Modelling of the internal mechanics in ship collisions

A method for analysis of the structural damage due to ship collisions is developed. The method is based on the idealized structural unit method (ISUM). Longitudinal/transverse webs which connect the outer and the inner hulls are modelled by rectangular plate units. The responses are determined by taking into account yielding, crushing, and rupture. Some plates of the outer and the inner shell subjected to large membrane tensions are modelled by membrane tension triangular/rectangular plate units, while the remaining shell panels are modelled by the usual plate units. The effect of stiffeners on the stiffness and the strength is considered as well. In order to include the coupling effects between local and global failure of the structure, the usual non-linear finite-element technique is applied. In order to deal with the gap and contact conditions between the striking and the struck ships, gap/contact elements are employed. Dynamic effects are considered by inclusion of the influence of strain-rate sensitivity in the material model. On the basis of the theory a computer program has been written. The procedure is verified by a comparison of experimental results obtained from test models of double-skin plated structures in collision/grounding situations with the present solutions. As an illustrative example the procedure has been used for analyses of a side collision of a double-hull tanker. Several factors affecting ship collision response, namely the collision speed and the scantlings/arrangements of strength members, are discussed.