مطالعه اثر شكل ذرات رسوب بستر آبراهه هاي باز بر ضريب اصطكاك

Effect of Shape of Sedient Particles at the Bed of Open Channel on Friction Coefficient

Hydraulic calculations of the flow in channel and over bank areas of flood plains require an evaluation of roughness characteristics. The Manning roughness coefficient (w), Chesy coefficient (C) and Darsy-Weis^ach coefficient ( /) are used to describe the flow resistance or relative roughness of a channel or over bank areas. Over the past decades many studies have been conducted to estimate the friction coefficient to the particle size but the effects of particle shapes are not clear so far. In this experimental research for determination of friction coefficient eleven types of particles; four angle rounded particles, four crushed particles and three spherical artificial particles have been tested under different hydraulic conditions in a flume of 10 meter long, 25 cm wide, 50 cm height and constant bed slope of 0.0005. The results show that in 11 mm sediment particles, the friction coefficient (/) for crushed particles are larger than angle rounded particles. In 27 mm sediment particles, the friction coefficient (/) in rounded and spherical artificial particles are equal nearly and values of friction coefficient (/) for crushed particles shows little difference with aforesaid particles. In this study equation has been proposed for prediction of friction coefficient (/).