Study On Ultimate Strength Of Ship Structure Under Extreme Cyclic Loading

Ultimate strength is one of the important parts in safety assessment of ship structures.At present,the ultimate strength assessment of ship structures is mainly based on the static ultimate strength,that is to say,the whole failure of ship structures is caused by one-off monotonic extreme external load.However,the whole collapse of ship structure is often caused by multiple extreme loads,and the plastic strain accumulation of the structure far from the neutralization axis under the alternating extreme loads leads to the reduction of the bearing capacity of the ship,eventually causing the hull girder to collapse.In order to solve this problem,the research on ultimate strength of ship hull under extreme cyclic loading is carried out in this paper.The research work is an important component and further development of ISSC 2021 Ultimate Strength Benchmark:(1)Based on the nonlinear finite element method,the ultimate strength criterion of the frame under monotonic load is studied,and the effects of initial deformation,welding residual stress and other factors on the ultimate strength of the frame structure are analyzed,the error between the numerical results and the ISSC 2021 panel test results is less than 2%,which verifies the accuracy of the nonlinear finite element method in calculating the ultimate strength of panel under monotonic load and paves the way for the ultimate strength of panel under subsequent cyclic load.(2)Considering the Bauschinger effect and ratchet effect of the materials under cyclic loading,the ultimate strength of the grillage under cyclic loading is studied,and the difference between the ultimate strength of the grillage under monotonic loading and cyclic loading is compared and analyzed,the change rule of ultimate load-carrying capacity and the plastic strain and failure of the structure under various cyclic loading conditions are mainly studied.(3)Taking a ship hull section with ore as an example,the ultimate strength of ship hull girder under monotonic load and cyclic load is studied,the accumulation of plastic strain,the evolution of failure mode and the variation of ultimate strength of ship deck structure under cyclic loading are analyzed,which lays a foundation for evaluating ultimate strength of ship hull under extreme cyclic loading.