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Resonant oscillations of a granular cluster

Driven granular media is a fascinating example of intrinsically non-equilibrium system. I consider an ensemble of inelastically colliding hard disks in a channel driven by two opposite thermal walls with different temperatures. When the inelasticity of collisions is large enough, a dense cluster, located closer to the colder wall, is formed. The steady state profiles are computed from the equations of granular hydrodynamics, and a good agreement with the results of molecular dynamics simulations is found. When the temperature of one of the thermal walls is varied periodically, a dense cluster develops oscillations. The oscillations amplitude reaches its maximum in a resonance, when the frequency of driving is roughly equal to the hydrodynamic frequency of oscillatory acoustic modes in the system. © 2008 Wiley Periodicals, Inc. Complexity, 2008. 
 
This article was submitted as an invited paper resulting from the “Understanding Complex Systems” conference held at the University of Illinois-Urbana Champaign, May 2006.