Shaking dry powders and grains

Abstract

Abstract The words‘fluidization of a non-cohesive granular material by low-frequency vibrations’cover the whole scope of phenomena which are described briefly with the use of precise examples. In most of them, the fluidized medium has a free surface since this condition seems to be required to obtain fluid-like behaviour and convective flows. I also give the example of sand liquefaction which occurs sometimes during seisms for which the existence of a free-boundary condition is not needed. I separate problems linked to the presence of air from those which are induced directly by slight changes in boundary conditions or by the vibrations themselves. If most of the time the convective patterns are produced with vertical vibrations, I demonstrate that other convective patterns are obtained with horizontal vibrations. All these convections occur above an amplitude threshold, which is higher for horizontal vibrations than for vertical vibrations. I demonstrate also that vertical vibrations may stop an hourglas...