Heap corrugation and hexagon formation of powder under vertical vibrations

Éric Falcon,1 Krishna Kumar,2 Kapil M. S. Bajaj,3 and Jayanta K. Bhattacharjee4

1Laboratoire de Physique Statistique, École Normale Supérieure, 24 rue Lhomond, 75005 Paris, France
2Physics and Applied Mathematics Unit, ISI, 203 B T Road, Calcutta 700 035, India
3Department of Physics and Centre for Nonlinear Science, University of California at Santa Barbara, Santa Barbara, California 93106
4Department of Theoretical Physics, IACS, Calcutta 700 032, India
Reference:

Physical Review E, 59, 5, 5716-5720 (1999).

Abstract:

We report free-surface instabilities in a deep bed of fine granular material of irregular shape under vertical vibrations. At low frequency of vibration, the conical heap due to convective flow becomes unstable above a critical amplitude of vibration and acquires an azimuthal dependence which makes the heap surface corrugated. At even higher amplitude, the heap is no longer stable and splits into small heaps on a hexagonal lattice. At high frequency, we observe standing waves (stripes) at the same frequency as the driving one. The main mechanism of these instabilities can be traced back to the presence of the surrounding gas, since they vanish under vacuum conditions. © 1999 The American Physical Society

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