Papers and Talks --
2D granular shear in an
Disks are put between two concentric cylinders, forming
an annular array (pictured above), and sheared with a serrated ring at
top. Although the bottom particles rarely move more than a fraction
of their diameter, the effect is to significantly compact the pile.
We're now tracking the individual particles to see how defects in the
crystal lattice move. Defects can't simply disappear; they must
either move to the surface or annihilate with another defect, leading
to long range attractive forces, even though the particles are
Random packing of
This simulation generates least-dense jammed packings of rods of
various length/width ratio. We study the nature of the jammed state,
looking for characteristic changes as the particles become long and thin.
Granular flow through hoppers
Hoppers are a natural system in which to study jamming, with many
practical applications. The statistics of jamming —
particularly how many particles exit the hopper before the flow stops
— are studied as both the particle length and size of the exit
aperture is varied. As the opening becomes larger the flow changes
from essentially two- to three-dimensional, with many interesting
changes in scaling.
We study rod-like granular materials: collections of long, thin
particles, piles of which are more "solid" than ordinary sand piles.
A complex system is one that:
- consists of many interacting components
- generates interesting features --- patterns, structures, chaos --- from the interactions between components
- produces collective behaviors often impossible to predict from
just knowing the individual interactions
Studying granular materials means looking at
- the collective effects of thousands of individual grains
- strange phenomena like arches, voids, slugging, and jamming
arising from simple friction and contact forces
- Random packing of rod-like particles
- granular flow through hoppers
- Column collapse of rod-like granular materials
- rheological properties of U-shaped particles
- 2D granular shear in annular-planar geometry
- Jamming of rods during filtration
- Jamming in 3D granular piles
- Connected networks in 2D rodpiles
- Static properties of 2D rodpiles
- Chaos in a bouncing dumbbell
Jamming in 3D Piles
What determines if 3D piles of rods form a solid plug? We found that
it depends not only on the particle aspect ratio, but also on the
container they're poured into.
Connected Networks in
When we push through a pile of rods spread on a table, sometimes all
the rods jam into a single connected network, as shown above. Why?
Chaotic Dynamics of
a Bouncing Dumbbell
Simulations show that a purely elastic, dumbbell dropped on a table
bounces in a quasi-periodic manner, with resonances occurring as the
initial drop height is increased.
Static properties of 2D piles
of Prolate Granular
2D piles of rods show large empty spaces (voids). Nevertheless, the
majority of the pile area is caused by the cumulative effect of lots
of small voids.