Granular medium under vertical tapping: change of compaction and convection dynamics around the liftoff threshold.
A granular medium submitted to vertical tapping reveals simultaneously compaction and convection. The two phenomena are directly coupled and their dynamics can be quantified by a characteristic compaction time and by an estimation of the convective downhill speed along the wall. A remarkable change of behavior is observed around the liftoff acceleration threshold of the whole packing, with a drastic slowing down of both dynamics below this threshold. Above it, a collective shock wave densifies the packing at each tap, whereas, below it, cumulative localized rearrangements will compact the entire system in the long time range.
Philippe
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G.M.C.M., Batiment 11A, Campus de Beaulieu, Université de Rennes I, F-35042 Rennes, France.
Bideau
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