Date of Award
Doctor of Philosophy (PhD)
John P. Borg
S. Goldsborough, James Rice, Hyunjae Park
The purpose of this work is to directly simulate shock wave structures without the use of artificial viscosity. The commonly used artificial viscosity model is replaced with an irreversibility model. Irreversibilities are not typically taken into account when modeling the shock processes because shocks are resolved in a large domain where the thickness of the shock is thin compared to the numeric grid resolution. The result is the shock is poorly resolved. In addition processes other than shock processes are adiabatic and reversible. The result is artificial viscosity, a form of irreversibility, is added to the numeric cells near the shock in order to account for the irreversibilities generated within the shock structure. In this work the shocks are resolved and the physical sources of irreversibilities, namely viscous dissipation and localized heat transfer, are directly incorporated within the shock process. The resulting simulations yield a more realistic shock structure, the shape of which can be integrated to determine the resulting increase in entropy of the shocked material. Metrics such as shock thickness and wave structure compare favorably to experimental results.
Irreversibility is traditionally accounted for by inserting artificial viscosity into the energy balance. Artificial viscosity reduces numerical overshoot, diminishes the total energy, and smears out the shock front over several cells thereby eliminating the need for nanoscale grid resolution necessary to resolve the shock front and numerically resolve the gradients. This approach fails to correctly model the shock wave structure of distended materials because their dynamic loading is a highly dissipative process and completely irreversible. Thus, the work described herein models on a bulk scale a thermodynamically consistent representation of the irreversibilities associated with shock wave formation such as viscous dissipation and heat conduction and seeks to determine if these sources of irreversibility are comparable to artificial viscosity.