Multiparticle simulation methods applied to the micromechanics of bed load transport

Abstract

We solve the Newtonian equations of motion to follow the trajectories of each of a large number of two‐dimensional circular bed load particles as they move in response to stresses exerted by an overlying fluid. The fluid is modeled as a moving layer or “slab” which exerts a velocity‐dependent drag force on embedded particles and satisfies its own momentum balance equation. Bed load mass flux and hop length and hop height statistics of simulated beds resemble those observed in the laboratory. By marking particles originally residing on the surface, vertical mixing of sediment is investigated. An injection of fine particles into a bed load system of coarse particles under traction illustrates the early stages of the evolution of sedimentary stratigraphy. Friction angles and their distribution are investigated as a function of bed transport history and particle size. The main thrust of the paper, however, is to describe and test a microscopic bed load model which engineers, geologists, and biologists may find useful for applications where particle arrangement and relative particle motion are important.