Journal of Hydraulics
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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
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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.The Effect of Anti-Vortex Plates on Vortex Dissipation, Discharge Coefficient and Inlet Loss Coefficient in Hydropower Intakes
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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.Using nonlinear programming method and gray wolf algorithm for estimating parameters of nonlinear Muskingum model
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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
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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
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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
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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
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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.Cellular Automata Model for Simulating Surface Runoff
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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.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.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.The experimental study of downstream scouring of trapezoidal Piano key weir type A under free and submerged flow
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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.The experimental study of the effect of splitter on the flow discharge Piano key weir
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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.Investigation of the effect of treated wastewater injection on the permeability of unsaturated and saturated porous media in the aquifer storage and recovery system
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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
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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
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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.Analysis of unsteady flow in open channel using Fourier series
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Introduction: The shallow-water equations in unidirectional form namely as Saint Venant equations (SVE) are a set of quasi-linear hyperbolic partial differential equations, having a wide range of applications in open channel and river flow analysis. Because of intrinsic non-linearity, there are no analytical solutions for these equations in most practical applications except for simplified versions. On the other hand, numerical solutions by finite difference or finite element methods are time-marching and for forecasting and timely management of floods are relatively lengthy and time-consuming. Recently, new solutions of SVE in frequency domain, using Laplace Transform (LT) or Fourier Series (FS) have been proposed to overcome these difficulties. In the LT method, input wave is converted into a unit hydrograph, a unit step, or a unit pulse. Despite of unconditional stability, the accuracy of this method depends on time step of decomposition of input information. In this research, however, the FT method is proposed to reduce the execution of real-time flood forecasting. Unlike finite difference models, this is not a marching method and the results may be generated at a given time, directly. Moreover, there is not any restriction in the decomposition of input data due to their independence from time.Methodology: The complete form of SVE, namely as full dynamic equations are used in the present work. Initial conditions are non-uniform and the up-and downstream boundary conditions are inflow hydrograph and stage-discharge rating curve. SVE are linearized around a steady-state situation using the Taylor expansion. Assuming that the changes in water depth and discharge follow a sine pattern, the linear equations of continuity and momentum are transferred from time domain to frequency domain using the FS and sine functions. The input wave to the model, not necessarily harmonic and periodic, is converted to a set of periodic waves using Fast Fourier Transform (FFT). Considering the initial condition of non-uniform flow in the model, the channel is divided into some intervals that may have equal or non-equal lengths with uniform flow at each part. All channel characteristics such as mean flow depth are computed at each interval separately. Then, transition matrices are constructed to interconnect the channel intervals at the boundaries. Finally, the frequency response of flow discharge and water level are obtained at each part of the channel.Results and discussion: This method could be used for all kinds of prismatic and non-prismatic channels, natural rivers with various types of flow (critical, sub-critical, and super-critical), different boundary conditions at the up- or downstream ends, and point or distributed lateral inflow. Rashid and Chaudhry (1995) performed their experiments in a rectangular flume. The flow was unsteady and non-uniform. FFT was used to decompose the input hydrograph into a complex sum of periodic waves. In this research, 256 waves with a frequency of 0.002 to 0.5 were used for accurate matching between the input hydrograph of the laboratory model and the hydrograph of the total waves analyzed by the fast Fourier transform. The result of the proposed method was compared with laboratory results of Rashid and Chaudhry, analytical model of Cimorelli, and numerical method of Preissman in time domain. The Nash&ndash;Sutcliffe efficiency coefficient (NSE) in the present study is more accurate than other models and in stations (2) and (5) are equal to 0.9893 and 0.9872, respectively. The peak of hydrograph in our model is more than the Cimorelli analytical model. The lag time of mean peak of hydrograph in the model is equal to the experimental results of Rashid and Chaudhry (1995). Execution time of the model is 11.84 seconds in comparison with Preissmann implicit method that is 54.48 seconds with the same computer. This run time is important in forecasting and warning models of floods. Visual comparison of theoretical and experimental hydrograph curves are satisfactory.Conclusions: The proposed method is unconditionally stable. Full dynamic unsteady flow equations of Saint Venant is solved using FFT and Transition Matrix. The upstream boundary condition is stage-hydrograph and the downstream boundary condition is a stage-discharge relationship. The effects of lateral inflows and non-uniform initial conditions are considered in the model. To evaluate the accuracy of the model, the results compared with experimental data of Rashid and Chaudhry, analytical model of Cimorelli and numerical model of priessmann in time domain, were satisfactory both quantitatively and qualitatively. Regarding the unconditional stability and the appropriate run time of computer, the code is suitable for flood forecasting, warning and optimization models. This method can be used to analyze the flow in natural rivers and irrigation canals with any type of flow regimeNumerical investigation of velocity distribution and flow characteristics over modified steps of stepped spillway
http://jhyd.iha.ir/article_158430.html
Introduction: Stepped spillways are a common structure for energy dissipation by creating frictional resistance to flow through the steps. Based on the studies and depending on flow conditions, the flow over a stepped spillway is usually categorized into three regimes: nappe, transition, and skimming. The stepped spillway is often designed for skimming flows. There were different studies investigating various aspects of stepped spillways, but what is important in this type of spillway is increasing the effectiveness of steps in the rate of energy dissipation. This can be done by a new type of step structure (i.e., inclination angles on steps or using a sill on the edge of a step and cases like that) or geometric alteration and change of steps called labyrinth stepped spillways. Therefore, it is scientifically beneficial to modify the shape of the step of the stepped spillway to increase its collision and roll to achieve energy dissipation. The present study deals with the design of step modification by creating cubic elements on the steps in different arrangements and different hydraulic conditions. This has been considered to improve the performance of stepped spillways by increasing the energy dissipation. For this purpose, using FLOW-3D software, the influence of geometric appendance elements on the steps on the velocity distribution, pressure, the turbulent kinetic energy (TKE), and finally the flow resistance and the energy dissipation on modified spillways was investigated and compared with the flat stepped spillway.Methodology: The physical model for verifying the numerical results was carried out in a rectangular flume with a length of 12 m, a width of 1.2 m, and a height of 0.8 m. The experiments were conducted on a stepped spillway with a slope of 26.60&deg; and consisted of 10 steps with step length (l) and height (h) of 0.06 and 0.12 m, respectively. Stepped spillway models in numerical study include flat models and models with cubic elements placed on the steps in four arrangements of two side, zigzag, center, and hybrid AE elements and two heights of elements h/2 and h/4 (h step height). The commercially available CFD program FLOW-3D was used for the numerical simulations. The RNG k-&epsilon; turbulence model was employed for the turbulence calculations. To obtain mesh-independent results, three different mesh sizes were used, and the grid convergence index (GCI) methodology was employed to select the appropriate mesh. As a result, the mesh consisting of a containing block with a cell size of 1.3 cm and a nested block of 0.95 cm was selected. In the fluid domain, the boundary conditions were set according to the experimental conditions. In the upstream of the domain, a discharge flow rate (Q) definition was set. The downstream section was treated as an outflow (O) boundary condition. The bottom and the sides behave as rigid walls (W). For the upper boundary, the atmospheric pressure boundary, and at the inner boundary conditions, symmetry (S) was used.Results and Discussion: The results showed that the appendance elements on the steps cause some fluctuations on the flow surface and increase the intensity of the current collision by deviating the flow from its parallel path. The result is reduced velocity by about 10%, an increase of 54% in TKE, and an increase of 6.42% in energy dissipation on modified models compared to the flat stepped model. There was no negative pressure on the horizontal plane of the steps, and the maximum pressure occurred in the middle of the steps and inclined to the end of the steps. The appendance elements reduce the negative pressure areas on the vertical surface of the steps and reduce the risk of cavitation. The hybrid element model performs best in other arrangements, and reducing the height of the elements improves their behavior.Conclusion: According to the obtained results, it can be concluded that the appendance elements on the steps improved the hydraulic performance of stepped spillways by increasing the roughness of the steps, increasing energy dissipation, reducing the flow velocity over the spillway and reducing the risk of cavitation by reducing the negative pressure in the vertical plane of the steps. The use of cube-shaped elements on the steps and in the hybrid arrangement is suggested.Laboratory investigation of the discharge coefficient of the rectangular piano key weir with a discontinuous sloping crest
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Introduction ود Spillways are simple and widely used hydraulic structures in water transfer and irrigation, and drainage systems. They are used in dams to pass excess water caused by floods and control the reservoir water level, as well as in irrigation and drainage canals to regulate the water level and measure the flow rate. Piano key weirs are the newest type of nonlinear weirs are piano key weir (PK weir), which this type of weir can increase the capacity of discharge coefficient 3-4 times to a linear spillway. However, the discharge coefficient of PK weirs decreases with increasing the head over the weir. MethodologyThis study aims to check the discontinuous wall over the crest of the piano key weir to improve the discharge coefficient of the piano key weir in the high heads. To achieve this goal, Two weirs with a ratio of W/B = 2/3 have been used (Figures 1 to 3). The desired weirs were installed and carried out in a rotating flume in the Tarbiat Modares University of Tehran (Figure 4). The range of testing was from Q = 55 lit/sec to Q = 180 lit/sec ; and with steps of 5 lit/sec. To conduct the tests, first, the tests were performed on the Rec-Base model, and then the tests were performed on the Rec-B1 model. The geometric features of these two models are presented in Table 1. In order to extend the results of the prototype to the real sample, the dimensional analysis of the weir has been done. For this purpose, the effective parameters are shown in Eq. 2, and then, after performing the dimensional analysis techniques, it can be seen in the form of Eq. 3. By removing the constant values, the discharge coefficient will depend on the parameters of Eq. 4. Results and DiscussionFigure 5 shows the Q-Ht curve of two Rec-Base and Rec-B1 models. According to this figure, the upstream head of the weir of the Rec-B1 model has increased by an average of 8.35% compared to the Rec-Base model. Also, regarding the behavior of the flowing blade, in the model (Re-Base) in the range of Ht&lt;8 cm, air penetrates under the flow blades, and the flow becomes aerated. In the interval (Ht &lt; 12 Cm &lt; 8 Cm), with the increase of water head, the flow under the blade goes to the free air, and the blade takes an oscillating state. At higher values (Ht &lt; 12 cm), The flow passes over the weir crest in the form of a thick blade. In this condition, fluctuations are observed on the flowing blade. Equation 5 has been used to calculate the discharge coefficient of the Rec-Base model. This issue is while Eq.12 has been used to calculate the water discharge coefficient of the Rec-B1 model. In this regard, QT is obtained from Eq. 10, and QE is the laboratory discharge. Figure 8 shows the discharge coefficient of the two models. According to this figure and the numbers in Table 2, the discharge coefficient has increased by 6.7% in the Rec-B1 model compared to the Rec-Base model. Figure 11 also shows a 7.22% increase in efficiency of the Rec-B1 model compared to the Rec-Base model. Also, coefficient C was calculated using equation 13 and its curve was drawn in figure 9. Figure 10 is also calculated according to Figure 14. Finally, Eq. 16 to estimate the water discharge coefficient has been presented. Also, the coefficients of this equation are presented in Table 3. Figure 12 shows the comparison between the estimated water discharge coefficient of equation 10 with the actual value of the discharge coefficient, which indicates the high accuracy of the presented equations. Table 4 indicates the equation proposed by other researchers to calculate the discharge coefficient of the PKW as well.ConclusionIn conclusion, it can be mentioned that although the slope over part of the weir crest increases the upstream head of the piano key weir, however the efficiency of the weir increase by 7.33%. Also, the discharge coefficient in the Rec-B1 model increases by 6.7% compared to the Rec-Base model. Considering that in the Rec-Base model, with the increase of the head, interference of the flow increase, it is possible to reduce the decreasing rate of efficiency in higher discharge by modifying the weir crest.KeywordsSpillway, rectangular piano key weir, weir crest, weir efficiencyLaboratory study of crossbeam structural design in control of asymmetric S- type jump of sudden expansion sections
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Laboratory study of crossbeam structural design in control of asymmetric S- type jump of sudden expansion sectionsIntroduction This paper presents an experimental study on a proposed dissipation structure, which consists of a series of cross beams, tested in different geometric configurations and hydraulic conditions. First, the effectiveness of this system was analyzed in terms of uniformity of flow and bed velocity and while, observing the dissipating mechanisms, in the next step, the system performance under variable tail water conditions by describing the three-dimensional flow patterns observed in the downstream channel with a gradual decrease in downstream level to 70%, 80% and 90% of tail water depth in the conditions the reference experiments were tested. Measurement of three-dimensional velocities to determine the parameters of flow uniformity, momentum and energy coefficients, and analysis of three-dimensional velocity distributions, turbulent kinetic energy, and supplementary studies on the development of isothermal line concentration and drop energy losses of reference experiments and optimal case compositions were examined. The results showed that in addition the similar qualitative trends of &beta; and &alpha;, the flexibility of the dissipation structure has a high efficiency in the effective homogenization of the flow in the abrupt expansion channel, even in the downstream water level conditions.Methodology The experiments were performed in the hydraulic laboratory of Shahid Chamran University of Ahvaz and in a horizontal rectangular open channel with a length of 12 m and a width of 1 m with a height of 0.87 meters. Flow supply was provided through an open tank with dimensions of 7 m by 5 m at a height of 2.5 m. Hydraulic S-jump was performed with sudden expansion and design and construction of ogee weir. With the formation of S-jump, the conditions for the depth of hS downstream in the end control section were set, equal to 0.19, 0.15 and 0.11 m, respectively, to create three 7.4, 8.7 and 9.5 Froude numbers. Measurement of longitudinal velocity at a fixed height of 0.5 cm from the bottom of canal and longitudinal sections of 0.25 from each other in the first 2 m of downstream canal, and the other ones at distances of 2.5, 3, 4, 6 and 8 m from sudden expansion. Finding the best configurations to achieve a uniform flow and reduce the velocity distribution was done in most of the critical areas downstream of structure. For the levels of reference experiments, 54 geometries of the energy dissipation system with different configurations of beam distances, s, number of beams, N, hb height, position of the first beam from expansion, P, and slope of the system, &theta;, were investigated. Each component of the structure includes an I-shaped beam, with a flange width of 1.5 to 2.5 cm, depending on the hb, in the direction of the channel width and vertically in the direction of the main stream. Results and Discussion The results showed the values of &beta;b and vmb2. &beta;b calculated for three Froude numbers and different geometric parameters of the system, which means the absolute distance of 1.65, 1.85, and 2.55 meters from the expansion section for P = 0.4, 0.6, and 0.8 meters, respectively the effectiveness of the system (beam configurations) in homogenizing the flow and reducing the bed velocity is clearly evident, even for the worst performance settings. When using the structure, the mean &beta;b is almost less than 1.1 with vmb2; the corresponding &beta;b was measured to be approximately 0.1 m2/s2. According to the observed efficiency of the beam system, 3 of the best performance settings of the structures were selected for Fr = 9.5 (which was the most difficult situation regarding the energy characteristics of the input current) to the flow characteristics along with the flow and downstream of the structure. Energy dissipation should be fully described. According to research results, the qualitative trends of &beta; and &alpha; are similar. Three-dimensional velocity distribution analysis showed that this type of structure has the flexibility to effectively homogenize the flow in abruptly expanding channels, even in the conditions of downstream water level varieties.Investigation of the turbulence kinetic energy, smaller vortices that contribute to turbulence at the surface and promote mixing in the flow interface until they reach maximum value during the study period, which was from x = 0.3 m to x = 2 according to the definition of the ratio of energy losses to initial energy as a relative energy loss or jump efficiency (&eta;), it was found that in all tested Froude numbers, the trend of increasing relative energy loss to a cross-section of 2.5 m after expansion section was increasing. Approximately X/Xexp = 4 reaches its peak and extends with a constant almost linear trend to the end of the section and the end.Conclusion In this research, a laboratory simulation application of a new structure with different geometric configurations of cross beams as a series of wide-wing beams to control asymmetric S-jump of sudden expansion sections was experienced. The use of different geometric configurations of cross beams shows the effectiveness of beams' contribution in homogenizing flow and reducing bed velocity.. The concentration of turbulent flow caused by the jet hitting the beam system, particularly the first beam, leads to a significant energy loss in the area between the first and 2nd beams. Before leaving the main system, the bubbles, leaving the system energy in the same evacuate the area and saw a calmer flow in after areas of the structure. The study of turbulent kinetic energy showed that the conversion rate of the high state from the mainstream after the beams (Conversion of mean flow) to turbulent flow occurs in some cases. Also, in all Froude numbers of reference experiments, the trend of increasing the relative energy loss to a cross-section of about 2.5 m after cross-section expansion is increasing. KeywordsSudden expansion, cross beams, hydraulic S-jump, flow patterns, energy dissipation, hydraulic structures, stilling basin.Numerical comparison of performance and stability of concrete and gabion retaining walls in riverbanks protection
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Introduction A retaining wall is a structure that maintains the pressure due to the situation in the level difference caused by an embankment, excavation, or natural factors. Since comparing the performance of two different types of walls from retaining walls is the subject of this article, in this research, from rigid walls, weight retaining wall (concrete) and flexible walls, gabion retaining wall (in weight form) with almost the same conditions, It is evaluated in terms of stability and performance. The geometry of the concrete weight retaining wall is chosen so that the result of the forces acting on it (including weight and lateral forces) is in the core of the base or its horizontal sections. The expected results of this study include the study of retaining wall performance in terms of soil material change behind the wall, river water depth, and retaining wall slope, and finally, comparison and selection of suitable retaining wall to protect the river wall between two types of concrete and gabion walls.Methodology Software SLOPE/W is the most advanced slope stability software for soil and rock slopes from the GEO-STUDIO 2012 software suite. SLOPE/W effectively analyzes various types of slip surface shapes and determines factors of safety, pore water pressure conditions, soil properties, and loading conditions. In this study, the Morgenstern-Price method has been used. In this method, the balance of forces and anchors for sliding sections is determined, and by Entry and Exit method, the factor of safety is determined.In this study, different factors such as type of wall and river bed materials, water depth in the river, type of retaining wall materials, the slope of retaining wall, and soil adhesion were investigated. Based on the critical conditions in the evaluation of the stability of retaining walls, the saturation state (the most critical state possible) was considered for the wall and river bed materials. To apply the soil properties behind the retaining wall in modeling, a homogeneous porous medium and isotropy (Kx/Ky = 1) were considered, and for the slip criterion of the Mohr-Coulomb resistance model, which is the most common method for expressing shear strength in geotechnical materials, used. To compare the results, the retaining wall was designed and modeled in mirror conditions, i.e. the vertical part of the wall on the riverside and the stair part of the wall under the soil. Results and DiscussionSince the permeability and hydraulic conductivity of medium gravel are higher than that of average sand, it has a greater capacity to drain excess water. It was observed that the active force and torque of the average gravel are 7% and 11% lower than the average sand, respectively. This is also true for the gabion retaining wall as well as the state of the river with a water depth of 2 meters and 4 meters. In a river, without water, the amount of active force and torque is about 20% more than in a river with a water depth of 2 meters and about 40% more than in a river with a water depth of 4 meters. In the retaining wall in the mirror state, in the river without water, the active force and torque have both increased by about 16%, and in the river water depth of 2 meters, it has increased by about 17% and in the depth of 4 meters, it has increased by 23%. The results of stability and factor of safety for two wall slopes in the conditions of water level drop showed that the factor of safety at a depth of 2 meters decreases by about 20% compared to a depth of 4 meters and Also, the factor of safety of the river without water is reduced by about 30% compared to a depth of 4 meters. The results showed that the retaining wall in mirror conditions has a better performance than other models in terms of factor of safety. Also, the index wall in the vertical position, at a depth of 4 meters, which is the same depth equal to the total height of the wall from the riverbed, has the lowest factor of safety. ConclusionIn this research, the stability and performance of two types of concrete and gabion retaining walls were examined with SLOPE/W software under similar river conditions. A total of 24 models were designed using two types of bank material (gravel and sand), two slopes of the retaining walls, and three river water depths. Also, 6 models of vertical walls were considered for comparison. The results indicated that the coarser-grained bank material produces a lower level of pore pressure, which in turn results in lower values of active force and torque by 11% and 7%, respectively, compared with the sand material. The results of this applied research can be used as a guideline for selection between two types of retaining walls (i.e. Concrete or masonry walls, and gabion walls) in different river conditions.