Instabilities in vertically vibrated granular beds at the single particle scale

The dynamics of granular motion have been studied in a vertically vibrated bed using positron emission particle tracking, which allows the motion of a single tracer particle to be followed in a noninvasive way. The particle movement is closely correlated with the oscillation of the bottom plate. Two types of granular motion have been observed in beds with heap formation: convection and fluctuation. The effects of system parameters, including vibration amplitude, frequency, and bed weight, have been studied. The particle cycle frequency was found to correlate well with the dimensionless acceleration. Cycle frequency appears to be inversely proportional to bed mass. The particle dispersion was determined by following the tracer particle trajectory. The system is highly anisotropic, as the horizontal dispersion is stronger than the vertical dispersion. (C) 2006 American Institute of Physics.