Ongoing

Segregation in vibrated granular mixtures: Granular mixtures shaken, and even stirred, segregate. Nobody really knows why. Segregation is important, both in Nature and in the industry. In Nature, avalanches and landslides preferentially deposit materials. In the industry it is often required to promote segregation -- as when separating pills in a pharmaceutical company or rice grains in a rice mill -- or to control segregation -- when attempting to make uniform mixtures. The particular problem that we  are attempting to nail is related to segregation in certain types of industrial machines that are known to work, but with little inkling as to why, or any knowledge of which parameters are important to control. We are employing an in-house discrete element code, experiments, and the kinetic theory of dense gases to study this problem.

This is an unusual project. It requires computational leanings and/or a desire to perform experiments. If you are theoretical, then kinetic theory and statistical mechanics are indicated.

Dormant

Saltation: The process by which desert sand moves is called saltation. The wind blows across sand, and carries with it sand-grains. These grains fall down due to gravity and impact upon the sand below. This impact loosens more grains that are picked up by the wind and carried further. This is one way that sand moves. An important piece in the model is to estimate the number of grains released by the impact of one grain on a grain bed. I have a model in place that requires a bit of tweaking. If you are a tweaker, meet me. The model holds much promise for other impact situations as well.

This problems demands knowledge of elasto-dynamics, asymptotics and a carefree and adventurous attitude towards mechanical modeling.

Quasi-static response of dense aggregates: How a densely packed reacts to shear and pressure loading is an old and unsolved problem. My interest in it is primarily to estimate the amount of energy dissipation in such structures due to applied oscillatory body forces. This in turn connects back to the effect of energy dissipation on the motion of freely tumbling bodies. I have done some work in this using a mean-field theory but newer approaches are possible, namely by including fluctuations about a mean field.

I really don’t know what this problem requires, as I don’t know how to solve it. Yet.