Quantitative study of a freely cooling granular medium
  We present a numerical study of a two dimensional granular medium consisting of hard inelastic disks. The evolution of the medium throughout a cooling process is monitored. Two different types of instabilities (shearing and clustering instability) are found to develop in the system. The development of these instabilities is shown to be in qualitative and quantitative agreement with the predictions of linearized hydrodynamic theory. 
Pierre Deltour and Jean-Louis Barrat