(172g) Measurement of Density Fluctuations in a Vertically Oscillated Granular Bed At the Onset of Vibrofluidization

Through measurements of vane power and density, three granular bed states, the static granular state, the pseudo-plastic state and vibro-fluidized state, along with the transitions between the states are identified.  A granular bed state phase diagram is constructed, mapping the effects of vibration frequency and intensity input.  The pseudo-plastic state contains two sub-classifications.  For vibration force less than the force of gravity at low frequency and all vibration force levels at high frequency and moderate acceleration, vibration has no measurable effect on the granular bed.  For the pseudo-plastic state subjected to low frequency vibration force greater than the force of gravity, the vane power, extrapolated zero-shear rate torque, and density change penetration into the bed are a strong function of the vibration force and frequency.  Measurements demonstrate hysteresis with changes in vibration acceleration and frequency.  The transition to a vibro-fluidized state at a critical dimensionless vibration acceleration is characterized by dramatic decreases in vane power, dynamic zero-shear rate torque and measurable fluctuations in density throughout the bed.  In the vibrofluidized state, the vane power and extrapolated zero-shear rate torque are weakly influenced by the vibration force and frequency in the vibro-fluidized state.  Within the range tested, particle diameter had little affect on the measurements of noncohesive granular media.