Dynamic FE simulations of ship collisions

The goal of this thesis was to study the possibilities of modelling external dynamics of a ship collision using explicit finite element code LS-DYNA. LS-DYNA is widely used for studying inner mechanics of ship collisions, but has not been used for simulating external dynamics. Inner mechanics deals with the behaviour of structures in a collision, external dynamics concentrates on the motions of the colliding vessels. The proposed model enables to calculate external dynamics and inner mechanics in the same simulation run. The motions of the ships are constrained to the horizontal plane. Gravity, buoyancy and restoring forces were excluded from the model as was hydrodynamic damping. Emphasis was on modelling masses and inertia of the colliding ships in order to achieve accurate results for contact force. The striking ship was modelled as a rigid bulb with attached mass points. Structure of the struck ship in the collision area was modelled in detail, the other regions of the vessel were also modelled using properly placed mass points. Hydrodynamic added masses were modelled in a way that they are activated only in certain directions. The results of the LS-DYNA model were validated with data from model-scale collision experiments. Three collision cases were investigated. First, a symmetric collision at right angle, second an eccentric collision at right angle and finally an eccentric collision at inclined angle. Results of all three simulation cases showed good agreement with model test data, which implies that the model is valid