Clustering

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in a Driven Granular Monolayer.

		gas phase
		cluster phase
Instantaneous Image	1 sec. Time-Average	D.I.L. '98

The above images are a visual demonstration of clustering in the 2D granular gas. While the instantaneous images in the left column look almost identical in the gas and cluster phases, a clear difference is seen in the time-averaged images in the right column for each phase.

In the gas phase, the time-averaged motion is completely random, or uncorrelated, as demonstrated by the nearly uniform distribution of particles in the composite image.

In the clustering phase, however, the composite image for particle positions over 1 second clearly show bright spots corresponding to unique particles that occupied locations relatively close to other particles over the entire 1 second interval. These are clusters.

The clusters appear in the collective particle motion as the acceleration of the 2D granular gas is lowered, effectively cooling the monolayer. For the above images, the number of particles is 8000. The acceleration, or driving, in the gas phase is 1.0g, while the acceleration in the cluster phase is 0.80g, where g is the acceleration due to gravity.