Berlin 2008 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 19: Granular matter I

DY 19.4: Vortrag

Mittwoch, 27. Februar 2008, 15:15–15:30, MA 004

Rheological Transition in Granular Media — •Zahra Shojaaee, Lothar Brendel, and Dietrich E. Wolf — Department of Physics, University of Duisburg-Essen, 47048 Duisburg, Germany

The Contact Dynamics method is being applied to investigate a two-dimensional non-cohesive granular material. The particles are hard discs, and Coulomb friction and volume exclusion forces are the only forces being exerted. The particles are confined between two parallel walls at the top and the bottom. The walls are being pushed inwards by the same perpendicular forces. They move horizontally with the same constant velocity in opposite directions.

The velocity profile is being studied. In the case of a bidisperse system the flow as function of the shear velocity shows characteristics comparable to a phase transition. The key quantities are the velocity of the center of mass of the system as well as its fluctuations. A finite size analysis suggests that it is a discontinuous “phase transition”. At high shear velocity the symmetry between the upper and lower wall is not spontaneously broken, whereas at slow shear rate the granular material has different slip at the two walls. For large systems the ergodic time seems to diverge exponentially below the critical shear velocity.