APS March Meeting 2006
Focus Session on Jamming

Title: Random-Packing Dynamics in Dense Granular Flow

Author: Martin Z. Bazant (MIT)

Abstract: The jamming transition of disordered hard spheres has
attracted much recent attention, but how do slightly less dense random
packings flow?  Here, we propose a simple mechanism based on diffusing
"spots" of free volume, which cause correlated displacements of
neighboring particles. A multiscale algorithm, alternating between
coarse-grained spot dynamics and microscopic particle relaxation, can
produce realistic flowing packings, and yet is also convenient for
mathematical analysis of mean flow and diffusion. We apply the model
to granular drainage from a silo and fit three basic parameters (spot
size, volume, and diffusivity) to brute-force simulations by the
discrete-element method. For a wide silo, we find that the spot
simulations can largely reproduce the dynamics of 100,000 frictional,
visco-elastic spheres in the DEM simulations, while running over 100
times faster, although a general model for the spot dynamics in
different geometries is still lacking.  This may come from a
stochastic reformulation of Mohr-Coulomb plasticity, where spots
undergo random walks along slip planes.