Investigation into the dynamic collapse behaviour of a bulk carrier under extreme wave loads

Abstract

The aim of this paper is to quantitatively evaluate the extent of collapse of a bulk carrier when the ship is subjected to extreme wave loads. A hydro-elastoplasticity theory, which was proposed by the present authors and takes into account the interaction between the large elasto-plastic deformation and the wave load evaluation, is applied to the ship’s structure with the assumption that a plastic hinge is formed in the midship region when the hull girder collapses in extreme wave conditions. The dynamic response of the hinge can be expressed by the relationship between the vertical bending moment and the curvature, which are obtained using nonlinear Finite Element Analysis (FEA). A comparative correct moment–curvature curve and a reasonable load evaluation are necessary for prediction of the severity of the collapse for the actual ship. A bulk carrier hull model with one frame space is constructed and analysed using an arc-length control method (Riks method). The geometric nonlinearity resulting from large deformations and the material nonlinearity are taken into account. The presence of an initial imperfection is considered using the consistent imperfection mode method in the FEA. A prediction of the extent of collapse for a bulk carrier subjected to an extreme wave load is carried out using the hydro-elastoplasticity approach. This analysis clarifies the extent to which the hull girder may collapse in extreme wave conditions at an exceedance probability of 1/1000 in several short-term sea states.