Publications

Abstract not provided.

Using random walk simulations we explore diffusive transport through monodisperse sphere packings over a range of packing fractions φ in the vicinity of the jamming transition at φc. Various diffusion properties are computed over several orders of magnitude in both time and packing pressure. Two well-separated regimes of normal "Fickian" diffusion, where the mean squared displacement is linear in time, are observed. The first corresponds to diffusion inside individual spheres, while the latter is the long-time bulk diffusion. The intermediate anomalous diffusion regime and the long-time value of the diffusion coefficient are both shown to be controlled by particle contacts, which in turn depend on proximity to φc. The time required to recover normal diffusion t∗ scales as (φ - φc)-0.5 and the long-time diffusivity D∞ ∼ (φ - φc)0.5, or D∞ ∼ 1/t∗. It is shown that the distribution of mean first passage times associated with the escape of random walkers between neighboring particles controls both t∗ and D∞ in the limit φ → φc.

The authors report and analyze the results of numerical studies of dense granular flows in two and three dimensions, using both linear damped springs and Hertzian force laws between particles. Chute flow generically produces a constant density profile that satisfies scaling relations suggestive of a Bagnold grain inertia regime. The type for force law has little impact on the behavior of the system. Failure is not initiated at the surface, consistent with the absence of surface flows and different principal stress directions at vs. below the surface.