Complex Systems@RIT

Professor Scott V. Franklin, Dept of Physics, RIT 		           
Lab Home--People-- Papers and Talks -- Future Projects
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

Current Projects

  • 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

Possible Future Projects

Past Projects

  • 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

Current Projects

2D granular shear in an
annular-planar geometry

Previously, an undergraduate and I investigated whether a local disturbance would cause a 2-dimensional sandpile to settle. We put disks between two concentric cylinders, forming an annular array (pictured above) and sheared the top particles with a serrated ring that could move up and down. The weight of the ring was transmitted to the bottom particles; we expected that the lower particles would move and gradually settle. Indeed, although the bottom particles rarely moved more than a fraction of their diameter, the pile did compact.

Future work in this area involves tracking the particles to see how the defects move around. Defects can't simply disappear; they must either move to the surface or annihilate with another defect. I'd like to look for long range attractive forces between the defects, even though the particles are completely non-attracting.

Random packing of rod-like particles


 

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.

Past Projects

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
2D Granular Materials

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 Materials

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.

Funding: