فهرست مطالب محمدرضا پیرستانی

Flip bucket is one part of dam spillways for energy dissipation. Flip bucket are a standard element of dam spillways for an efficient energy dissipation if takeoff velocities are large, and stilling basins cannot be applied.
This study investigates the hydraulic performance of a triangular-shaped, rather than the conventional circular-shaped, bucket placed at the takeoff of flip bucket. In this research we survey and compare some hydraulic parameters like depth, velocity, frude number and cavitation number on triangular and circular flip bucket. In simulation, we used volume of fluid(VOF) method and k-ε (RNG) turbulence model.
Analyze of results of this research proposed a kind of triangular flip bucket instead of circular flip bucket and also shows that the circular flip bucket has a middle behavior in compare with two kinds of triangular flip buckets in investigation in depth, frude number and cavitation number.
Investigation in behavior of cavitation number of these three flip buckets shows that flip bucket A is a good and proper substitution in contrast with triangular flip bucket B. Also surveying of connection between frude number and cavitation number in end of chute and flip bucket which has critical point that maximum potential of cavitation and this point is not necessary in maximum discharge.

If there is a high speed flow on a spillway and it is impossible to use a stilling basin because of its high cost or installation condition, the flip bucket may be used for energy dissipation. Flow-3D software was used in this research to simulate the flow on the chute spillway with ogee crest and flip bucket by volume of fluid (VOF) procedure and k-ε (RNG) turbulence model. At first, the numerical simulated trajectory of the jet flow was compared with the trajectory of the flow in the physical model, and also with the results of USBR, US Army and Kavakami equations. Then the effect of gate opening on the range length and the maximum height of the jet flow trajectory was studied. At last, the effect of the circular flip bucket shape and the two kind of triangular flip bucket named A and B on jet trajectory were studied. Results showed that USBR equation was more accurate than the numerical model and other empirical relationships in determination of the jet range length. Based on the results, two relationships were presented between gate opening VS reduction percentage of the range length and the maximum height of the jet. Comparison of the hydraulic characteristics of the circular and triangular flip buckets showed that the characters of the triangular flip bucket type A was more similar to that of the circular flip buckets in comparison to the type B and due to its easier implementation could be used instead of the circular flip bucket. In addition, results of the numerical model showed error ranges length of 12 and 8 percent for the maximum jet range length and maximum height, respectively. Therefore, applying numerical model of Flow-3D in estimating effects of bucket shape is recommended.

Nowadays the importance of reservoirs management makes the use of gates on the spillways crucial .This causes the change in hydraulic flow over the spillway and the aim of this study is to explore some of these hydraulic changes. In this research by using Flow-3D and volume of fluid (VOF method) and k-ε (RNG) turbulence model , chute spillway with ogee crest and flip bucket has been simulated. Additionally investigation on the effects of 4 openings 15%, 30%, 45% and 100% which is done by radial gates. has shown that the increscent of openings causes increscent velocity, depth and cavitation potential on spillways. Also in some openings with low discharge, due to the formation of low discharge which is lower than sweep discharge, formation of flow aggregated on the spillway is possible and the hydraulic effects of this phenomena should be should be taking into consideration. Also by simulation of jet trajectory from the flip bucket, Results showed low error in length and maximum height of the trajectory. In conclusion, using Flow-3D for prediction of tail water preservation is highly recommended. Eventually, two correlation for the dependency of length of the trajectory, maximum height, flow discharge and opening gate ratio were presented.

One of the common methods to dissipate energy of the flow passing over a dam is using flip bucket spillways to create free falling jet to the downstream. However, the collision of the falling jet to the downstream bed will cause topography changes due to scour threatening the stability and safety of the hydraulic structures. In case of precise analysis of the downstream topographic conditions due to the falling jet, such structures perform better than other dissipaters. Experimental results show that the dimensions of scour hole are dependent upon upstream water depth, discharge and tail water depth. Due to water and sediment flow complexities and the effect of different geometric-hydraulic parameters on bed profile variations, more studies are needed.In the present study, the effect of flip bucket tooth and upstream gate opening on downstream bed topographic changes due to falling jet was investigated using a flat flume having dimensions of 2m*0.5m*0.5m. The free falling jet was controlled using a sluice gate located upstream of the flume. Falling jet hit a downstream sedimentation basin having dimensions of 2 m long, 1.5 m wide and 0.7 m deep. Tail water depth was controlled using a gate located at the end of the sedimentation basin. Spillway and flip bucket of the Karoon III dam were modeled considering a 1.165 scale. Experiments were carried out on a normal (simple) and slotted flip buckets. Slot dimensions were selected as 2 cm according to USBR (1987) recommendations. To control the water surface level at upstream of the spillway for different discharges, a sluice gate was used at the spillway inlet. To investigate bed topographic changes, sedimentation basin was filled with non-uniform silica sediments with a mean particle diameter of d50=2.76 mm, the geometric standard deviation of σ=2.11 mm, uniformity coefficient of Cu=4.07 and a specific gravity of γs=1.52 gr/cm3 according to grading curve up to a depth of 40 centimeters. Researches show that several geometric-hydraulic parameters influence bed topography changes at downstream of the flip buckets. Most important parameters include input flow velocity to the flume (V), tail water depth (Yt), flow density (ρ_w), kinematic viscosity (μ), acceleration of gravity (g), specific or mean diameter of bed particles (d50), bed particles density (ρ_s), falling jet height from the bucket edge to sediment level (Hw), gate opening height (L), bucket tooth height (h), Manning coefficient of shoot surface (n), flip bucket radius (R), time (t), sedimentation basin width (B) and geometric standard deviation of non-uniform materials (σ). Using dimensional analysis and combining dimensionless parameters, the dimensionless densimetric Froude parameter (Frd) is achieved.In this study, after depiction of the longitudinal profile changes of the hole and mound scour due to falling jet, variations of the obtained dimensionless parameters were first investigated. Then, using statistical analysis, experimental relations to estimate the scour hole depth and downstream sediment mound height were presented. For this purpose, the effect of a tooth located at the end of a flip bucket on downstream bed topography changes was experimentally investigated considering different discharges, spillway gate opening percentages and tail water depths. After leveling bed sediment surface at the beginning of each experiment, discharge was adjusted using the electromagnetic flow meter and water depth was controlled using a spillway sluice gate. Besides, tail water depth was stabilized using a gate available at the end of the sedimentation basin and the falling jet was finally released to the basin. In order to determine experiment’s equilibrium time, several primary experiments were carried out considering different discharges in different time periods. By drawing equilibrium time curves, 360 min time duration equal to formation time of 88% of the total scour hole depth was considered as experimental time duration. Therefore, a total of 54 experiments were carried out considering the studied variables in this study. Water jet was released from 57 centimeters height of the bucket end level to the non-uniform bed sediments during 360 minutes experiments. Bed topography changes were measured at the end of each experiment using a dot sounder with 0.01 mm precision and depicted using Surfer V. 9.0. By calculating the changes of bed sediment volume, the influence of the slot on reduction of the scoured sediment volume can be evaluated in comparison to the normal condition. It was found that scour hole dimensions enlarge with discharge, but increase in tail water depth shows a descending procedure. In addition, in the case of slotted flip bucket in comparison to the normal one, by increasing gate opening by 33%, the hole volume increased by 125.64 %, and increasing gate opening by 66% and 99%, the hole volume decreased by 45.92 % and 22.85 %, respectively.

Flow at a bent river is exactly three dimensional، complexes and related with ratio of curvature radius to river width. According to the researches، flow pattern in the curves have different behavior from itself. Therefore، curved channels with different development rate are simulated by numerical model of Delft 3D and results such as، flow pattern، longitudinal profile، transverse profile، secondary flow power، have obtained at a curve of river. At the same time results verified by the same laboratory model that has ran at TarbiatModares Laboratory. As a result، answers reached by numerical model had accordance with laboratory result. At the end part of simulation obtain that، whatever has decreased ratio of curvature radius to bent width، therefore، its secondary flow power will have increase. Nonetheless results showed that whatever secondary flow power in the bent have increase، longitudinal current has will strongly effect on flow pattern than secondary flow power. At the end of article has compared between graphs obtain.

Submerged vanes are plane structures placed on river bed with an angle to the approach flow which cause secondary flow. They can be used to reduce sediment entrainment to water intake structures. Studying the effect of submerged vanes on the strength of secondary flow and possible sediment diversion near the bed are the goals of this paper. The simulation includes two cases, one in which submerged vanes are placed in front of the intake and the other for no vanes. Therefore, three-dimensional Reynolds-Averaged Navier-Stokes equations for turbulent flow in front of intake in 180° bend was solved numerically. The CFD solver FLUENT was used to solve equations and the results of numerical models were compared with available experimental data. Investigations showed that the secondary flow around vanes was at the same direction of main secondary flow. Therefore by intensifying, it causes more deviation of near bed streamlines toward the inner bank and surface streamlines toward the outer bank. Furthermore, it causes more water diversion with less amount of sediment. The separation zone at main channel is widening near the surface of inner bank and the vanes prevent the formation of the saddle stagnation zone and reverse flow toward the intake in main channel, so that less sediment enter into the intake.

In the first day, the human has been struggling in order to shape the ecosystem. In fact, the most intensity was when they decided to have noting migrant and to be a resident life. The most deep-seated environmental modification against the nature that had been realized in the history of the human being has started at this time. Even the development and downfall of civilizations are correlated to this interaction between the human being and nature. It is undoubtedly true that Dams are one of the most important hydraulic structures in water resources. They were usually constructed before gaining complete information about hydrology, Hydraulic and hydromechanics parameters. However, construction of dams has any positive effects, for instance flood controlling and water supply. The most reason of the possible negative impacts in the form of increasing socioeconomic challenges, lack of water and flood, droughts, migration of people and animals, pollution, declining soil quality, infectious and other diseases, threat of earthquakes and other problems that could harm the quality of life and flora and fauna. The mentioned effects have taken into account in the environmental impact assessment concept.

The diversion flow pattern is quite 3-D and nonuniform. In general, diversion flow occurs either naturally like streams or artificially like lateral intakes. According to the performed investigations the intake location affects the rate of diversion discharge and entry of sediments to the diversion channel. Since the main purpose of lateral intakes is to facilitate water transfer without sediments, and most rivers are zigzagged through their path, therefore, more research on the location of the lateral intake and its angle in the bending channels seems necessary. For this purpose, to determine the velocity and secondary flow fluctuations caused by hydraulic parameters changes in domain of lateral intakes with no diversion dam in winding channels a U-shaped flume with rectangular cross section was built. A straight channel with rectangular cross-section was used as a diversion channel. Based on the past researches, water intake was performed from the outer bend with 60˚ diversion angle at different locations (40˚, 75˚, 115˚) and with Froude numbers 0.27, 0.41, and 0.55, respectively. The obtained results of velocity distribution, secondary flow strength and radial flow momentum in a bend channel with diversion channel showed that the maximum variation of the above hydraulic parameters occur in the intake entrance.

Diverted flow has been the subject of interest for researchers and hydraulic engineers for many years. In general, diversion flow can be categorized as natural and artificial flow. Natural flow diversion usually occurs as braiding or cutoff in meander rivers, while artificial flow is man-made to divert flow by lateral intake channels for water supply. According to the research done so far, flow patterns have been identified to be non-uniform and three dimensional in the vicinity of the lateral intake. The rate of flow diversion is influenced by the separation zone, resulted from vortices. In most of the research works, the main hydraulic and geometric parameters that have been studied are intake location, diversion angle, main channel flow and Froude number. To assess the flow diversion rate in rivers, experimental studies were made on a rectangular fixed bed U-shape channel with a rectangular fixed bed straight channel as a lateral intake. Experiments were carried out for different Froude numbers, intake locations and diversion angles to obtain a relationship between the so-called hydraulic parameters and diversion flow rate.