Role of friction in
pattern formation in oscillated granular layers
Abstract:
Particles in granular flows are often modeled as frictionless (smooth)
inelastic spheres; however, there exist no frictionless grains, just as
there are no elastic grains. Our molecular dynamics simulations reveal
that friction is essential for realistic modeling of vertically
oscillated granular layers: simulations of frictionless particles yield
patterns with an onset at a container acceleration about 30% smaller
than that observed in experiments and simulations with friction. More
importantly, even though square and hexagonal patterns form for a wide
range of the oscillation parameters in experiments and in our
simulations of frictional inelastic particles, only stripe patterns
form in the simulations without friction, even if the inelasticity is
increased to obtain as much dissipation as in frictional particles. We
also consider the effect of particle friction on the shock wave that
forms each time the granular layer strikes the container. While a shock
wave still forms for frictionless particles, the height and time
dependence of the hydrodynamic fields differ for the cases with and
without friction.
Phys. Rev. E 69,
031301 (2004).
Manuscript
available in PDF and PS formats.