Bending Moment Horizontal Shear Force
Location
Following equations are considered while calculating the moments in a full 3D model direct strength analysis: M
M
y ( Aft Shear)
z ( Aft Shear)
xfore xaft Q
x x fore aft Q 2
2
v( T )
xeq Qv( FEM) xeq
x QH( FEM) xeq
H( T ) eq
where; xeq is preferred location on the girder. Qv,QH,Mv,MH could be calculated by following equations:
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
Influence of local loads are determined by taking a simple beam for the hull girder. these local loads induce shearing forces and bending moments. Direct strength method is the one applicable to the superimposition method. The superimposition stress is given by:
M
sim
v( T )
M
H( T )
Iy
Iz
z N
y
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
Saint Venant’s Principle, Introduction and Stress Concentration theory:
A few assumptions in the geometrical behaviour: a. Every cross section rotates as a rigid body b. Rate of twist remains constant: k c. Warping allowance in the axis (z)
When we consider deflections due to the torsion: d z dz
& k z
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
Derivative of angle alpha with respect to z, is rate of twist k- a constant
u(x,y,z)=rα(-sinβ)…..(1) v(x,y,z)=rα(cosβ)…..(2) z(x,y,z)=w(x,y)…….(3)
Thus, the displacements are independent of z From the basic theory of the finite element analysis, we already have stress strain equations in the form of Shear and young’s modulus. After a long handmade calculations, we can finally rewrite the case for torsion for orthotropic material as follows: d dz
T GJ
J= Polar moment of Inertia, torsion constant α=twist angle GJ= Torsional rigidity
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
The final result is; T
r J
……………….Shear Stress, Torque and Torsional constant.
The shear along y and x axes prove that there is displacement and Stress Concentration in the axis of torsion.
The above equation can be similar to the x
Mz
I
The stresses and strains in a body at points that are sufficiently remote from points of application of load depends only on the static resultant of the loads and not on the distribution of loads._ (MIT paper)
Point loads on a surface give rise to a stress concentration near the point of application. A stress concentrations an increase in stress along the cross-section that may be caused either by such a point load or by another discontinuity, such as a hole in the material or an abrupt change in the cross-sectional shape. Since we have already shown strain to be proportional to stress, we can get a good idea about the magnitude of normal stress by examining the normal strain in a material as it is being subjected to some loads. To allow this, we can draw lines parallel to the normal plane and see if they remain plane during load application. In each of the following cases, witness how near the discontinuity there is a non-uniform distribution in the strain field, while farther away the distribution is linear.
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
TECHNIQUES AND APPROACHES USED
Finite Element Analysis for finding out torsional responses by the ship structure. Midship section of a bulk carrier as shown in the figures above reflect a box with longitudinal stiffeners and transverse frames. Ship as a symmetric structure, we have to model the entire 3D model to analyse the effect in torsional loading in the secondary structure near the hatch opening area. Boundary conditions is a challenging task for offshore structures as they are floating and their supports and resting grounds keep changing depending upon the intensity of the load. Therefore, we use a simple case of structure being welded to the next cargo hold and torsional loading acting on the bulkhead on the other side, similar to a case of wave load impacting obliquely. For the observations we take a small value of torsional load and increase it along with a loading factor for extreme loading. The comprehensive load acting on the structure includes self-weight, cargo, ballast, wave load and hydrostatic pressure on the outer hull. we in the further part of the project discuss these loads individually, focussing more on the torsion and its effects, stress concentration, safety factors and effect on the inner secondary structures. Modelling issues: the solid elements in the ANSYS program is exceeding the number of nodes that could be accessed by the Ansys solver module, so we decide to use only surface elements with different thickness patterns for all the structure. Importing the rhino model in Ansys. The intricate model, which could not overcome connections at the filleted hull plates.
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We will consider steels’ structural properties, both linear and nonlinear. Ansys workbench’s automatic option for nonlinear response is clearly observed in the results for a beam or axial loading increments.
MODELLING AND BOUNDARY RESTRICTIONS
ANSYS Workbench 14.0 allows an option of importing geometry from the Rhinoceros 4.0 in .iges format. That helps us create a user-friendly model for creating the geometry and create different element types as we go about forming the real structure. Hull plates are modelled as plates, or surfaces in rhino and the secondary structural components such as stiffeners and joints in solid elements in the rhino. Scantlings of the design are mentioned as below:
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
Double Bottom Height
1.5m
SOLAS Requirement
Thickness of Hull plate
0.025m=25mm
Ship’s hull, DNV Standards
Thickness of the
0.02m=20mm
Standard stiffener sizes
Longitudinal Stiffeners
We will be focussing on the region close to the hatch openings of the Midship section where there is a lot of stress concentration and effect on the inner secondary structure inside of the hull plating. Torsional loading causes combined loading effect which could be elaborated by St Venant’s Principle in the Ansys analysis in the next part. We can take situation of symmetry into the consideration as the structure is symmetric about the central axis of the ship. but that will make the boundary conditions too ideal or increase approximate stiffness of the structure. The partitioning of the total loading is automatically
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
performed in the Ansys program. therefore it reduces the necessity of modelling the Midship section in symmetric or anti-symmetric manner. The entire model, however increases the bandwidth of the solution and its time, giving out close to exact solutions.
One more graphical pattern of shear stresses could be generalised as follows; which depicts shear force in tons caused by wave bending moment: (Structural analysis of a containership under combined loading; ship structure committee) In order to fully represent the structural response of hull girders to a torsional loading due to the action of oblique wave loading at 60o, it is necessary to model the entire cross section. (Model shown in an extra sheet in landscape print.)
ANALYSES& RESULTS The Material properties: Name
Structural Steel
Density
7850 kg/m3
Coefficient of Thermal Expansion
1.2e -5 C-1
Specific Heat
434 J/kgC
Ulimate Tensile Strength
460MPa
Tensile/Compressive Yield Strength
250MPa
Elasticity coefficients:
Young’s
Poisson’s
Modulus
Ratio
2e11
0.3
Bulk Modulus
Shear Modulus
1.667e11
7.6923e10
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
Complete Cargo Hold Torsional Loading
The Entire model’s Geometry. (imported in ansyswokbench from Rhinoceros 4.0):
Meshing of the entire cargo hold:
With the usage of advanced size function and coarse relevance centre, we meshed this model, with continuous nodes and without any flying nodes as below. Initially the nodes were discontinuous and not smooth, the change of sizing in Ansys and numerous changes brought this smoother meshing as we have put in the picture, which nullifies the abrupt stress changes in the mesh. After many attempts the below size of the mesh gave us the relatively better meshing as in the picture below. The mesh size is 0.235280m
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
Boundary Conditions:
The torsional loading is practically shown in the ansys by fixing one end of the structure. The mid-ship section is welded to the next cargo hold via the edges in the blue that are shown in the diagram below. We can assume that the structure is fixed by the edges where an oblique wave does not impact during the wave load. For the simplicity and to avoid general errors during analysis we fix the one end of the cargo hold by its edges, hose are 44 edges to be welded to the next cargo hold.
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
Torsional Loading:
Torsional Load: 50Nm applied across the face, and then we move on to the finite element analysis of the structural response to the torsional load to find out stresses in different directions and yield check. The results of this analysis could be multiplied by the factor we multiply the load, if only the applied force is uniform over the surface.
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
Results:
Equivalent Stress
Maximum shear stress= 14.986Pa, if we multiply the loading by the factor of increment, we can see the ten times of loading could be sustained in shear by the joints near the crosssection as it would not exceed the shear stress strength. Total Deformation
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
in this result we can clearly see the St Venant’s principle being proved. The structure upon torsional loading, deforms in longitudinal direction as well. The deformation at the forward end of the bulker is large than the central part Middle Principle Stresses:
Middle Principle stresses show us the stress concentration along the hatch opening corners. the maximum stress is 51MPa (factor of 10 multiplied upon further increment) The corners need extra secondary structures supporting and reducing the stress concentrations.
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
Shear Stress:
Maximum Shear Stress: 36.139MPa.
Quantity
Directional
Von Mises
Deformation
stress
-8
Shear Stress
Maximum Shear Stress
Max
3.6346e m
149.86MPa
36.139MPa
77.796MPa
Minimum
0m
3.35e-2 MPa
-41.152Mpa11
1.87Mpa
Substructure Torsional Loading After comprehensive structural analysis in the previous section, we will focus on the substructure which includes secondary structural members such as hopper tank hull plates, we exclude the transverse plates in this analysis so as to extract the effect of torsion on the supporting structure
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
6.2.1 Geometry
6.2.2 Mesh the substructure is made of surface elements and thus is meshed by quad elements in Ansys. the mesh size is the same as that of mentioned in the earlier model for complete cargo hold torsional loading. mesh size:
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
6.2.3 Boundary Conditions
6.2.4 Torsional Load
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Results Equivalent Stress
Equivalent Stress does not exceed the failure criteria of the steel, von mises failure criteria, thus the structure (substructure is safe)
Shear Stress
In this analysis, shear stress represents the compression and tension in the
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
Torsional Deformation
Longitudinal Strength By Cargo Load
6.3.1 Geometry:
6.3.2Mesh:
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
6.3.3 Boundary conditions for longitudinal Strength:
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
6.3.4 Load:
6.3.5Results: Equivalent Stress:
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
Shear Stress:
Transverse Hydrostatic Pressure Effect: 6.4.1 Geometry:
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421 6.4.2 Meshing:
6.4.3 Boundary Conditions:
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421 6.4.4 Load:
6.4.5 Results: Equivalent Stress:
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421 Safety Factor:
CONCLUSIONS Consolidated Results: Condition
Equivalent Stress (Pa)
Total Deformation(m)
Shear Stress (Pa)
Max
Min
Max
Min
Max
Min
Complete Structure
149.86
10.735
3.69e-6
0
36.139
-41.151
Substructure
150.62
8.184
1.28e-6
0
62.298
-65.452
From the analyses, we could observe the St Venant’s Principle executed in a moderate format. Maximum Deflection in z (axis of torsion) was= 3.69mm During the same torsional loading the structure had stress concentrations on the hard edges of joints of primary and secondary structures. The substructure as in the second analysis, took compressive stress during torsional loading. More the number of transverse frames along the length of the bulk carrier, the substructure deformed less.
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
shear force diagram in the analysis, shows weather deck platform under negative shear force and inner substructure under compressive stress. The values that were proposed to be found out, were calculated with the help of the ANSYS program and MATHCAD. During the analysis, we faced a lot of times when the solver could not get through because of boundary condition errors. After detaield studies of the uniaxial case of laoding, the boundary conditions were changed to fixing one end of the strucutre. The thesis improved my understanding of detailed strucutral analysis, bringing about practical boundary conditions and calculating strength of the whole structure. We found that cargo load and the hydrostatic load acting on the strucure tends to deform the structure, but upon still water conditions,
On a different analysis, we got a deformed shape of the structure, which is given by; which explores shear stress concentration and deformed shape of the entire structure under torsional loading.
FURTHER STUDIES After the bulk carrier’s structural analysis Finite element analysis for bottom structural design, we will focus on structural analysis of containership under individual as well as
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Aditya Prakash Bodhe MSc in Ship and Offshore Structures Reg. No. 201272421
combined loading of vertical, lateral and torsional moments using finite element analysis. I would like to learn naval architectural design and structural analysis of oil tankers; I am going to focus on the bodyline diagrams and ship stability calculations. a. Individual load response in the whole structure. b. Fracture analysis of the ship structural response in Ansys APDL c. To calculate dynamic structural response in Orcaflex and study loading patterns on the ship structure.
BIBLIOGRAPHY
1. SSC-243 (SL-7-3)- Structural analysis of cargo ship, under combined loading, Ship Structure committee 2. Standard Ship Designs by Robert Scott 3. Ship Structural Design by Owen F. Hughes 4. Ship Stability for masters and mates, SWBM and Wave Loading by D. R. Durrett 5. DNV website updates 6. Rules for Classification of Bulk carriers, IACS Common Structural Rules 7. DNV CSR from the DNV website 8. ES 222, Strength of Materials by Dr. Whelan 9. Fundamentals of Torsion theory by Paul A. Lagace, Ph.D. 10.
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