Velocity fluctuations of a piston confining a vibrated granular gas

TL;DR

This study investigates the velocity fluctuations of a piston in a vibrated granular gas using molecular dynamics simulations, revealing violations of energy equipartition and agreement with kinetic theory predictions.

Contribution

It introduces a detailed analysis of piston velocity fluctuations and compares piston and gas temperatures, highlighting deviations from classical equipartition in granular systems.

Findings

Piston temperature can be higher or lower than gas temperature depending on system parameters.

The temperature ratio aligns with kinetic theory predictions under weak inelasticity.

Energy equipartition is strongly violated in the studied granular system.

Abstract

The steady state velocity fluctuations of a movable piston located on the top of a vibrated granular gas are studied by means of molecular dynamics simulations. From the second moment of the distribution, a temperature parameter for the piston is defined and compared with the granular temperature of the gas located just below it. Then the two temperature parameters refer to two interacting macroscopic systems. The equipartition of energy valid in usual molecular systems is strongly violated, and the temperature of the piston can be larger or smaller than the one of the gas, depending of the parameters defining the system at the particle level. The simulation results for the ratio of temperatures are in agreement with some theoretical predictions from kinetic theory assuming the validity of a hydrodynamic description in the limit of weak inelasticity of the gas.