عنوان مقاله [English]
نویسندگان [English]چکیده [English]
The bed and sidewall average shear stresses in smooth trapezoidal open-channels are determined by solving the continuity and momentum equations. The isovels and orthogonals for a trapezoidal channel section with 1:1 sidewall aspect ratio were obtained by using conformal mapping technique. New equations were drived by determining a portion of bed shear stress from total shear stress. As a first approximation, the boundary shear stress equations were obtained after neglecting the secondary currents and assuming a constant eddy viscosity. In comparison with laboratory measurements, the first assumption overestimated the average bed stress by 20% but it underestimated the average sidewall shear stress by -24%. The second approximation was then presented by introducing two lumped empirical correction factors for the effects of secondary currents, variable eddy viscosity and other unexpected effects. Comparison between laboratory measurements and those from the second approximation, showed an excellent agreement (R2>0.993 and average relative error less than 1.2%) between them with experimental measurements over a wide range of width-depth ratios.