Residual Strength Assessment Of Ship Hull Under Combined Moments

The residual strength of damaged ship structure is an important criterion of structural design.Currently,many foreign rules have classified the residual strength into ship structural strength assessment system.However the method to assess the residual strength in the domestic is not comprehensive.Experiments show that the critical load of damaged ship in oblique waves is likely to exceed the vertical ultimate moment in head sea.So it is necessary to propose a residual strength assessment method under combined moments.In this paper,the main contents are as follows:1)The Smith method is studied on account of the basic assumptions and calculation process.The failure modes of structural unit and stress-strain relationships are presented for analyzing the residual strength.According to LR naval ship rules,the parameters of breach are defined.The results of residual strength respectively by using analytical and Smith method are compared.In addition,the influence of breach on horizontal moment is given.2)The structural nonlinear problems and the dynamic analysis on explicit nonlinearity are described by the NFEM method.And the modeling principles for nonlinear finite element analysis are established.The ultimate bearing capacities consider the vertical moment,horizontal moment and torsional moment.And the assessments on the three directions are presented respectively.In the same time,the results are compared among the NFEM method,analytical method and Smith method.3)The three-dimensional potential flow theory of damaged ship to calculate the hydrostatic load and wave load is studied.The equations on motion of damaged ship are built and solved.Finally,the design loads by rules and direct calculation are given.4)The interaction equation for damaged ship under the combined moments is derived.The reliability and deterministic assessment methods of damaged ship residual strength are established by considering the combined moments.