Close-packed floating clusters: granular hydrodynamics beyond the freezing point?

TL;DR

This paper demonstrates that Navier-Stokes granular hydrodynamics can accurately describe close-packed granular clusters in driven inelastic hard sphere systems, even beyond the freezing point, supported by molecular dynamics simulations.

Contribution

It shows that a variant of Navier-Stokes granular hydrodynamics effectively models close-packed clusters in granular flows beyond the freezing point.

Findings

Density profiles match hydrodynamic predictions

Close-packed clusters are supported by low-density regions

Hydrodynamics remains valid beyond traditional freezing limits

Abstract

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 "thermal" plate. 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.