Sound From Sand

Abstract

Various methods of producing sound from 'sounding' sand in the laboratory are explored. Low amplitude sound with frequency similar to that of 'booming' during spontaneous avalanches was produced in a small inclined chute and rotating flask. Shearing of dried sand with a stylus, and pouring from buckets or shaking in a jar produced loud sound in 200-500Hz range. Dryness of the sand and flowrate have significant effect on the produced sound. A model based on kinetic theory is proposed to explain the production of oscillations in avalanching flows. The avalanching layer behaves like a breathing mode with infinite wavelength, and perturbations in volume fraction allow oscillatory behaviour to be sustained in the inclined shear flow. Finally, a phase transition model is used to explain the presence, and characteristics, of oscillations observed in numerical simulations of inclined flows near their stopping angle.