RHALE: A MMALE Shock Physics Code for Arbitrary Meshes*

This paper describes RHALE, a two and three-dimensional, multi-material, arbitrary Lagrangian-Eulerian (MMALE) shock physics code written in C++. RHALE is the successor to CTH, Sandia’s 3-D Eulerian shock physics code, and will be capable of solving problems that CTH cannot adequately address. RHALE employs a three step solution algorithm for the equations of motion: (1) a Lagrangian step capable of solving for either structural or hydrodynamic responses, (2) a remesh step to prevent mesh tangling or to facilitate Eulerian hydrodynamic algorithms, and (3) an Eulerian remap step. The Lagrangian step is solved using finite elements on an unstructured grid. RHALE incorporates new Lagrangian capabilities, which include arbitrary mesh connectivity, superior artificial viscosity and spurious vorticity control, and improved equations of state The arbitrary Lagrangian-Eulerian (ALE) algorithm comprises both the remesh and remap steps. The multi-material extension to ALE is termed MMALE and has been generalized for arbitrary grids in both two and three-dimensions in RHALE. The MMALE feature in RHALE provides the accuracy of a Lagrangian code while allowing a calculation to proceed under very large mesh distortions. Coupling an arbitrary connected grid to the MMALE algorithm facilitates modeling of complex shapes with a minimum number of computational cells. RHALE allows regions of a problem to be modeled with Lagrangian, Eulerian or ALE meshes. In addition, regions can switch from Lagrangian to ALE to Eulerian based on user input or mesh distortion. For arbitrary meshes, new node locations are determined with equipotential schemes. Element quantities are advected with donor, van Leer, or Super-B algorithms. Nodal quantities are advected with second order schemes developed by Benson and Margolin which uses the element advection algorithms. Currently, material interfaces within an element are determined with a SLIC algorithm; however, more accurate two and three dimensional versions of interface trackers are being investigated.