جستجوی مقالات مرتبط با کلیدواژه "حوضچه آرامش" 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 order to prevent damages caused by the extraordinary energy of water at supercritical speeds and to eliminate the additional kinetic energy in such water, it is generally necessary to use special structures called (Energy dissipators) that are made downstream.In addition to removing water energy, these structures are also a mean of controlling and restraining hydraulic jump and creating conditions for its occurrence in a specific location.In this research, which has been compiled by descriptive research method, after introducing and recognizing hydraulic jump and resting basin, researches on the geometric arrangement of resting ponds were investigated and finally three different expansion ratios and five different heights of overflow edges were investigated.

The purpose of controlling hydraulic jump order to prevent damages caused by energy water in supercritical speeds of the research. To control the hydraulic jump and to prevent damage caused by water energy at supercritical speeds, at the end of structures such as spillways, special structures called energy dissipation are used which are built downstream. A further part of the research carried out by various researchers is expressed. Results show that the rough bed in comparison with the smooth bed, will decrease the jump relative depth in an average of 56.7 percent and the relative energy dissipation increases 69 percent and the shear modulus increases 2.6 percent. The goal of this study is reducing the hydraulic jump ̓s length to prevent the damage caused by the energy of water and reducing the length of the stilling basin, in the supercritical flow that passing the spillways.

The experiments had performed in a flume with a width of 0.3 m, a length of 10 m, its height that was 0.75 m at first 2.5 m of the flume and 0.45 m in its remaining flume length, and zero slopes in the hydraulic laboratory of Behbahan Khatam Al-Anbia University of Technology. In all experiments, hydraulic characteristics including jump length, rolling length, crossing discharge from the spillway, crossing discharge from the jet, second depth, tail water depth, water depth the back of the spillway, water height on the spillway, spillway water head recorded. The flow depth measured depth gauge with an accuracy of 0.1 mm at three fixed points and their average. In this research in order to determine the best model of energy dissipation and economization of the stilling basin with smaller dimensions for modeling the using several methods such as creating a slot in the spillway-body, on the floor of the stilling basin, and end of the stilling basin. In total 65 experiments with a Froude number of 4.56 to 10.18 were performed. In all experiments, the cross-section of the slot (jet) was constant and discharge was 16,12,8 L/s.

Four series of experiments with different landings were performed to determine the evaluation of different models to reduce the length of the hydraulic jump and select the best model. The first stage test (control test) will be used using a without jet spillway to determine the jet flow rate and compare the jump length with other models. The results of these experiments, similar to previous studies, show that with increasing discharge spillway, the Froude number decreases, and the length of the jump and the length of the roll increase. The experiment of the second series (slot in the body of the spillway) By creating a slot with an angle of 45 degrees in the body of the spillway, we came to the conclusion that the slot in the body of the spillway was able to reduce the jump length between 14.28 to 4.76 percent in different flows. Third stage experiment (slot in the floor) Comparison of the results of the tests of the effect of the slot in the floor spillway with the control experiments showed that the use of the slot in the floor of the spillway at all distances reduced the hydraulic jump length compared to the control experiments at similar discharges. Also, the effect of using a slot in the floor on reducing the length of the hydraulic jump has increased as the slot approaches the spillway. The best way to reduce the jump length is related to the slot attached to the spillway, which has reduced the jump length by 59 to 67% for different discharges of the spillway compared to without a jet mode. Third Stage Experiment (slot in floor) Comparison of the results of the stilling basin floor impact tests the free experiments showed that the use of the stilling basin floor slot at all distances reduced the hydraulic jump length compared to the free experiments at similar discharges. Also, the effect of using the slot in the floor on reducing the length of the hydraulic jump has increased with the slot approaching the spillway, so that the best way to reduce the jump length is related to the gap attached to the overflow, which is 59 to 67% for different discharges without jet reduced. Fourth Stage Experiment ( the jet at the end ) The jet at the end of the stilling basin at all distances experiments showed that the jet at the jump was submerged because the momentum caused by the discharge passing through the flow over the spillway caused it to push water. The spillway water a submerged jump mode has been created the jump energy has been depleted. The experiments showed all discharge inflow tested, the closer the jet is to the spillway, the best jump length. The best mode was to reduce the jump length of the jet attached to the spillway, which reduces the jump length by 80 to 88% in different discharges to the spillway compared to without a jet mode.

In these experiments, by examining the effect of the jet on different models, the results showed that using the jet at the end of the stilling basin at different distances and discharges has a better performance compared to other models. The jet at the end in the stilling basin had a jump length of maximum discharge 88% reduction, the slot jump length in the floor of the stilling basin 67.42% reduction and finally the slot jump length in the spillway body 14.28% reduction, which has the lowest reduction in jump length compared to other models of this research .In this study, the jet at the end of the stilling basin in different discharges reduces the level of the upstream water level, which in the maximum flow was able to reduce the upstream water level by 5.67%.

In practical applications, for instance, at the downstream of hydraulic structures, in some cases the width of the basin may be larger than the upstream supercritical flow (sudden expansion in flow section). In such cases, an expanding hydraulic jump with symmetrical or asymmetrical shape will be developed at the downstream. Under the design of three parallel gates, the operation of the side or middle gate can be lead to the asymmetrical or symmetrical hydraulic jump, respectively. According to the position of jump toe, expanding hydraulic jump can be classified into four types. The present study focuses on a T-shaped hydraulic jump which the toe is established at the beginning of the divergence section.Most of the previous studies are related to the symmetrical expanding hydraulic jump. In this case, the downstream diverging channel is symmetric on the central axis of the channel. However, a systematic study investigating the effect of symmetry and asymmetry on the expanding hydraulic jump was not found in the literature. In this study, using the momentum principle, some theoretical equations were derived to determine the sequent depths ratio of symmetrical and asymmetrical expanding hydraulic jump. Also, some regression relations were proposed to estimate the length of expanding hydraulic jump. The new proposed equations were also extended for the presence of a sill. The equations were calibrated using available experimental data from this study and the literature. This research also considered the characteristics of expanding hydraulic jump under the symmetrical and asymmetrical operation of parallel gates.

To calibrate the new proposed relations and investigate the effects of different parameters on the expanding hydraulic jump characteristics, two experimental data sets were used. In addition to the data set from Bremen (1990), the experimental data from the present study were used. The data were collected from a hydraulic model of three parallel radial gates for operating the side or middle gate which corresponds with the asymmetrical or symmetrical expanding hydraulic jump, respectively. The experiments provided a wide range of different parameters as the approaching Froude number, hydraulic jump length, sequent depths ratio, divergence ratio, sill height and relative length of gate separator wall.

Equation (4) was developed to determine the ratio of the sequent depths of expanding hydraulic jump based on the Momentum equation. For the presence of a sill, a combination of Equations (4), (7) and (8) can be used to calculate the ratio of sequent depths under the asymmetric and symmetric developments, respectively.Determining the ratio of the sequent depths requires the calculation of the adjacent water depths of the closed gates. For this purpose, in addition to developing the regression equation (Equation 13), Equation (12) was proposed which based on the calculation of the hydraulic jump profile. It was observed that under the calibration range, the regression equation is more accurate. However, Equation (12) is recommended for the range outside of the experimental observations. The results showed that:As the divergence ratio increases, the ratio of sequent depths approaches to the classic hydraulic jump.By decreasing the relative length of the gate separator wall and decreasing the width of the gate on the downstream channel width, the relative depth at the side gate and consequently the ratio of the sequent depths will decrease.For the lower length of separator wall and under operation of the middle gate, more lengths are needed to develop the jump than the side gate. However, as the length of the separator wall increases, the length and sequent depth of hydraulic jump due to the side gate increases on the middle gate.In the presence of a sill, the relative length of hydraulic jump decreases and the ratio of secondary depths increases.It was observed that the hydraulic jump due to the operation of the middle gate leans toward the left or right side of the channel due to oscillatory behavior.Under operating the middle gate and in the absence of a sill, an asymmetric hydraulic jump is formed in the channel face when the length of the separator wall is less than 38% of the classical hydraulic jump length. For the presence of a sill, the minimum length of the separator wall decreases to about 26%.By decreasing the initial depth of the hydraulic jump on the width of the gate and converting the output jet into a linear jet, the relative development length will increase.
As the sill height increases, the difference in the depths attached to the side gates will decrease and the hydraulic jump will develop more symmetrically.As the relative height of the sill decreases, the minimum length of the separator wall to form a symmetrical hydraulic jump in the flanks, increases.

This research developed a set of theoretical and regression relationships for estimating the length and sequent depth ratio of expanding hydraulic jump. Moreover, the effects of sill height, divergence ratio and the length of the gate separator wall, were investigated. This study compares the effects of side and middle gate operations based on the variation of jump length and sequent depth ratio. The results can be used as a guide for the hydraulic structures operators to reduce the asymmetric severity of the expanding hydraulic jump and achieve the complete development under the minimum length.

The hydraulic jump takes place in both natural and manufactured systems. As it can be seen in streams, rivers and water distribution and irrigation networks formed downstream of hydraulic structures such as spillways, sluice gates, and drops. Generally, it is necessary to construct special structures downstream of flow in order to prevent damage caused by the high energy of water in supercritical velocities and also to dissipate the extra kinetic energy of hydraulic jumps. Stilling basin is one of these structures which is constructed downstream of spillways or waterfalls. Baffle blocks are often used to stabilize the jump, decrease its length and increase the energy dissipation. In order to make stilling basin with its dissipating equipment effective, the design should be in a way that the tailwater depth becomes greater than or equal to the sequent depth, otherwise, the jump doesn’t occur completely and will be swept out of the basin, resulting in scour of the downstream channel. If the flow rates become more than the design discharge, the tailwater depth will be greater than the one required for a free hydraulic jump. These situations are common in low head hydraulic structures including low diversion dam spillways and gates. Under such conditions, the hydraulic jump will be submerged. For submerged hydraulic jumps with blocks, two different types of flow have been observed, the deflected surface jet regime (DSJ) and reattaching wall jet regime (RWJ). There was also a transition state in which the flow could be changed from one state to the other by some external disturbance. In this article, a numerical study was conducted to investigate the influence of some parameters, consist of block height and shape, Froude number and distance of blocks from the gate, on the performance of submerged hydraulic jumps with blocks as energy dissipators. 3D RANS simulations have been applied by Fluent software. RSM turbulence model was used which illustrated much precise results in verification. In total fifty-four models with different geometrical and hydraulic situation according to the four mentioned parameters have been created and the percentage of dissipating energy is presented in each case to find the most effective condition. It was observed that the Froude number is the most important factor in the study of dissipating energy; such that the percentage of dissipating energy increases almost ten percent per one unit raise in Froude number. Furthermore, the existence of a slope at the back of blocks does not have an effect on energy dissipating, but it can be implemented to avoid cavitation. In addition, the percentage of dissipating energy goes up as the blocks are mounted closer to the gate and also provided the condition which leads to the deflected surface jet regime. The more turbulence in the deflected surface jet regime makes the desirable condition in which baffle blocks perform more efficiently as energy dissipators in comparison to reattaching wall jet regime. Finally, it can be concluded that for effective energy dissipation, block dimensions and all conditions should be provided in a way to form submerged hydraulic jump as the deflected surface jet regime.

In this research 3D hydrodynamics of Mill-Mugan diversion dam at a domain with a length of 500 meters was simulated numerically using large eddy simulation (LES) method. All of the components of the dam such as radial gates and stilling basin were considered and the causes of destruction occurrence at the downstream basins were investigated under various operating conditions. Simulated stage-discharge curve of a single radial gate was compared with data reported by dam consultant and also with relationships available in the literature, which confirms the validation of the numerical model. Furthermore, flow patterns of the numerical model were compared with images taken from the study area. Study domain were discretized using 25 million cells. Numerical simulation was performed using parallel processing and to provide the steady state condition, simulation was continued for up to 1000 seconds. Results showed that in all scenarios of the symmetric operating condition, hydraulic jump downstream of the radial gates formed inside the main stilling basin. However, the high end sill caused hydraulic obstruction and as the subcritical flow passed over the sill, critical flow formed at its top followed by a supercritical flow thereafter. Consequently, another hydraulic jump occurred when flow reached the subcritical flow in the protection trench, located downstream of the main stilling basin. Due to the diverging geometry of the side walls, a radial hydraulic jump occurred further downstream. Hydraulic jumps exert strong dynamic loads to the flexible concrete blocks inside the protection trench and it causes rupture of the chains connecting the concrete blocks. Under asymmetric operating conditions of the radial gates, hydraulic jump is swept out of the main stilling basin and it exacerbates unfavorable hydraulic conditions downstream of the dam.

If too many variables with multiple levels for investigation of hydraulic phenomenon are effective, finding the optimum combination of variables in full experimental study is very time-consuming and costly. In many other sciences instead of full factorial method, Taguchi method is used. Taguchi method uses fractional factorial combination and meanwhile reduces number of experiments, tunable comparison of all the variables will be ensured. The purpose of this research is to find out whether using Taguchi method and reducing the number of tests could yield results closer to the results of experiments designed with full factorial method. If the answer is yes, what will be the amount of errors in the results? On the other hand, how reliable is the optimum value for each variable. Moreover, how much time and money could be saved from application of the Taguchi method in the study of a hydraulic phenomenon. For this purpose, experimental studies were made to evaluate the effect of height and position of baffle block under different flow conditions in order to minimize the scour downstream of the stilling basin. In addition to the analysis of the results, the results of Taguchi and full factorial methods are compared from different aspects. The results showed that Taguchi method predicts the optimum combination of variables with high accuracy and saves up to 74% of the total time spent.

The hydraulic jump in the stilling basin can be considered macroscopically as a time-averaged steady, abruptly varied flow characterized by a free surface discontinuity and the formation of strong vortex that generates macro turbulent fluctuations.This paper are discussed the characteristics of pressure fluctuations in spatial hydraulic jumps with sudden expansion stilling basin. The effects of the channel expansion ratio and inflow condition on the dimensionless standard deviation of pressure fluctuations (cp') and extreme pressure fluctuations (Cp, Cp-) in the hydraulic jump were examined. In this study many tests were conducted in a relatively large flume size of 0.8 meter wide and 12 meter length. data were presented for Froude numbers from 2.5 to 9.5 and channel expansions ratio (B1/B2) was 0.33, 0.5, 0.67 and 1. Pressure data were recorded by means of pressure transducers systems. A sampling frequency of 40 Hz was selected. The results show that the dimensionless standard deviation of pressure fluctuations and extreme pressure fluctuations of the hydraulic jump are dependent on the inflow Froude number and position from the toe of the jump. Fluctuating pressure at the position of about (10-30)Y1, can reach the maximal value. And indicates that the sudden expansion at the hydraulic jump decreases pressure fluctuations. The dimensionless standard deviation of pressure fluctuations (Cp') decreases on the order 43%, 38% and 19% for expansions ratio β = 0.33 , 0.5 and 0.7, respectively compared with classic jump.

Scouring is one of the issues that is important in the design of various types of hydraulic structures. One of these structures is a stepped spillway. The aim of this study is to evaluate the similarity between the profiles of scour holes downstream of the stepped spillway. To do so، results of 67 experiments in two different experimental models were used; these results were in a wide range of particle Froude number، the stilling basin length، downstream depth، sediment particle size distribution and two different slopes of stepped spillway. In this study، 5 different lengths of stilling basin، from 37 cm to 120 cm، were used. Also، the range of utilized discharge was from 8. 43 lit/s to 88. 95 lit/s. Duration of the tests were selected to be 6-hours، 8 hours، 12 hours and 24 hours and، in total، 834 scour profiles and approximately 85000 points to were used derive required relations and to performother analyzes. Based on the experiments results، the similarity between scour-holes located in downstream of stepped spillway was analyzed. In this process، two methods were used to make the profiles dimensionless. Based on statistical parameters، best method was selected and similarity of downstream profiles were shown. Relations that predict maximum scour depth، the distance from maximum depth to the end of the stilling basin and volume of transported sediments are developed based on the dimensionless parameters in different time periods. Furthermore، impact of different parameters on the geometry of scour holes were studied. When the Froude number increases، while all other parameters are constant، the dimensions of the scour-hole increases. When the stepped spillway slope increases، the dimensions of the scour-hole decreases and، moreover، when the tail water depth increases، while all other parameters are constant، a deeper hole with longer longitudinal distance forms. Overall، 8 cross section profiles under different conditions were taken. These profiles indicate transverse development of the scour-hole، in addition to longitudinal development.

Hydraulic jumps occur in natural systems like streams and rivers as well as manufactured systems. Samples of the latter occurance are jumps in water distribution and irrigation networks formed downstream of hydraulic structures such as spillways, sluice gates, and drops. These structures are usually designed for a specific tailwater depth. Stilling basins with baffle blocks are frequently used as energy dissipators downstream of hydraulic structures. Baffle blocks are often used to stabilize the jump, decrease its length and increase the energy dissipation. If the flow rates become more than the design discharge, the tail water depth will be greater than the one required for a free jump. These situations are common in low head hydraulic structures including low diversion dam spillways and gates. Under such conditions the hydraulic jump will be submerged. The performance of the blocks in submerged jump (SJ) condition differs from the free jump (FJ) case. According to some factors such as Froude number, block shape and location and submergence factor, flow regimes on baffle blocks in condition of submerged hydraulic jumps which occurs in stilling basins, are classified into two regimes, the deflected surface jet (DSJ) and reattaching wall jet (RWJ). In this article a numerical study was conducted to investigate flow pattern, vortexes and the magnitude of vorticity in submerged hydraulic jumps with baffle blocks downstream of a sluice gate. The results were compared to ones in same conditions without blocks. 3D RANS simulations have been applied by Fluent software. RSM turbulence model were used which illustrated much precise results in verification. Three numerical models have been created; Submerged wall jet without blocks, submerged hydraulic jumps with baffle blocks in the condition of deflected surface jet flow regime and submerged hydraulic jumps with baffle blocks in the condition of reattaching wall jet flow regime. Flow pattern has been exhibited for each model and results were compared with each other. Vortexes formed in such situations classified into three groups according to axis which they whirl around. It was observed that deflected surface jet regime has more vortexes in comparison to the two other conditions. In addition, by measuring the average magnitude of vorticity in cross-sections it has been concluded that z-vortexes –vortexes which rotate around z axis– much more powerful than x- and y-vortexes as they determine the kind of flow regime. Furthermore, this magnitude is about two times larger in deflected surface regime than two other situations. This fact leads to more turbulence in the flow that makes deflected surface jet regime the desirable condition in which baffle blocks perform more efficiently as energy dissipators in comparison to two other investigated models. In order that, from energy vantage point, conditions should be provided in a way to form submerged hydraulic jump as deflected surface jet regime.

The generated kinetic energy at the toe of spillways should be dissipated in the shortest basin to provide normal condition downstream of the river. This research aims to introduce the roughened stilling basin by means of roughness elements (dentate blocks) with new geometry form and arrangement. The study also investigates the effect of different parameters of hydraulic jump on this new stilling basin for the Froude numbers in the range of 11 to 14. The experimental results show a reduction of hydraulic jump parameters on dentate blocks stilling basin while compared to the smooth bed. Length of hydraulic jump and sequent depth was reduced by about 50-60% and 10-12%، respectively. Finally the required roughness length and length of hydraulic jump on dentate blocks stilling basin were compared with the smooth bed basin. For dentate block length of basin was 50-60 percent less and the length of hydraulic jump was only 35-40 percent less than the smooth basin.

Stilling basins are used for dissipation of kinetic energy downstream of hydraulic structures such as drops, weirs, chutes and gates. In this study hydraulic jump characteristics in presence of a submerged vane was evaluated in a flume, 12 meters long, 0.4 meters wide and 0.4 meters high. The heights of vanes were 1.1, 2.2, 3.3 and 4.4 centimeters and they were located in front of the flow with an angle of attack of 10, 20, 30 and 90 degrees. Sixty four experiments with upstream Froude numbers in the range of 3 to 8 and four different discharges of 15, 20, 25 and 30 liters per second were used in this study. Results show that use of submerged vanes can decrease length and downstream depth of hydraulic jump up to 25 and 10 percent, respectively. The bed roughness under this condition increase the bed shear stress 12 times higher compared to smooth bed and this condition occur for the vane with 4.4 centimeters hight and angle of attack of 90 degrees.

In this paper, the effect of clay content on the local scouring downstream of a rigid apron due to a submerged horizontal jet has been studied experimentally. Seven different mixtures of cohesive sediments with clay content equal to 0, 10, 15, 20, 25, 30 and 40 % were used. Results showed that the clay content has an important effect in the scouring process. It shows that with clay content equal to 40%, the maximum depth of scour may be reduced up to 80% of the non-cohesive materials. Using dimensional analysis, a new non-dimensional parameter is introduced which includes the effect of both the grain densimetric Froude number and clay content. It was also found that there is a critical value for the mentioned dimensionless parameter, where no erosion occurs below that value. Also, dimensionless equations and graphs are presented to determine the characteristic lengths of the scour hole including the maximum scour depth, the maximum longitudinal extension of the hole and the sand wave height.

In this study, effects of shape of roughness elements on the length of hydraulic jump have been investigated experimentally. For the purpose of this study, prismatic roughness elements with different shapes (rectangular, triangular, circular, lozenge and hexangular) have been tested in a rectangular flume 7.5m long and 30cm wide. Experiments were performed in the hydraulic laboratory of Shahid Chamran University, Ahwaz, Iran. The roughed elements are glued on the bed of flume downstream of ogee spillways in such a way that the incoming water jet is just above the element surface. It should be noted that in previous studies the rough elements have been tested such that the incoming jet was at the same level of the element bottom so the elements act as baffle blocks. Each rough element was tested under different flow conditions. The incoming Froude number was in the range of 4.5 to 12. During each test the water surface profile, the roller length and the jump length were measured. In few tests the longitudes and vertical flow velocity were measured. The results indicate that the presence of rough element can reduce the hydraulic jump length and the amount of the reduction depends on the Froude number and the roughness shape. The lozenge element shape was found to produce lesser jump length (up to 40% of the smooth bed jump). Relations have been presented in this study to predict jump length, roller length and the amount of energy which is dissipated. Comparison of this study with previous results reveals that using the rough element can reduce the hydraulic jump as much as the block elements do, and the rough element can not cause separation of flow which might be subject to cavitations.