عنوان مقاله [English]
Determining the friction coefficient in erodible beds plays an important role in the design of alluvial canals. In most of the previous studies, an impact of the hydraulic parameters on the friction coefficient has been studied for non-erodible bed conditions. In this research, by performing a laboratory model in the erodible substrates, the effects of the bed slope parameters and bed load transfer rate on the bed friction coefficient were investigated. The experiments were carried out in the discharge rate of 0.90 to 4.75 l/s and the slopes of 2, 3 and 5 percent on the uniform non cohesive particles with the grain diameter of 1.7 and 3.29 mm. The roughness Reynolds number was in the range of 82 to 343, Froude numbers of these currents in the range of 0.93 to 1.51, and non-dimensional bed load transport rate was calculated in the range of 0.004-0.311. The experimental results showed that between the slopes of 3% to 5%, the bed friction coefficient and the roughness Reynolds number of the erodible bed increased significantly, while in the slope range of 2% to 3%, no significant increase was observed. Analyzing experimental results showed that by increasing the bed transport rate, the frictional resistance of flow (fc) decreased and subsequently, the bed loading movement resistance (fm) increased. Applying dimensional analysis, the effective parameters on fm were determined and an empirical equation to determine fm was designed and results were validated by laboratory outputs obtained by former researchers. Validation results have been proved acceptable.
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