Ben J. Zimmerman

Computational Validation of Nuclear Explosion Energy Coupling Models for Asteroid Fragmentation

The objective of this research is the formulation, implementation, and validation of a numerical method to accurately model and simulate explosion blast and shock waves for the disruption of asteroids. While the cases presented in this paper are not explosions caused by actual nuclear devices, they will aid in validation of the numerical model for future nuclear-explosion simulations. Current work employs the two-dimensional highorder correction procedure via reconstruction (CPR) method with explicit time-stepping to solve the Euler equations. Accurate capturing of shocks is obtained through a shock detector coupled with a slope limiter. The CPR method is compared with simulations from AUTODYN, a commercial hydrodynamics code by ANSYS, where excellent matchings are obtained. Additionally, all numerical simulations are completed using NVIDIA CUDA (Compute Unified Device Architecture), where superior computational speeds are demonstrated. Finally, surface and subsurface explosions are simulated, and the energy transfered to a target body is monitored. Coupling factors are computed and the desired results are obtained. This new computational tool is to be incorporated into a mission design software tool for the analysis and design of an asteroid disruption mission.

Graphics-Processing-Unit-Accelerated Multiphase Computational Tool for Asteroid Fragmentation/Pulverization Simulation

The simulation of asteroid target fragmentation or pulverization is a challenging task that demands efficient and accurate numerical methods with large computational power. To this end, the high-order spectral difference method is implemented with graphics-processing-unit computing. Hypervelocity kinetic-energy impactors are of practical interest, which generate high-pressure deformational shock waves in the target bodies upon impact. Due to the extremely short deformation time associated with hypervelocity impact, the material behaves in a similar manner to a compressible fluid, and the compressible Euler equations can be applied. To model the multiple material interactions, an n-phase equation model is adopted into the spectral difference method. All simulations presented are solved with graphics processing units, producing solutions orders of magnitude faster than the central-processing-unit counterpart. Several impact cases are compared, including a heavy impactor and multiple impactor system, against...

High-Order Spectral Difference: Verification and Acceleration using GPU Computing

A high-order spectral difference (SD) method has been developed with graphics processing units (GPUs) using compute unified device architecture (CUDA). It solves the three-dimensional Navier-Stokes equations on unstructured hexahedral grids with RungeKutta time integration. The method is efficient since operations are completed in a onedimensional fashion and the equations are solved in differential form, removing explicit surface and volume integral calculations. Additionally, solution and flux reconstructions are completed locally per cell, increasing the parallelization of the implementation. Due to this efficiency, the application of GPU computing is appealing. This paper presents the SD method implementation with GPU CUDA computing and presents accuracy studies with isotropic vortex propagation and Couette flow, verifies the high-order accuracy of the solver with a numerical sensitive aero-acoustic problem, and compares the developed solver and a high-order finite difference solver with a case presented in the 1st International Workshop on High-Order CFD Methods. Finally, the GPU solver is compared to a similar central processing unit (CPU) solver, where speed-ups ranging from 20-40x faster are illustrated.