Hull Girder Ultimate Strength Research Based On Smith Method

Through load iteration with the mechanical properties of stiffened plate elements,the Smith method obtains the moment-rotation curve of hull girder and the largest moment is the ultimate bending moment.The Smith method can reflect the actual failure process and the post-buckling characteristics of the members with good accuracy and convenient application,which is a recommended method for calculating the hull ultimate moment in HCSR.The accuracy of Smith method depends on the member stress-strain curves and the position of neutral axis.The HCSR has given the member stress-strain curves under typical failure models,but it's not clear whether it's suitable for high-strength steel members while high-strength steel is widely used in ship structure.Furthermore,the positioning method in HCSR can only consider the vertical translation of the neutral axis by force equilibrium criterion which is only suitable for symmetrical section of intact ship but not for asymmetric section especially for damaged hull section.Therefore,it's necessary to carry out the research on the improvement of traditional Smith method,especially on stress-strain curves of high-strength steel members and positioning method of neutral axis.The main contents of this paper are as follows:1)The program development of the Smith method.The principles,assumptions and process of Smith method were introduced,and the traditional Smith program based on HCSR was developed.2)Research on stress-strain curves of high strength steel members.Because of the particularity of high-strength steel material curve,the member stress-strain curves under different material models was studied by NFEM to verify whether the stress-strain curves in HCSR is suitable for high-strength steel members.3)Research on neutral axis positioning method.Considering the translation and rotation of the neutral axis by force equilibrium criterion and force vector equilibrium criterion,the multi-objective particle swarm optimization algorithm was used to search for the position of neutral axis by setting the neutral axis displacement and rotation angle as the optimization variables,the force equilibrium criterion and the force vector equilibrium criterion as the optimization objective,which effectively improved the positioning accuracy and intelligence.4)Research on combined hull vertical and horizontal ultimate strength.The sample points of hull vertical and horizontal ultimate strength were calculated by Smith method by changing load angle,then the ultimate moment envelopes were plotted and the ultimate state equation was fitted,with which the hull ultimate strength was evaluated.