Numerical simulations of granular dynamics II. Particle dynamics in a shaken granular material

摘要

Surfaces of planets and small bodies of our Solar System are often covered bya layer of granular material that can range from a fine regolith to agravel-like structure of varying depths. Therefore, the dynamics of granularmaterials are involved in many events occurring during planetary and small-bodyevolution thus contributing to their geological properties. We demonstrate that the new adaptation of the parallel N-body hard-spherecode pkdgrav has the capability to model accurately the key features of thecollective motion of bidisperse granular materials in a dense regime as aresult of shaking. As a stringent test of the numerical code we investigate thecomplex collective ordering and motion of granular material by directcomparison with laboratory experiments. We demonstrate that, as experimentallyobserved, the scale of the collective motion increases with increasingsmall-particle additive concentration. We then extend our investigations to assess how self-gravity and externalgravity affect collective motion. In our reduced-gravity simulations both thegravitational conditions and the frequency of the vibrations roughly match theconditions on asteroids subjected to seismic shaking, though real regolith islikely to be much more heterogeneous and less ordered than in our idealisedsimulations. We also show that collective motion can occur in a granularmaterial under a wide range of inter-particle gravity conditions and in theabsence of an external gravitational field. These investigations demonstratethe great interest of being able to simulate conditions that are to relevantplanetary science yet unreachable by Earth-based laboratory experiments.