Goldman, Daniel I.

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Continuum-type stability balloon in oscillated granular layers

1998-08-17 , De Bruyn, John R. , Bizon, C. , Shattuck, M. D. , Goldman, Daniel I. , Swift, J. B. , Swinney, Harry L.

The stability of convection rolls in a fluid heated from below is limited by secondary instabilities, including the skew-varicose and crossroll instabilities. We observe a stability boundary defined by these same instabilities in stripe patterns in a vertically oscillated granular layer. Molecular dynamics simulations show that the mechanism of the skew-varicose instability in granular patterns is similar to that in convection. These results suggest that pattern formation in granular media can be described by continuum models analogous to those used in fluid systems.

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Absence of inelastic collapse in a realistic three ball model

1998-04 , Goldman, Daniel I. , Shattuck, M. D. , Bizon, C. , McCormick, W. D. , Swift, J. B. , Swinney, Harry L.

Inelastic collapse, the process in which a number of partially inelastic balls dissipate their energy through an infinite number of collisions in a finite amount of time, is studied for three balls on an infinite line and on a ring (i.e., a line segment with periodic boundary conditions). Inelastic collapse has been shown to exist for systems in which collisions occur with a coefficient of restitution r independent of the relative velocities of the colliding particles. In the present study, a more realistic model is assumed for r: r=1 for relative velocity equal to zero, and r decreases monotonically for increasing relative velocity. With this model, inelastic collapse does not occur for three balls on a line or a ring.