Frequency-amplitude behavior in the incipient movement of grains under vibration

The onset of the movement of particles placed on a horizontal rough surface subject to a vertical sinusoidal vibration is investigated through tracking experiments,theoretical analysis,and numerical simulations. The frequency of vibration needed to move particles decays exponentially with the amplitude of the oscillatory input.This behavior is explained through a simple mechanism in which a forced damped harmonic oscillator with a spring constant represents all the interactions between the particle and the surface.The numerical results compare well with experimental data,demonstrating that the forces included in the numerical calculations suitably account for the main particle response,even though the complexity of the surface is not fully taken into account.Describing the way in which frequency varies with amplitude could be relevant to technological applications such as cleaning of material surfaces.

Movement initiation of millimeter particles on a rotating rough surface: The role of adhesion

We performed experiments to determine the critical moment for movement initiation of a millimeter bead on a rotating rough surface.The corresponding critical angular velocities were measured for glass and stainless-steel ball bearings over two different rough surfaces with glued glass beads.A basic theoretical analysis was developed to explain the observed results.Although the expectation of a simple approach with the presence of the obstacles offered by a rough surface could be sufficient to describe the problem,we prove here that the sole con sideration of these obstacles,and even friction,are insufficient to explain the results in the range of a few-millimeter glass particles.Where the thermodynamic work of adhesion between surfaces is significant,the adhesion forces must be considered in the force balance for particle detachment:.This effect is a determinant for describing theoretically and numerically the dynamics of millimeter particles.

Mineral dust resuspension under vibration: Onset conditions and the role of humidity

The vibration of dusty surfaces inevitably causes re-entrainment of particles into the atmosphere.Given that movement of mineral dust particles deposited on a surface begins at a critical frequency (fc) and amplitude,an experimental laboratory study was conducted to determine the onset conditions for resuspension of a vibrated granular soil.We determined the resuspension state diagram as a function of frequency and amplitude of a sinusoidal vibration,the granulometry of the dust and the thickness of the soil bed.The mitigation effect of humidity was also evaluated.Critical frequencies ranged between 2.5 and 23 Hz when amplitudes were less than 12 rmm.These results were independent of bed thickness and perturbation type.For all particle sizes observed,fc decreased monotonically with A,contrasting with behavior observed for individual particles.In dry samples,fe for large size classes was markedly less when A was greater than 6 mm;while thefc for fine fractions only decreased once amplitudes reached 10 mm.Experiments with wet granular soils demonstrated that wetting above an optimum humidity did not necessarily impede movement and caused agglomeration.This study provides guidelines for managing resuspension of granular soils subjected to vibrations.