Nonlinear Finite Element Analysis For The Ultimate Strength And Residual Strength Of Ship Hulls

Common Structure Rules (CSR for short) introduced Limit Ultimate Strength to the strength criteria of bulk carrier and double hull oil tanker in2006, and an advanced nonlinear finite element method of assessment is explicitly allowed. However, CSR has no detailed explanation about this method.Since the CSR issued, some queries from ship building industry had come out soon. Now each classification society belongs to the IACS (International Association of Classification Societies) has reached a consensus, i.e. in the near future they would establish an harmonized common structure rules (HCSR for short) for instead. In HCSR some details about FEM technology, senior buckling and limit ultimate strength would be amended. Some new concept such as Structure Redundancy and Residual Strength might be appended in HCSR as well.This thesis includes two major part:(a) make further research of assessment procedure of ship’s ultimate strength as well as some influencing factors by using nonlinear finite element methods;(b) Study of the residual strength assessment criteria for ships after collision and grounding.The fore part of the thesis is about calculation of ship’s ultimate strength by using MARC (a general FEM code). Another code ANSYS is used to apply initial imperfections, which should trigger the minimum failure mode of structure. A qualitative investigation involves initial imperfection, grid scale, model region, element type, boundary conditions et al. is carried out.The latter is about residual strength assessment index of ships after collision and grounding. Finally a container’s residual strength is assessed with a nonlinear finite element procedure, by using the index based on ultimate strength and extreme loads.In this thesis, main study works are as following:(1) Proposing a FEM simulation method for the initial imperfections of ship structures. Making a discussing of the influence from shape and amplitude of initial deflections and orientation and distribution of weld induced residual stresses, respectively. (2) Centre on the origins of nonlinear finite element, calculating the limit ultimate strength of several classic box girders. Comparing the experiment results to prove the reliability of method in this thesis.(3) Make a benchmark study of ultimate hull strength of4classic-type ships by using a nonlinear finite method, and assessing the ultimate strength of a standard type inland-water ship.(4) Taking account of effect of lateral pressure on the progressive hull collapse behaviour of ships subject to vertical bending moments.(5) Using a nonlinear finite element method to finish the assessment of residual strength of a container ship.