Flocking in the gas-Fluidized Bed

Lynn Daniels

We use a gas-fluidized bed to simulate swarming behavior often seen in
biological systems, e.g. bacteria or migratory birds. Swarming behavior is
essentially collective motion in which particles maintain coherence as a group.
Particles moving in a gas-fluidized bed behave stochastically. However, by
including an attractive interaction between particles and assuming that the
particles maintain a constant absolute velocity, theoretical models have been
able to simulate both translational swarming behavior, in which particles
translate as a group in a chosen direction, and vortex behavior, in which the
particles rotate about a common center. We have observed swarming behavior in a
bidisperse system; however, all the relevant models have used a monodisperse
system. To that end, we experiment with physically polar particles, having a
"head" and a "tail" which are physically distinguishable, that have a
preferential direction of motion and broken third-dimension symmetry. These
polar particles exhibit behaviors distinctly different than symmetric objects
including preferential motion and ordering.