Journal of Hydraulics
http://jhyd.iha.ir/
Journal of Hydraulicsendaily1Fri, 23 Sep 2022 00:00:00 +0330Fri, 23 Sep 2022 00:00:00 +0330Experimental study of scouring of cohesive sediments caused by free fall jets
http://jhyd.iha.ir/article_143345.html
Introduction Most of the times, flow passing above, through or below hydraulic structures is in the form of jets, which can cause downstream soil material erosion. When the amount of clay in soil materials is more than 10%, they can be considered as cohesive soils. If the results of cohesionless sediment research are generalized to cohesive sediments, the scour values obtained will be more or less than the actual values. On the other hand, there are no specific conversion ratios to estimate the characteristics and temporal changes of the scouring of cohesive sediments from cohesionless sediments. The duration of reaching maximum scour depth in cohesive sediments has shown to be longer than that of cohesionless ones.Previous works on cohesive sediments are often performed on flumes or by using a submerged vertical jet device. However, the jets formed below the hydraulic structures are mostly horizontal or oblique which are examined in this paper.Based on dimensional analysis, it was determined that the parameters of nozzle diameter, jet drop height, jet angle, jet velocity, tailwater depth, fluid density, dynamic fluid viscosity, critical shear stress and gravity acceleration affect the scour of cohesive sediments caused by the jet which is studied here.Methodology Experiments were carried out at the Hydraulic Lab of Tarbiat Modares University in a rectangular flume 0.6 m wide and 0.6 m high. A 0.2 m deep hole is created on the floor to place cohesive sediments. The laboratory channel is equipped with a 2m3 inlet tank, from which water is pumped into the jet tube. Froude numbers 3, 5, 7, and 9 are established based on common hydraulic structures and previous works.The experiments were performed using horizontal, oblique and vertical jets using tubes with nozzle diameters of 10, 15, 20 and 25 mm and with 3 tailwater depths of 5, 10 and 15 cm and 3 jet drop heights of 20, 50 and 60 cm. The cohesive sediments used were produced from a combination of fine sand with clay (including kaolin and bentonite at a ratio of 3 to 1). The amount of clay was considered to be 20% by weight of the total soil based on natural soils and previous works.Prior to the start of tests, tailwater was established on the sediment layer in order to allow it to saturate. After reaching equilibrium in the experiments, water was completely drained from the channel and the scouring hole and bed profiles were extracted by a laser distance meter device.Results and Discussion Erosion of cohesive sediments has the greatest scouring potential in the initial stage and in the later stages, the sediment bed becomes rougher and its resistance to scouring increases until equilibrium establishes.A sedimentary ridge is formed at the end of the scouring hole by horizontal and oblique jets and around the scouring hole by vertical jets. In horizontal and oblique jets, the maximum scour depth does not necessarily form on the centerline. The growth of the length and width of scouring hole stops almost simultaneously, but deepening of it continues after that. This is in accordance with findings of Mazurek et al. (2001), Ansari et al. (2002), and Mazurek et al. (2003).As the jet height rises, the time it takes to reach equilibrium increases and leads to maximum scouring occur at a greater distance from the jet nozzle. In horizontal jets, the location of the maximum scouring depth shifts in the early stages of scouring but stabilizes after approximately 2 hours. Increased shear stress due to jet flow increases the scouring rate.Increasing the ratio of tailwater depth to jet drop height (Yt / H) has a dual effect on the maximum relative scour depth. So that the maximum relative scour depth first increases with increasing Yt / H to about 0.3 for horizontal jets and about 0.35 for vertical jets, then the trend reversed and with increasing Yt / H ratio the scour rate relatively reduced. Increasing the Froude number increases the amount of scouring. Also, the amount of scouring at two angles of 0 and 30 degrees relative to the horizon, are very close to each other. At larger angles, except for the 90 degree angle, the scour depth increases as the jet angle increases. The 45 degree angle jet creates the maximum scouring depth.Conclusion As the jet height rises, the time it takes for the scouring to reach equilibrium increases. It also leads to maximum scouring to occur at a greater distance from the jet nozzle. Increasing shear stress by jet flow, increases the scouring rate.At lower values of Yt/H, with increasing this ratio, the maximum scour depth increases until it reaches the maximum value and then. the trend reverses.By increasing Froude number, scour rate increases. By steepening jet angle, the scour depth almost increases but when the jet becomes vertical, lower scour depths are observed.Using nonlinear programming method and gray wolf algorithm for estimating parameters of nonlinear Muskingum model
http://jhyd.iha.ir/article_145204.html
AbstractBackground and objectives: Flood routing is an important issue in river engineering. The flood routing methods are categorized into two groups of hydraulic and hydrologic methods. Hydraulic routing methods require considerable input data and time-consuming calculations. But hydrological methods need less input data and are less complicated in comparison with hydraulic routing methods. The hydrological routing methods are based on the continuity equation and a relationship between inflow/outflow values and flood storage. Linear Muskingum is a hydrological routing method commonly used in rivers routing. However, as the relation between channel storage and the inflow/outflow is nonlinear, the nonlinear form of this model is developed which has received special attention in recent years and several types of it have been proposed. Using the Muskingum method, while saving time, valuable information about the flood depth and hydrograph is obtained. However, the performance of these models is highly dependent on the optimal estimation of their parameters considering the study area characteristics.Materials and methods: Although the nonlinear Muskingum models have special advantages over the linear Muskingum model. The hydrologists avoid from the nonlinear Muskingum models, because of the difficulties in estimation of their parameters. Therefore, researchers have attempted to estimate these parameters using the optimization algorithms. In this research, the nonlinear Muskingum model type 5 (NL5) is considered for flood routing and Nonlinear programing (NLP) is used for estimation of the optimal values of model parameters. The results are compared with the metaheuristic optimization algorithms of genetic algorithm (GA), particle swarm optimization algorithm (PSO) and Gray wolf optimizer (GWO). The objective function of the optimization algorithms was set to minimize the sum of squares of the difference between the measured and simulated values of flows (SSR). Wilson flood hydrograph (first case study), Wy River flood hydrograph in England (second case study) and the hydrograph presented by Vatankhah (2014) (third case study) were used as the case studies of this research.Results: The performance of NL5 model was very good in the all considered cases. In the first case study, the maximum absolute error is less than seven percent. Also, in the second and third case studies, the maximum absolute errors are less than 20 percent and 10 percent, respectively. MARE, NSE, CC, DPO and DPOT measures were used to further evaluate the model performance. The closer values of MARE, DPO and DPOT to zero and the closer the values of the NSE and CC measures to one, show the better the performance of the model (Kult et al., 2014). In the first case study, the MARE values for NLP, GWO, PSO and GA algorithms are 0.011, 0.011, 0.012 and 0.012 m3/s, respectively. For the second case study, the MARE values are 0.104, 0.105, 0.103 and 0.104 m3/s, respectively; The values of this measure in the third case study for the mentioned optimization methods are 0.0301, 0.0301, 0.0301 and 0.0303 m3/s, respectively. The values of this measure show the perfect performance of NLP, GWO, PSO and GA techniques in estimation of NL5 parameters. DPO, DPOT, NSE and CC indices also show the same finding. SSR values in the first case study for NLP, GWO, PSO and GA optimization methods are 5.44, 5.44, 5.47 and 5.88, respectively. Also, SSR values for the second case study are 30837.6, 30848.2, 30880.1 and 30929.1, respectively. For the third case study, these values are 7356.7, 7432.1, 7391 and 7412.3. The simulation times for NLP, GWO, PSO and GA methods show that the processing time in the NLP method is much less than the other methods. The optimization methods are ranked based on their results accuracy and simulation time. NLP method is ranked first in the regard while is followed by GWO, PSO and GA in the next ranks, respectively. The comparison of the obtained SSR values in the current study and the previous studies which used the cases one and two, show that the NLP optimization method has better performance in estimation of NL5 model parameters. In this study, for the third case study (Vatankhah, 2014 data), which has not been routed by the Muskingum method previously, the results of routing with NL5 are compared with the results obtained with the Rang Kota method (Vatankhah, 2014). The SSR value when using NLP as the optimization tool for estimation of NL5 model parameters is 7356.8 m6/s2, while in the Rang Kota method it is 14441.3 m6/s2. Therefore, in this case study, the NL5 model has performed better than the Rang Kota method.Conclusion: In the present study, NLP technique and powerful GWO algorithm were used to estimate the optimal values of NL5 model parameters and the results were compared with GA and PSO algorithms. The performance evaluation results indicate that the NLP method, in addition to being more accurate, also requires less time to estimate the optimal value of the parameters. The values of the objective function for the first case study for NLP, GWO, GA and PSO methods are 5.44, 5.44, 5.88 and 5.47 m6/s2, respectively, while these values for the second case study are 30837.6, 30848, 30929.1 and 3088.1 m6/s2 and for the third case study are 7356.7, 7432.1 7412.3 and 7391 m6/s2. NLP processing time is at least 10% less than the other considered optimization methods. Therefore, the NLP method is the best choice for estimating the optimal parameters of Muskingum type five by considering two factors of accuracy and speed of simulation even though all of the methods showed a very good performance. Also, in the third case study, which was not routed previously, by the Muskingum method, the results were compared with the Rang-Kota method, and the results showed that the NL5 model, which was solved by the NLP method, performed better. After NLP, GWO, PSO and GA methods had the better performance in estimating the NL5 parameters, respectively.Experimental Investigation of non-suppressed sill effect with different geometry on flow pattern and discharge coefficient of sluice
http://jhyd.iha.ir/article_146469.html
Introduction: The ease of installing sluice gates and simplicity of their equations resulted in sluice gates as one of the most widely used hydraulic structures in regulating and controlling the water level. Several factors are discussed on the discharge coefficient of the sluice gate, including the effect of sill under the gate. The most important application of sill under sluice gate is to increase its discharge coefficient. Geometry and widths of sill is one of the important factors on discharge coefficient. also use of non-suppressed sills changes the flow pattern and the general equation of discharge coefficient. discharge coefficient of sluice gate with sill was studied by Jalil et al. (2016). In this study, the effect of sill under sluice gate was experimentally investigated on flow discharge coefficient. Results showed that the coefficient of discharge decreases with an increase of relative sill height to the head upstream. Rezavand (2018) investigated the effects of the hydraulic parameters on the flow discharge coefficient by Fluent software. Results showed that the sill under the gate has a positive effect on the flow discharge coefficient. The goal of this study is to investigate the geometry of sill with changes in its width on flow pattern and discharge coefficient in free-flow conditions. According to previous studies effect of sill width parameter with different geometric shapes on discharge coefficient and flow pattern has not been studied.Methodology: The experiments were performed in a hydraulic laboratory with flume dimensions of 5 m in length, 0.30 m in width, and 0.45 m in height. The walls are made from Plexiglass in order to provide good visibility. The inlet flow were measured by two rotameters with&plusmn; 2% accuracy. Rotameters were installed at the outlet of the pump and measured with a point gage with an accuracy of 1 mm. a sluice gate with a 1 cm thickness is installed with the distance of 1.5 m away from the inlet of flow. The gate opening was fixed at 4 cm in all experiments. Sills including cylindrical, semicylindrical, pyramidal, and rectangular cubic were prepared in order to investigate the shape effect. All four sill shapes were prepared with widths of 5, 7.5, 10, 15, and 20 cm in order to study the effect of sill width under the gate. The height of all sills in this study was considered to be a fixed value of 3 cm. A total of 20 physical models were tested. In this study, flow discharge in the range of 475 to 700 liters per minute was applied to all models. A total of 200 experiments were performed in order to investigate the effect of sill shape and width on flow pattern and discharge coefficient in free conditions.Results and Discussion: Results of sluice gate patterns with sill and without sill situations were investigated. The results of these experiments, similar to previous studies, show that a sluice gate with sill increases the discharge coefficient. The results showed that sills with different geometries affect flow under the gate. Also, using non-suppressed sills under the gate breaks the flow lines. As the downstream progress, v-shaped sections are formed. Investigation of flow patterns in cylindrical and semi-cylindrical and pyramidal sills showed pyramidal sill causes a significant uniformity flow lines compared to other geometric shapes due to its sloping side at downstream. while sill with rectangular cube geometry improves rotational flows at downstream of sill. The results of placing sill in different geometric shapes under sluice gate indicate that using semicy-lindrical sill compared to other shapes increases in discharge coefficient and the highest values of discharge coefficient after this sill are allocated to cylindrical, pyramidal and rectangular cubic sills, respectively. semicylindrical average discharge coefficient increased 19.1 percent compared with the gate without sill. According to the laboratory findings, it was observed that increased sill width with decreased gate opening increases the discharge coefficient. Placing a sill with a width of 20 cm in all geometric shapes increases the discharge coefficient by an average of 10% compared to a sill with a width of 5 cm. Conclusion: The study of discharge coefficient in 20 physical models showed that the highest values of discharge coefficient after semicircular sill are allocated to circular, triangular, and square sills, respectively. This increase is expressed because the semicircular, circular, triangular, and square sills at the smallest width (b = 5 cm) increased discharge coefficient by 6.5, 5.6, 3.5, and 1.6% compared to non- sill state, respectively. Changing sill width from 5 to 20 cm showed that discharge coefficient of semi-cylindrical, cylindrical, pyramidal and rectangular cubic increased by an average of 19.1, 17.2, 14.7, and 12.1% compared to non- sill state.Numerical study of the effect of flow velocity and flood roughness components on hydraulic flow performance in composite sections with converging floodplains
http://jhyd.iha.ir/article_146912.html
Intrpduction: The need to control floods and their dangers is not hidden from anyone. In addition, a wide range of economic, social and environmental issues are affected by this phenomenon. The first step in the design and optimal management of flood control methods is the correct identification of river behavior during floods. In most river engineering projects such as flood routing, determining the bed and river area, etc., calculating the average values of hydraulic parameters of the river section is sufficient. Today, the use of numerical and analytical methods in the study of fluid environment have grown and developed. Due to the production of reliable results, they have been able to be a good alternative to physical models. Today, with the rapid development of numerical models and increasing the speed of computer calculations, the use of 3D numerical models is preferred and also due to the fact that measuring the velocity distribution and shear stress in rivers is very time consuming and expensive, the results of 3D numerical models It will be valuable. On the other hand, the present studies show that comprehensive numerical research using FLOW-3D model has not been performed on composite sections, so a suitable ground for research is provided. Therefore, the innovation of the present study is the numerical study of the effects of parameters such as roughness on the status and hydraulic performance of the flow in non-prismatic composite sections, which are accompanied by divergent and convergent floodplains, which have received less attention numerically.Methodology: Younesi (2013) research has been used to validate the results of numerical simulation. In these experiments, first the hydraulic flow in composite prismatic and non-prismatic sections with fixed bed was examined and then, while maintaining the conditions, sediment transfer experiments were performed in prismatic and non-prismatic mode. The experiments were performed in a research channel 15 meters long. This canal is a composite canal with two symmetrical floodplains with a width of 400 mm with a flow rate that can be provided for recirculation in the system of 250 liters per second and a longitudinal slope of 0.0088 000. The depth of the main canal to the edge of the floodplain is equal to 0.18 meters and the width of the main canal is equal to 0.4 meters (Figure 1). In order to roughen the bed and walls of the main canal, sediments with an average diameter of 0.65 mm have been used and at each stage, the walls and bed of floodplains have been roughened by sediments with an average diameter of 0.65, 1.3 and 1.78 (mm). A triangular overflow is used to measure the inflow to the canal, upstream of the canal. In order to measure the flow velocity in experiments with relative depth of 0.15 and 0.25, a micromolina with a diameter of 14 mm and in experiments with relative depth of 0.35, a three-dimensional speedometer (ADV) was used. The water level was also taken by depth gauges with an accuracy of 0.1 mm.Result and Diccussion: In the present study, in order to validate the numerical model of water surface profile, average depth velocity distribution and boundary shear stress in the three sections at the beginning, middle and end of the divergence zone) in experiments 0.25-2-11.3-NP and 0.25-2-5.7-NP and Also, the 0.25-2-2 P test of the prismatic composite section has been evaluated. In Table (1) the values of RMSE and NRMSE indices related to the P.20-2-2-P test of the prismatic composite section, and also in Table (2) the values of the RMSE and NRMSE indices in the experiments 11.3-2-0.25-NP and -0.25. 2-5.7-NP is provided. The results related to the validation of the average depth velocity of the experiments 0.25-2-5.7- NP-11.3-2-0.25, NP and P.2.0-2-2-P are shown. In 0.25-2-5.7-NP experiment, the amount of NRMSE in elementary, middle and final grades was calculated to be 5.7, 11.8 and 10.3%, respectively, which is in the excellent grade in the elementary grade and good in the middle and final grades. Placed. As can be seen, the RMSE values are calculated as 0.026, 0.037 and 0.026, respectively. In the experiment 11.3-2-0.25, NP, the NRMSE values in the primary, middle and final levels were calculated as 7, 11.2 and 15.4%, respectively, which are in the excellent category in the primary level and in the good category in the middle and final levels. Take. As can be seen, the RMSE values are calculated as 0.032, 0.038 and 0.04, respectively. In the 0.25-2-P experiment, the NRMSE value was calculated to be 1.7%, which is in the excellent category. As can be seen, the RMSE value is also calculated to be 0.004. Regarding the medium-depth velocity distribution, it can be said that the numerical model has an acceptable compliance with the laboratory results and only a small error has been entered in the junction area, which can be considered as a result of the movement of secondary cells towards the corners.Conclusion: in this research The flow pattern in waterways with composite prismatic and non-prismatic sections was investigated using Flow 3D software that is capable of three-dimensional flow analysis. For three different relative roughnesses (1, 2 and 2.74) as well as three relative depths (0.15, 0.25 and 0.35) and divergence angles of 5.7 and 11.3 degrees, changes in the longitudinal component of velocity, The average depth velocity distribution, the boundary shear stress distribution as well as the flow rate transmitted by the floodplains were investigated. The results showed that with increasing the width of floodplains along the canal, the amount of velocity decreases. Also, the study of the effect of roughness on the flow pattern showed that in general, with wall roughness, the amount of velocity has decreased in all sections and also the flow pattern at the junction of the main canal and floodplain is more affected by wall roughness. The results also showed that with increasing relative depth or decreasing relative roughness, the velocity gradient between the main channel and floodplains decreasesAnalyzing the Key Factors Affecting Transient Pressures Occurring During Pipe Filling Using a Numerical Approach
http://jhyd.iha.ir/article_146913.html
Introduction:It is common in practice to partially drain the pipelines for inspection and repair. If not properly controlled, refilling of the pipeline may expose them to significant transient pressures which can compromise the integrity of the pipeline and associated joints. Implementing a safe filling protocol requires that the location and size of hydro-mechanical equipment are calculated. Such information can be obtained through analysis of different filling scenarios, but unfortunately, such a detailed analysis is usually ignored in the design stage, not surprising why pipe incidents usually happen during operation.With the aid of numerical explorations, this paper aims to shed some light on the key factors affecting the filling hydraulics. To this end, a numerical model is proposed to calculate the filling hydraulics. The model uses the method of characteristics to solve the water hammer equations and employs the Discrete Gas Cavity Model (DGCM) to treat column separation. The model is validated with the experiments. Extensive numerical explorations reveal that lack of a safe filling protocol as well as lack or inadequate sizing of the required hydro-mechanical equipment can result in water hammer pressures. The results also show that without a properly sized bypass and air valve, it is impossible to control transient pressures during filling.Methodology: Extensive numerical explorations are conducted with a hypothetical water pipeline to analyze the key factors affecting the transient pressures which occur during filling. The pipeline has an undulating profile with the diameter, length, and acoustic wave speed of 0.9 m, 15900 m, and 1000 m/s respectively. The pipeline is supplied by a reservoir with a constant water depth of 5 m which is located at the upstream end of the pipeline. It is assumed that the last 1600 m of the pipelined is drained and an air valve at the end of the pipeline allows air management during the filling. A bypass line located at the upstream end of the empty zone is also equipped with a flow control valve to control the filling flow rates. Several numerical solutions are conducted with the different sizes of the air valve, bypass line and different opening times of the flow control valve, and the maximum and minimum pressure heads induced during filling are recorded. Results and Discussion: Analyzing the results obtained from the numerical explorations show that when the flow control valve opens, the empty pipeline starts being filled with a filing flow rate which depends on the size of the bypass and the rate of opening of the flow rate. A large bypass line and rapid opening of the flow control valve result in the rapid filling of the empty pipeline and a significant down surge on the upstream side of the bypass line. The progressing water column in the empty pipe serves as a piston and pushes the air out of the system through the air valve. If the outlet orifice of the air valve is large enough, the air pressure in the empty pipeline does not increase significantly otherwise higher air pressures are built up which can slow down the filling water column. When the last air is eventually released from the system, the water column comes to rest and significant water hammer pressures result. The magnitude of the resulting water hammer pressure depends on the velocity at which the water column hits the pipe&rsquo;s end as well as the acoustic wave speed of the pipe. Numerical exploration shows that the maximum and minimum pressures induced during filling depend on the diameters of both the outlet orifice of the air valve and the bypass line as well as the opening time of the flow control valve. For this particular case study, it is found that the bypass line diameter = 0.2 m, the outlet orifice diameter = 1.5 cm, and the flow control valve opening time = 40 s can control maximum and minimum pressure head within the acceptable range without unreasonably prolonging the filling time. Conclusion:&bull; The proposed model can be successfully assisted in analyzing the hydraulics of filling and in designing a safe filling protocol&bull; Without a proper filling protocol, the resulting transited pressures can be strong enough to rupture the pipeline &bull; Without a proposedly sized bypass, it is impossible to control negative pressures in the pipeline &bull; The rate of opening of the flow control valve might play an important role in controlling the induced maximum and minimum pressures during filling&bull; Reducing the diameter of the outlet orifice of the air valve significantly reduces the resulting transient pressures but at the same time prolongs the filling. &bull; An optimum filling protocol can be obtained through an iterative procedure in which the bypass and air valve diameters, as well as the opening time of the flow control valve, are determined in such a way that the induced maximum and minimum transient pressures remain within the acceptable level and the filling is performed as fast as possibleExperimental study of Hydrodynamic Performance of Floating Oscillating Water Column as Wave Energy Convertors
http://jhyd.iha.ir/article_147836.html
Introduction Population increasing along with the environmental crisis due to the use of fossil fuels has led humans to seek to use renewable energy sources. One of the most important sources of renewable energy is the waves of the seas and oceans, which can meet some of the human needs for energy resources. One of the key steps in the development of wave energy renewable technology is the design and validation of physical models. Although physical models can not accurately simulate all the details and performance of the original prototype, they can be a very valuable source of information for researchers, developers, and inventors in this area. Due to its simple mechanical structure, the oscillating water column has become one of the most common tools for converting wave energy in the world. The oscillating water column could be used as a breakwater on the shores in addition to generating energy from the waves. Due to the complexities related to the hydrodynamic conditions of air and airflow inside the system, it is necessary to use laboratory models to study it more precisely. Methodology In the present study, laboratory flume model GUNT HM162 with a length of 12.5 m, width 0.31 m, and height 0.47 m with glass walls and the metal floor was used. A centrifugal pump with a flow rate of 165 m3/h and a height of 16 meters was used for the experiments. A wave generator with a frequency of 0.5 to 1.11 Hz was applied to create a wave in the laboratory flume. All experiments were performed at a constant flow depth of 200 mm. Three values were chosen for the distance of the OWC device from the water surface in the normal state (d), according to the chamber length (B). Therefore, distances of 10%, 25%, and 45% of the OWC chamber length were used as parameter d. To investigate the effect of back wall height (Z) on OWC efficiency, three physical models were made in three modes without back wall and with 5 and 10 cm back wall. In this research, the power generated by the wave inside the device was performed to evaluate the performance of the OWC. In addition, a two-way analysis of variance test was used to investigate the effect of independent parameters such as back wall height, the depth of the system, and the frequency of waves on the output power to determine the main and interaction effects.Results and Discussion The results show that with increasing the installation depth of the system, initially the amount of output power increased but then had a decreasing trend. Accordingly, the depth with the best performance must be considered for OWC. In this study, it was found that 0.25 B (chamber length) installation depth has better performance than the other two cases. Comparison of the effect of the back wall on the performance of the device at a depth of 0.25B shows that the models with the back wall have better performance comparing with the model without a back wall. The performance of the two back walls at frequencies less than 0.8 is similar, but for higher frequencies, the 10 cm back wall has better performance than another back wall. All the main effects have a significant influence on the output power, which the frequency of the waves and the height of the back wall have a higher effect. The results related to the interaction effects of independent parameters show that the interaction effects have a high influences on the amount of output power. Among the interaction effects, (Z &times; d) and (Z &times; Frequency) have a significant effect on the output power, which indicates the effect of the back wall on the total power. The results of the margin averages show that at the maximum frequency used, the 5 and 10 cm back wall were increased the efficiency of the OWC by 98% and 182%, respectively, compared to the model without a back wall.Conclusions Based on the result of the experiments, the presence of the back wall has a high effect on the OWC output power so that in the best installation depth (d =0.25B) and frequency of 1.1 Hz, the 5 and 10 cm back wall, increases the output power by 1.18 and 1.83, respectively. Two-way analysis of variance was used to investigate the effect of different parameters on OWC efficiency. The result of two-way ANOVA shows that the frequency of the waves and the back wall had the greatest effect on the output power. On the other hand, the interaction of the back wall with the frequency and installation depth also had a significant difference at the level of 0.01. The performance of the two back walls used at low frequencies was similar, but for the higher frequencies, the 10 cm back wall performed better. Accordingly, it can be concluded that the presence of a larger back wall cannot produce more power in all frequencies.The experimental study of downstream scouring of trapezoidal Piano key weir type A under free and submerged flow
http://jhyd.iha.ir/article_147939.html
Introduction: Weir is a structure that is made in the body or support of the dam to safe drain the excess volume of water in the tank. Weirs are mainly considered for free flow mode, but in some cases there is a possibility of immersion in them. Submersion in weirs occurs in two general and local ways. General submersion will occur if the downstream water level is higher than the weir crown level. This is more likely to occur for weirs in canals and rivers and if the weir acts as a diversion dam. Local submersion is observed in the downstream part of weir due to local flow conditions. Weirs are divided into linear and non-linear weirs based on the shape in the plan. Piano key weirs are the newest type of non-linear weirs which recently due to its advantages. Non-linear Piano Key Weirs enjoy not only a higher water passage but also a relatively simple and economic structure compared to linear weirs. Methodology: All experiments of this research were performed in a channel with a long 10 m, wide 0.75 m and high 0.8 m in Tarbiat Modares University hydraulic laboratory. A view of the laboratory flume is shown in Figure (3). The required water was supplied through an underground reservoir. In this research, trapezoidal piano key weir types A, made of thermoplastic with a thickness 1.2 m, slope of the input and output keys 28 degrees and a height 0.2 m was used. The weir has 6 keys (3 input keys and 3 output keys) with the same slope in the input key and the output key. Uniform bed materials with an average diameter 2.2 mm were used. Flow discharge was measured with an ultrasonic flowmeter and flow depth and bed level were measured with a laser level gauge. According to the selected discharges, the flow depth upstream of the weir was considered to be more than 3 cm so that the effect of surface tension is not significant. In this study, experiments were performed with five discharges 30, 40, 50, 60 and 70 liters per second. Under submerged flow for each discharge, two percent submersion and under free flow for each discharge, the tailwater depth was considered to be 0.13 m.Results and discussion: Flow characteristics are affected in case of weir submersion. During the test, after the flow hit from the input switch to the tailwater surface, due to the amount of tailwater depth, surface rotations (at low tailwater depth) and surface turbulence (at high tailwater depth) are observed. Part of the flow moves downwards and after hitting the bed surface, a weak rotational zone is created in the range of the input switches. The flow enters the downstream in the form of a submerged jet after the output switch and, due to the momentum to the upper fluid, causes a severe rotational zone in the range of the output switches. In the free flow, more turbulence is observed in the range of the output switches due to the intersection of the flow passing through the weir lateral wall and the falling current from the upstream and downstream crowns. Less tailwater depth in free flow limits the deep growth and development of the sedimentary hill in downstream of the scouring hole, and sedimentation occurs with longer length and lower elevation. However under the submerged flow, due to the greater tailwater depth and lower fall height, the flow strength is more depleted and the flow strikes the bed with less energy, and result in less scouring. In this case, the flow does not have the power to transfer all the sediments to the downstream and most of the sediments accumulate on top of each other and a sedimentary hill is created as a point. As a result, a sedimentary hill with a higher height and less length is visible under submerged current than free flow. Therefore, in the free flow than in the submerged flow, the length and depth of the scour hole occur more, and sedimentation occurs with less height and longer length. Under submerged flow, most of the sediment bed remains unchanged, while under free flow most of the sediment bed is affected by scouring and sedimentation. Of course, changes vary depending on the hydraulic conditions. In the early times, in both free and submerged currents, scouring occurs with greater intensity, but over time, its severity decreases and scouring reaches a stable state. In this case, sediments are rarely transported downstream. The surface of the sedimentary hill downstream of the scour hole in the open stream is almost smooth and in the submerged stream is sharp. Conclusion: The results showed that most of the scour hole changes occur in 20% of the initial time of the experiment and the changes in the free flow are faster than the submerged flow. The depth and length of the scour hole in free flow is greater than in submerged flow. Relative scour depth with increasing 77% in tailwater depth for Froude numbers of particle 0.029, 0.037, 0.045, 0.052 and 0.058, respectively 42, 45, 21, 28 and 27% and with increasing the tailwater depth 123% is reduced by 95%, 92%, 90%, 75% and 68%, respectively. With increasing 18% in the submersion ratio in the Froude number of particle 0.029 and increasing 96% in the submersion ratio in the Froude number of particle 0.058, the maximum relative scour depth decreases by 92 and 56%, respectively. The location of the maximum scouring is also a function of Froude number of particle and the tailwater depth. Maximum scour depth at the tailwater depth 0.13 m at a distance 0.18 to 0.30 m from the weir toe, at the tailwater depth 0.23 m at a distance 0.18 to 0.36 m from the weir toe and at a tailwater depth 0.29 m is at a distance 0.03 to 0.30 m from the weir toe.Investigation of particle movement pattern in Vortex Settling Basin based on particle tracking technique
http://jhyd.iha.ir/article_147978.html
Investigation of particle movement pattern in Vortex Settling Basin based on particle tracking technique1. Elnaz Mehrabani/ M.Sc student in Water Structures, Ferdowsi University of Mashhad, Iran.2. Ali Naghi Ziaei/ Professor, Department of Water Science and Engineering, Ferdowsi University of Mashhad, Iran.3. Neda Sheikh Rezazadeh Nikou/ Postdoctoral researcher, Ferdowsi University of Mashhad, Iran.4. Mahmoodreza Golzarian/ Professor, Department of Biosystems Engineering, Ferdowsi University of Mashhad, Iran.Introduction The quality of water required for agriculture, industry, drinking, etc., has made it necessary for the solids particle in the water flow to enter its permissible level in irrigation and drainage or urban water networks. The Vortex Settling Basin (VSB) makes use of the vortex flow inside the chamber for the separation of sediment particles from the flow.Elaborate studies have been made on investigation flow pattern at VSB that includes: (Paul, 1988 and 1991; Athar et al., 2003; Gheisi, et al, 2006; Ziaei et al., 2007; Chapokpour et al., 2011; Mulligan et al, 2016; Rehman et al., 2017; Huang et al., 2017; S. R. Nikou et al., 2021).Elaborate studies in hydraulic sciences apply particle tracking and image processing method for investigation ( Sun et al., 2015; Shin et al., 2016; Mulligan et al., 2016 and 2018; Rosberry et al., 2019; Witz et al., 2018; Duinmeijer et al., 2019).The investigation of vortex flow is very sensitive to measuring instruments, for example, ADV, which is the most common instrument for measuring the velocity, increases disturbance of flow. Therefore, it is recommended to use the non-interference particle tracking method to measure velocity components.Methodology The experiments were performed in the hydraulic laboratory of the water science and engineering department at the Ferdowsi University of Mashhad, Iran on an acrylic laboratory setup. Spherical particles with a relative density of 1.41, at distances of 37 cm and 1.5 m from the chamber (sediment injection site in the study of Athar et al., (2003)) and in these two longitudinal distances, left at 9 points and each experiment is repeated 5 times (Figure 2).In this research, two iPhone 7 Plus cameras have been used for taking photos. The camera of this phone has one of the most advanced cameras in terms of expertise and technology. In this study, due to the high volume of data at different points, image processing is presented in the highest probability of trapping (point 4), the position of this point is as follows: 5 cm from the floor, 2 cm from its right wall (sloping to the chamber), 18 cm from the sloping wall to the outlet channel and 6.5 cm to the water level. The input flow to the channel is 8 and 13.7 l/s.Results and Discussion The highest probability of trapping for a particle at two longitudinal distances is at point 4 with a probability of 60%. The process of particle displacement and the time series of three velocity diagrams in the vortex settling basin of the present study are sinusoidal. In sections 150&deg;-210&deg; and 330&deg;-30&deg;, the particle is inclined toward the wall and in other sections, it is inclined toward the orifice, affected by the location of input and output channels (S. R. Nikou et al., 2021). There is a meaningful correlation between the two components vx and vy, and in almost all places where the x velocity component is extreme, in the same position y component is zero, and vice versa. This result is quite justifiable given the motion of vortex flow. The extreme values of the velocity component in the x direction become closer as they approach the orifice, indicating an increase in velocity near the orifice and the chamber floor and a smaller curved path around the vortex core. Notably, the absolute value of the maximum velocity in the x direction is 1.61 m/s and in the z direction is 0.13 m/s, which indicates that the particle tends to enter the orifice more in a rotating passage than falling position, having said that, centrifugal force is dominated over the action of dewatering. The mean relative error of water surface profiles by image processing method compared to laboratory data is estimated to be 0.002 and 1.36%, respectively, which confirms well with the experimental measurements.Conclusion The results showed that the distribution of the velocity components of the particle in all three dimensions has a sinusoidal trend. The higher value of the maximum velocity in the x-direction than the z-direction indicates the dominance of the centrifugal force over the dewatering operation in the vortex flow.According to the obtained results, particle tracking and image processing can be used as an accurate method with a higher operational speed to investigate the flow patterns and determine the water surface profile in vortex settling basins.KeywordsPTV, Particle tracking, Orifice at the center, Point gauge, Velocity distributions.Cellular Automata Model for Simulating Surface Runoff
http://jhyd.iha.ir/article_147979.html
Introduction: Understanding hydrological phenomena is essential for the optimal use of water resources. Surface runoff is an important part of the hydrological cycle. Accurate runoff estimation can make a significant role in water engineering and the proper utilization of resources for the various uses of agriculture, drinking, hydropower and the environment. Therefore, the use and development of accurate and reliable methods to model the runoff of the catchments are essential. One of the new methods of runoff calculations is cellular automata. Cellular automata is a fundamental method for simulating complex systems.Methodology: In cellular automata, the lattice space is divided into a number of cells and creates a cellular space (Fig2). A set of cells adjacent to the central cell is called a neighborhood (Fig1). In the runoff production process, the cell state is the water level, which is the sum of the cell height and water depth. The height of the cell is determined from the digital elevation model and the determination of water depth is controlled by the effective precipitation at the present time step and the balance between inlet and outlet flow at the last time step. The transition rules in the cellular automata model determine the behavior of cells at different time steps and define the future state of the cell. The first transition rule determines which neighboring cell can get water from the central cell at each time step (Fig3). The second transition rule is used to calculate the amount of flow to neighboring cells, in which the Manning equation is used. The first and second transition rule applies to all cells at each time step and as a result, the output flow from each central cell to its neighbors is determined. In the general view, each central cell is a neighbor of other cells, as a result, a third rule must be used for calculating the total flow for each cell. The evaluation of the cellular automata model is performed using the statistical indicators of correlation coefficient and root mean square error and Nash-Sutcliffe efficiency coefficient.Results and Discussion: First, the runoff is simulated on a uniform rectangular surface and the results of the cellular automata model are compared with the results of the Akan analytical solution. In order to evaluate the efficiency and accuracy of the cellular automata, the statistical parameters of the models were calculated. The results showed that the cellular automata model has high accuracy and efficiency (Fig 5). Then runoff in the Con catchment is simulated. This catchment is located in the northwest of Spain. (Fig 6). The results showed that the cellular automata model has been able to simulate runoff well in the catchment surface (Fig 7). At the outlet, the discharge is calculated based on the cellular automata and compared with the observed discharge. The results of the cellular automata model are shown with three different time steps (Fig 8). So far, various mathematical models for rainfall-runoff estimation have been proposed. In integrated models, the whole catchment is considered as a unit. These models have a simple structure and appropriate computation time, but are accompanied by many assumptions and the spatial distribution of variables is not considered. Therefore, integrated models are not suitable for large catchments. In semi-distributed models, the catchment is divided into a number of sub-catchments. In these models, important features of the catchment are shown, but for each sub-basin, moderate data is considered and the exact spatial distribution of data is not considered. In distribution models, spatial distribution data is considered, but the time required for computation and modeling is high. Therefore, it seems necessary to develop methods that have a simple structure and high accuracy at the same time. Due to the accuracy of the results and the ability to access the required information anywhere in the catchment, the cellular automata model can be used to predict runoff.Conclusion: The results showed that the cellular automata model has a high accuracy compared to the Akan analytical solution. Also, in simulating the runoff of the con catchment, the runoff network at the catchment surface was well simulated. Comparing the computational discharge results from the cellular automata model and observational data, the values of the correlation coefficient, mean the square root of error and Nash-Sutcliffe coefficient were 0.99, 0.11 and 0.97. As the result, due to the accuracy of the results and the ease of implementation, the cellular automation model can be used to predict runoff in catchment without data and reliable results can be achieved.Modelling of air entrainment in dropshafts
http://jhyd.iha.ir/article_149546.html
Introduction The vertical shaft is one of the most important hydraulic structures that is often used in urban drainage systems. The function of the vertical shaft is to transfer water from an arbitrary level to lower levels.The issue of air entering the vertical shaft is very important. The transfer of a significant amount of air into the pressurized tubes can lead to the formation of high-pressure air masses, which gradually grow and may burst into the tubes as they enlarge. (falvey, 1980) which causes damage to the shaft and the pipes that connected to it and also reduces the shaft permeability, which is also undesirable.Due to the lack of attention to the hydraulics of the vertical shaft and the consequences of its incorrect construction, the study on the amount of inlet air seems necessary. In this study, measuring the amount of inlet air at the intensity of different flows is desired. Finding the minimum amount of incoming air can help to better design the projectile shaft. By comparing the behavior of the projectile shaft in different states, the correction efficiency of the shaft can be obtained.Methodology The model is adapted from a laboratory study conducted at the University of Alberta.The vertical shaft under study has a height of 7.72 meters and a diameter of 0.38 meters. The diameter of the inlet pipe of the shaft is half the diameter of its main body (0.19 m) and the diameter of the outlet pipe and its length are equal to 0.38 m and 1.5 m, respectively, and the flow of outlet water is discharged into the open air. the upper part of the shaft is blocked and the ambient air is allowed to enter the shaft only with a circular tube with a diameter of 0.10 m located at 0.20 m above the shaft. An air shaft with a diameter of 0.15 m is located at 0.5 m from the shaft outlet for air circulation, which is connected to the upper part of the shaft.The software used in this research is open foam.In this networking, a total of 121947 elements are used. The KOmegaSST turbulence model is used to solve the current turbulence term. Boundary conditions are defined for velocity (u), pressure (p), fluid type index (&alpha;) and turbulence (k, omega, nut) parameters. The initial value of velocity and pressure was assumed to be zero. To consider the initial value of the fluid type index, the number zero is entered so that this shaft is empty of water at first.Results and Discussion as the speed increases, the pressure decreases sharply, causing the pressure inside the shaft to become negative and air to be drawn in from the outside into the shaft.The more intense the water inlet flow, the more air enters the shaft from the surrounding environment. As the dimensionless flow of water inflow increases, the relative demand decreases by 85%.As the inlet current increases, the amount of return air through the air shaft into the vertical shaft increases. As the inlet current intensifies at low current intensities, the amount of air supplied by the air shaft increases, but in higher current intensities this value is almost constant. As the amount of air circulated by this shaft increases, the pressure gradient between this point and the upper part of the shaft is expected to increase. As the water inlet velocity increases, it can be seen that as the inlet flow rate increases more, both the amount of air supplied by the air shaft and the amount of inlet air from outside the shaft do not change significantly, which can create a semi-closed area. At the top of the shaft to allow air to flow and move down.The pressure inside the shaft increases from the bottom to the top and the highest pressure gradient is seen in the middle points, which are called the rainfall area. There is not much difference in the intensity of low inlet currents between the performance of the two types of shafts, but as the amount of inlet water to the shaft increases, the effect of the air shaft on reducing the amount of inlet air becomes apparent. the pressures inside the shaft are almost equal at low current intensities and are spaced apart at high current intensities.Conclusion The amount of inlet air increases with increasing intensity of water inlet flow. By increasing the intensity the amount of air demand decreases.the air shaft performs better at higher current intensities. There is not much difference in the intensity of low inlet currents between the performance of the two types of shafts, but as the amount of inlet water to the shaft increases, the effect of the air shaft on reducing the amount of inlet air becomes apparent. Also, the value of the pressure in the modified shaft is clearly reduced.The experimental study of the effect of splitter on the flow discharge Piano key weir
http://jhyd.iha.ir/article_149727.html
AbstractIntroduction: Introduction: The newest type of nonlinear labyrinth weirs are piano key weirs. The initial study on this weir indicated that it increases the discharge significantly and has a simple and economical structure. In the past years, different researches are done to check effective factors on flow discharge and optimization of this weir. But to a limited extent is referenced about ventilation mechanism and aeration of this weir at outlet and the only solution that has been presented for aeration at outlet is gallery aeration at downstream. Another problem that is discussed in the case of piano key weirs and generally over flow of weirs is Nappe oscillation after the cross of weirs crest. Past research considered the use of splitter to be effective in reducing the nappe oscillation in linear weir. By getting ideas from this method (use of splitter), three piers with different geometries (circular, square, and rectangular) has been used in piano key weir to reduce nappe oscillation.Methodology: All experiments of this research were performed in a rectangular channel with a width of 75 cm, metal floor, unbreakable glass walls and a height of 80 cm in the hydraulic laboratory of the Department of Water Engineering and Hydraulic Structures, Tarbiat Modares University, Tehran The water flow from the underground tank is entered to the flow calming tank by two pumps with a maximum discharge of 85 liters each per second, and it reaches to weirs after passing through the calming plates, and falls into the underground tank by passing over weir at the end of the flume. This cycle continues during various tests under different hydraulic conditions.The discharge was measured by ultrasonic flowmeter with an accuracy of 0.01 liters per second, after the pumping and before entering to the calming tank. All experiments were performed under free flow conditions. Upstream flow deep was measured by a point gauge with an accuracy of &plusmn;1 mm. This depth gauge is moved by rails on the wall of the channel and the water depth is measured at desired points.The piano key weir used in this research is of three types of A piano key weir with different rectangular, triangular and trapezoidal designs in the plan. splitter with three circular, square and rectangular cross-section geometries were installed on the weir crown and in the downstream corners of the weir keys.Results and discussion: The results showed that splitter, in addition to separating the flow after the splitter and creating a space for the connection of free surface air with the lower part of the outflow from the weir, also reduces the nappe oscillation intensity of passing through it. The use of splitter does not have a negative effect on the flow discharge in the rectangular and trapezoidal piano key weir and only in the triangular piano key weir, it has reduced the discharge by 3%.The performance of square and rectangular splitter was similar on water discharge and separation. The effect of flow separation in a rectangular splitter is evaluated better than on a square base. Also, the effect of these two splitter on the current separation is more appropriate than a circular splitter. Regarding the comparison of the discharge coefficient of these three types of weir, it was observed that at H_t/P&lt;0.2, the discharge coefficient in the rectangular and trapezoidal piano key weir is higher than the triangular piano key weir, which is due to more flow suction (due to vacuum created below the weir inlet key) in this head for these two weirs. By increasing H_t/P up to 0.4, the difference between the discharge coefficient of the rectangular and trapezoidal piano key weir relative to the triangle gradually decreases to the point that after H_t/P&gt;0.4, the discharge coefficient of the triangular piano key weir relative to the trapezoidal and rectangular piano key weir has increased, which ventilation performance of this weir type is one of the main reasons for that.Conclusion: Regarding the increasing use of piano key weir due to its advantages and the need for aeration in the downstream to improve its performance, this study aims to provide an economic solution (using splitter instead of aeration gallery) to improve ventilation performance in the downstream of the piano key weir. Therefor it has studied the effect of splitter with different circular, square and rectangular sections on the flow discharge of this weir type with three rectangular, triangular and trapezoidal designs in the plan. In general, the results obtained in this study can be summarized as follows: In the total head less than 0.08 m, the rectangular piano key weir in constant discharge, about 5 and 15%, has a smaller head than the trapezoidal and triangular piano key weir. But at a total head greater than 0.08 m, a trapezoidal piano key weir at a constant discharge, has a smaller head than a rectangular piano key weir about 5% and on average about 8% than a triangular piano key weir. Splitter show the best flow separation performance in the case of H_t/P&lt;0.6, but in the case of H_t/P&gt;0.6 this performance is affected by high water flow, so that with increasing discharge, the correlation the bottom of flow is reduced with open air and it is not possible to ensure relative to the complete correlation of the open air with the downstream and the outlet of the piano key weir. In terms of the splitter geometric shape, square and rectangular splitter showed similar performance in flow discharge and separation. But the separation of the current at the rectangular splitter is evaluated better than the square splitter. Also, the geometry of these two splitters is more suitable for flow separation than circular geometry.Experimental study of the effect of sidewall slope over the triangular PK weir
http://jhyd.iha.ir/article_150872.html
One of the critical consequences of climate change is prolonged droughts with floods. In these conditions, maintaining the maximum possible water level without wasting it and high discharge capacity in critical situations is essential to preserving the reservoir's health. The most suitable solution for sending excess water can be considered as creating a proper spillway. According to ICOLD, one-third of dam failures are due to weir disproportion. Unfortunately, due to the designers' lack of experience in using the nonlinear spillway, irreparable accidents sometimes happen. Therefore, choosing the proper spillway with the appropriate discharge have undeniable importance. This paper focuses on a new solution to improve the piano key weir capacity. By correcting the sidewalls of weirs, three goals were pursued simultaneously. In the first step, better performance than conventional PK weirs on the occasion of a flood. The second goal is to store the maximum water level upstream in non-critical situations and use only part of the weir.The ultimate goal is to make this method economical. This research is a continuation of previous research on PK weirs. Figure 4 shows the rotating flume environment, which experiments were performed in that laboratory at the Tarbiat Modares University of Tehran (Dimensions: 10 meters long, 2 meters wide, and 0.9 meters high)( Figure 4). Experiments have been performed on a triangular weir with a zero slope (i.e., Tri-Base model) (Fig. 1 and 2) and 10 degrees in the flow direction (Fig. 1 and 3). In this article, Pk weir with horizontal and sloped crest is called Tri-Base and Tri-B1 models. The weir characters used in the laboratory are provided in Table1. Eq (4) and (5). The dimensional analysis of the (Tri-B1) model, and the (Tri-Base) model, respectively. In the analysis of laboratory data, an effective length (wet length of walls) was defined for the weir. Then for this geometry, Eq. (6) and (7) were provided to calculate the discharge coefficient, which in addition to the new weir, is used in typical weir (i.e., The Tri-Base model) can also be used with great precision. Fig.10 shows the comparison of measured and calculated values of triangular pk weir.For the Head-Discharge curves, firstly, the discharge-head curves for triangle Pk weir with horizontal crest (Fig. 7) have been plotted and compared with the present study and other researchers' results. The differences between results are because of the differences in geometric characteristics shown in Table 2. Because the head and weir height changes for every discharge, Fig. 6 and have been plotted curves of (Q-P+Ht). Based on these figures, water height in triangle PK weir with a sloped crest (i.e., The Tri-B1 model) is higher than triangle pk weir with a horizontal crest (i.e., The Tri-Base model), but head height over the (Tri-B1) model is less than the (Tri_Base) model. On the other hand, for the (The Tri-Base) model, discharge coefficients have been plotted in Figure 8.This figure also compared the results of other researchers the results with this study. Fig. 9 also shows the discharge coefficient for the (Tri-B1) model. The discharge coefficient in the (Tri-B1) model has increased by an average of 3.8% than the (Tri-Base) model, with the maximum and average discharge coefficients shown in Table 3.Also, about the flowing blade, in the weir of a triangular Piano key weir with a horizontal crest, at 8 Cm 〖&gt;H〗_t &gt; 4 Cm, air penetrates under the blades of the flow, and the flow is vented. At higher values (12 Cm 〖&gt;H〗_t &gt; 8 Cm), the flow under the blade is connected to the open-air with increasing water head. In this case, have been seen fluctuations in the current blade. At higher values ( H_t&gt;12 Cm), the flow completely covers the weir (immersion) and passes over the weir. In these conditions, the fluctuations of the flowing blade can be observed. According to Fig. 5 in Q=40lit/sec have seen an Air cavity on the weir body. Also, in analyze were seen, the weir of a piano key weir with a sloping crest (i.e., The Tri-B1 model) increased. But with the sinking whole of the weir, the discharge coefficient rate decreases. Also, in connection with the weir blade of the Pk weir with a sloped crest (The Tri-B1 model) in some discharges, all three types of flow blades can be seen on the sidewalls of the weir (i.e., sticky, compressed, and free baled. In conclusion, in Pk weir with slope crest, have been seen the level of water behind the weir increases while the head of water on the weir decrease. So this means that in drought seasons and when the level of water decreases in the reservoir, this spillway can increase the water level. Use this weir's high capacity in the critical season (especially during flood time). On the other hand, this spillway has a high capacity in all situation and increase the discharge coefficient.Analysis of Water Surface Profiles in Coarse-Grained Porous Media with Radial Flow Using the Gradually Varied Flow Theory
http://jhyd.iha.ir/article_151038.html
IntroductionNon-darcy flows into two categories: parallel flows (such as gravel dams, gabions, etc.) and radial flows (such as flows near wells drilled in coarse-grained alluvial beds, etc.) are divided. In the first category, streamlines are almost parallel so that there is no curvature or contraction of streamlines in the plan view. This type of flow is found in both pressurized and free-surface modes. Radial non-darcy flow analysis has many applications in the fields of civil engineering, geology, oil, and gas. The equations governing the radial non-darcy flow are solved using numerical methods of finite differences, finite elements and finite volumes. Solving these equations requires boundary conditions and a lot of data and is almost bulky, time consuming and costly. While, gradually varied flow theory, requires much less data and is easier and less expensive. For this reason, in the present study, for the first time, using experimental data recorded in a large-scale (almost real) device, the application of the gradually varied flow theory in radial non-darcy flows with free surface has been investigated. In other words, since the calculation of water surface profiles in a radial rockfill is of great importance. In the present study, using large-scale (almost real) experimental data and the gradually varied flow theory, the water surface profile in radial non-darcy flow with free surface and in steady state has been investigated.MethodologyIn the present study, due to the compatibility of cylindrical coordinates and its adaptation to the physics of problems related to radial flows, a device has been constructed in the laboratory of Bu Ali Sina University in the form of a semi-cylinder with a diameter of 6 meters and a height of 3 meters. The dimensions of this device are made on a large scale and the effects limitations have practically no effect on the testing process. To measure piezometric pressure, piezometric grids have been used. The device has a volume of 14,000 liters and a capacity of materials weighing approximately 40 tons. Four pumps are installed in parallel at the top of the device to generate the required flow. Coarse-grained river materials with a diameter between 2 to 10 cm, a porosity of 40%, a Cu of 2.13, and a Cc of 1.016 have been used. To perform the tests, the model is first filled to a certain height (53, 60, 70, 85, 95, 110, 120, 140, 150, and 160 cm) by pumping operations. The flow rate created in these experiments is in the range of 49.94 to 53.16 L/s.Results and DiscussionOne-dimensional analysis of steady-non-darcy flow using gradually varied flow theory and two-dimensional analysis using Parkin equation solution. Most research has been done in parallel flow rockfills. Also, solving the Parkin equation in both parallel and radial flows requires a lot of data such as boundary conditions upstream and downstream, as well as the boundary condition of the water surface profile, and the calculation process is complex and time-consuming. The gradually varied flow theory requires much less data than solving the Parkin equation, and the water surface profile obtained from it is also used as the main boundary condition in solving the Parkin equation. In other words, calculating the water surface profile in a radial rockfill is very important to studying the movement of water. Also, the water surface profile is the main boundary condition in the two-dimensional analysis of steady flow (solving the Parkin equation), and with it, upstream and downstream boundary conditions will be practically available. For this reason, in the present study, using large-scale (almost real) experimental data and the gradually varied flow theory, the water surface profile in the case of radial non-darcy flow has been calculated. To calculate the flow depth at different points (water surface profile) using the gradually varied flow theory, the amount of flow depth at one point and the coefficients m and n must be available. Since the flow depth measurement in the well (downstream of the desired interval) can be measured, in the present study, the calculations started from the downstream (depth of flow in the well).ConclusionIf the gradually varied flow theory is used to calculate the water surface profile in the case of radial non-darcy flow with a free surface, the mean relative error in the case of pumped heights is 53, 60, 70, 85, 95, 110, 120, 140, 150 and 160 cm are equal to 1.56, 0.96, 0.61, 0.45, 0.28, 0.19, 0.13, 0.16, 0.11 and 0.05 are calculated, respectively. In other words, the average mean relative error (MRE) of calculating the water surface profile for different heights of pumped water is equal to 0.45%. Also, according to the obtained results, the greater the depth of water pumped upstream, the higher accuracy of the gradually varied flow theory.KeywordsRadial Non-Darcy Flow, Steady Flow, One-Dimensional Analysis, Gradually Varied Flow Theory.The Effect of Anti-Vortex Plates on Vortex Dissipation, Discharge Coefficient and Inlet Loss Coefficient in Hydropower Intakes
http://jhyd.iha.ir/article_151039.html
Introduction The formation of vortices at the intake and the air entertainment into the intake duct is an important hydraulic phenomenon that usually occurs in the dam intakes and causes such problems as energy loss and reduction of intake discharge coefficient. Among different types of intakes exposed to the vortex phenomenon are hydropower intakes used to supply water to turbines and generate electricity. These intakes are mainly horizontal. To prevent the formation of strong surface vortices, their strength must be physically controlled. A practical solution for this is to use anti-vortex structures. These structures mainly eliminate the vortex by reducing the flow velocity near the intake, lengthening the flow path between the free water surface and the mouth of the intake, as well as energy dissipation. Some studies on the structural methods of vortex dissipation have been done by Amiri et all (2011), Tahershamsi et all (2012), Monshizadeh et all (2018), Taghvaei et all (2012). In this study, the effect of horizontal perforated plates on the dissipation of the strong vortices, the intake discharge coefficient and inlet loss coefficient of the intake is studied, so far no special studies have been done in this area. MethodologyIn the present study, a physical model was used to investigate the performance of horizontal perforated plates. This model was designed to produce the strongest type of vortex with air core and different strengths. The main components of the experimental setup are: reservoir, intake duct, pump and electromotor speed controller device. The dimensions of reservoir is 1.3 m in wide, 3.5 m long and 2 m high. The mouth of intake extends 20 cm into the reservoir and is positioned so that the side walls and the bottom of the reservoir do not affect the flow conditions. The length of the intake pipe is 4.5 m and its diameter is 16 cm. At a distance of 2 m upstream of the intake in the reservoir, some blades are installed vertically that by changing their angle relative to the intake axis, the angle of inflow to the intake can be changed. This makes it possible to strengthen the upstream vorticity to reach stronger vortices. For modeling the perforated anti-vortex plates, some plastic mesh with different openings and different thicknesses were used. For each plate, the corresponding mesh was placed in a metal coil and this coil is screwed to the reservoir wall so that the perforated plate be placed on the mouth of the intake. By creating 36 types of strong vortices, the performance of 10 types of perforated plates with different dimensions, thicknesses and openings was tested.Results and DiscussionCalibration tests showed that in the range of 1.5D to 2D (D is the diameter of the intake pipe) for submergence depth, flow discharges of 15 to 30 lit/s and blade angles of 0 to 20 degrees, the stable strong vortices are formed. A total of 36 strong vortices (three relative submergence depths, four flow discharges and three blade angles) were formed with different strengths in the model. In order to consider the appropriate confidence limit in this study, the performance of each of the anti-vortex plates in the model was considered so that it is able to dissipate vortex type-six or decrease to type-two vortices. Therefore, the conditions in which the strength of a type-six vortex was reduced by the relevant anti-vortex plate to a type-three (or higher) vortex are known as critical conditions. It should be noted that the type of vortex is determined based on its appearance. Finally with 360 tests it was concluded that the effect of opening of the plates to eliminate the vortex strength is more than the dimensions and the thickness of the plates. In addition, the effect of using perforated horizontal plates on discharge coefficient and inlet loss coefficient of the intake was investigated. It was concluded that the use of perforated anti-vortex plate with openings of 70%, 58% and 50% reduces the intake discharge coefficient by 5.9%, 10.5%, and 13.4%, respectively. It is also caused 12.9%, 24.7% and 33.5% for inlet loss coefficient of the intake, respectively.ConclusionThe effect of submergence depth on the vortex strength is greater than the flow discharge and it is also greater than the geometric asymmetry. Dimensions of the plate have little effect on the vortex dissipation. The thickness of the plates has little effect on the vortex strength. The opening rate of the plates has a great effect on the vortex and a plate with 50% opening, was able to dissipate all strong vortices. The vortex strength has a direct relationship with the inflow angle and the flow discharge and is inversely proportional to the submergence depth. As the flow discharge increases, the discharge coefficient decreases and the inlet loss coefficient increases.An experimental study on the process of mixing and dilution for the discharge of dense effluent
http://jhyd.iha.ir/article_151091.html
Introduction: In recent years, scarcity of freshwater resources and the increasing water demands due to population growth and industrialization, have turned the issue of supplying drinking water into a global subject. Therefore, exploiting unconventional water resources, such as saline and brackish water using emerging technologies for desalination, has emerged as a promising solution in coastal areas. Desalination through Reverse Osmosis (RO) technology besides freshwater produces brine effluent as a byproduct, which has more salinity and density than the feeding water. Improper disposal of this effluent into coastal bodies will have serious environmental impacts on the receiving environment and can severely affect the aquatic ecosystem. To prevent the negative impacts, the effluent is discharged through submerged nozzles diagonally, with a high initial velocity and momentum, at a distance far enough from the shore. Using this method, the outflow is mixed with the seawater due to disturbances and the concentration is reduced down to the tolerance of the marine environment. In this study, the results of an experimental study were reported in the stationary environment to investigated the time evaluation of the discharge, and the process of mixing and dispersion for 60o inclined dense discharge.Methodology: The planar laser-induced fluorescence technique (PLIF) has been used to capture the flow central plane in this study. The system consisted of two swift scanning mirrors to provide a flat laser sheet across the centerline of the flow. The laser sheet was formed by the oscillation of a 100 milliwatts green Diode-pump solid-state laser (DPSSL) beam with 0.5mm width. With an infinitesimal quantity of a fluorescent dye (Rhodamine 6G), the discharged effluent would be fluoresced under the laser. The reflected light is captured by a CCD camera (Mars 640-300G 1/4"@4.8um) in the grayscale form at the rate of 100 frames per second. The procedures were controlled by a computer server equipped with an I/O board and controlling software and the images were continuously downloaded to the hard disk of the server for later processes. The captured images were then modified and calibrated for laser attenuation and sensor response for each pixel using clear and dyed water of known concentration. Using this technique, the system can illuminate the instantaneous behavior of the flow and the production, development, and dissipation of turbulent eddies along the flow. By capturing the flow instance behavior, the formation of turbulent eddies and their impacts on turbulent diffusion and flow mixing and entrainment have been investigated. Also, concentration fluctuations at the centerline, the effects of Kelvin-Helmholtz instability, and shear entrainment on the flow mixing process were discussed.Results and Discussion: By illuminating the flow behavior, the development of flow regime in jet and plume-like region and the formation of instabilities, and the dissipation of eddies were studied&lrm;. For this purpose, the instantaneous images of the flow evolution for different times were extracted and depicted using a non-dimensional parameter developed specifically for this purpose. The different processes of flow mixing and dilution along the jet and plume &lrm;regions were analyzed by describing the physics of eddies formation and dissipation long the inertial subrange. The formation of flow packets out of the main path is affected by the intensity of &lrm;velocity fluctuations. The vortices take their energy from the averaged velocity and transfer it from the biggest formed scale i.e. integral scale to the smallest vortices i.e. Kolmogorov's viscous subrange in a cascade of energy. The Energy Cascade is basically an energy spectrum that characterizes the turbulent kinetic energy distribution as a function of length scale. The scales of turbulent structures are directly a function of velocity fluctuation in each region and direct the process of the entrainment that led to the increases of dilution from the nozzle tip to the seafloor. These days, numerical simulations are becoming a common way for modeling the brine discharge in the marine environment. It is time-consuming and needs high expertise. The models are usually unsteady and after full development, the flow time-averaged image of the last 45 to 60 seconds is used for identifying the flow geometrical and mixing behavior. Using these experiments, it observed that the non-dimensional time required to flow fully developed and reach the impact point is about T*=5.7. Knowing that will help engineers find the optimal duration of time needed for the simulation and modeling. Conclusion: It is known through the basics of physics that the maximum range for projectile motion happens when it is launched at an angle of 45 degrees. However, the previous experiments exhibited that the maximum dilution at the impact point occurs at the nozzle with 60o inclinations where the flow path is the longest. It was carefully examined by explaining the complex action of turbulence on flow mixing and dilution. The formation of eddies initially begins due to Kelvin-Helmholtz instability and it leads to velocity fluctuations with different time and length scales in the body of flow. The result is concentration dispersion with different magnitude along the flow path in inclined dense discharges.Numerical Investigation of Straight Longitudinal Training Walls on the River Bank Protection
http://jhyd.iha.ir/article_151383.html
Introduction: River training is the stabilization of the channel in order to maintain the desired cross-section and alignment. Channel stabilization and restoration efforts have been increased dramatically with excessive cost since 1990. However, it is estimated that at least 50% of these projects fail and others may not perform as expected. Therefore, stream restoration today is more of an art than a science. Rivers have been trained for centuries by series of transverse groynes which are structures constructed at an angle to the flow in order to deflect the flowing water away from critical zones. This generally results in damages to their ecosystems as well as in undesirable long-term morphological developments. To maintain a navigable channel and improve flow conveyance by dividing the channel into main and side channels, engineers have recently proposed constructing longitudinal training walls as an alternative to the traditional transverse groynes. The effectiveness of longitudinal training walls in achieving these goals and their long-term effects on the river morphology have not been thoroughly investigated yet. In particular, studies that assess the bed and wall shear stresses of the parallel channels separated by the training walls are still lacking.Methodology: In the present study, the performance of longitudinal training walls on bed and wall shear stresses was compared with the traditional transverse groynes. Three-dimensional Reynolds-averaged Navier-Stokes equations with the k-ɛ turbulence model were solved numerically by applying finite volume method using Flow-3D software. Results of the single groyne simulation were validated based on experimental data with a good agreement. The experimental channel had rectangular cross-section of width B=0.9144m and slope S0=10&minus;4, groyne was a parallelepiped of length b=B/6=0.1524m and thickness of 3 mm. In addition, results of the series of groynes simulation were compared to the available numerical data, shown a good agreement. After validation, continuous longitudinal training walls were simulated with equivalent length to a series of groynes with uniform and non-uniform configuration in three transverse positions y/B=1/2, y/B=1/3 and y/B=1/6. Uniform configuration of groynes was included three groynes with D/b=6 and 23 spacing and non-uniform configuration was included nine groynes, first five groynes with D/b=1.5 and four other groynes with D/b=6 spacing. Also, non-continuous longitudinal training walls were simulated with the same transverse positions for D/b=23. The hydrodynamic behavior of the bed and wall shear stresses was investigated, since the starting point of longitudinal training walls affects the morphodynamic behavior of the flow, the starting position of the walls was fixed and only different transverse positions with different lengths were simulated. Results and Discussion: Here we analyze the bed and wall shear stresses in open channel flow by training channel in a new way by subdividing their channel in parallel channels with specific functions with longitudinal training walls. The results showed that the longitudinal training walls system reduces the bed shear stress compared to the groyne system and as a result we will have less erosion in the bed. However, some small increases in wall shear stresses were seen in all simulations of longitudinal training walls. The closer the transverse position of the longitudinal training walls to the channel wall, the lower wall shear stresses. Furthermore, if the longitudinal training wall system is implemented in non-continuous form, due to the drop in flow energy at the beginning and end of each wall, the flow energy drop leads to a decrease in velocity and due to the direct relationship between velocity changes and shear stress, bed and wall shear stresses in side channel can be reduced further, that this reduction depends on the transverse position and, more importantly, whether or not this transverse position has created a mild flow conditions in the side channel. Therefore, this system by providing a mild flow conditions in the side channel which is shallower channel, has a favorable effect on aquatic habitat, ecosystem, and wall shear stress. Besides, by providing a deep navigable main channel, can increase the ability of transferring additional flood discharge. Conclusion: In this study, twelve simulations were performed with different lengths for longitudinal training walls in different transverse positions with continuous and non-continuous forms. The results showed that this system, compared to the traditional groyne system, introduces less bed shear stress and by providing a mild flow conditions in the side channel, has the ability to control the wall shear stress dynamically. This system has a favorable effect on aquatic habitat and ecosystem, beside high ability to transfer additional flood discharge. So, longitudinal training walls can be used as an appropriate replacement for traditional transverse groynes.Identification of transition flow zone in rectangular side orifice, experimental study
http://jhyd.iha.ir/article_153274.html
Introduction Side sluice gates, side weirs and side orifices are commonly used flow diversion structures provided in the side of a channel to spill or divert water from the main channel. They are widely used in irrigation engineering, wastewater treatment plants, flocculation basins, sedimentation tanks, aeration basins, etc. Flow through a side orifice is similar to the flow through side weirs and side sluice gates. When water level is lower than upper limb of a slot, the slot behaves as side weir. When water level in the main channel is above the upper limb of the slot, the flow behaves like an orifice. For orifice spillway Hussain et al., 2014 reported orifice flow condition required head over the crest 1.5-1.7 times the height of the orifice opening. In the literature no study was found about the transition flow condition requirement of side orifice. In this paper, an experimental study has been carried out related to transition flow zone of side orifice which have not been taken up earlier.Methodology In this study, first, the variables affecting the transition flow zone are listed and then, non-dimensional parameters extracted using dimensional analysis. The experiment was carried out in a rectangular channel of 8 m length, 0.8 m width and 0.6 m depth at the Hydraulic and water structure Laboratory of department of water engineering, Shahid Bahonar university of Kerman. The channel was fitted with a sluice gate at the end of the channel to regulate the depth of flow, and a rectangular side orifice in the right side of the channel. Experiments were performed for four size of side orifice length (L) equal to 0.15, 0.2, 0.25 and 0.3 m and width (b) 0.05, 0.1 and 0.15 m. The channel consists of a smooth horizontal well painted steel bed with a vertical glass sidewall. The collection channel is 1.2 m wide and 2 m deep, and situated parallel to the main channel. Each size of orifice installed in two different height equal to 0.09 and 0.14 m above of channel bed. For each experiment used nine flow in main channel with different Fr number in such a way that water level changes from lower to upper than limb of side orifice. For each run, the output discharge of side orifice, water surface profile along main channel were measured. The non-dimensional stage discharge of side orifice calculated and for each run output discharge from orifice calculated by Hussain et al.,(2011) and Embroiled et al., (2009) equations for side orifice and side wire respectively. To evaluate the accuracy of the equations, the average percent error (APE) were used.Results and Discussion The non-dimensional stage-discharge curve and water surface profile along the main channel are plotted in order to estimate the transition flow zone in side orifice. The results of non-dimensional stage-discharge curves (figs 3-6) reveals that the length to width ratio of orifice b/L is, indeed, the predominant parameters which affect the transition zone. For values b/L smaller than 0.2 the transition zone not clearly detected. The results show that the distance of lower limb of orifice to the bottom of channel, W, is other effective parameter in forming of transition zone. When the lower limb of orifice is closer to the channel bottom the ratio b/L becomes insignificant parameter. Based on water surface levels along the channel and the side orifice, figures 7 and 8, for values b/L smaller than 0.2 the transition zone happen only in very small area below upper limb of a side orifice, but for b/L greater than 0.2 the transition zone occurs above and below of the upper limb of a side orifice. The calculated and observed output discharge in different situations were used to check the accuracy of discharge equations of side weir and side orifice when the transition flow occurred. The results (figure 9) shows that in transition zone the accuracy of exiting side and orifice discharge equations is well. Conclusion The present study provides an experimental examination of the transition flow of a rectangular, sharp crested side orifice. As a result of dimensional analysis, the results indicate that the dimensionless parameter b/ L is the predominant parameters which affect the transition zone. The transition flow zone occurred when the b/L is greater than 0.2, but in these situations transition flow zone depends mainly on the distance of lower limp of side orifice to the bottom of channel. The average percentage error of exiting discharge equations showed that these equation can be used to estimate the discharge of side orifice in transition flow zone.Numerical modeling of the cavitation phenomenon in components Glory spillway
http://jhyd.iha.ir/article_153481.html
IntroductionThe morning glory shaft is a type of spiral inlet which including of three main components: an inlet morning glory spillway, a vertical shaft, and an outlet tunnel. The Glory spillways are one of the major hydraulic structures in dams, which are appropriately designed to pass the flow properly and effectively. Therefore, for correct and optimal designing, various conditions should be examined to avoid negative pressures at the spillway crest and other parts of the glory spillways which may cause instability in the spillway structure and damage to the concrete surface of the spillway due to cavitation. This study has been inspired by the physical model of Torogh dam spillway located on the Torogh River at the city of Mashhad, Iran. The glory spillway of Torogh dam was chosen in order to the numerical model. To simulate the flow discharge on the glory spillway, three flow discharges with various return period were employed.MethodologyComputational ﬂuid dynamic (CFD) is a technique for modeling ﬂow characteristics on hydraulic structures (Fluent User Manual, 1995). Ansys Fluent (v.19.0) computational package was used to carry out numerical simulations that solve the three - dimensional equation for both laminar and turbulence flow. Several turbulent models are presented in Fluent such as Standard k-&epsilon;, k-&epsilon; renormalization group (RNG), Realizable k-&epsilon; and shear stress transport k-&omega; which solve two additional transport equations to determine the flow turbulent kinetic energy (k) and its dissipation rate (&epsilon;). Therefore, three mesh blocks were used in the numerical model using the finite volume method and the turbulence model (RNG). To this purpose, to measure the flow velocity, static and dynamic pressure and volume fraction, the physical model of glory spillway Torogh dam depicted into the Ansys Fluent model. Results and DiscussionTo investigate the cavitation index in the glory spillway of Torogh dam, hydraulic parameters including static and dynamic pressure, flow velocity and volume fraction of water calculated in Ansys Fluent model. The results of numerical models were presented as velocity, static pressure, dynamic pressure, cavitation number and water - Air volume fraction. The result of velocity on the three blocks shows that by increasing flow over the structure, the velocity in the pipe bend was marginally rose. in the external arch of the pipe bend reaches less velocity. The maximum velocity enhances the values of much than 3.4 m/s; however, the external pipe bend attains less value than 1.5 m/s. Due to the discharge with 1000 years return period, the static pressure values are positive along the glory spillway. By increasing the discharge, some points near the internal arch of the pipe bend were faced by negative pressure. however, the static pressure reaches positive values near the external pipe bend. By increasing the flow discharge to the maximum value, the intensity of negative and positive pressure along the internal and external arch of the pipe bend was increased. The values of the dynamic pressure are increased by increasing the velocity. The dynamic pressure into the block No 2 and 3 show that by increasing flow discharge, In the internal arch of pipe bend, the dynamic pressure reaches the maximum that it seems the cause of maximum velocity occurred in this position. In block 1, with increasing flow discharge the cavities number increases so that in the wire left side the cavitation number is greater than on the wire right side. Also, with increasing flow discharge, cavitation damage for submerged and partially- submerged becomes serious. In block 2, for all flow mods, the cavitation risk is less than 0.17 and level damage is the major damage, and also with increasing flow discharge, the cavitation number on the left side of the spillway is more than the right side of the spillway.Also in block 3, with increasing flow discharge, the cavitation number increases. For all discharges on the left and right of the spillway for &sigma;&lt;0.17 occur major damage. In order to show the air and water regions, the water fraction contour plots were extracted from numerical information. By filling the spillway cross-section due to PMP flow near the spillway inlet, the water fraction is formed 0.65 which it indicates the cavitation phenomenon has caused air mixing in this section. Meanwhile, the air mixture has been not seen in the discharges with 1000 and 10000 return period times. It indicates that by increasing the flow discharge on the glory spillways, the flow separation is predicted near the spillway crest.ConclusionThe present study has employed the Ansys Fluent model to investigate the hydrodynamic characteristics of the glory spillway. The flow simulation was done on Torogh glory spillway by considering three different discharges with 1000, 10000, and PMP return period time. In order to calculate the cavitation number and finding the cavitation positions, the glory spillway was divided into three blocks. Finally, the cavitation number was calculated on these blocks to realize the points and positions with a high risk of the cavitation.The results of this study were presented as follow:1- A comparison between the velocity contour plots and cavitation number illustrates that the most important factor to create the flow regions with a high risk of cavitation is the velocity and flow deviation through the pipe bend. 2- Investigating of the static pressure over the glory spillway shows that the risk of cavitation at the internal arch of the pipeline is higher than the external arch. However, the positive pressure results from flow deviation along the external arch significantly prevent the cavitation.3- By increasing the flow discharge, the result of water-air volume fraction shows that the region with lower pressure and air mixing was developed at the crest of glory spillway. It can be clarified that in the free flow condition the pipe bend position was a threat by cavitation phenomena. Additionally, the spillway crest was a threat by cavitation at the submerged condition.Investigation of the effect of treated wastewater injection on the permeability of unsaturated and saturated porous media in the aquifer storage and recovery system
http://jhyd.iha.ir/article_154000.html
Extended Abstract:Introduction: The permeability of porous media due to clogging of pores is one of the problems of aquifer storage and recovery (ASR) systems. The more pore clogging occurs when treated wastewater is used as water resources for ASR In addition to physical clogging, the biological clogging also plays an important role in reducing the permeability and hydraulic conductivity of the porous media. In most of previous studies, the infiltration and clogging of the unsaturated zone have been evaluated by measuring the input-output flow from the soil columns. In this study, the permeability and hydraulic conductivity variations due to the passage of treated wastewater through the unsaturated and saturated zone have been evaluated simultaneously. Methodology: The main goal of this study is the investigation of permeability and clogging variations in unsaturated-saturated zones in the aquifer storage and recovery system using the treated wastewater. For this study, an experimental model was designed with 2.5 m vertical height (unsaturated layer) and 12.5 m horizontal length (saturated layer). It was made with a PVC pipe with a diameter of 200 mm.Results and discussion: The input-output flow rates had been measured for a period of 70 days. The reduction of inlet and outlet flow is due to physical and biological clogging of soil pores. The physical clogging usually occurs earlier and in the early parts of the model and then there is a gradual decrease of infiltration velocity and hydraulic conductivity. The rate of increase of biological clogging is slower than physical and with the growth of bacteria, its amount increases to a constant rate. Then, as the bacterial population decreases, the flow rate in the porous media increases and results in a temporary increase in permeability and outlet flow rate. The bacterial growth cycle in a closed environment consists of four stages. This growth pattern corresponds to the fluctuations of the discharge output from the end of the setup. In the first stage (lag phase) when the bacterial population is the smallest, the output discharge is maximum. Then, entering the second stage (log phase), the bacterial population increases up to the maximum. With this increase in growth, the output discharge is reduced to a minimum. After that, the bacterial population enters the third stage (stationary phase) and their population remains constant, and the output discharge in this stage is also almost constant. Then the growth of bacteria enters the fourth stage (death phase) and some of the bacteria die to regain balance and the output flow increases to an almost constant value. This bacterial growth cycle and discharge output continues. In fact, what causes biological clogging is the activity of bacteria. The gases produced by their activity clogged some of the pores of the porous medium. The nitrate concentration decreases to some extent as the treated wastewater passes through the unsaturated soil. Then, as it continues to move in the saturation zone, its concentration decreases much more and at a distance of 7 meters from the beginning of the setup, its value reaches less than 0.5 mg / liter and this concentration is almost constant at the end of the path. The main reason for the large decrease in nitrate concentration is due to denitrification phenomenon. This is also hydraulically justified by the height of the water inside the piezometers along the flow path. The hydraulic head had many fluctuations in piezometers, which are largely proportional to the output flow fluctuations. The quantitative (inlet and outlet flow and pressure) and qualitative (nitrate concentration) measurements on the model indicate the types of clogging in the porous media.Conclusion: The output flow of the experimental model after two days from the start of injection reached its maximum value of about 6.7 liters per day and after 6 days began to decrease to about 2.6-2.1 liters per day and had a variation of the same range for about 30 days. Then, its amount has been increased to 4.1 liters per day for 6 days and decreased to 2.1 liters per day in 70 days after the injection. The hydraulic conductivity of the soil also changes in proportion to the changes in the output flow. Before injecting the treated wastewater into the soil column, the amount was 1.32 meters per day and gradually decreased to 0.47 meters per day. The maximum and minimum soil permeability is 14.8 and 4.33 cm per day, respectively. After the injection of treated wastewater, over time, part of the pores of the porous medium is clogged for physical, chemical and biological reasons and reduces the permeability. This permeability reduction can initially be up to 70%, which is the simultaneous effect of three factors of physical, chemical and biological clogging, but with the entry of bacteria into the fourth phase, the effect of biological clogging decreases and the permeability increases so that the penetration rate is 35% less than its original value. If the clogging of the pores is physical, the reduction of permeability and hydraulic conductivity becomes almost permanent, but if the clogging is biological, the reduction of permeability and hydraulic conductivity is temporary. Therefore, a cycle of biological clogging changes in the treated wastewater injection system and using the dry and wet interval periods in accordance with this cycle, the performance of injection ponds can be significantly increased in terms of quantity and quality.Experimental study of the effect of the apron installation on reducing scour depth at the downstream of stepped weirs with labyrinth sill
http://jhyd.iha.ir/article_154188.html
Introduction: The movement of water flow in rivers and streams of the erodible bed causes the cycle of erosion and sedimentation. Although this is a natural process, its occurrence occurs along sections of a river course that conflict with different uses, ranging from agricultural damage to structures built along rivers or riverbeds (Esmaeili Varaki et al., 2021).Stepped weirs are one of the effective structures in flow energy dissipation. Due to their shape and geometry, these structures implement to reduce energy and erosive power of water flow and also to reduce the cost of energy consuming structures that should be built downstream of dam weirs (Chanson, 1995; Khatsuria, 2005). In the present study, the simultaneous effect of creating an apron at the downstream of a stepped weir and installing sills with different geometries on its stairs on the downstream scour depth under different flow conditions and apron length was examined in a laboratory.Methodology: The experiments of this research were performed in the hydraulic laboratory and physical-hydraulic models of the Department of Water Engineering of the University of Guilan in a flume of 12.5 meters long, 1.5 meters wide and 1 meter high with glass walls and metal floors. In order to provide the flow rate, a centrifugal pump was used that can provide a flow rate of up to 90 L/s. In this research, two different weir slopes (1:2 and 1:3), aprons with lengths of P/3 (0.135 m) and 2P/3 (0.27 m) and sill with different geometries, were examined. In order to supply sediment particles, mineral sand with a uniform diameter of 2.68 mm was prepared and placed in the sediment bed with a length of 2 m, a width of 1.5 m and a height of 0.3 m at the downstream of the weir. Long term experiment was conducted to find the corresponding time of equilibrium scour depth. Comparison of results showed that after 6 hours, the scour depth reached equilibrium condition and no noticeable change occurred, so in all experiments, measurements were performed during the mentioned period. For each experiment, after installing the weir, the sills and aprons the downstream sedimentary bed was leveled. Then, according to the desired flow, the necessary adjustments were made for the relevant engine speed. After the flow entered the flume, the flow depth gradually increased and by adjusting the downstream tail gate, desired tail water depth was adjusted. In each experiment, instantaneous scour profiles were recorded at 5, 10, 15, 30, 45, 60, 90, 120, 180, 270 and 360 minutes from the start of the experiment using digital camera and then digitized using Grapher9 software. The final scour profile was also measured at the end of each experiment using a laser meter with an accuracy of &plusmn; 1 mm.Results and discussion: Experimental observation showed that by installation of sills, nappe thickness increased from yc/2 to yc, in which yc is critical flow depth. Furthermore, installation of sills reduced angle of imping jet to sedimentary bed from 58 to 34 degree. Consideration of the length of falling jet form the last step of weir to the downstream sedimentary bed indicated that by reduction of the weir slope from 1:2 to 1:3, length of falling jet increased. Comparison of the temporal development of scour depth showed that at the low discharge, installation of sill increase temporal scour depth. However, by increasing flow discharge and corresponding flow velocity over steps, installation of sills reduced temporal scour depth. From different geometry of sills and length of apron, weir of S2Si2LA2 have the best performance and decrease dse/p form 0.23 and 0.45 in range of low and high flow discharge to 0.1 and 0.24. by reduction of the weir to 1:3, installation of sill have not positive effect to reduction of the temporal scour depth.Conclusion: Comparison of the results of the installation of apron with different lengths on the maximum scour depth in the range of minimum and maximum flow discharge, i. e., relative critical depth (yc/ h) from 0.06 to 0.34, showed that stepped weir with and without sill at a slope of 1:2 showed by installation apron of lengths LA1 (P/3) and LA2 (2P/3), the relative maximum scour depth (dse/p) reduced from 0.23 to 0.19 and 0.11, respectively. By installation of different sills, the relative maximum scour depth decreased to 0.22 and 0.17, respectively. By reduction of weir slope to 1:3, installation of apron with length of P/3 and 2P/3, reduced the relative scour depth to 0.18 and 0.14. by installation of different sills geometries, dse/p reduced to 0.24 and 0.1, corresponding to the length of aprons P/3 and 2P/3, respectively.Optimal Estimation of Secondary Flow Coefficient in Compound Channels with Vegetated Floodplains
http://jhyd.iha.ir/article_154658.html
This study adopted the Shiono-Knight model (SKM) to estimate the lateral distribution of the depth-averaged velocity within rectangular and trapezoidal compound channels with emergent vegetation in floodplains. To implement the SKM, it was required to estimate the eddy viscosity coefficient, friction coefficient, and secondary flow coefficient. The present study estimated the friction coefficient using the Colebrook&ndash;White equation modified by Rameshwaran and Shiono for vegetated beds. An analysis of eddy viscosity models across compound channels indicated that the model was not sensitive to the eddy viscosity coefficient; thus, the eddy viscosity coefficient could be assumed constant across the channel. However, the negligence of the secondary flow in the model would lead to a significant error, and it was required to calibrate the secondary flow coefficient. Thus, this study used a genetic algorithm (GA) to develop equations for the secondary flow coefficient for different sections of the compound channel under two different approaches: (1) the approach of Abril and Knight (2004), who proposed constant values for the main channel and floodplains, and (2) the equations of Devi and Khatua (2017), which related the secondary flow coefficient to the relative depth and width ratio. It was found that the secondary flow coefficient was dependent on the relative depth and width ratio. As a result, the equation optimized based on the Devi-Khatua approach outperformed the Rameshwaran-Shiono technique in estimating the lateral distribution of the velocity, with a 10.2% lower error. This paper employed SKM to estimate the depth-averaged velocity within three compound channels of rectangular and trapezoidal cross-sections with a vegetated floodplain at small and large scales. To solve the SKM, it was required to calculate the friction coefficient, eddy viscosity coefficient, and secondary flow coefficient. The friction coefficient was calculated using the modified Colebrook&ndash;White equation. Several eddy viscosity models were adopted to implement the SKM. It was found that the eddy viscosity coefficient had no significant effect on the performance of SKM. The present study focused on calibrating the secondary flow coefficient as it played a key role in the flow simulation of compound channels using SKM. Two approaches were adopted to calibrate the secondary flow coefficient: (1) the approach of Abril and Knight (2004) and (2) the approach of Devi and Khatua (2017). The latter defines the secondary flow coefficient as a function of the relative depth and width ratio. The optimal secondary flow coefficient was obtained using a GA and experimental data for different geometric and hydraulic conditions. A comparison of the predicted and observed velocities demonstrated that the Devi-Khatua calibration method improved the predictive accuracy of SKM by nearly 10.2%. The secondary flow coefficient was found to be dependent on the relative depth and width ratio. It was calculated to be positive in both the main channel and floodplain, suggesting clockwise secondary flows. The difference between the observed and predicted velocities was larger in the floodplain than in the main channel, which could have arisen from flow complexities around vegetation.