Two types of oscillation in unequally compartmentalized granular gases.

Granular oscillation in an unequally two-compartmentalized system is investigated experimentally, yielding two time periods: τ(LS) represents the time period for particles moving from the large to the small compartment, and τ(SL) is the time needed for movement in a reverse direction. We construct the phase diagram for the unequal system, discovering that there exist two different granular oscillation states. In the GOI state, τ(LS)>τ(SL) is observed, and (τ(LS)-τ(SL)) increases as the difference between the two compartment widths is enlarged. In contrast, τ(LS)<τ(SL) is found in the GOII state, where the total number of particles is considerably lower than that in the GOI state. A flux model, accompanied by a proposed generalized granular temperature, is adopted to quantitatively calculate the observed time periods for both granular oscillation states. We find that the proposed temperature in each compartment is crucial in discriminating τ(LS) from τ(SL), and this is supported by the molecular dynamics analysis of mean kinetic energy of particles in a single compartment.