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Title: Calculation of movable bed friction factors
Authors: Madsen, Ole Secher
Wikramanayake, Palitha Nalin
Keywords: Ocean bottom--Mathematical models
Continental shelf
Sediment transport--Mathematical models
Turbidity currents
Dredging Research Program (U.S.)
Publisher: U.S. Army Engineer Waterways Experiment Station
Series/Report no.: Contract Report (Dredging Research Program (U.S.)) ; no.Contract Report DRP-94-5
Abstract: When wind-generated waves propagate from the deep ocean onto the continental shelf, they begin to feel the effects of the bottom. These bottom effects are accounted for as bottom friction, which arises due to the no-slip flow condition on the bottom. This condition gives rise to a bottom shear stress and a thin boundary layer where significant energy dissipation can take place. The goal of this study was to develop a simple, physically realistic method to predict the friction factor over a movable sand bed under field conditions. Since reliable field measurements are available only for ripple geometry, laboratory data were used to derive the friction factor. Laboratory experiments are outlined in this report along with a brief description of the methods involved in the model derivation. The model is formulated in two stages, deriving predictive relations for the ripple geometry of a given wave condition, and developing a relationship among flow, ripple geometry, and the resulting friction factor. The relation between ripple geometry and roughness and the relationship between the friction factor and the wave, sediment, and fluid parameters are analyzed. Finally, simple relationships for the prediction of the roughness of a movable bed under regular and irregular waves are proposed and numerical examples illustrating use of the relationships are given.
Description: Contract Report
Gov't Doc #: Contract Report DRP-94-5
Rights: Approved for Public Release; Distribution is Unlimited
Appears in Collections:Contract Report

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