Study On Residual Ultimate Strength Of Crack Damaged Ship Structures

Ships will experience severe and complicated sea conditions when sailing in the open sea.Once the ship structure is damaged,it is difficult to be effectively repaired and strengthened in a short time.In this case,it is necessary to quickly evaluate the residual ultimate strength of the structure in the damaged state of the ship,so as to provide a reliable basis for the captain’s decision.At present,most of the research on the residual ultimate strength of cracked ship structures is limited to the evaluation and analysis of the ship design stage,and a real-time engineering application evaluation method has not been proposed.Therefore,it is necessary to propose a calculation formula for the residual ultimate strength that comprehensively considers the influence of multiple parameters,and to establish a residual ultimate strength database to achieve a rapid assessment of the residual ultimate strength of complex hull structures under arbitrary crack lengths.In addition,the evaluation of the residual ultimate strength of the structure generally assumes that the crack does not propagate,and the effect of the crack tip stress state on the residual strength of the structure cannot be fully considered.Therefore,it is necessary to propose a new residual strength evaluation method based on fracture mechanics theory.This paper investigates the effect of various crack parameters on the residual ultimate strength of the structure under different load forms.First of all,under the tensile load,comprehensively considering the influence of various crack characteristics on the residual ultimate strength of the stiffened plate structure,an improved empirical formula for faster and accurate assessment of the residual ultimate strength is given.Then,for the flat plate structure under uniaxial and biaxial compressive loads,the effect of any crack position on the buckling half-wave peak is summarized.On this basis,the relevant factors that have an important influence on the nonlinear response are considered,and the problem of non-convergence of the nonlinear finite element calculation of the complex hull structure is solved.For the most dangerous cases,typical crack locations and different crack lengths are established.Database of residual ultimate strength of actual ship structure,so as to achieve rapid assessment of residual ultimate strength at any crack length.By comparing the numerical simulation results,the accuracy of the database established in this paper is verified,which reflects the good engineering application prospects.Finally,from the perspective of elastic fracture mechanics,a residual strength evaluation method based on singular element method and equivalent integration area is proposed,which can obtain the stress intensity factor of the precise crack tip position and achieve accurate prediction of the residual strength.The above method is used for crack arrest research.