This thesis is submitted for evaluation at Ålesund University College. - PDF

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MASTER THESIS TITLE: STRUCTURE ANALYSIS OF BOW STRUCTURE CANDIDATE NAME: Yingwei Liu DATE: COURSE CODE: COURSE TITLE: RESTRICTION: IP MSc THESIS STUDY PROGRAM: PAGES/APPENDIX: LIBRARY

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MASTER THESIS TITLE: STRUCTURE ANALYSIS OF BOW STRUCTURE CANDIDATE NAME: Yingwei Liu DATE: COURSE CODE: COURSE TITLE: RESTRICTION: IP MSc THESIS STUDY PROGRAM: PAGES/APPENDIX: LIBRARY NO.: SHIP DESIGN 82/30 SUPERVISOR(S): Sollied, Arne Jan ABSTRACT: The bow structure presents a significant portion of the hull structure weight, cost and fabrication time. In this thesis, with the purpose of the reduction of the weight, we arrange three of the panel configurations of the ship bow we have definited in different way, changing optimal parameters we have studied such as stiffener direction, stiffener spacing, support member spacing and plate thickness in the bowimpact spreadsheet in Naticus Hull, to find the optimal dimensions of the structure whose results should meet relevant DNV rules, and then simulate the optimal panel in nx to test strengthening enough to resist bow impact pressure. Lastly, the performances of optimized ship bow structure designs were then compared and it is concluded which configuration is better, and discussion and future work has been made in the last part. Key words: Bow structure, Stiffened panel. Structure Optimization. This thesis is submitted for evaluation at Ålesund University College. Postal adress: Visit adress Telephone Fax Bank Høgskolen i Ålesund Larsgårdsvegen N-6025 Ålesund Internett Enterprise no. Norway NO AALESUND UNIVERSITY COLLEGE PAGE 2 MASTER THESIS 2015 FOR STUD. TECHN. YINGWEI LIU THSIS TILE: STRUCTURE ANAYLSIS OF BOW STRUTRUE Here some background information about problem: This master thesis will deal with structrue optimzation of layout of the stiffened panel on the ship bow. The objective is to evaluate and compare a series of optimum deisgn(different configuration of the stiffened panel in the ship bow) with respect to weight, fabrication and performance. The performances of optimized ship bow structure designs were then compared and it was concluded which configuration is better, and how it works in the real situation. Furthermore, optimization parameters that play an important role in the weight optimization of ship bow are studied. Under this circumstance, the objectives of the present work are constituted by the following sub-tasks: 1) Brief description of calculated vessel including structural lay-out and the scantlings of the panels. Review of typical load cases and characteristic action used in the design. 2) Review of relevant characteristic resistance formulation given in DNV for stiffened plates. The theory background for the various requirements shall be explained for BowImpact2008Jan.xls of Rule Check Analysis in the Naticus Hull. 3) On the basis of characteristic action effects supplied by the theory rules of HULL STRUCTURAL DESIGN SHIPS WITH LENGTH 100 METRES AND ABOVE. January 2008, determine the dimensions of the stiffened panel. Perform parametric studies where e.g. the plating thickness, spacing of stiffeners and support member length are varied in the BowImpact2008Jan.xls to determine the optimum dimensions of the panel. 4) Develop one of the optimum panel in Finite element analysis in Siemens NX to test the structure strength such as flection and stress, and see if it exceeds the yield strength. 5) Compare and identify weight of each optimum panel to make Conclusions, discussion, and recommendations for further work. Thesis format The thesis should be organised in a rational manner to give a clear exposition of results, assessments, and conclusions. The text should be brief and to the point, with a clear language. Telegraphic language should be avoided. AALESUND UNIVERSITY COLLEGE PAGE 3 The thesis shall contain the following elements: A text defining the scope, preface, list of contents, summary, main body of thesis, conclusions with recommendations for further work, list of symbols and acronyms, references and (optional) appendices. All figures, tables and equations shall be numerated. The supervisors may require that the candidate, in an early stage of the work, presents a written plan for the completion of the work. The plan should include a budget for the use of computer and laboratory resources which will be charged to the department. Overruns shall be reported to the supervisors. The original contribution of the candidate and material taken from other sources shall be clearly defined. Work from other sources shall be properly referenced using an acknowledged referencing system. The report shall be submitted in one printed copy, and one electronic as a pdf-file version on a CD. Thesis supervisor at Aalesund University College: Sollied, Arne Jan Supervisor Deadline: May, AALESUND UNIVERSITY COLLEGE PAGE 4 PREFACE This report is the result of the Master Thesis for stud, techn, Yingwei Liu at Aalesund University College. Spring The work herein is a new project provided by my supervisor, so the process of performing this thesis is very tough in the starting point, this is due to the experience on learning how to use bowimpact xls, spreadsheet in Nautcis Hull, because there are lots of knowledge, theoretical basis behind the software, and thanks for my supervisor, so that my work can be finished before deadline. And with an agreement with some jobs like expend the size of the panel simulated in the nx has not performed in this thesis, and will be recommended in the future work. Performance of this thesis, besides essential knowledge about buckling of component structures of the panel, I have a chance to work with practical rules of DNV GL, which I don't have this when I was working in the shipyard in china for one year, and this helps me to get some practical knowledge and understand how to apply for optimal design in this thesis. During the thesis work, problems were frequently discussed, in particular would like to express a deep sense of gratitude and thanks profusely to Master Thesis supervisor Prof. Sollied, Arne Jan(AAUC) who help me not only knowledge in this thesis, but also gave me method in order to solve a problem in research as well as in real life. And also thanks for Yael Pericard in NX part. Yingwei Liu Aalesund University College AALESUND UNIVERSITY COLLEGE PAGE 1 TERMINOLOGY... 3 SYMBOLS... 3 ABBREVIATIONS INTRODUCTION TO THE CALCULATED VESSEL PROJECT BACKGROUND PROBLEM FORMULATION OBJECTIVES AND SCOPE OF WORK ASSUMPTION INTRODUCTION TO THE CACULTED VESSEL GENERAL GENERAL THEORETICAL BASIS FOR STIFFENER PLATING BUCKLING BUCKLING OF STIFFENED PLATES The impact pressure The thickness of shell plating BUCKLING OF STIFFENERS Shear Area Check Plastic Section Modulus Web Thickness Check BUCKLING OF SUPPORT MEMBERS Web Thickness fitted Section modulus and Web area Shear stress and Normal stress BUCKLING CONTROL OF SUPPORT MEMBERS Buckling control in the BowImpact2008Jan.xls Buckling control in the Buckling sheet OPTIMIZING LAYOUT FOR TRASVESE STIFFENED PANEL INTROUDCTION ANALYSIS WITH THE BOWIMPACT2008JAN.XLS SPREADSHEET Optimal design for panel with transverse stiffener (n= 5) and stringer spacing l = 2.1m Optimal design for panel with transverse stiffener (n=5) and stringer spacing l = 1.4m 30 5 OPTIMUMLAYOUT FOR LONGTIDINAL STIFFENED PANEL INTRODUCTION Optimal design for panel with longitudinal stiffener (n=5) and girder length l = 3m Stringer Web Frames Weight Eveluation FINITE ELEMENT ANALYSIS SIMPLICATION MODEL DESCRIPTION... 41 AALESUND UNIVERSITY COLLEGE PAGE General FE model Detail and Property Results of constant pressure Results of variable pressure DISUCUSSION-CONCLUSION-FUTRUE WORK REFERENCE APPENDIX APPENDIX A-CALCULATED SPREADSHEET OF TRANSVERSE STIFFENER (N=5) AND STRINGER SPACING l = 2.1M APPENDIX-B CALCULATED SPREADSHEET OF TRANSVERSE STIFFENER (N=5) AND STRINGER SPACING l = 1.4M APPENDIX C-CALCULATED SPREADSHEET OF LONGITUDINAL STIFFENER (N=5) AND STRINGER SPACING l = 3M APPENDIX D-BOW IMPACT PRESSURE IN ALL THE WATERLINE TO LONGITUDINAL ANGLE AALESUND UNIVERSITY COLLEGE PAGE 3 TERMINOLOGY Symbols L rule length in m B rule breadth in m D rule depth in m T rule draught in m C B V rule block coefficient maximum service speed in knots on draught T S girder span in m. s stiffener spacing in m, measured along the plating l stiffener span in m, measured along the top flange of the member. h 0 K r vertical distance (m) from the waterline at draught T to point considered Roll radius of gyration GM k TR Metacentric height in m Roll damping parameter in m Roll period in s φ Roll angle in [ ] θ Pitch angle in [ ] a B C W R σ τ t s l E Common acceleration parameter Wave coefficient (reduced) Radius of curvature of shell plating in m Nominal allowable bending stress in N/mm2 due to lateral pressure The shear stress, of the web plate for the support members thickness in mm of plating shortest side of plate panel in m longest side of plate panel in m length in m of stiffener, pillar etc. modulus of elasticity of the material N/mm2 for steel σ ee σ c τ ee the ideal elastic (Euler) compressive buckling stress in N/mm2 minimum upper yield stress of material in N/mm2, and shall not be taken less than the limit to the yield point the ideal elastic (Euler) shear buckling stress in N/mm2 AALESUND UNIVERSITY COLLEGE PAGE 4 σ c τ c σ a Z n Z a f 1 the critical compressive buckling stress in N/mm2 the critical shear stress in N/mm2 calculated actual compressive stress in N/mm2 vertical distance in m from the baseline or deckline to the neutral axis of the hull girder, whichever is relevant vertical distance in m from the baseline or deckline to the point in question below or above the neutral axis, respectively = material factor = 1.0 for NV-NS steel 1) = 1.08 for NV-27 steel 1) = 1.28 for NV-32 steel 1) = 1.39 for NV-36 steel 1) = 1.47 for NV-40 steel. 1) η n Wyb β Lw stability (usage) factor = σ a σ c = τ a τ c number of stiffeners located within the span length S section modulus about Y-axial flare angle waterline to longtidudinal angle Welding length ABBREVIATIONS FEM Finite Element Method AALESUND UNIVERSITY COLLEGE PAGE 5 1 INTRODUCTION TO THE CALCULATED VESSEL 1.1 Project background Thin-walled structures are widely used in the maritime industry because they make the structure more cost-effective by offering a desirable strength/weight ratio. Reduction in the structural weight of ships will increase their cargo-carrying efficiency. This increase in efficiency is obtained by either carrying more cargo with the same displacement or by increasing the speed of the ship. Moreover, the substantial decrease in material cost supersedes the higher production costs. One can easily predict that both improvements are also important from a sustainability point of view. Less emission of hazardous gases produced by marine diesel engines and reducing the use of natural resources are the examples of these structures advantages in terms of sustainability. Figure 1.1 Typical Bow region. Different types of materials such as steel, aluminium, composite and plywood are used structure design. Utilizing alternative materials to produce lightweight in marine structures will lead to weight reduction in. However, this advantage is overshadowed by the significant manufacturing and material costs. As a result of this, the focus in the marine industry has been shifted toward the structural designs and optimization of panels and ship bow, either by means of modifying the dimensions or utilizing alternative configurations for the panel structures. In this thesis, a methodology based on Rule Check together with bow impact spreadsheet is presented to investigate the possibility of obtaining weight reductions in ship bow while carrying out rule check and hull structural analysis in the panel according to the DNV Rules for ships and the IACS Common Structural AALESUND UNIVERSITY COLLEGE PAGE 6 Rules. This is to be done by BowImpact2008Jan.xls fully integrated in the Nauticus Hull system and share common ship data with the other Nauticus Hull modules. Figure 1.2 BowImpact2008Jan.xls. Windows 1.2 Problem formulation The structural design of a ships bow is a complex matter. In this context, the term ship s bow refers to the forward 10 percent of the ship s length above the summer load waterline. Figure 1.3 Definition of the Ship Bow AALESUND UNIVERSITY COLLEGE PAGE 7 The bow structure presents a significant portion of the hull structure weight, cost and fabrication time. In this thesis, we should arrange the panel configuration in different way such as changing optimal parameters stiffener spacing, support members, spacing and plate thickness in order to make bow design balance which should meet relevant DNV rules, and the contributing factors include the additional strengthening required to bow impact pressure and at the same time to save the weight and some practical reasons such as wok space enough to let the shipbuilding works welding or installing such kinds of work. 1.3 Objectives and Scope of Work The main objective with this thesis is to evaluate and compare a series of optimum design (different configuration of the stiffened panel) with respect to weight, fabrication and performance in the ship bow. The performances of optimized ship bow structure designs were then compared and it was concluded which configuration is better, and how it works in the real situation. Furthermore, optimization parameters that play an important role in the weight optimization of ship bow are studied. Under this circumstance, the objectives of the present work are constituted by the following sub-tasks: 1) Brief description of calculated vessel including structural lay-out and the scantlings of the panels. Review of typical load cases and characteristic action used in the design. 2) Review of relevant characteristic resistance formulation given in DNV for stiffened plates. The theory background for the various requirements shall be explained for BowImpact2008Jan.xls of Rule Check Analysis in the Naticus Hull. 3) On the basis of characteristic action effects supplied by the theory rules of HULL STRUCTURAL DESIGN SHIPS WITH LENGTH 100 METRES AND ABOVE. January 2008, determine the dimensions of the stiffened panel. Perform parametric studies where e.g. the plating thickness, spacing of stiffeners and support member length are varied in the BowImpact2008Jan.xls to determine the optimum dimensions of the panel. 4) Develop one of the optimum panel in Finite element analysis in Siemens NX to test the structure strength such as flection and stress, and see if it exceeds the yield strength. 5) Compare and identify weight of each optimum panel to make Conclusions and recommendations for further work. AALESUND UNIVERSITY COLLEGE PAGE Assumption In order to make the simple calculation, radius of curvature of shell plating R is zero, as we know, some shell plating of the ship has a radian which means it is not a plane, but in our calculation, all of the panels are panel. Figure 1.4 Idealization of the curvature of shell plating 2 INTRODUCTION TO THE CACULTED VESSEL 2.1 General The offshore vessel is built based on the experience data and DNV Rules for ships, and it will be set up as input in BowImpact2008Jan.xls. of the Nauticus hull which is a software package for strength assessment of hull structures. Table 1 Main data of the calculated vessel Rule length L [m] Speed V [knots] Block coefficient C B 0.70 Service area notation None Depth D [m] Draught T [m] 7.00 Breadth B [m] Roll radius of gyration K r [m] 3.96 Metacentric height GM [m] 1.68 Roll damping parameter k 0.8 Roll period TR [s] 6.11 Roll angle φ [ ] Pitch angle θ [ ] Common acceleration a B 0.50 parameter Wave coefficient (reduced) C W 8.34 AALESUND UNIVERSITY COLLEGE PAGE 9 s 1 L 2 S n = Girder 2. Web Frame 3. Stffener Figure 2.1 Side Views of general layout of stiffened panel in the ship bow. As we know, the results of weight eveluation should be compared in the kilogram per square meter(kg/m 2 ), therefore we can definite the dimension of the stiffened panel in the views of the shipbuilding, which could be explained that, from the dimension of the vessel, the distance between tween deck and upper deck is 5 meters, therfore the length(viertical distance) of the panle can be varied from 2 to 5m, and the span of the panel can be equal to the spacing of the frame which is practical estimated from 3m to 6m or more, and the feasibility of the layout will be verified after deisgn. The diference between stiffened panel of the hull and stiffened panel of the ship bow is the web angle between stiffener and shell also the angle between support members and shell, for the stiffened panel of the hull, this angle is 90 degree, but the web angle φ w for the stiffened panel of the ship bow is depending on the hull form of the ship bow hul, demonstrated as follows: AALESUND UNIVERSITY COLLEGE PAGE 10 φ w φ w Transverse Stiffener Configuration Longitudinal Stiffener Configuration Figure 2.2 Typical two kinds of layout of the stiffened panel on the ship bow. Because of the time limitation, we make caculation of the general 3 configrations of the stiffened panel in the BowImpact2008Jan.xls, and general dimensions of the panel is shown as follows: Transverse Stiffener: 1) l = 2.1m, s = 0.50m, 0.55m, 0.60m, 0.65m, and 0.70m. 2) l = 1.4m, s = 0.50m, 0.55m, 0.60m, 0.65m, and 0.70m. Longitudinal Stiffener: 3) S = 3m, s = 0.50m, 0.55m, 0.60m, 0.65m, and 0.70m. AALESUND UNIVERSITY COLLEGE PAGE 11 3 GENERAL THEORETICAL BASIS FOR STIFFENER PLATING BUCKLING The general theoretical of the requirements in this section applied to design ship s side structure on the ship bow. The formula are given for plating, stiffeners and girders are based on the structural design principles outlines in the BowImpact2008Jan.xls spreadsheet. Direct stress calculations based on side structural principles and as outlined in 3.4 will be considered as alternative basis for the scantlings and will be applied in the BUCKLING.xls Sheet in the Nauticus Hull. Figure 3.1 Stiffened plate under combined loads Figure 3.1 shows a stiffened plate under combined loads. σ x.ss is the axial load (considered as the uniformly distributed load); σ y1.ss and σ y2.ss are the transverse loads (maybe uniformly or linearly distributed loads); τ ss is the shear stress and the above stress values will be identified in the Buckling control in BUCLLING.xls sheet in the Natiucs Hull. And P ss is the lateral pressure (this term is constant in BowImpact2008Jan.xls spreadsheet and BUCKLING.xls Sheet.). Nowadays, there are many available rules, codes and guidelines for buckling design of stiffened panels in the ship structures as well as for the offshore structures.these rules are especially useful in quick design or quick calculation. However, the simple design rules presently recommended by classification societies will handle the optimum design of stiffened panels in the ship bow, if the designed load is the combinations of the compression in both longitudinal and transverse directions and lateral pressure, see Section 3.4 in this chapter. In this respect, this study proposes a simplified procedure in order to optimize the stiffened plate under these designed loads. The results of this procedure are also then calibrated against AALESUND UNIVERSITY COLLEGE PAGE 12 numerical analysis which will be carried out in this report. The ultimate goal of this thesis is to develop a robust tool that can give the optimum design of the stiffened plate under this kind of designed load. 3.1 Buckling of stiffened plates The impact pressure The impact pressure given in Eq 3.1 applies to areas away from knuckles, anchor bolster etc. that may obstruct the water flow during wave impacts. In way of such obstructions, additional reinforcement of the shell plate by fitting carlings or similar shall generally be considered. The design bow impact pressure shall be taken as: Psl = C(2.2 + Cf)(0,4Vsin β + 0,6 L) 2 (3.1) C = 0.18 (CC 0.5h 0 ), maximum 1.0 Cw C f γ φ, θ α β = wave coefficient as given in Sec
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