Sedimentation can result in the growt h of rough interfaces. Although sedimentation has been widely investigated in various areas of geology and engineering, the rough interface aspect of sedimentation is still unstudied. Since hydrodynamic forces are in principle long range, rough interfaces formed through sedimentation provide a significantly different growth situation for comparison with other studies of apparently similar final interfaces. This leads us to the question of the possible existence of universal phenomena in sedimentation and if there are universal phenomena, can one use noise plus a simple growth law to explain them?

Using the diffusing void model of granular flows, we study the dynamic response of granular materials, in particular, the relaxation of granular pile, pipe flow of granular materials, and the convection of granular media in a two dimensional box subjected to vibrations. We first study the relaxation of a one dimensional granular pile of height L in a confined geometry under repeated tapping within the context of the diffusing void model. The reduction of height as a function of the number of taps is proportional to the accumulated void density at the top layer. The relaxation process is characterized by the two dynamic exponents z and z' which describe the time dependence of the height reduction, Δh(t) ≈ tz and the total relaxation time, T(L) ≈ Lz'. While the governing equation is nonlinear, we find numerically that z=z'=l, which is robust against perturbations and independent of the initial void distributions. We then show that the existence of a steady state traveling wave solution is responsible for such a linear behavior. Next, we examine the case where each void is able to maintain its overall topology as a round object that can subject itself to compression. In this regime, the governing equations for voids reduce to traffic equations and numerical solutions reveal that a cluster of voids arrives at the top periodically, which is manifested by the appearance of periodic solutions in the density at the top. In this case, the relaxation proceeds via a stick-slip process and the reduction of the height is sudden and discontinuous. We then carry out the long wave analysis to demonstrate the existence of the KdV solitons in the traffic equations. Finally, we show our preliminary studies on granular convection in a box. We observe the appearance of two rolls when the control parameter exceeds the critical value, which then undergoes bifurcations to four rolls.

We report an experimental study of the ascent of a large disc imbedded in a 2D packing ofsmall beads vertically vibrated. Two distinct mechanisms leading to size segregation are observed in situ. At high acceleration, the convection process associated with surface trapping is predominates. At low acceleration, we examine the effect of the size ratio on the dynamics of the segregation which is either intermittent or continuous. This isdue to the successive formation and destruction of arches.

We study granular materials using both event driven (ED) and molecular dynamics (MD) methods. In the MD simulations we implement linear as well as nonlinear forces and also hysteretic interactions. For multiple collisions the two methods show differences: MD calculations lead to weak, whereas ED methods result in rather strong dissipation, as determined through an effective restitution coefficient.

We study a one-dimensional granular system, excited by white noise, with inelastic interactions between the particles. When the coefficient of restitution,η, is one, the particles are totally uncorrelated. As η decreases the particles cluster. A computer simulation of the system shows equilibrium clustering with a power law particle-particle correlation function. This correlation function is independent of the average kinetic energy of the particles but depends strongly on η We give simple analytical arguments to describe this clustering. We also present an “equation of state” for the particles, which relates the noise amplitude to the particle density and the average particle speed.

Binary mixtures of granular media having differing diameters are combined in a horizontal cylinder and rotated like a drum mixer about its long axis. Within a few minutes of rotation at 15 rpm axial segregation occurs and the mixture separates into relatively pure alternating bands of the individual components along the axis of rotation. We describe an experimental system whereby the mixed state can be restored by changing the speed of rotation. The sensitivity of the reversible axial segregation effect to systematic variations of the glass bead diameter is reported. Measurements of the dynamic angle of repose of the mixed and segregated phases support an explanation for the reversible axial segregation effect involving the competition between axial drift and diffusion currents, leading to a diffusion equation with a negative effective diffusion coefficient.

We report experimental measurements on mixing properties in bidimensional rotating drum. Using an image processing device, we follow the trajectories of tracer particles in a monodisperse assembly of beads. Tracer particles with different size ratios exhibit a violent segregation effect: a smaller particle has a tendency to stay in the centre and a larger one will rather dwell on the edges. Furthermore, for a tracer of identical size, we evidence a specific dispersion property where the centre and the edges are competing attractors of the mixing dynamics.

In this work, I study the supersonicrupturepulse in a two dimensionalelastic sheet. There is a friction force acting at the edge of the sheet which is composed of a term that dependson the local displacement at the edge and a viscous dissipation term. I consider the case where the sheet is driven forward by a force acting in the bulk, but is held back by the interfacial friction. I present the equations which describe such a system and then look for solutions which describe a slip pulse propagatingthough a region which is uniformly stressed. Such a pulse will allow the entire interface to move forward and partially relieve the stress. I present the integral equation that such a pulse solution must satisfy, and then discuss the behavior observed in numericalsolutions of this equation.

We study the flow under gravity of a granular model system submitted to shear in a rotating cylinder. The system is confined in a vertical 2D geometry which allows visualisation of the bulk and direct measurements of the velocity and density fields. We establish the existence of scaling properties displayed by velocity and density profiles for a large range ofdifferent flow rates.