Pattern formation in oscillatory granular flows

Abstract

An experimental device has been used to examine the behavior of granular materials under vertical, horizontal and combined bi-axial vibrations. Containers with square, rectangular and circular cross sections geometries were used, with glass spheres, millet and lentil as granular media. The oscillating frequencies varied from 0 to 35 Hz, with amplitudes between 0 and 5.5 mm. Flow visualization was made possible with high-speed video cameras providing frontal and lateral views of the granular motion. Four different phenomena: heaping, arching, small amplitude surface waves and large amplitude surface waves were found. The onset of these phenomena depends basically on two dimensionless parameters; one involving the amplitude and frequency of oscillations coupled with gravity and the second one representing the amount of material in the vibrating container. In the case of vertical vibrations, results agreed well with those of Wassgren et al. (1996), although some discrepancies were found. For horizontal vibrations, convective cycles appeared rotating in opposite directions as well as lateral waves with one half the frequency of excitation. For the case of combined vibrations, a superposition of effects between those of horizontal and vertical vibrations was found and analyzed. Finally, comparison was made between experiments and numerical predictions based on molecular dynamics. The numerical solution agreed extremely well with experimental observations, particularly for the new results of combined vibrations.