On the translational and rotational granular temperatures in periodically excited 2D granular systems

Abstract

We present numerical results on mean ratio of the translational to the total kinetic energy of periodically excited 2D granular gases as a function of inelasticity and packing density. The excitation comes from periodic energy injections at two walls into neighboring grains. We observed that the mean ratio decreases with increasing inelasticity at fixed density, and reaches a plateau. We also observed that it has a weak decreasing relation with the packing density at fixed inelasticity, up to values close to Random Close Packing, where it drops considerably. It occurs due to a marked increase of the packing rotational energy, and we believe it to be an instance of the recently reported cooperative-rotational state. In all cases below RCP, the steady state is formed by a large cluster of particles (which takes, in all cases, most of the particles in the system), surrounded by a dilute granular gas, and that most of the contribution to the mean kinetic energy ratio comes from the particles in this gas. Close to RCP, the gas disappears, and the results are determined by the whole compressed packing, in which the grains form a contact network that allows them to keep their rotational motion.