Bridging the Spatial and Temporal Scales in Dense Granular Systems Description of Dense Granular Shear Flows

Kondic DMS-0605857 The project centers on analyzing and understanding the nature of information propagation through dense granular systems. The properties of the signals are then used to deduce the basic physical mechanisms of the force and energy transmission. These mechanisms have been the subject of considerable study lately because it is crucial to understand whether the forces between granular particles propagate in a manner that can be described under an elliptic, hyperbolic, or parabolic framework. The starting point of this project is development of large scale discrete element simulations that are used to analyze response of dense granular systems to space- and time-dependent perturbations. The results of the simulations are then employed to help formulate effective models for bridging the scales between micro (grain scale) and meso (hundreds or thousands of grains) descriptions of granular systems. Both static and dynamic granular systems are considered, making it possible to analyze the interplay between granular dynamics and signal propagation. This setup also allows for considering some important features of dense granular flows, such as the role of force anisotropy and underlying microstructure. The project is carried out in close collaboration with experimental work performed at Duke University. Dense granular systems are one of the most challenging systems in the field of soft condensed matter, in particular because they are subject to jamming, and fall in between solid and liquid states of matter. Analysis of signal propagation through these systems allows us to understand how granularity on a micro scale influences macroscale behavior. The novel research techniques used here also can be applied to other soft condensed matter systems that experience jamming, such as emulsions, colloids, gels, and foams. In addition, signal propagation through granular systems is of considerable importance in a number of practical problems including oil recovery, vibrofluidized beds, and some important humanitarian efforts, such as detection of land mines. The project addresses basic issues in statics and dynamics of dense granular systems; understanding of these basic concepts allows for future progress in developing better models needed for numerous applications of granular materials.