Long time simulations of granular hydrodynamics : instabilities and   attractors
  Using a hydrodyamic model of granular flows, we present very long time simulations of a granular fluid in two dimensions without gravity and with periodic boundary conditions in a square domain. Depending upon the values of the viscosity, thermal conductivity and dissipation, we find for intermediate times a metastable clustering state. For longer times the system is attracted to either a shear band or a vortex state. Our results are in general agreement with molecular dynamics simulations. 
Srikant Marakani and Gene F. Mazenko