Distribution of local speed in granular gas of monosized spheres excited by vibration; evidence for two local temperatures and two "pressures" in the direction of vibration 

The main topic of this report is the interpretation of data from
extended simulationsconcerning the dynamics of N equal-size spheres in
a 3d rectangular cell excited along Oz in 0 gravity.(N=100, 500, 1000,
1200, 2000, 3000, 4000, 4500). Different Oz excitation kinds have been
used (symmetric and non symmetric bi-parabolic, symmetric and non
symmetric saw teeth, thermal wall). No rotation is included,
dissipation is introduced via a restitution coefficient e= V’n/Vn ,
where V’n and Vn are the relative ball speed along normal to ball
centres after and before collision. It is proved that the local speed
distribution along z is fundamentally dissymmetric in most part of the
cell while the mean local speed is 0. This demonstrates the inability
of a model based on a thermal bath (with a single local temperature)
to describe this dissipative-granular-gas-system, even when assuming
that this temperature varies in space. This analyse will be copmpared
to (and conforted by) real experimental data on" vibratied granular
gas in 0g" obtained during parabolic flights in Airbus-A300-0g, in
rocket (MiniTexus 5, Maxus 5, Maxus 7) and with stellites (chinese
SJ8). We will also sum up other few experimental results obtained in
the very low density regime.