Use Of Particle Image Velocimetry To Characterize The Dynamics Of Avalanches On A Conical Bead Pile

We experimentally investigate avalanche behavior using a critical bead pile system. The pile is slowly driven by dropping individual 3 mm steel beads onto the apex of the pile. Our previous work [Lehman, Gran Matt 14, 553 (2012)] explored how the probability distribution function for avalanches of different size scaled with drop height; these results match well with a mean-field model of slip avalanches [Dahmen, Nat Phys 7, 554 (2011)]. This analysis is based on statistical data for a series of avalanches. To gain information about the dynamic motion for individual avalanches and enable a deeper comparison with the model predictions, we now image the pile using a high-speed camera and analyze the motion using particle image velocimetry (PIV). With this approach, the mean velocity at different locations on the surface of the pile is tracked and analyzed for every frame during the avalanche. Our preliminary results of avalanche duration for data runs at different levels of cohesion (due to an applied magnetic field) show that the effect of cohesion on the avalanche dynamics varies according to the avalanche size. While smaller avalanches become longer in duration for higher cohesion, large avalanches are shorter in duration at high cohesion.