Simulation of hydrodynamic ram phenomenon using MSC Dytran

Abstract

Hydrodynamic ram (HRAM) refers to the damage process due to high pressures generated when a high-velocity projectile penetrates a compartment or vessel containing a fluid. A Finite Element model was developed using MSC Dytran to investigate the structural response during the initial phase of HRAM and conduct parametric studies on factors that could affect the tank wall response. The Lagrangian structural shell elements were coupled to the fluid Euler elements using the ALE coupling technique, whereas the projectile was coupled to the fluid using the general coupling technique. This study focused mainly on the structural back wall response where critical components or main structural members on the aircraft could be located. Results from this study show that initial shock wave pressure upon projectile impact is unlikely to have detrimental effects on the exit wall of tank due to its rapid extinction in the fluid. The presence of free surface with lower filling levels reduced both the initial shock pressure and subsequent drag phase pressure. Projectile mass was found to have a strong effect on the exit wall response during the shock phase, but once projectile penetrated the entry wall, results for the drag phase for different projectile mass investigated were inconclusive. Other factors examined included the tank’s material properties and fluid density. Of all the factors being studied, projectile’s velocity was found to have the strongest influence on exit wall response and fluid pressures. Therefore, the damage to exit wall of the tank could be greatly reduced if the entry wall is able to slow the projectile significantly.