Numerical Optimization Analysis of Cruise Vessels Submitted on 31st August 2020 by LUNGU Daniela-Laura| Erich-Schlesinger-Str. 19, Room 1.5.4.1 | 18059 Rostock | [email protected] Student ID No.: 219 200 149 First Reviewer: Second Reviewer: Prof. Dr. Eng./Hiroshima Univ. Patrick Kaeding Dipl.-Ing. Stefan, Griesch Pro-Rector of Studying, Teaching and Evaluation Senior Project Engineer Universitätsplatz 1, Room 124 MV WERFTEN Wismar GmbH 18055 Rostock 18119 Rostock Germany Germany Master Thesis i [This page is intentionally left blank] ii Declaration of Authorship I, Daniela-Laura Lungu, declare that this thesis and the work presented in it are my own and have been generated by me as the result of my own original research. Where I have consulted the published work of others, this is always clearly attributed. Where I have quoted from the work of others, the source is always given. With the exception of such quotations, this thesis is entirely my own work. I have acknowledged all main sources of help. Where the thesis is based on work done by myself jointly with others, I have made clear exactly what was done by others and what I have contributed myself. This thesis contains no material that has been submitted previously, in whole or in part, for the award of any other academic degree or diploma. I cede copyright of the thesis in favour of the University of Rostock. Date: Signature: 31st of August, 2020 iii [This page is intentionally left blank] iv ABSTRACT One of the most important aspects to consider in ship design is the structural integrity for which yielding plays a decisive role. In order to have good strength in a ship, specially cruise vessels, which are large and complex structures, yield check is required to assure the safety under extreme loading conditions. To provide a good structure and maintain costs as limited as possible, structural optimization is carried out. In this thesis, the main optimization methods are explained with emphasis on the two methods used for the strength analysis of the vessel. These are size (scantling) optimization and change of material and an optimization algorithm has been developed in order to implement these methods. They are assessed as two separate methods in the optimization process, implemented for one structural model, selected at the midship of a cruise vessel, between two transversal bulkheads, subjected to two independent loading conditions, sagging and hogging. The main objective of the optimization is to minimize production costs, whether it is by minimising the mass through thickness change of the panels, or by changing the material used to a material with better properties, such as higher strength allowance. For the validation of the optimization algorithm strength analysis has been carried out in ANSYS Academic Research Academic and CFD, version 18.2, with license provided by the University of Rostock. The results obtained from the iterative process show that the two methods achieve structural optimization, but at different costs. The size optimization is a time-consuming method, and complicated to the extent that panel thicknesses have to be uniformly distributed for good weldability. On the other hand, the material change method is more practical from a shipyard point of view, since normal steel and high tensile steel have similar densities, providing almost similar mass, therefore, better structural strength with no need of considering thickness differences between panels. For both methods there are improvements to be considered for further analysis. v [This page is intentionally left blank] vi TABLE OF CONTENTS ABSTRACT .......................................................................................................................................... iv TABLE OF CONTENTS .................................................................................................................... vi List of Figures ..................................................................................................................................... viii List of Tables ........................................................................................................................................ ix List of Abbreviations and Symbols..................................................................................................... ix 1 INTRODUCTION ......................................................................................................................... 1 1.1. Problem Formulation and Approach .................................................................................. 1 1.2. Structure of the Thesis .......................................................................................................... 2 2. THEORETICAL APPROACH IN STRUCTURAL OPTIMIZATION .................................. 4 2.1. FEM and FE Analysis in Mechanical Engineering ............................................................ 4 2.1.1. FEM Procedure ................................................................................................................ 4 2.1.2. Equilibrium Equations ..................................................................................................... 5 2.1.3. Strain-Displacement Relations ........................................................................................ 6 2.1.4. Stress – strain constitutive equations ............................................................................. 7 2.1.5. Boundary conditions ....................................................................................................... 8 2.2. General Aspects of Structural Optimization ...................................................................... 8 2.3. Types of Optimization .......................................................................................................... 9 2.3.1. Topology Optimization .................................................................................................. 10 2.3.2. Shape Optimization ....................................................................................................... 11 2.3.3. Material Optimization (Change of material grade) ....................................................... 14 2.4. The Objective of the Optimization Process ...................................................................... 14 2.5. Constraints ........................................................................................................................... 15 2.5.1. Technological Constraints ............................................................................................. 15 2.5.2. Geometrical Constraints ............................................................................................... 16 2.5.3. Structural Constraints ................................................................................................... 16 2.6. Design Variables .................................................................................................................. 19 2.7. Steel Properties and Behaviour ......................................................................................... 20 2.7.1. Linear Elastic Material Condition .................................................................................. 20 2.7.2. Yield Criteria .................................................................................................................. 21 2.8. Load Condition .................................................................................................................... 23 2.8.1. Sagging .......................................................................................................................... 24 2.8.2. Hogging ......................................................................................................................... 25 3. NUMERICAL MODEL ............................................................................................................. 27 vii 3.1. ANSYS Parametric Design Language (APDL) ................................................................ 28 3.2 Sample Model Description ................................................................................................. 29 3.2.1 Boundary Conditions and loads .................................................................................... 30 3.3 Main Model Description ..................................................................................................... 30 3.3.1 Boundary Conditions and Loads ................................................................................... 33 3.4 Algorithm Development ..................................................................................................... 35 4. NUMERICAL OPTIMIZATION ANALYSIS......................................................................... 37 4.1 Change in Plate Thickness ................................................................................................. 37 4.1.1 Sagging .......................................................................................................................... 38 4.2 Change in Material (Steel) Grade ...................................................................................... 47 4.3 Results .................................................................................................................................. 52 4.3.1 Sagging .......................................................................................................................... 53 4.3.2 Hogging ........................................................................................................................