جستجوی مقالات مرتبط با کلیدواژه « افت انرژی » در نشریات گروه « عمران »

One of the most famous hydraulic phenomena to reduce flow energy is hydraulic jump, which is used downstream of dam overflows in river sections and structures established in irrigation and drainage canals. It is very important to control and reduce the kinetic energy resulting from this phenomenon at smaller distances from the place of formation. Among the examples of depreciation structures, we can mention the roughness of the bed and the construction of stilling basin and making expansion, but it must be said that it causes pressure fluctuations and damage to the bed of the canals and river. The existence of the submerged jet can reduce this pressure fluctuation and change the flow downstream to subcritical. The purpose of this research was to investigate the presence of a submerged jet system on the characteristic of asymmetric hydraulic jump in corrugated beds so that this phenomenon can be controlled and ensure the safety of structures and beds downstream. For this reason, the experiments were carried out in a flume with a fixed peak overflow with a central flow rate range of 26 to 67 liters per second and 3 mutual submerged jet flow rates. This investigation showed that the corrugated bed in the region of gradual expansion has reduced the length of the jump compared to its absence and the changes in the flow depth have also decreased. Also, the impact of the opposite jet in the submerged shape improved this process; So that energy consumption was reduced by 25-30% and jump length by 50%. Therefore, the effective role of this combination of jet system and continuous corrugated bed was shown.

In this research, a rotary gate has been used along with a rectangular-semi circular transition in order to measure and control the flow. The hydraulic efficiency of this type of transition and gate has been investigated using factors such as the level of the water level of the approaching flow and the opening angle of the gate, which is effective on the geometric location of the transition wall. The depth measurement of the flow from the upstream of the gate to its downstream was done by a depth gauge with an accuracy of 0.1 mm. The flow rate passing through the rotary gate is also estimated based on the stage-discharge curve and basic hydraulic equations, as well as three angle separation methods, data aggregation method and break point method. to check and calculate the error values in each discharge estimation method, indexes such as: average relative error index (Error), root mean square error (RMSE), standard error (SE) and normal root mean square error (NRMSE) were used. The analysis of the results obtained using the statistical indicators of the three methods mentioned above shows that all three methods have high and acceptable accuracy. In the method of using all the data and the breaking point method, the discharge is calculated by having the depth of flow at upstream, the radius and opening of the gate. Since relatively short calculations are performed in these two methods, it is sufficient for initial estimates. The results showed that the method of using each angle seems more accurate because the number of calculations in it is more. The error percentage index for the separation method is 1.30%, in the aggregated data method it is 3.29% and the breaking point method is 3.98%.Therefore, according to the results of this research, it can be seen that by using this gate and the design and construction of transition in rectangular channels, it is possible to measure the flow in irrigation and drainage networks with very good accuracy. Investigating the amount of energy loss due to the hydraulic jump of the flow after the gate shows that the amount of energy loss decreases with the increase of the opening angle.

Hydraulic jump is a fast and irreversible variable flow that occurs downstream of hydraulic structures and the result of which is the rapid transformation of supercritical flow into subcritical flow, which increases the depth of the flow and causes a significant loss of energy. By examining the previous studies, it is clear that the roughness bed or the divergence plays an important role in hydraulic jump characteristics.  FLOW-3D is one of the suitable software in hydraulic Phenomenon modeling. In order to ensure the appropriate capability of FLOW-3D software in simulating hydraulic jump, first, a research related to this issue which has been investigated in the past in a laboratory, is simulated in the software. Then, by comparing the results of the numerical simulations with the laboratory data and ensuring the proper functioning of the software, new simulations are made. The experiments related to the physical model used were carried out in a laboratory flume with walls and floors made of transparent plexiglass, 5 meters long, 0.3 meters wide, 0.45 meters high, and zero longitudinal slope. To create a supercritical flow, a steel valve with a height of 0.65 meters and a thickness of 3 mm and an opening height of 1.7 cm was used for a non-prismatic channel with a divergence ratio of 0.33. In order to create symmetrical opening ratios of 0.33, glass boxes with a length of 0.5, a height of 0.2 and a width of 0.1 meters were placed on both sides of the flume. After the simulation and by checking the R2, MAE and RMSE parameters, the k-ɛ model and the mesh with the number of 687600 cells were selected as the optimal mesh. In this research, according to the selection of four types of bed (smooth bed, rough bed with hemispherical roughness and diameter of 3, 4 and 5 cm) and three divergence angles (7, 14 and 90 degrees) and five Froude numbers (Froude number: 4.34, 5.71, 6.95, 8.17, and 9.37) in total, Simulated for 60 different experiments.  The results showed that for the maximum discharge for the sudden divergent channel, the roughness of the bed with a diameter of 5 cm causes the amount of the flow depth to decrease by 19.77% compared to the smooth bed. Also, the sudden divergence of the bed reduces the flow level by 23.75%. In all cases, the value of y2/y1 increases with increasing Froude number. With the increase of the Froude number from 4.34 to 9.37, the value of y2/y1 on the flat bed increases by 15.54%. With the increase of the Froude number from 4.34 to 9.37, the value of y2/y1 on the rough bed with a diameter of 3 cm decreases by 5.67% on average compared to the smooth bed. As the roughness diameter increases from 3 to 5 cm, the value of (Lj/y1) decreases by 15.58% on average. The results show that the (EL/E1) ratio increases with the application of bed roughness. So that by applying a roughness with a diameter of 5 cm, the value of (EL/E1) compared to a smooth bed increases by about 5% on average, and by applying a sudden divergence, the value of (EL/E1) compared to a bed diverging under an angle of 7 degrees The average increases by 4.58%. FLOW-3D is a good software to prediction of hydraulic jump characteristics in divergent channel with smooth bed and rough bed and The k-ɛ turbulence model was selected as the optimal turbulence model. Increasing the bed roughness size decreases the secondary depth for all values ​​of 𝐹𝑟1. The sudden expanding of the rough bed with a roughness of 4 cm reduces the y2/y1 by 12.98% compared to the bed with a divergence under 7 degrees. Increasing the size of the roughness decreases the length of the hydraulic jump. According to the results, the length of the hydraulic jump in the rough bed with a diameter of 5 cm compared to the smooth bed decreased by 26.12%. Also, by increasing the roughness diameter from 3 to 5 cm, the value of (Lj/y1) decreases by 15.58% on average. By applying roughness with a diameter of 5 cm, the value of (EL/E1) increases by about 5% on average compared to the smooth bed. Results show that the divergence angle of the bed is effective on streamlines. But, increasing the roughness of the bed, there is no noticeable change in the streamlines. However, increasing the bed roughness size, increases the amount of disturbance energy in the section.

In order to calculate and predict the discharge flow through and over the gabion weir, 33 experimental broad-crested gabion models were carried out through the sand bed condition. The flow conditions through and over the gabion were presented as three classifications which involved partial flow conditions through a gabion, fully gabion flow through a gabion weir, and overflow on a gabion weir. These classifications were considered due to the free flow conditions. Based on the partial and fully gabion flows, an equation was proposed to calculate the gabion flow. Moreover, the flow discharge over the gabion was considered based on the broad-crested weir formula and then, the coefficient discharge of broad-crested gabion weir was proposed based on experimental measurements. Comparison between the proposed values and experimental measurements illustrates that good agreement is between the proposed and experimental flow discharges. Also, the investigation of flow variations through the gabion showed that the error of gabion equation increased significantly due to overflowing on gabion weir. In order to raise the accuracy of the calculation process of flow discharge through the gabion an equation was proposed based on the geometry and Darcy Wisbech’s parameters. The porosity, length, and particle size were defined based on Darcy Wisbech equations. Some math indexes were considered for this equation and by employing the Mathematical software, these parameters were presented based on the non-liner technique. The error was measured based on the experimental and proposed values and the result of the comparison pointed to the suitable agreement between the two groups of values. Finally, the maximum scour hole was measured by point-gauge along the longitudinal section. Based on threshold velocity and geometrical and hydraulic parameters, an equation was proposed to predict the maximum scour hole depth at the downstream of the broad-crested gabion weir.

In this study, different components that affect energy dissipation on flow over gabion-stepped spillways were investigated using physical models, and comparisons were made with the other studies. Flow over gabion spillway was conducted in both through flow and overflow simultaneously. The discharge is in the range of 5 to 65 liters per second.  Uniform particles with three medium diameters of 10, 25, and 40 mm were used. The height and width of the physical models were 60 and 40 cm, respectively, with 3 steps and the downstream slope of weirs was 1:1, 1:2, and 1:3 (V: H). Tow end sills including rectangular and inclined shapes were used. The results showed that the effect of end sills in gabion-stepped weirs with lower slope is more than that of weirs comprising higher slope. The effect of the end sills on the energy dissipation in the weir for d50=40 mm and S=1:2 is about 10% more than the weir with d50=10 mm and S=1:1. In weir including d50=10 mm and S=1:2 is about 30 to 35 percent more than the weir with d50=10 mm and S=1:1. Therefore, the existence of end sills in the weirs with the body of materials of d50=10 and 40 mm have the highest and the least effects on the energy dissipation. On the other hand, the effect of the rectangular end sill on the energy loss is about 3-4% more than that the effect of the triangular end sill.

Hydraulic jump is a phenomenon in which the flow regime changes from supercritical to subcritical. The characteristics of hydraulic jump are rapid expansion of the flow with turbulence, high local energy loss and increase in the height of the free surface of the water. Due to the nature of the flow, the specific force remains constant before and after the hydraulic jump.In this phenomenon, the water depth increases in a short distance and consequently the flow velocity decreases. This increase in depth and decrease in velocity, together with a noticeable decrease in energy, causes turbulence in the flow and converts the kinetic energy of water into heat energy. The turbulence created in the stream decreases as it approaches the end of the jump. Installing obstacles with different geometries on the path of flow have an important effect on controlling the jump location, reducing the length of the hydraulic jump and increasing the energy dissipation of flow during the hydraulic jump.The research flume is 6 meters in length and 60 centimeters in height.The flume is trapezoidal with a floor width of 16 cm and the side of the trapezoid has a slope of 75 degrees and in the length has a slope of zero degrees. Water is pumped from a storage tank to the reservoir at the beginning of the flume (Figure 1). To provide the water load required to achieve higher froude numbers, a sediment tank at the beginning of the flume, which is cylindrical in shape, has been used. This tank is measured by a gauge with an accuracy of 1 mm to read the height of the water inside the tank. In order for the flow to be developed at the beginning of the channel, a part called the jet box is used. By controlling the opening of this part and the pump flow, the desired head in the tank can be reached as well as certain froude numbers (Figure 2). A total of 60 experiments were performed. The blocks have three heights and the distance between the rows of blocks in three modes, so the arrangement of the blocks is divided into nine types. The height of the stream is considered in six different cases. To draw the jump curve, water depth was measured at three points including the end of the blocks, the point equal to the middle of the jump length, and the water depth at the end of the jump.The ratio of the secondary depth of the hydraulic jump to the primary depth is one of the most important parameters used in the design of relaxation ponds. According to Figure 9, the ratio of hydraulic jump conjugate numbers related to the experiments of this research can be defined by the mean curve of the relation 5. Comparing this formula with the experiences of previous researchers shows a good agreement. The results of previous studies by other researchers also show a decrease in the ratio of conjugate depths to smooth surface if obstacles in the waterway are used. with the diagram of figure 10, it can be said that the secondary depth of hydraulic jump is reduced if rectangular blocks are used. Also, to reduce this depth, increasing the height of the block has a greater effect than increasing the distance between the blocks. Also by shortening the length of the hydraulic jump, the length of the required pond will be shortened and it will be more economical. According to Figure 12 and 13 the length of the hydraulic jump compared to the flat bed decreased by an average of 49.5%. In a hydraulic jump, when the flow lines collide with each other, the perturbation created in the flow path, the kinetic energy related to velocity, is converted into heat energy and causes the kinetic energy of the flow to be depleted and its regime to change from supercritical to subcritical. Therefore, calculating the amount of kinetic energy consumption and jump assessment is one of the important topics in this discussion. Figure 14 shows the ratio of energy drop to initial flow energy versus initial froude number in all experiments. According to the graph, with increasing the froude number, the value of this ratio also increases, which in the maximum value is approximately equal to 85.5% energy loss. To determine the effect of rectangular blocks on changes in this energy loss ratio, parameter G is defined as Equation 19. According to Figure 15, the maximum value of this parameter is 84.8% and the minimum value is 0.8%.A diagram related to the dimensionless profile of the water surface shows that the profiles related to all experiments can be defined by a regression curve with a good approximation. The ratio of sequent depths of hydraulic jump with rectangular blocks to smooth bed decreases. This decrease is more noticeable within higher froude numbers. The maximum value of parameter D of the hydraulic jump in this study is equal to 9.4%, which indicates the effect of increasing the height and the distance between the blocks on the secondary depth of the jump. The maximum drop of flow energy on rectangular blocks is equal to 85.5%. Increasing the height of the blocks has a more effective role in reducing the flow energy than increasing the distance between the blocks.

Gabion stepped weir is a simple hydraulic and environment friendly structure that can be used to dissipate flow energy in different dams or to control downstream erosion of various structures. Most researches have been related to concrete and rigid stepped spillways, so studies on gabion stepped weirs are very small. In this research using the experimental method and physical model various components that affect the energy loss in gabion stepped weirs have been studied and comparisons with other studies by researchers have also been made. The flow passes in gabion stepped weir was carried out both in overflow and inflow (both simultaneously) and the amount of energy dissipation along the structure was calculated based on the energy relation. In this study, completely uniform particles with three diameters ( ) of 10, 25 and 40 mm were used. The height and width of physical models made of gabion stepped weirs were 60 cm and 40 cm respectively, with stairs of 3, 6 and 12 and height of stairs 5, 10 and 20 cm and the slope of the weirs are 1:1, 1:2 and 1:3 (2 and 3 horizontals, 1 vertical). In the gabion stepped weirs, the downward slope of the weir has a negligible impact on the energy dissipation. As the number of steps increases (for constant ), the energy loss decreases. The average diameter of the particles of 10 mm for and the average diameter of the particles of 40 mm for has the highest of relative energy loss.

Energy conversion efficiency of water to the water flow depends on the blade of the turbine wheel depends on the blade surface. Heat water in a collision with turbine blades, friction on the surface of the water during passage through the turbine blades, nozzle head loss and air friction resistance pelton turbine energy resources are wasted. When the water jet passes around the turbine blades, ideal against the current because of non-slip surface and thus the boundary layer is created. The formation of the boundary layer and its thickness depends on the blade surface roughness. In this research the mathematical relationships to help the border layer, a model for the calculation of the flow passing through the wasted power of pelton turbine blade is presented in which the effect of the friction and pressure changes on the flow along the path of the blade come into account.

The use of the cylindrical structures has some advantages such as low cost, simple design, easy construction and the higher discharge coefficient. Masoudian and Gharahgezlou [1] performed several experiments on free over flow on a cylindrical weir to determine the discharge coefficient (Cd) and found that the Cd raises with increasing the nondimensional ratios of [Hw/R], in which R: cylinder radius, [Hw/yup] and non-dimensional numbers of Re and We. Masoudian et al. [2] performed a laboratory study on geometric and hydraulic parameters effect on the flow through the cylindrical weir that demonstrates with increasing the dimensionless ratio of [yup/D] and [yup/a], Cd goes up. They indicate that for a constant value of [yup/D] ratio, the Cd decreases with the increasing gate opening height as well as, cylindrical gate discharge coefficient is more than a sliding gate discharge coefficient [2]. Along with the vertical movement of cylindrical weir-gate, three different flows of over flow on weir, combined flow thought the weir-gate and under flow the gate can be observed. As a result, discharge coefficient of combined flow and the energy loss will also change. This structure can be used for precise control and measurement of passing flow in the low and high water levels for instant during the drought or flood conditions, therefore, in present research, an experimental study on the effect of vertical movement of cylindrical weir gate on flow hydraulics was performed.