Granularity and Jamming: A New Approach to Understanding and Predicting Near-Threshold Sediment Transport
Abstract
Landscape evolution, such as the formation and erosion of rivers, results from fluid-driven sediment transport. Predicting sediment transport rates is essential for modeling landscape change and protecting infrastructure. Current approaches, which typically focus on fluid dynamics while neglecting granular dynamics, predict transport rates that are often off by more than an order of magnitude. In this proposal we seek a new approach, that describes a river bed as the interface between a jammed disordered solid and a shearing fluid. We study bed load particles, particles frequently in contact with the river bed, because they probe the near-yield phase space along this jammed-flowing interface. However, the very concept of yielding on this interface is slippery, and historical approaches to understand this phenomenon emphasize momentum-based hydrodynamic transport laws, which break down for intermittent bed load transport. The effects of collective particle modes and mechanical constraints have a contribution of growing importance on the interfacial dynamics near-yield, which could be understood as a type of jamming transition, but data exploring these effects are lacking. We seek to experimentally acquire data on the most fundamental variables characterizing the dynamics of grains driven by a fluid, the positions and velocities of particles in the bed, using unobtrusive but direct methods. To do so, we have pursued two strategies. In the lab we have constructed a unique apparatus, in order to extract the positions of every particle in a region of space using the method of refractive-index matching and laser scanning. We are also working to compare findings from this small, viscous experiment with a larger 2D flume in which inertial effects (particle collisions and fluid turbulence) are significant, to isolate the origins of observed dynamics.
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 05, 2019
- Accession Number
- AD1080634
Entities
People
- Douglas J. Jerolmack
Organizations
- University of Pennsylvania