**Boundary effects and self-organization in dense granular flows**

L. E. Silbert, G. S. Grest, S. J. Plimpton, D. Levine, Physics of Fluids, 14, 2637-2646 (2002).

Boundary effects in gravity-driven, dense granular flows down inclined
planes are studied using large-scale molecular dynamics
simulations. We find that the flow behavior and structure of the
flowing pile changes dramatically as we vary the roughness of the
supporting base. For a rough, bumpy base, there are three principal
flow regimes that depend on the inclination angle theta : at small
angles theta < theta *sub r*, where theta *sub r* is the angle of
repose, the system does not flow; for large angles theta > theta *sub
max*, where theta *sub max* is the maximum angle for which stable,
steady state flow exists, the flow is unstable; and for theta *sub r*<
theta < theta *sub max*, the energy input from gravity is balanced by
that dissipated through friction and the system reaches a stable,
steady state flow. In the stable regime, we find no slip boundary
conditions with a bulk density that is independent of the height above
the base. For a chute base that is ordered, the steady state regime
splits into a further three distinct flow regimes: at lower angles,
the flowing system self-organizes into a state of low-dissipation flow
consisting of in-plane ordering in the bulk; at higher angles, a
high-dissipation regime similar to that for a rough base but with
considerable slip at the bottom is observed; and between these two
sub-regions we observe a transitional flow regime characterized by
large oscillations in the bulk averaged kinetic energy due to the
spontaneous ordering and disordering of the system as a function of
time.

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