مجله هیدرولیک
سال سیزدهم شماره 3 (پاییز 1397)

Friction factor plays a substantial role in hydraulic computations. In coarse-bed rivers, friction ‎factor depends on grain size and bed forms. A wide range of particle sizes and developing ‎armor layer have great effects on friction factor. Therefore, determination of form friction ‎factor of armored river beds has been investigated in this study and, a friction equation was ‎developed based on computing grain friction factor of the total friction factor. Analysis of ‎obtained equation showed that the friction factor is rather independent of grain-size ‎distribution of the material forming the bed and the maximum grain size of this material. The ‎major controlling parameter is the slope of the energy grade line. These results are explained by ‎the coupling of the friction factor with the incipient motion problem and the rearrangement of ‎the grains of the coarsest fraction in the armor coat. To verify the equation, Keulegan method ‎was used which results 80% agreement between two methods‏.‏‎ Also, including the major part of ‎total friction factor to form friction factor (40%) shows the great effects of bed form on flow ‎resistance. The results of the current study showed that making and development of armor ‎layer increase bed roughness and friction factor and decrease average flow velocity causing a ‎reduction in threshold Shields parameter and augmentation in bed stability. Field observations ‎are employed to test the methods.‎

Spur dikes are known as the most popular hydraulic structures which are utilized to reduce shores and river banks erosion. These structures change the flow and sediment transport pattern and so they can control hydraulic conditions and prevent shores erosion and cause sediment trapping. In this paper effects of changes in angles and various arrangement of spur dikes (small to large or vice versa) for group of parallel, unequal, non-submerged and impermeable spur dikes are numerically investigated on flow pattern, bed erosion and sedimentation. Validation of results of Flow-3D numerical model with experimental data, shows the high precision of the numerical model. Also the results show that scour depth in large to small arrangement of the spur dikes and 45 degrees orientation has 55% reduction and in small to large arrangement and 135 degrees orientation has 72% reduction in comparison with group of equal length spur dikes perpendicular to the shore.

Shear stress on the floor and walls of rivers and channels is one of the most important parameters of open-air flows. The presence of barriers in the flow path causes significant changes in the shear stress distribution on the channel and river floor. In the preliminary research, the distribution of shear stresses around impervious angular barriers and permeable angular barriers of Gabion and double rod with two cases along with zigzag have been presented. The results are presented using extracted laboratory data. The experiments were carried out in a rectangular channel with a Froud number of 0.26 under clear water conditions and the threshold of motion of the particles of the floor. The experiments were carried out by placing obstacles at angles of 135 and 45 degrees relative to the flow path. In this study, depth-Average velocity method was used to calculate shear stress. Also, the kinetic energy of the total flow through each section in the sections before and after each obstacle was calculated and the kinetic energy depreciation was calculated due to the presence of various obstacles. The results show that the shear stress distribution of the substrate in the impervious barrier of shear stress is higher in permeable barrier permeability with 30% porosity. Also, in permeable barriers, the two-row rod along the zigzag and the shear stress distribution are approximately similar, so that the effect of the geometric arrangement of the bars on the shear stress distribution on the floor is not high and the performance of the barrier barriers is two The row is close to each other. In comparison with energy depreciation, the results also show that energy depreciation in Impervious barriers is more than permeable barriers, and in the case of permeable barriers with the same opening percentages, energy depreciation in lattice barriers is more than barrier barriers Regardless of their geometric arrangement, they relate to barrier angles of energy deformation to the geometric arrangement of bars, as the zigzag bar barrier barriers along with the obstacles along the way depreciate more energy.

In recent decades, the hydrosuction technique is known as one of the efficient methods that has been used for dredging sediments deposited in dams’ reservoirs. This technique has obvious advantages compared to other sediment removal techniques such as no need for extra energy (due to the use of the difference between water surface energy at the upstream and downstream of the dam) and the possibility of transporting dredged sediments to a specific area. This technique is influenced by several geometric and hydraulic factors such as the suction tube diameter (Dp), the water head or the difference between the water height at the upstream and downstream of the dam (H), and the distance of the suction mouth from the surface of the sediment (hp). In the current research, the effects of suction opening intervals on sediment (SP class) surface was studied using a physical model. The results of the experiments showed that by increasing the hp factor, the discharge rate of the sediment and also the sediment concentration of the outlet flow would be increased. The results also indicated that the sediment evacuation process continued with the minimum value for hp/Dp=-1.33; for values less than -1.33, the tube obstructed due to accumulation of sediments in the inlet opening.

Scouring damage around bridge piers is consider as foremost detriment and researchers proposed hydraulic or non-hydraulic treatment to solve scouring problems. In this research, a new eco-friendly method has been proposed to reduce not only length and depth of scouring circular bridges but also volume of pits created by removal of river bed materials. Since clay and cationic poly acryl amid (PAM) have good compatibility with the river system and its ecology, the mobile bed sediment was combined with two different grains included %10 clay and %5, %10 PAM injected into clay. Their effects on scouring reduction in four different discharge and three different pit depths were investigated. The results indicate the enhancing effects of adding clay and PAM in reducing the length and depth of scouring. The best performance in the present research is related to the mixture of clay and PAM %10 with scouring depth was %27.24 and %46.78 for grain size 0.6mm and to %26.9 and %45.18 for grain size 0.15mm. The scouring length for both grains decreased by %17.73 and %31.22, respectively. This investigation shows that the utilization of clay and PAM has a positive effect on reducing scouring and its treatment in rivers while being compatible with the ecology of the system, will have an acceptable performance in reducing the depth and scour length.

Circular vertical Spillway with various inlet forms is very effective, when there is not enough space for the other spillway. Hydraulic flow in vertical circular spillway is divided into three groups: free, orifice and under pressure (submerged). In this research, hydraulic characteristics are investigated in vertical circular spillway by using numerical model. Hydraulic characteristics are investigated such as upper and lower nappe profiles, relation between discharge and upstream water levels, and discharge coefficient in numerical modeling and experimental conditions. The mesh with 10602 nodes, turbulent model k- standard and the standard wall function, provide the best results for modeling the flow in a vertical circular Spillway. There was a good agreement between numerical and experimental results in the upper and lower nappe profiles. In study of water level over crest and discharge, in low water levels, the results of numerical modeling are good agreement with experimental, but with increasing water level, the difference between the numerical and experimental discharge to be more. In the study of the flow coefficient, by decreasing in P/R ratio the difference between the numerical and experimental result increases.

Bed material is one of the factors affecting the deposition and entrapping of cohesive sediments. In this work, entrapment of cohesive sediment in gravel bed (D50= 2.4 and 9.4 mm) and smooth bed was investigated using circular flume. For this purpose, the effect of gravel bed sediments on the entrapping and deposition of suspended sediments in different concentrations and different flow turbulence has been tested. The experiments were carried out in two modes of smooth and rough beds for initial concentrations of 5, 10 and 20 g/l and flow velocity 0.14, 0.24 and 0.34 m/s. The results showed that, in two modes of bed, the concentration of suspended sediments decreases with time, but the bed contains coarse sediment increases the amount of deposition rate and the time of reaching to an equilibrium concentration. The results also showed that the entrapping coefficient in bed containing sand and gravel beds was about 5.7 and 3.5 times more than that of smooth bed, respectively. Increasing the entrapping coefficient in larger shear stresses can be explained by the effect of coarse-grained bed sediments on reducing the flow velocity and generating bursting - sweep phenomena due to flow turbulence.

In this study first the meshless local Petrov-Galerkin (MLPG) method by Radial Basis Function (RBF) has been explained entirely. In this way the governing channel flow expression that is expanded. The Results show that MLPG method presented high accuracy and capability for solving the governing equation of the problem. Also, The seepage problem in steady state form is analyzed by the written code in MatLab . On the other hand the velocity field is approximated in middle of nodes by RBF (MatLab code was adopted) in the uniform flow in a sloped channel problem. Finally in the fluid flow in dam breaking problem, the Mass and momentum conservation laws are governing equations of flow which are solved by pressure correction in Lagrangian approach and compared with another methods results. The obtain results explain that Application of meshless method in Fluid flow modeling in hydraulic Problem the applicability and efficiency of the meshless local Petrov-Galerkin method by Radial Basis Function method.

Understanding the transfer of cohesive sediment is very important for the development and maintenance of dam reservoir and transfer channels in estuaries. Obviously, more data is needed in area for better understanding of the behavior especially rate of erosion of the fine sediment. Thus in this research the sediments of Karkheh dam reservoir have been investigated. For this propose with use circular flume located in Shahrekord university water and soil science laboratory of Water Resources Research Center, trend of concentration of eroded sediments, threshold erosion shear stress and erosion rate for different periods of consolidation (3, 14 and 30 day) have been investigated. The result showed The concentration of eroded sediment varied as a function of consolidation age and shear bed stress. It was also period of consolidation influenced the threshold shear stress of the Karkhe reservoir sediment, which obtained values were 0.16, 0.22, and 0.31 N/m2 for the 3, 14, and 30 day consolidation, respectively. The result showed that the erosion rate is inverse relation with the period of consolidation, so that in the same stresses, the increase of the consolidation period will reduce the erosion rate.

Canal structures with lateral contraction are commonly used to measure discharge in open channel. According to three dimensional flow, extracting rating curve for these structures is done by using a physical or three dimensional mathematical flow models. A considerable amount of time and money iare required when utilizing these models. Boussinesq equations, which is extracted by considering streamline curvature and slope, exhibit high accuracy in predicting hydraulic properties in structures with varying bed. In this paper, the equations are developed for contraction. The extracted equations are used for obtaining the rating curve of Parshall flume and predicting water surface profile of Khafagi flume and rating curve s of Parshall flume. Comparing experimental data with equations shows the high accuracy of Boussinesq equation to predicting water surface profile and the rating curve of structures with contraction and varying bed. The time for solving the one dimensional equations is much less than the three dimensional model FLOW3D.