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Comparison of Methods to Calculate the Shear Velocity in Unsteady Flows

Author(s): G. Bombar

Linked Author(s): Gökçen Bombar

Keywords: No keywords

Abstract: The shear velocity is a significant parameter in all areas of hydraulics; therefore it is essential to calculate it correctly. There exist various approaches to obtain the shear velocity in steady flows, but the literature on the application of these procedures to unsteady flows is scarce. In this study, an artificial triangular-shaped hydrograph was generated in a rectangular flume of 70 cm wide and 18 m long. The time series of the shear velocity was obtained by several methods and compared, such as, u * SV by applying the Saint-Venant equations, u * L by adopting the methodology given by Clauser Method, u * P by employing the parabolic law, u * UN by applying the momentum equation presuming the slope of energy grade line is equal to bed slope and finally u * avg by using the average velocity equation. In order to examine the hysteretic behavior of depth variation with point velocity, a hysteresis intensity parameterηwas proposed. Looking at the variation ofηwith normalized elevation as z/h base, one can observe that there is a strong relation between these two dimensionless parameters and an equation was proposed. After an analysis of existing literature data, it is revealed that the coefficient and power of the equation depends on the unsteadiness parameterα.

DOI:

Year: 2016

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