Surface ship structure and shipboard equipments must be designed to withstand severe shock excitations induced by underwater explosion. The ship shock test/trials identify the design and construction deficiencies giving a serious negative effect on the survivability of ship, equipment and crew, and also validate the shock hardening criteria and performance. Unfortunately, the ship shock trials are very time consuming and expensive. With the advent and ongoing advances in simulation capabilities and sophisticated simulation tools, numerical modeling and simulation has become a viable, less costly alternative as well as more reliable aids to ship shock test/trials.
Surface ship shock simulation under underwater explosion is generally complicated by free surface effects, such as bulk cavitation, local cavitation and cavitation closure pulses, in addition to the complex fluid-structure interaction phenomena and the complicated dynamic behavior of the ship and shipboard equipments. Shock response analysis of a floating surface ship could be performed using a large scale finite element model of a coupled ship and surrounding fluid using LS-DYNA/USA code considering the effects of cavitation.
In this paper, the effects of bulk cavitation and fluid mesh size were investigated on the shock response of floating structure using both LS/DYNA3D and LS-DYNA/USA and on its reliable shock response under underwater explosion, respectively at the first step. The shock responses of the MIL-S-901D SFSP (Standard Floating Shock Platform) under underwater explosion were analyzed using LS-DYNA/USA, where surrounding fluids as well as the SFSP were included in 3-dimensional finite element model for the consideration of bulk cavitation effects. Through the numerical simulations, the nonlinear effects of the resilient mounts and flexibilities of the SFSP were also investigated on the shock response characteristics of the equipments, whose results were compared with NRL test results.
It might be confirmed that the simulation results could predict the shock behaviors of the SFSP accurately, and that the shock responses of complex structure-foundation-equipments interaction could be applied to the whole ship analysis effectively.