Physics Colloquium, MIT
March 3, 2005

Title:   Dynamics of Random Packings in Granular Flow

Speaker: Martin Z. Bazant
	 Associate Professor of Applied Mathematics 
	 MIT

Abstract: 

The geometry of static sphere packings is an age-old problem, but how
do random packings flow? This question is at the heart of condensed
matter physics for liquids, glasses, and granular materials, and yet
it remains poorly understood at the microscopic level.  Here, we
consider the case of granular drainage (e.g. sand in an hourglass) and
test the hypothesis that particles rearrange cooperatively, in
response to diffusing ``spots'' of free volume.  We find that 
spot-based simulations with only five fitting parameters can
accurately reproduce packing dynamics in discrete-element simulations
with 200,000 spherical, frictional, visco-elastic grains. The spot
simulations run over 100 times faster and demonstrate the possibility
of multiscale modeling for amorphous materials.