Simplified modelling of surface ship whipping response to underwater explosion

This paper presents a simplified method to assess the whipping response of a surface ship subjected to underwater explosion, without modelling explicitly the surrounding water. The early-time action of the shock wave generated by the detonation is treated using Taylor’s theory. Then, a bubble of gas starts to pulse and the incident pressure coming from resulting water flows, which usually couples with hull beam dynamics, is applied to the ship hull. Lumped added masses are calculated using Lewis coefficient method and distributed on the ship hull to represent water inertial effects. The validation process is first to compare natural frequencies and mode shapes of a given surface ship with the ones obtained by modelling explicitly the surrounding fluid. Then, the whipping response of the ship to both the shock wave and gas bubble pulses is simulated using Ls-Dyna finite element code and the contribution of water inertial forces is highlighted.