چكيده به لاتين
Local scouring occurs by placing obstacles such as abutments in flow direction. Increasing the resistance of bed materials and decreasing the power of erosion factors are the ways to stand against local scouring. To decrease the power of erosion factors (horseshoe and wake vortex), equipment such as collars, submerged vanes and etc. are being used. One of the ways of controlling and reducing local scouring, is to create roughness on abutments.
In this study, by creating roughness on semi-elliptical abutment, their effects on reducing scour depth are investigated and also is being compared whit simple abutment. The length of the semi-elliptical abutment is 6 cm and the rough dimensions are with characteristics (p=0.17L ,p=0.117L,p=0.083L),(d=0.17L, d=0.47L,d=0.283L).Where p is the protrusion, d is the distance between the roughnesses and t = 0.05L, t is the roughness thickness which was considered constant in all roughness cases and L is the length of the abutment.The experiments were conducted for three depths of flow with values (9 cm, 12 cm and 15 cm).Experiments were conducted in a rectangular flume with length of 13 m, width of 0.46 m, in clear water scouring conditions with uniform sediment.
In this study, the results show that in the case of roughness, by increasing the flow depth from 9 to 15 cm, the scouring depth increases and by applying the roughness, the scouring depth decreases for all roughness cases, so that for roughness with dimensions (p 0.17L , d 0.17L) Less scouring depth has occurred. In other words, in this study, roughness with shorter distance and more protrusion has created less scour depth.A significant relationship was found to reduce the flow depth in the rough state for three depths in the form of d⁄p ratio so that for the ratio d⁄p = 1 for three flow depths there is less scouring depth which shows that with increasing d⁄p the amount of scour depth increases .
As the flow depth increases, the slope of the scour hole increases in the no-roughness state, and in the roughness state, the slope decreases for all three flow depths.
For abutments without roughness, the slope increases from 0 to more than 90 degrees, while in roughness, the slope increases from 0 to 90 degrees and decreases from 90 degrees onwards.And has the highest value between angles of 50 to 70 degrees, and in the roughness state with dimensions (p 0.17L , d 0.17L) in this study, a lower slope than other roughness states for three depths occurred.
