تاثير جريان كندشونده بر توزيع تنش برشي و ضريب زبري در يك كانال آزمايشگاهي با پوشش گياهي روي ديواره ها و شن در كف

چكيده انگليسي :

Influence of Decelerating Flow on Shear Stress Distribution and Roughness Coefficient in a Channel with Vegetation on Sides and Gravel over Bed Maryam Moradian Moradian65@yahoo com Date of submission February 21 2012 Department of Water Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiH Afzalimehr Assoc Prof Supervisor Hafzali@cc iut ac irM Heidarpour Professor Supervisor Heidar@cc iut ac irAbstractRiver optimization requires a profound understanding of flow pattern from morphodynamic point of view Vegetation on banks of natural channels exercises a significant influence on the flow structure In open channelhydraulics vegetation often causes changes in the flow resistance usually resulting in the increase of flood stage The interaction between vegetation and the flow structure impacts sediment and contaminant transport resistance toflow fluvial geomorphology and riparian life Understanding the impact of vegetation on flow is thereforeimportant in river restoration and determining the retardation in channels is important in design of restorationworks There exists no information for decelerating flow with small aspect ratio in open channels and vegetation onbanks even though flow in many sections of rivers including in pools in coarse bed rivers is decelerating Therefore the objectives of this study are 1 to experimentally study the effect of vegetation on banks on flow ingravel bed channels 2 to assess the validity of the log law and the Coles law for decelerating flow when vegetationis present on banks 3 to observe the Reynolds stress distribution under decelerating flow when vegetation ispresent on banks and 4 to compare the results with the case of flow in gravel bed channels without vegetation onbanks Experiments were carried out in an 7 m long 32 cm wide and 35 cm high recirculating flume at theHydraulics Laboratory of Isfahan University of Technology The flume had glass banks and glass bottom on whichgravel particles were deposited The gravel particles used had a median diameter d50 of 33 7 mm the bottom slopewas obtained by varying the thickness of the gravel layer along the flume to obtain the slope of 2 An AcousticDoppler Velocimetry was used to measure parameters of turbulent flow Experiments carried out in five series 1 Gravel bottom bare bank and uniform flow 2 Gravel bottom bare bank and decelerating flow 3 Gravel bottom rice stems on banks and decelerating flow 4 Gravel bottom straw stems on banks and decelerating flow 5 Gravelbottom typha stems on banks and decelerating flow The whole stems situated inside the water were fixed on thebanks The measurement reach was situated between 5 5 x m 6 5 where x was measured from the flumeentrance Within this measurement reach the flow was considered to be fully developed To investigate theinfluence of bank vegetation cover on velocity and the Reynolds stress at each section flow velocities weremeasured at different distances from the bank D 0 03 0 05 n showing no and 0 15 m The results showed that inthe presence of vegetation in the velocity distribution took on a convaxe shape and velocity distribution is differentfrom bare bank channels Validation of log law makes possible to estimate shear velocity and obtain a betterestimation from resistance to flow in gravel bed channels with the vegetated banks and maximum velocity occursunder the water surface Vegetated banks alters the velocity Rynolds Sress and RMS distributions showing non linear shap with maximom value under the water surfer Keywords Decelerating flow Vegetated banks Gravel beds Aspect ratio Rynolds Stress

مراديان، مريم

تاثير جريان كندشونده بر توزيع تنش برشي و ضريب زبري در يك كانال آزمايشگاهي با پوشش گياهي روي ديواره ها و شن در كف