Reliability Assessment Of Containerships Based On Response Surface Method

A reliability assessment of containership's longitudinal ultimate strength based on response surface method is carried out,aiming at estimating the overall bending load level and providing reference for reliability assessment.The target ship is on full-load condition and the capacity of which is 10000 TEU.An improved moving least-square method is proposed and then applied to structural reliability assessment.According to the improved method,sampling point's weigh is redefined by not only the distance between itself and center point but also the distance between itself and response surface.The improved method is also combined with vector projection method thus forming a combination method.Numerical results indicate the improved method has higher accuracy and the compound method has higher efficiency.Longitudinal ultimate strength of target ship is calculated by nonlinear FEM using a part-cabin model.Arc-length method and quasi-static method is both applied to solve this nonlinear equation but Arc-length method failed in convergence.Besides,results corresponding to different loading speed is compared.Overall longitudinal bending moment includes still-water bending moment and wave-induced bending moment generally.Still-water bending moment treated as a fixed variable here and long-term extreme value's probability distribution of wave-induced bending moment is obtained.Slamming and whipping are considered but when ship is in full-load condition,vertical bending moment due to whipping is relatively small compared to wave-induced bending moment according to numerical result performed in this paper.As a result of this bending moment due to whipping is neglected.Based on the content of the previous study,failure probability of target ship under sea state of the North Atlantic is obtained,showing a high reliability of this containership.