The Dynamics of Granular Flows

Jerry Gollub

Haverford College and University of Pennsylvania

How can we best describe materials composed of particles that flow like fluids, like sand, powders, or the sediments found in geophysical settings? We normally describe fluids by partial differential equations, but the possibility of doing so reliably for granular systems is still unclear. I will discuss studies of the anomalous behavior of granular materials that illustrate their unique properties compared to other condensed matter systems. For example, when sheared, random granular matter can crystallize, dramatically affecting its flow properties. In some cases both ordered and disordered states coexist, with the disordered state being metastable. These and other experiments raise interesting questions about how prior history is recorded in the internal structure of granular packings, affecting their instantaneous rheology. Additional puzzling issues include: The role of polydispersity, anisotropy, and chirality; the onset of stick-slip motion and its connection to fracture; the behavior of internal stress networks during time-dependent flows; and the statistics of fluctuations in granular systems.

Jerry P. Gollub,
Professor in the Natural Sciences (Physics)
Physics Department,
Haverford College
370 Lancaster Avenue
Haverford, PA 19041