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Water 2018, 10(1), 43; doi:10.3390/w10010043

A Hydraulic Friction Model for One-Dimensional Unsteady Channel Flows with Experimental Demonstration

State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, Nanjing 210098, China
College of Hydrology and Water Resources, Hohai University, Nanjing 210098, China
Division of Hydrologic Sciences, Desert Research Institute, Las Vegas Nevada, NV 89119, USA
College of Harbor, Coastal and Offshore Engineering, Hohai University, Nanjing 210098, China
Author to whom correspondence should be addressed.
Received: 13 November 2017 / Revised: 26 December 2017 / Accepted: 4 January 2018 / Published: 8 January 2018
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As a critical parameter of the steady uniform friction model, the roughness coefficient changes with flow unsteadiness in flood events; i.e., the flow conditions of the stream segment significantly affect the flow resistance. In this study, a modified formula was established to improve the unsteady friction simulation; ten terms relating to the first- and second-order time and space partial derivatives of hydraulic parameters were selected as additional terms. The results of a hydraulic experiment show that the hysteresis between flow depth and mean cross-sectional velocity cannot be neglected in unsteady flows that disturb the performance of a steady uniform friction model. Six terms have a strong correlation with objective friction. Further, three of them have a small variance in correlation coefficient. Then, the composition of the proposed formula was determined. The results show that adding too many additional terms provides better performance in the calibration phase, yet reduces the accuracy of the validation phase because of an overfitting phenomenon. The optimal number of additional terms is three, and the established formula can improve the unsteady friction simulation. View Full-Text
Keywords: unsteadiness; nonuniformity; one-dimensional friction model; hysteresis effect; partial derivatives unsteadiness; nonuniformity; one-dimensional friction model; hysteresis effect; partial derivatives

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Bao, W.; Zhou, J.; Xiang, X.; Jiang, P.; Bao, M. A Hydraulic Friction Model for One-Dimensional Unsteady Channel Flows with Experimental Demonstration. Water 2018, 10, 43.

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