Influence of coupling in the prediction of ship collision damage

This paper studies the influence of coupling between the ship motions and the structural resistance in predicting ship collision damage. Several collision scenarios are simulated using coupled and decoupled approaches. A coupled approach implies a time domain simulation, in which a precise description of the whole collision process together with the full time histories of the motions and forces involved is achieved. In this approach, the ships’ motions are evaluated in parallel to the structural deformations, that is, the coupling between the external dynamic and internal mechanics is preserved. A decoupled approach is based on the conservation of momentum and allows fast estimation of deformation energy without providing exact ship motions. This method is based on the ship masses and velocities, and there is no coupling with the structural behaviour. The extent of deformation is defined by applying some calculation method, such as a finite element method for example, to evaluate the penetration depth along some prescribed path required to absorb this energy. The comparison of the outcomes of two methods reveals that while the deformation energy is predicted with a reasonable accuracy using both methods, the difference in penetration path is significant. The decoupled approach precisely predicts the penetration in symmetric collision, but in non-symmetric collisions under oblique angles, the results differ from those of the coupled solution and also from the experimental measurements. The forward velocity of the struck ship does not significantly influence the precision of the decoupled approach.