Collapsing cavities and converging shocks in non-ideal materials

TL;DR

This paper investigates the collapse of cavities and converging shocks in non-ideal materials, extending classical solutions beyond ideal gases, and characterizes the conditions under which such solutions exist for realistic materials.

Contribution

It introduces a framework for analyzing collapsing cavities and shocks in non-ideal materials, deriving new equations and identifying families of materials that admit scaling solutions.

Findings

Infinite-dimensional families of materials admit scaling solutions.

Constant-speed cavity collapse is heuristically possible.

A concrete non-ideal solution is constructed using a pseudo-Mie-Gruneisen EOS.

Abstract

As modern hydrodynamic codes increase in sophistication, the availability of realistic test problems becomes increasingly important. In gas dynamics, one common unrealistic aspect of most test problems is the ideal gas assumption, which is unsuited to many real applications, especially those involving high pressure and speed metal deformation. Our work considers the collapsing cavity and converging shock test problems, showing to what extent the ideal gas assumption can be removed from their specification. It is found that while most materials simply do not admit simple (i.e. scaling) solutions in this context, there are infinite-dimensional families of materials which do admit such solutions. We characterize such materials, derive the appropriate ordinary differential equations, and analyze the associated nonlinear eigenvalue problem. It is shown that there is an inherent tension between boundedness of the solution, boundedness of its derivatives, and the entropy condition. The special case of a constant-speed cavity collapse is considered and found to be heuristically possible, contrary to common intuition. Finally, we give an example of a concrete non-ideal collapsing cavity scaling solution based on a recently proposed pseudo-Mie-Gruneisen equation of state.