(372b) Transition in a Dense Granular Flow Down an Inclined Plane

A granular flow down an inclined plane exhibits a discontinuous transition from a disordered, random state to an ordered state consisting of layers of particles with in-layer hexagonal order, when there is a small change in the roughness of the base. The rough base was created using a random arrangement of frozen particles at the base, and the roughness was varied by varying the ratio of the frozen and moving particle diameters. The transition base roughness depends on the interaction model used for the particle interactions, but is independent of the layer height
and angle of inclination. In the ordered state, there are layering of particles into distinct layers sliding on each other, and ordering of particles in the layers. The volume fraction in the ordered state is higher than that in the disordered state, but the resistance to flow is much lower and there is an increase in the flow rate by two orders of magnitude when there is a disorder-order transition. The velocity profile in both the ordered and disordered states follow the Bagnold law, but the Bagnold coefficients are very different. In addition to base roughness created by
frozen particles, the effect of a different forms of base roughness, which are sinusoidal perturbations of varying amplitude and wavelength, is examined. The results indicate that the results for the roughness are not a linear superposition of sinusoidal modes of different amplitude, and the response to an external perturbation also do not exhibit the exponential decay at low amplitudes expected from linear response theories.