5 research outputs found
Two-dimensional Packing in Prolate Granular Materials
We investigate the two-dimensional packing of extremely prolate (aspect ratio
) granular materials, comparing experiments with Monte-Carlo
simulations. The average packing fraction of particles with aspect ratio
is . We quantify the orientational correlation of
particles and find a correlation length of two particle lengths. The functional
form of the decay of orientational correlation is the same in both experiments
and simulations spanning three orders of magnitude in aspect ratio. This
function decays over a distance of two particle lengths. It is possible to
identify voids in the pile with sizes ranging over two orders of magnitude. The
experimental void distribution function is a power law with exponent
. Void distributions in simulated piles do not decay as a
power law, but do show a broad tail. We extend the simulation to investigate
the scaling at very large aspect ratios. A geometric argument predicts the pile
number density to scale as . Simulations do indeed scale this way,
but particle alignment complicates the picture, and the actual number densities
are quite a bit larger than predicted.Comment: 6 pages + 10 ps/eps figure
Compaction of Rods: Relaxation and Ordering in Vibrated, Anisotropic Granular Material
We report on experiments to measure the temporal and spatial evolution of
packing arrangements of anisotropic, cylindrical granular material, using
high-resolution capacitive monitoring. In these experiments, the particle
configurations start from an initially disordered, low-packing-fraction state
and under vertical vibrations evolve to a dense, highly ordered, nematic state
in which the long particle axes align with the vertical tube walls. We find
that the orientational ordering process is reflected in a characteristic, steep
rise in the local packing fraction. At any given height inside the packing, the
ordering is initiated at the container walls and proceeds inward. We explore
the evolution of the local as well as the height-averaged packing fraction as a
function of vibration parameters and compare our results to relaxation
experiments conducted on spherically shaped granular materials.Comment: 9 pages incl. 7 figure