A phenomenological approach to relaxation in powders

This work is a phenomenological attempt to understand the dynamic response of a granular pile to vibration. We model the effect of vibration on a granular pile as random noise in its interior, and write down a form for the relaxation of the compactivity parameter X. The compactivity, which characterises the packing of the pile, is shown to settle to a value that reflects a balance between the amplitude of the noise and a restoring force such as gravity.