Granular gases under extreme driving

¹ Department of Physics, University of Massachusetts - Amherst, MA 01003, USA
² Theoretical Division and Center for Nonlinear Studies, Los Alamos National Laboratory Los Alamos, NM 87545, USA

^a wfkang@gmail.com
^b machta@physics.umass.edu
^c ebn@lanl.gov

Received: 4 February 2010
Accepted: 30 July 2010

Abstract

We study inelastic gases in two dimensions using event-driven molecular-dynamics simulations. Our focus is the nature of the stationary state attained by rare injection of large amounts of energy to balance the dissipation due to collisions. We find that under such extreme driving, with the injection rate much smaller than the collision rate, the velocity distribution has a power-law high-energy tail. The numerically measured exponent characterizing this tail is in excellent agreement with predictions of kinetic theory over a wide range of system parameters. We conclude that driving by rare but powerful energy injection leads to a well-mixed gas and constitutes an alternative mechanism for agitating granular matter. In this distinct nonequilibrium steady state, energy cascades from large to small scales. Our simulations also show that when the injection rate is comparable with the collision rate, the velocity distribution has a stretched exponential tail.