Hydrodynamic ram is observed when projectiles impact fluid filled tanks at high velocities. The hydrodynamic ram effect is characterised by the penetration of the projectile into the tank, and the propagation of shock waves through the fluid. A combination of these effects can lead to catastrophic failure of the tank and adjacent components. As the manufacture and test of tanks and alleviation mechanisms is expensive, the requirements are:
- To develop methodologies using computational techniques to accurately predict the performance of fuel tanks.
- To assess hydrodynamic ram alleviation concepts.
Application Areas
- The modelling of warhead fragment impact on the fuel tanks of military aircraft.
- The modelling of tyre bursts and runway debris on the fuel tanks of civil aircraft.
- The modelling of hydrodynamic ram effects in ballistic missile warheads.
The modelling capability is based on the coupled fluid structural functionality in LS-DYNA, but other computer programs have been benchmarked to assess their suitability. The modelling methodology has been validated by comparison with an extensive experiment programme. The picture (right) shows an example of the calculations that have been carried out on a simple tank. The tank is rectangular, and the projectile is shown penetrating the front face from the right hand side at a high velocity. A section has been taken through the tank to enable the projectile, the fluid and the walls to be displayed. The walls of the tank are pushed outwards as a result of the raised pressure in the tank. A spherical shock wave that is shown in green, proceeds ahead of the projectile and is reflected by the rear wall of the tank.
Validation has been carried out by comparison with experimental measurements for:
- The pressures at user defined locations
- The velocity of the projectile.
- The strains on the walls of the tank.
All of these parameters are being used to determine the accuracy of the analysis.
