Equilibrium Scour-Depth Prediction around Cylindrical Structures
Publication: Journal of Waterway, Port, Coastal, and Ocean Engineering
Volume 143, Issue 5
Abstract
Offshore gravity base foundations (GBFs) are often designed with complex geometries. Such structures interact with local hydrodynamics, creating an adverse pressure gradient that is responsible for flow and scour phenomena, including the bed shear stress amplification. In this study, a method is presented for predicting clear-water scour around cylindrical structures with nonuniform geometries under the force of a unidirectional current. The interaction of the flow field with the sediment around these complex structures is described in terms of nondimensional parameters that characterize the similitude of water-sediment movement. The paper presents insights into the influence the streamwise depth-averaged Euler number has on the equilibrium scour around uniform and nonuniform cylindrical structures. Here, the Euler number is based on the depth-averaged streamwise pressure gradient (calculated using potential flow theory), the mean flow velocity, and the fluid density. Following a dimensional analysis, the controlling parameters were found to be the Euler number, pile Reynolds number, Froude number, sediment mobility number, and nondimensional flow depth. Based on this finding, a new scour-prediction equation was developed. This new method shows good agreement with the database of scour depths acquired in this study . Measurements of the equilibrium scour depth around nonuniform cylindrical structures were used to show the importance of the Euler number in the scour process. Finally, the importance of the remaining nondimensional quantities with respect to scour was also investigated in this study.
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Acknowledgments
The authors express appreciation for the financial support and expertise provided by HR Wallingford and to the Engineering and Physical Sciences Research Council for the grant funding this research. J.M.H. and R.J.S.W. acknowledge funding from HR Wallingford’s strategic research program.
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Journal of Waterway, Port, Coastal, and Ocean Engineering
Volume 143 • Issue 5 • September 2017
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© 2017 American Society of Civil Engineers.
History
Received: Sep 23, 2016
Accepted: Jan 25, 2017
Published online: May 11, 2017
Published in print: Sep 1, 2017
Discussion open until: Oct 11, 2017
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