A Study on Ultimate Strength of Ship Hull Girder under Slamming

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(1) First, this study deals with estimation methods for the ultimate strength and post ultimate behavior of ship stiffened plate structures under in-plane combined loads using finite element method considering elasto-plastic large deflection effects. Collapse mechanisms of stiffened structures are mainly classified into two collapse modes. One is the overall buckling mode, which means collapse of both stiffeners and panels. And another is local bucking mode, which means collapse of panels or stiffeners locally. To analyze these modes and their interactions, analyzed region is decided in this study. Satisfying the boundary continuity between adjacent structures under combined loads, Multi-freedom Dependent Constraint Method is applied for boundary condition.(2) Next, this study deals with collapsing behavior and reliability analysis of ship hull girder under longitudinal bending moment. A simplified estimation method is presented for collapsing behavior of ship hull girder under longitudinal bending by using Smith's method. Stress-strain curves of rectangular panels, which are used in Smith's method, are obtained from numerical database based on finite element method considering large deflection and elastic-plastic behavior. This method is applied to reliability analysis and statistical values such as standard deviation and reliability indexes are investigated by Monte Carlo simulation and sensitivity analysis.(3) Finally, a system is developed for collapsing behavior analysis of ship hull girders under extreme wave loads using a method combined with hydrodynamic force analysis and finite element analysis. The applicability of the system is also investigated through numerical examples applied to a basic box-type girder under extreme wave loads.