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Whither heapeth the dancing sands?

Granular materials on vibrating surfaces sometimes congregate into stable patterns (SN: 8/31/96, p. 135). Although these intricate patterns--including hexagons, squares, stripes, and circular heaps--are stationary, the individual particles that constitute them are constantly moving.

Applying the basic laws of mechanics to collisions between two particles can be difficult enough. Trying to keep track of thousands of grains of sand or salt as they bounce off each other presents a computational nightmare.

Harry L. Swinney, Chris Bizon, and their colleagues at the Center for Nonlinear Dynamics at the University of Texas at Austin have now developed a way to predict the collective behavior of these bouncing grains. They describe their computer simulation in the Jan. 5 Physical Review Letters.

The researchers modeled the motion of particles inside a rigid box being shaken up and down at different frequencies. Rather than attempt to track the movement of particles during short time steps of fixed length, the team used the known positions and velocities of the individual grains to calculate when the next collision would occur, then marched their simulation forward one collision at a time.

This program--the first to analyze patterns in granular materials moving in three dimensions, Swinney says--led to a technique simple enough to be run on a desktop computer. The researchers verified their model with experiments using up to 60,000 small lead or bronze spheres.
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Title Annotation:researchers develop way to predict behavior of moving granular particles
Author:Monastersky, Richard
Publication:Science News
Article Type:Brief Article
Date:Feb 7, 1998
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