[See below for recent publications]

Granular materials are poorly understood at a fundamental level. While there is a number of continuum models, usually based on elastoplastic type of constitutive relations, it is still very difficult to understand some basic features of granular materials based on continuum picture alone. One of the reasons are fluctuations, whose which are not necessary small, as it is emphasized by this picture of stress chains in slowly sheared granular system.

Molecular dynamics / Discrete element simulations appear to be a natural approach to gain better insight into these systems. During last few years, I have been developing 2D and 3D MD simulations with the goal of explaining some basic features of granular materials. Currently, a significant part of this research concentrates on a sheared granular system in Couette geometry. This research, sponsored by NASA Microgravity Program , and performed in close collaboration with the granular group at Duke University lead by R. P. Behringer , was supposed to lead to an experiment at the International Space Station .

The figure below shows an example of the `force chains' that appear as granular particles experience as they are being sheared.

More information about this research project can be found here.

Selected recent publications on granular materials:

(see here for the complete list).

On velocity profiles and stresses in sheared and vibrated granular systems under variable gravity, with O. Baran, Phys. Fluids 18, 121509 (2006).

Velocity profiles, stresses, and Bagnold scaling of sheared granular system in zero gravity, with O. Baran, Phys. Fluids 17, 073304 (2005).

Stabilization of nonlinear velocity profiles in athermal systems undergoing planar shear flow, with N. Xu and C. O'Hern, Phys. Rev. E., 72, 016001 (2005).

Velocity Profiles in Repulsive Glassy and Athermal Systems under Shear , with N. Xu and C. O'Hern, Phys. Rev. Lett. 94, 016001 (2005).

Elastic Energy, Fluctuations and Temperature for Granular Materials , with R.P. Behringer, Europhys. Lett. 67, 205 (2004).

Segregation by friction , with S.G.K. Tennakoon, B. Painter, R. Hartley, and R.P. Behringer, Europhys. Lett. 61, 742 (2003).

Granular friction, Coulomb Failure, and Fluid-Solid transition for horizontally shaken granular materials, with G. Metcalfe, S.G.K. Tennakoon, D.G. Schaeffer, R.P. Behringer, Phys. Rev. E 65, 031302 (2002).

Onset of a flow in horizontally vibrated granular bed: convection by horizontal shearing , with S.G.K. Tennakoon and R.P. Behringer, Europhys. Lett. 45, 470 (1999).

Dynamics of the particles on a surface: About collision induced sliding and other effects, Phys. Rev. E 60, 751 (1999).