Monodisperse granular flows often develop regions with hexagonal close packing of particles. We investigate this effect in a system of inelastic hard spheres driven from below by a athermal late. Molecular dynamics simulations show, in a wide range of parameters, a close-packed cluster supported by a low-density region. Surprisingly, the steady-state density profile, including the close-packed cluster part, is well described by a variant of Navier-Stokes granular hydrodynamics (NSGH). We suggest a simple explanation for the success of NSGH beyond the freezing point.
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We are grateful to Stefan Luding for comments and ?>for sharing with us his unpublished results on the ?>shear viscosity divergence. We thank Igor Aronson, Detlef Lohse, and Arkady Vilenkin for discussions. ?>This research was supported by the Israel Science Foundation (Grant No. ) and by Deutsche Forschungsgemeinschaft (Grant No. PO ).