Numerical Simulation of Impact and Penetration in Regolith with Fluid Model Considering Irreversible Compression and Hardening

Abstract

To simulate the crater formation into the granular material covering the majority of the surface of a planet, a satellite, a comet nucleus or an asteroid by high-speed impact of a natural or artificial object, the Euler equations with the Compressible and Non-Expanding (CNE) fluid model were numerically solved by the finite volume method in the framework of the macroscopic continuum fluid dynamics. The irreversible nature of the granular material in the compression process was considered assuming a higher speed of sound at unloading than compression, which enables the fluid to have higher density after unloading than the initial uncompressed density. The pressure that represents the resistance against the compression was defined as a function of the density, and the hardening effect was considered assuming the pressure function whose slope increases with the increase in the density. In the two-dimensional crater formation problem, the result with the CNE fluid model seems more realistic than that with the conventional compressible fluid model, because the high-density zone compressed by the impact was allowed to remain at the bottom of the crater in the former case. The effects of the hardening and the sand box size on the crater formation were numerically investigated by the CNE fluid model. Finally, the usefulness of the present method for the development of impact probes was discussed.