Simulation of Hydrodynamic Ram and Liquid Aeration

During the past several years, research within BAE SYSTEMS has concentrated on developing a capability for simulating Hydrodynamic Ram (HRAM). In this paper we demonstrate how the ALE technique in LS-DYNA can be used to simulate the principal stages of HRAM with liquid aeration. LS-DYNA is used to simulate the impact of a small steel sphere at 2km/s into a water-filled container manufactured from 3.2 mm thick aluminium alloy L165. The simulation results are compared with laboratory experiments from a two-stage gas-gun facility showing close agreement with peak pressure and impulse values. In additional simulations, aeration is modelled using an effective equation of state, which describes the compressibility of the water (on a macro-scale) inside the container. The simulation results show that aeration can be used to alleviate the shock wave that forms ahead of the projectile in order to reduce damage on the surrounding structure.