Two-Dimensional Clustering Transitions in Vibro-Fluidized Hard Spheres

Nicholas Jonathan Hanson

An investigation of the clustering transitions of a vibro-fluidized granular material in two-dimensions was conducted. Steel ball bearings, 1 mm in diameter, were placed in a rectangular Plexiglas container and oscillated horizontally with a mechanical vibrator that was powered by a function generator. Covering fractions between 0.01 and 0.15 were studied. The system exhibited three phases; the gas, clustered, and networked phases. Transitions between the phases were observed by visual inspection of the system. A phase diagram of the system was constructed, however no direct correlation was found between the covering fraction of particles and the acceleration amplitudes at which phase transitions occurred. Electrostatic effects greatly interfered with accurate measurements of the phase transitions. Clustering of particles was observed, and the nature of the cluster growth process was determined to vary with the rate of at which the acceleration amplitude of the system was quenched. Video of a "charged cloud" of particles was recorded and analyzed. Velocity distributions of the particles in the charged cloud showed that the velocities of the particles, and subsequently the granular temperature of the system, were anisotropic. The results of this investigation are presented along with possible improvements and routes for further study.