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

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KondicDMS-0605857 The project centers on analyzing and understanding thenature of information propagation through dense granular systems. The properties of the signals are then used to deduce the basicphysical mechanisms of the force and energy transmission. Thesemechanisms have been the subject of considerable study latelybecause it is crucial to understand whether the forces betweengranular particles propagate in a manner that can be describedunder an elliptic, hyperbolic, or parabolic framework. Thestarting point of this project is development of large scalediscrete element simulations that are used to analyze response ofdense granular systems to space- and time-dependentperturbations. The results of the simulations are then employedto help formulate effective models for bridging the scalesbetween micro (grain scale) and meso (hundreds or thousands ofgrains) descriptions of granular systems. Both static anddynamic granular systems are considered, making it possible toanalyze the interplay between granular dynamics and signalpropagation. This setup also allows for considering someimportant features of dense granular flows, such as the role offorce anisotropy and underlying microstructure. The project iscarried out in close collaboration with experimental workperformed at Duke University. Dense granular systems are one of the most challengingsystems in the field of soft condensed matter, in particularbecause they are subject to jamming, and fall in between solidand liquid states of matter. Analysis of signal propagationthrough these systems allows us to understand how granularity ona micro scale influences macroscale behavior. The novel researchtechniques used here also can be applied to other soft condensedmatter systems that experience jamming, such as emulsions,colloids, gels, and foams. In addition, signal propagationthrough granular systems is of considerable importance in anumber of practical problems including oil recovery,vibrofluidized beds, and some important humanitarian efforts,such as detection of land mines. The project addresses basicissues in statics and dynamics of dense granular systems;understanding of these basic concepts allows for future progressin developing better models needed for numerous applications ofgranular materials.