Couette geometry

Simulations of granular systems in Couette geometry (2001-2005)

[In collaboration with Robert P. Behringer , Duke University) and the engineering group at NASA Glenn Research Center].

This research centers on the study of phase transitions in granular materials, in particular in the dense phase, when the volume fraction is close to random close packing. These phase transitions are strongly influenced and modified by gravity. In order to understand the basic physical picture it would be therefore very useful to perform experiments in zero gravity. These experiments were prepared both at Duke and at NASA Glenn Research Center. At NJIT, we supported the experimental efforts by performing 2D and 3D simulations of granular systems. These simulations were developed both for zero gravity, and for the Earth gravity case.

3D simulations were developed in collaboration with Oleh Baran, who was a postdoctoral associate in the Department of Mathematical Sciences at NJIT 2004-05.

Earth bound experiments were developed by Karen Daniels, former postdoctoral associate at Duke (currently at North Carolina State University), under the supervision of R. P. Behringer. These experiments, have already provided some very interesting insights into the granular dynamics.

Here is the link to the project web page at Nasa Glenn.

We have also developed simulations of a 2D granular system sheared between two concentric cylinders. These simulations use soft-particle approach to model interaction between the system particles, and between the particles and the walls. This method is applicable to systems of variable density, and will be also suitable for modeling experiments performed by using different kinds of particles characterized by varied elastic and frictional properties.

The figure and the animation below shows the force that granular particles experience as they are being sheared by the rotating inner wheel. One can also observe dilation close to the rotating wheel. (The particles are shown smaller than their actual size).

Preliminary results of these 2D simulations suggest that there is plenty to learn regarding force propagation mechanism, as well as regarding dynamic properties of this granular system. This insight will be extremely valuable for 3D simulations in the cylindrical/annular geometry, which are currently being developed.

Animation is here ).

Animations of a granular system sheared in channel geometry can be found here:

Polydisperse system: Short version