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I present results of a simulation study of inelastic hard-disks vibrated
in a vertical container. Varying the relevant parameters (inelasticity,
number of layers at rest, intensity of the gravity) we are able to obtain
a qualitative agreement of our results with recent hydrodynamical
predictions [1]. Increasing the inelasticity, a first continuous
transition from the absence of convection to one convective roll is
observed, followed by a discontinuous transition to two convective rolls,
with hysteretic behavior. At fixed inelasticity and increasing gravity, a
transition from no convection to one roll can be evidenced. If the gravity
is further increased, the roll is eventually suppressed. Increasing the
number of monolayers the system eventually localizes mostly at the bottom
of the box: in this case multiple convective rolls as well as surface
waves appear. We analyze the density and temperature fields and study the
existence of symmetry breaking in these fields in the direction
perpendicular to the injection of energy. We also study a binary mixture
of grains with different properties (inelasticity or diameters). The
effect of changing the properties of one of the components is analyzed.
The presence of a low-fraction of quasi-elastic impurities is shown to
determine a sharp transition between convective and non-convective steady
states.
[1] X. He, B. Meerson, and G. Doolen, Phys. Rev. E {\bf 65}, 030301(R) (2002); E. Khain and B. Meerson, Phys. Rev. E {\bf 67}, 021306 (2003). |