Granular Material - Pattern Formation

Pattern Formation

Excited granular matter is a rich pattern-forming system. Some of the pattern-forming behaviours seen in granular materials are:

• The un-mixing or segregation of unlike grains under vibration and flow. An example of this is the so-called Brazil nut effect where Brazil nuts rise to the top of a packet of mixed nuts when shaken.The cause of this effect is that when shaken, granular (and some other) materials move in a circular pattern. some larger materials (Brazil nuts) get stuck while going down the circle and therefore stay on the top.
• The formation of surface patterns in vibrated granular layers. These patterns include but are not limited to stripes, squares and hexagons. These patterns are thought to be composed of fundamental excitations of the surface known as oscillons.
• The formation of sand ripples, dunes, and sandsheets

Some of the pattern-forming behaviourshave been possible to reproduce in computer simulations. There are two main computational approaches to such simulations, time-stepped and event-driven, the former being the most efficient for a higher density of the material and the motions of a lower intensity, and the latter for a lower density of the material and the motions of a higher intensity.