Ultimate Strength Analysis Of Hull Structures Under Cyclic Loading Based On Thermal Elastic-Plastic Finite Element Method

The ultimate strength assessment of the ship’s hull is essential to ensure the safety of hull structures,and the initial deformation and residual stresses generated during the welding manufacturing process will reduce the ultimate strength of hull structures.It is an important precondition for ultimate strength analysis to accurately obtain the welding initial deformation and residual stresses of hull structures.The majority traditional studies on the ultimate strength of hull structures focus on assessing the maximum load carrying capacity of hull structures under a single load.However,when the hull structure experiences the cyclic and repeated action of wave loads,the hull structure is very likely to generate plastic strain and accumulate continuously with the number of cyclic loads increasing.The continual accumulation of plastic deformation under cyclic loading will make the ultimate strength of hull structures lower than the ultimate strength under single load.The hull plates and stiffened plates are the basic components of hull girders,and the study of its ultimate strength characteristics under cyclic loading is essential for an indepth understanding on the overall collapse of hull girders.This study uses the thermal elastic-plastic finite element method to carry out welding numerical simulation of hull plates and stiffened plates,based on which the ultimate strength analysis of hull plates and stiffened plates under cyclic loading is carried out,the following work is mainly accomplished:(1)Using the thermal elastic-plastic finite element method,the welding numerical simulation for the solid element model and the shell element model of rectangular plates was carried out.The two models were compared and analyzed for the temperature of each layer,longitudinal residual stress and vertical deflection,and the computational efficiency of the two models was further compared.(2)Using the thermal elastic-plastic finite element method,the welding process numerical simulation of butt-welded hull plates and fillet-welded hull stiffened plates shell element model was carried out.The effect of plate thickness on the longitudinal residual stress and vertical deformation of hull plates is studied,and the influence of plate thickness on the calculated results for hull stiffened plates fillet welds is analyzed.(3)The welding calculation results are used as predefined field loads for the hull plate and flat bar stiffened plate ultimate strength analysis finite element model under cyclic loading.The nonlinear finite element method was used to perform the ultimate strength study of hull plates and stiffened plates under cyclic loading.The effect of plate thickness on the(residual)ultimate strength of hull plates and flat bar stiffened plates under cyclic compression-tension loading was investigated.(4)Using the nonlinear finite element method,the effect of plate thickness on the plastic yield zone distribution of hull plates and flat bar stiffened plates at the moment of ultimate strength under single compression and cyclic compression-tension loading is investigated.And,the influence of material properties on the residual ultimate strength of hull plates and flat bar stiffened plates under cyclic compression-tension loading is also discussed.(5)The differences on the ultimate strengths of hull plates and flat bar stiffened plates under single compression and each cyclic compression were investigated by using the nonlinear finite element method.The effects of load patterns and plate thickness on the residual ultimate strength of hull plates and flat bar stiffened plates under cyclic compression-tension loading are further discussed.