An Arbitrary Lagrangian-Eulerian Finite Element Method for Shock Wave Propagation: Validating Simulations of Underwater Explosions

Abstract: Underwater explosions are often modeled with Arbitrary Lagrangian-Eulerian (ALE) Finite Element Methods. The objective of this thesis is to validate the simulation method, with respect to the propagating shock wave. A two-dimensional axisymmetric model of a spherical TNT charge submerged in water is simulated using LS-DYNA. The explosive is modeled with the Burn Fraction technique and the Jones-Wilkins-Lee equation of state. Water is modeled as a non-viscous fluid, with the Grüneisen equation of state. The convergence for different mesh resolutions, the effect of different advection methods, and varied constants in the artificial viscosity are examined. Generally, the simulations agree well with empirical results, but the maximum pressure diminishes more rapidly with distance compared to experiments. The excessive dampening is most notable in the early stages of the propagation. Also, unexpected oscillations are observed near the discontinuity. The choice of advection scheme and constants in the artificial viscosity do not resolve the issues suggesting that other numerical techniques for treating the discontinuity should be considered.