Comparing Flow Thresholds and Dynamics
for Oscillating and Inclined Granular Layers*

C. Puls, S. Aumaitre, and J.P. Gollub

Haverford College and University of Pennsylvania

 

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The onset and dynamics of flow in horizontally oscillating granular layers are studied as a function of the depth of the layer (see the experimental devices). Measurements of the flow velocity made from the top and side are presented in the frame of reference of the container (see movies). The rheology of the material is found to vary in time during the cycle in surprising ways. If the inertial force (proportional to the container acceleration amplitude) is slightly higher than what is required to produce flow, then the flow velocity grows as soon as the inertial force exceeds zero in each cycle, but flow ceases long before the inertial forces return to zero, possibly due to the buildup of internal stresses. At higher accelerations, the motion is fluid-like over the entire cycle (more ...). As is also found for avalanches of inclined layers, the thresholds for starting and stopping of flow are slightly different. The variation with depth of the starting acceleration for the oscillating layer matches (approximately) the corresponding variation of the tangent of the starting angle for avalanches in the same container (see curves). However, the fraction of the cycle during which the layer is mobile is typically far higher than what one would predict from static considerations or the behavior of the inclined layer.

 

*Supported by NSF-DMR -0405187.