Microgravity and Dissipative Granular Gas in a vibrated container: a gas with an asymmetric speed distribution in the vibration direction, but with a null mean speed everywhere

TL;DR

This paper analyzes the dynamics of a dissipative granular gas in microgravity, revealing asymmetric speed distributions along the vibration direction and challenging thermal bath models, based on extensive simulations of particles in a vibrated cell.

Contribution

It demonstrates that local speed distributions are fundamentally asymmetric in a dissipative granular gas, invalidating simple thermal bath models even with spatially varying temperature.

Findings

Local speed distribution along vibration axis is asymmetric.

Mean local speed remains zero despite asymmetry.

Thermal bath models are inadequate for this system.

Abstract

The main topic of this paper (part 4) is the interpretation of data from extended simulations published in previous Poudres & Grains (see P&G 17, #1 to #18) concerning the dynamics of N equal-size spheres in a 3d rectangular cell excited along Oz in 0 gravity.(N=100, 500, 1000, 1200, 2000, 3000, 4000, 4500). Different Oz excitation kinds have been used (symmetric and non symmetric bi-parabolic, symmetric and non symmetric saw teeth, thermal wall). No rotation is included, dissipation is introduced via a restitution coefficient e= -V'n/Vn, where V'n and Vn are the relative ball speed along normal to ball centres after and before collision. It is proved that the local speed distribution along z is fundamentally dissymmetric in most part of the cell while the mean local speed is 0. This demonstrates the inability of a model based on a thermal bath (with a single local temperature) to describe this dissipative-granular-gas-system, even when assuming that this temperature varies in space. The other (1-3) parts sum up few results obtained in the very low density regime.