Particle dynamics in a vibrated submerged granular bed as revealed by diffusing wave spectroscopy

The behaviour of agitated submerged granular media is of wide relevance technologically and in nature. Recent modelling of such systems has invoked a kinetic theory description. Such descriptions involve the so-called granular temperature, which is directly related to the mean-square of the velocity fluctuations about the mean flow velocity. The better formulation of these models and their subsequent validation demand the experimental elucidation of the dynamics and granular temperature of submerged granular media undergoing excitation. Such elucidation, based on the non-invasive optical technique of diffusing wave spectroscopy (DWS), is reported here. The particle dynamics and granular temperature have been studied for a periodically forced submerged granular bed as a function of the forcing conditions. Rather unexpectedly, it was found that the granular temperature scaled with the square of the acceleration of the forcing rather than the square of the peak forcing velocity as in dry vibro-fluidized beds. It was also observed that the granular temperature increased with distance above the base of the bed where the forcing was applied.