Pattern formation and fluidization in vibrated granular layers, and grain dynamics and jamming in a water fluidized bed

This work examines the behavior of granular materials forced away from equilibrium in two different experimental systems. We study pattern formation in vibrated granular layers, and fluidization of grains near the onset of fluidization in a water fluidized bed.;We studied the behavior of the layer near the onset of patterns. Below onset, for Gamma < 2.5, we found that although no visible patterns were excited, the noisy state contained spatial structure. In addition, we studied the formation and the evolution of order in square patterns after a rapid change in Gamma from below to above onset. We found that the pattern formed in two distinct stages: a rapid ordering with universal properties, followed by a slower non-universal ordering. We also examined the behavior of the average wavelength of the patterns during the first stage ordering, and found that the evolution of the wavelength was accompanied by a change in the effective fluid depth of the layer. The condition for a rapid layer fluidization was shown to be governed by a previously studied grain mobility transition.;Fluidization in a water fluidized bed occurs when the pressure drop Delta P developed by the flow Q through packed grains balances the buoyant weight of the grains, (rhop - rho f)gh, where rhop and rhof are the solid and fluid densities and h is the height of the grains. For increasing Q, fluidization is characterized by an increase in void fraction, 1 - phi, where phi is the solid particle fraction. Using a light scattering technique called Diffusing Wave Spectroscopy, we studied the dynamics of grains for smooth increases and decreases of Q near the onset of fluidization. We found that the behavior was strongly influenced by the initial packing fraction of the grains. Loosely packed grains near Random Loose Packed (RLP), with 1 - phi ≈ 0.45, moved immediately at the onset of fluidization and remained in motion. (Abstract shortened by UMI.)...