LOCAL FLUCTUATIONS IN A FLUIDIZED GRANULAR MEDIUM

Molecular dynamics simulations have been carried out on a two-dimensio nal model granular material made up of inelastically colliding discs s ubjected to gravity. The granular system is fluidized by a constant en ergy input from a vibrating base, and a stationary non-equilibrium sta te is achieved. Density and granular temperature profiles are determin ed, while the former goes through a maximum at intermediate altitudes, the latter exhibits a minimum at a higher altitude, beyond which the granular temperature is found to increase. Local density fluctuations are characterized by the time-displaced density autocorrelation functi on. Longitudinal compression (sound) waves propagating in the horizont al direction are found to be strongly damped, while they are overdampe d in the vertical direction at the longest accessible wavelength.