Boundary conditions and the dynamics of a dissipative granular gas: slightly dense case

TL;DR

This paper investigates how different wall motions affect the dynamics of a dissipative granular gas, revealing nonlinear excitation transfer and conditions for particle rest or biphasic cloud formation.

Contribution

It demonstrates that wall motion and speed distribution significantly influence granular gas behavior, challenging the thermostat analogy in vibrating cells.

Findings

Wall motion type affects particle speed distribution.

Nonlinear excitation transfer depends on particle speed.

Conditions for particle rest and biphasic cloud formation identified.

Abstract

The effect of different possible kinds of motion of the exciting walls (cyclic, random, ...) is investigated on the dynamics of a granular dissipative gas. It is shown that the real distribution of speed of the wall which interact with the balls depend strongly on the real ball speed, due to a screening effect, so that the transfer of excitation from the walls to the cloud of particles may drastically depend on the ball speed itself. This makes the excitation quite non linear, with a change of efficiency law. This may explain the observation of a biphasic cloud when the mean free path of balls is slightly smaller than the cell size L, or may predict that the particles in the cloud is merely at rest as soon as the mean free path is smaller than L/10. It is obvious that the vibrating cell cannot be considered as a thermostat.