Introduction

The importance of understanding the processes governing the transport of granular materials [jae96] has long been recognized, particularly because of its industrial relevance. Methods analogous to MD modeling turn out to be appropriate for the study of granular matter, although the constituent particles are, of course, no longer the atoms and molecules of MD.

Mere inspection reveals the complexity of granular matter. The grains themselves are irregularly shaped, often covered with asperities, and are normally polydisperse. Grain collisions are highly inelastic and friction is important for forming heaps. The wear and tear of collisions can alter the shape of the grains to some extent; electrostatic forces, moisture, adhesion and the presence of air can all affect the behavior. Which of these, and other, characteristics must be incorporated into the model to reproduce the key features of the behavior can only be established empirically.

The goal of this brief departure from simulation at the molecular scale is to demonstrate the wider applicability of the approach, but not to provide a survey of either granular dynamics simulation techniques or applications; reviews of the subject include [bar94, her95]. The discussion of this chapter deals with methods based on soft-particle MD and, while there are many fascinating granular systems to choose from, the examples here deal with vibrating layers [biz98, rap98], mainly because of the visual impact of the results. The methods are readily extended to other kinds of problem.