Surface instability of a vertically oscillating granular layer

In the study of the surface instability of a vertically oscillating granula r layer, rye obtained experimentally the phase diagram for the surface stat es of the layer in the driving frequency-acceleration plane, and measured t he dispersion relation for the surface waves in a granular layer in compari son to that in viscous fluids. Our experiments show that the onset dimensio nless acceleration increases with the driving frequency, and the wavelength of the surface waves increases with the depth of granular layer. These exp erimental results are in agreement with our theoretical model qualitatively .