DRAG FORCES ACTING ON EMERGENT RESISTANCE FOR NON-UNIFORM OPEN CHANNEL FLOWS

Abstract

 It is important for the calculation of river flows to evaluate the drag force acting on river structures and vegetation. But, the evaluation method of drag coefficient has not been revealed enough to be applied to non-uniform flows. In this work, laboratory experiments were conducted by using difference resistant elements in uniform, acceleration and deceleration flows.The drag coefficient was obtained as a function of Froude number from the experiments for uniform flows. In deceleration flows, the calculation results provided good agreements with the experimental results.However, the drag forces in acceleration flows were underestimated. This result is caused by the pressure reduction in separation area due to the existence of longitudinal pressure gradient. For the acceleration flows So, we proposed an evaluation method of drag coefficient for non-uniform flow. The method was validated through the comparisons with experimental water drpth plofiles.