About the group

Our research combines theory, experiment, and simulation with the aim of developing new mathematical models for granular materials. Motivated by core dynamics in pebble-bed nuclear reactors, we focus on the poorly understood regime of slow, dense flow, which exhibits fundamentally different behavior from normal molecular fluids due to long-lasting contacts and strong many-body interactions. We are interested the microscopic dynamics of random packings, the macroscopic dynamics of frictional stresses and plastic flow, and, ultimately, a unified multiscale model. Our research complements the study of traditional “wet fluids” in the Fluid Dynamics Group.

Picture of a granular simulation
DEM Simulation of 55,000 visco-elastic grains in a pseudo-2D container.

Pebble-Bed Reactor project

Our basic scientific research also has a practical motivation. We collaborate closely with the Modular Pebble-Bed Reactor project in the Department of Nuclear Engineering at MIT. Our goal is to understand and predict the dynamics and burn-up of fuel and reflector pebbles in the reactor core, which is not well described by any traditional models. To this end, we perform real experiments in our new laboratory using a high-speed digital video camera to track individual particles in dense granular flows.

Parallel simulation

We complement these measurements with computer “experiments” (large-scale simulations) using a variety of old and new models to provide more detailed microscopic information. Our simulation effort takes full advantage of the new Applied Mathematics Computational Laboratory and a fruitful collaboration with Sandia National Laboratory, which has developed a parallel code to simulate granular materials by the discrete-element method.