Confined packing of granular rods: Simulations*

We model the packing of rodlike particles in confined geometries. Simulations are optimized for parallel processing on a Graphics Processing Unit. Simulated particles are spherocylinders (cylinders with hemispherical end-caps) of aspect ratios ranging from 4 to 32. Infinitesimal particles are distributed at random in a cylindrical container and allowed to expand until they overlap. A conjugate gradient method is used to minimize the elastic potential energy that accompanies overlap, and the growth/minimization process continues until the energy can no longer be minimized to an infinitesimal value. We find the jamming packing fraction decreases as the container becomes small, and is consistent with the idea of a boundary layer of randomly packed particles. From simulations we extract the large-container asymptotic packing fraction Φ_∞, the decrease in packing fraction within the boundary layer δΦ and the size of the boundary layer δL. We also characterize orientation in the boundary layer at the container wall, floor and ceiling.