ABSTRACT Proposal Number: CTS 9634261 Principal Investigator: McLean This is a grant to support the investigation of the mechanics of sediment entrainment and transport in situations where near-bed mean flow and turbulence structure is significantly different than that of steady, uniform flows. This will be done within the context of an overall goal of developing the capability to predict the flow and sediment dynamics over an erodible bed and the resulting topographic response. Existing relations between flow characteristics and sediment transport developed in steady, uniform flows yield inaccurate results for more complex flows. This error arises through the alteration of the distributions of lift and drag forces on sediment grains making up the bed as a result of the effects of spatial and temporal accelerations on the turbulence field. These effects are a critical part of the mutual interactions between flow structure, sediment transport, and bed morphology that give rise to a wide spectrum of erodible bed phenomena, such as the formation and stability of ripples and dunes. The principle aims of this research are threefold: a) to extending the knowledge gleaned from two-dimensional bedforms to three-dimensional features b) to determine the response of a sediment particle to complex flow and c) to extend this information to suspended particles through the use of a multi-frequency acoustic backscatter system as well as with an imaging fiber optic system for observing very near-bed processes. Measurements will be combined with an advection/diffusion model for suspended sediment to investigate the nature of the relationship between local entrainment at the bed and the near-bed flow field and how this affects the evolution of the bedforms.
