| One of the issues in modeling suspensions is the separation of scales between the length scales of the flow, and the small size of the particles. We focused on improving the Force-Coupling Method, which is able to capture macroscopic properties of the suspension, at the expense of accurate modeling on microscopic scales. We investigated the behavior of the method for close particle interactions and developed and tested a lubrication parameterization to improve the results. Several issues concerning the dynamics of sedimentation flows are still open questions. In particular, velocity fluctuation screening mechanisms are not well understood. In this context, we evaluated the effect on the bulk flow of using different types of collision barriers for interactions between particles in a homogeneous suspension. Small changes in the suspension microstructure were produced, which affected the mean particle velocities and velocity fluctuations in a systematic fashion.; Wall boundary conditions may play a role in the screening of fluctuations. We considered simulations of transient sedimentation in a cell with top and bottom wall boundaries and periodic boundaries in the horizontal. We considered several different box sizes, in an attempt to elucidate the connection between particle velocity fluctuation levels and box width. A vertical density stratification formed during the settling process. We quantified the particle microstructure, and proposed a mechanism for the decay of fluctuations.; We investigated a Rayleigh-Taylor instability of a suspension layer above clear fluid. In this scenario, an initially exponentially growing plume was observed, with a growth rate similar to that predicted by a simplified model. Subsequently, the growth of the mixing layer was a linear function of time. We derived a scaling for the mixing layer growth rate. The last stages of the instability process were seen to be similar to the quiescent sedimentation problem. |
