# Simulations of dense granular gases in zero gravity

# with
impact-velocity-dependent restitution coefficient

**Sean McNamara**^{1} and Eric Falcon^{2}

^{1} Institut für
Computerphysik, Universität Stuttgart, 70569 Stuttgart,
Germany

^{2} MSC, Université Paris Diderot - Paris 7, CNRS
UMR 7057, 75 013 Paris, France

### Reference:

Powder
Technology
182, 232 (2008)

**Abstract:**

#### We report two-dimensional simulations of
strongly
vibrated granular materials without gravity. The coefficient
of
restitution depends on the impact velocity between particles by
taking
into account both the viscoelastic and plastic deformations of
particles, occurring at low and high velocities
respectively. Use
of this model of restitution coefficient leads to new unexpected
behaviors. When the number of particles N is large, a loose
cluster
appears near the fixed wall, opposite the vibrating wall. The
pressure
exerted on the walls becomes independent of N, and linear in the
vibration velocity V, quite as the granular temperature. The
collision
frequency at the vibrating wall becomes independent of both N and
V,
whereas at the fixed wall, it is linear in both N and V. These
behaviors arise because the velocity-dependent restitution
coefficient
introduces a new time scale related to the collision velocity near
the
cross over from viscoelastic to plastic deformation.

**PDF file **