Velocity Correlations in Driven Two-dimensional Granular Media 1

Simulations of volumetrically forced granular media in two dimensions produce states with nearly homogeneous density. In these states, long-range velocity correlations with a characteristic vortex structure develop; given sufficient time, the correlations fill the entire simulated area. These velocity correlations reduce the rate and violence of collisions, so that pressure is smaller for driven inelastic particles than for undriven elastic particles in the same thermodynamic state. As the simulation box size increases, the effects of velocity correlations on the pressure are enhanced rather than reduced.