Computational test of kinetic theory of granular media

Kinetic theory of granular media based on inelastic hard sphere interaction s predicts continuum equations of motion similar to Navier-Stokes equations for fluids. We test these predictions using event-driven molecular dynamic s simulations of uniformly excited inelastic hard spheres confined to move in a plane. The event-driven simulations have been previously shown to quan titatively reproduce the complex patterns that develop in shallow layers of vertically oscillated granular media. The test system consists of a period ic two-dimensional box filled with inelastic hard disks uniformly forced by small random accelerations in the absence of gravity. We describe the inel asticity of the particles by a velocity-dependent coefficient of restitutio n. Granular kinetic theory assumes that the velocities at collision are unc orrelated and close to a Maxwell-Boltzmann distribution. Our two-dimensiona l simulations verify that the velocity distribution is close to a Maxwell-B oltzmann distribution over 3 orders of magnitude in velocity, but we find t hat velocity correlations, of up to 40% of the temperature, exist between t he velocity components parallel to the relative collision velocity. Despite the velocity correlations we find that the calculated transport coefficien ts compare well with kinetic theory predictions. (C) 1999 Elsevier Science B.V. All rights reserved.