Journal of Hydraulics
https://jhyd.iha.ir/
Journal of Hydraulicsendaily1Wed, 20 Mar 2024 00:00:00 +0330Wed, 20 Mar 2024 00:00:00 +0330Laboratory investigation of the discharge coefficient of the rectangular piano key weir with a discontinuous sloping crest
https://jhyd.iha.ir/article_170434.html
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 efficiencyInvestigation of flow characteristics at the confluence of two compound channels (Numerical study)
https://jhyd.iha.ir/article_177242.html
Introduction The junction of open channels is one of the most important points that must be carefully studied. Because the phenomenon of the intersection of channels or rivers is very common, from nature to cities. On the other hand, the flow behavior at these points is very fast, complex and different due to the connection of two or more flows with different characteristics. Many and different studies have been done on this field, with different conditions and forms of the channel section. But the main goal of this article is to investigate the flow behavior at the junction of two compound channels. But according to the literature review and past researches, it can be concluded that the most of the researches included channels with a rectangular section, while most of the natural sections are closer to the compound section. Therefore, here the intersection of channels with a compound section is investigated.Methodology Until the last three decades, the study of fluid movement and the investigation of existing phenomena in this field, were only using experimental or analytical methods, with many assumptions to simplify it. But with the advance of computers, researchers were able to investigate more complex phenomena. One of these scientific fields that has made significant progress with the increase in computing power, is computational fluid dynamics or CFD, and one of its branches is hydraulic. Microscopic investigation of water behavior in natural streams is complex. Solving the existing theoretical models, in their complete form and with all the improvements, does not have the ability to correctly simulate its changes. But with the advance of computers, the science of CFD was able to successfully simulate and predict the behavior of water by using turbulence models. which There are different turbulence models with different applications that are used according to the type of problems. For calibration the model, the simulation&rsquo;s results is compared with the experimental data. If the amount of error was small, it is concluded that the modeling has sufficient accuracy. So it is possible to continue the research and simulating other samples that have not been done in the laboratory, using Flow-3D software, and the effect of different parameters is investigating.Results and Discussion The profile of the water level in all cases of the intersection of two channels is such that the height of the water reaches a maximum in the middle of the intersection and then decreases to a minimum at a distance of about one meter from the intersection. After this point, the height of the water increases again to reach the equilibrium state. . However, among the effective parameters on the depth of water inside the channel, the effect of ratio of width of the channels, ratio of the flows and trapezoidal channel were investigated, with the assumption of constant angle of intersection of two channels (90 degrees).Reducing the slope of the channels wall up to 10.5%, reducing the ratio of the main flow to the side channel up to 4.2% and reducing the ratio of the width of the main channel to the width of the side channel up to 33%, leads to a decrease in the minimum water depth compared to the base model (with a rectangular cross-section and a flow ratio of 0.25). Also with increasing the ratio of flow to maximum, the minimum depth increased by 7.5%.The velocity and the turbulence energy were investigated for four specific simulations in order to get a better understanding of the intersection of two compound channels.Conclusion The main changes and characteristics of the intersection of two channels, are related to the characteristics of the sub-channel and are the result of the effect that the momentum of the sub-flow has on the main flow. U-velocity in the trapezoidal channel, decreased by 13.76% compared to the rectangular channel, and also the u-velocity in the minimum flow ratio was 1.33 times higher than the model with the maximum flow ratio. This indicates the importante effect of the sub-channel.Experimental and numerical evaluation of the effects of dam reservoir sediments on sediment transfer mechanism due to dam failure
https://jhyd.iha.ir/article_175418.html
Introduction Dams are considered one of the most important infrastructure facilities of a country, which play a very important role in economic prosperity through storage, regulation of water, and also energy production. Due to the volume of water stored in the reservoir of these dams and sometimes their proximity to residential areas, the failure of dams can lead to a lot of human and financial losses, which can be prevented by having sufficient information and proper forecasts of dam failure. The flow resulting from the dam failure is turbulent, mainly a mixture of fluid and sediment particles. Therefore, after the dam's failure, sediment transport leads to significant morphological changes downstream. Based on this, the analysis and evaluation of the instantaneous failure of the dam have been one of the main challenges of the profession of engineers and activists in this field. By examining the research background, it is clear that the studies focused on fluid flow in non-erodible bed conditions, and a small part of numerical and laboratory research has been focused on the evaluation of changes in the morphology of the bed sediment layer. In addition, one of the effective parameters in the mechanism of sediment transfer and the pattern of morphological changes of the bed is the sediments of the dam reservoir, which has received less attention from researchers. Therefore, in this research, we have evaluated and experimental-numerically modeled the phenomenon of sediment transport due to the sudden failure of the dam, taking into account the sediment layer in the dam reservoir.Methodology In this study, two variables (1- the type of sediment particles (fine sand and coarse sand) and 2- the thickness of the sediment layer in the reservoir and downstream of the dam) have been investigated as the main parameters in the evaluation of the sediment transport mechanism (changes in bed morphology). Based on this, scenarios have been defined for laboratory and numerical modeling. In this research, to evaluate the phenomenon of bed sediment transfer based on the phenomenon of instantaneous dam failure, four tests have been defined and implemented in the hydraulic laboratory flume of Babol University in different conditions. This flume is 10 meters long, 50 cm wide, and 50 cm high and is equipped with an ultrasonic level gauge and a digital pressure gauge. In these experiments, two parameters of the type of bed sediment materials (A, B) and also the thickness of the sediment layer downstream of the dam and the reservoir of the dam have been considered as modeling variables. Type A materials are gravel particles with an average diameter of 20 mm, and type B materials are sand particles with an average diameter of 3 mm.Results and Discussion According to the research variables, four scenarios for laboratory modeling and six scenarios for numerical modeling of the phenomenon of sediment transfer based on instantaneous dam failure have been defined. The results of the numerical modeling showed that the numerical model of the research had acceptable accuracy in simulating the phenomenon of sediment transfer due to dam failure, so the modeling error for two-dimensional numerical models (the first four models based on Table 2) is respectively equal to 2.75%, 4.31%, 2.59%, 5.52% compared to laboratory tests.The results showed that in the models of type B sediment materials, the amount of reduction in the thickness of the sediment layer is greater than in the models with type A sediment materials; in other words, the amount of reduction in the thickness of the sediment layer in type B materials is more than type B. The material was A. Therefore, the decrease in the diameter of the sediment particles has caused an increase in the thickness of the sediment layer (bed morphology) due to the failure of the instantaneous dam. In addition, by examining the results obtained from laboratory and numerical models, it was determined that the reservoir sediment layer of the dam is an effective parameter in the rate of sediment transfer and the occurrence of changes in the morphology of the bed based on the dam failure currents, in such a way that with the increase in the thickness of the sediment layer of the reservoir Compared to the downstream sediment layer of the dam, the changes in the thickness of the bed layer have increased by about 10%, as well as the rate of sediment transfer in these conditions.By evaluating the results of dam failure modeling in three-dimensional space, it is clear that the thickness of the sediment layer in the 3D_DB1_NB1 model with type B materials has decreased more compared to the 3D_DB1_NA1 model with type A materials. In addition, according to the contour of the changes in the thickness of the bed layer, it is clear that the type of material of the sediment particles (diameter of the sediment particles) was an effective factor in evaluating the phenomenon of sediment transport in the 3D modeling space. In both 3D models, the thickness of the sediment layer in the area of the dam valve (failure area) has decreased and increased in the range of 1.8 to 2 meters and decreased from 2.2 to 3 meters.Conclusion In this research, the main goal is to evaluate the mechanism of sediment transfer due to the sudden failure of the dam, focusing on the effect of the sediment layer in the dam reservoir, which has been implemented in the form of laboratory and numerical modeling. Also, the effect of three parameters, the type of sediment particles and the thickness of the sediment layer in the reservoir and downstream of the dam axis, has been studied.Based on the results of this research and the evaluation and comparisons made between the numerical models and the laboratory model, it is clear that the numerical model created in both two-dimensional and three-dimensional spaces has an acceptable accuracy in simulating the phenomenon of sediment transfer due to dam failure.Determining the discharge coefficient in model of the triangular-rectangular combined weir and sliding gate
https://jhyd.iha.ir/article_176090.html
Introduction: Measuring flow rate in water transmission channels has always been important. weirs and gates are more useful than other measuring tools and methods due to their low cost, ease of installation, ability to regulate and control the water level, as well as relatively simple and accurate relationships. Of course, each of these structures alone has weak points; For example, the settling of sediments behind the weir and the accumulation of floating materials behind the gate reduce their efficiency. In order to eliminate or reduce the weak points of weir and gate, the combination of these two structures in different ways and the research on hydraulics and the accuracy of the flow coefficient of the combined structure have been considered by researchers for some time. Therefore, in the current research, a triangular-rectangular combined weir structure and a sliding gate were built and its flow coefficient was investigated in different hydraulic conditions by a laboratory model in the hydraulic laboratory of Birjand University.Methodology: The experiments of this research in a laboratory flume with a length of 10 meters and a width of 0.3 meters in order to determine the discharge coefficient of the combined triangular-rectangular weir structure and the sliding gate, in two states of fixed opening of the gate and different flow rates and different opening of the gate and constant flow rates. And it was done in two slopes of 0.002 and 0.004. Finally, according to the existing relationship, the discharge coefficient of the structure was determined in different conditions. Dimensional analysis technique was used to generate dimensionless parameters and investigate the effect of these parameters on the discharge coefficient of the combined structure.Results and discussion: The results of the experiments were analyzed after checking the correctness and refinement of the data, and the discharge coefficient of the combined structure was analyzed according to the collected data and the geometrical and hydraulic parameters of the structure. The discharge coefficient of the combined structure was calculated in constant gate openings and different discharges and different gate openings and constant discharges. Also, in order to control some of the tests performed, the discharge coefficient of the combined structure was examined in two different slopes. In all these researches, the discharge coefficient of the combined structure was between 0.6 and 0.9, and the results became more uniforme with the increase of the upstream depth (y/D). The extraction of the gate of the combined structure downstream of the structure had an effect on the numerical value of the discharge coefficient of the combined structure.Conclusion: The test results showed that with the increase of y/D, the discharge coefficient first reaches its lowest value and then increases after the flow enters the rectangular weir and tends to 0.7. Also, by reducing the opening of the gate (H_g/D), the discharge coefficient tends to 0.7. Also, the intake of the gate of the combined structure increases the discharge coefficient of the structure. Slope changes have no effect in determining the discharge coefficient of the combined structure. The results of the current research with the results of other researchers who have worked in this field; It matches well.Experimental Evaluation of Performance of the New Design of Bed Protection Models (F-jacks) in Altering the Flow Pattern around Bridge Piers
https://jhyd.iha.ir/article_176700.html
Introduction The various methods have been extensively studied by different researchers to reduce scouring around bridge piers, such as riprap, concrete blocks (CAU), collars, sacrificial piers, creating slot and roughness on the pier, and flow guide vanes, and their results generally relate to determining the size, location, and scope of installation and other geometric characteristics of the devices. Many countermeasures to prevent or reduce local scour around bridge piers, did not have the desired effective, and the concrete armor units (CAUs), which are made to protect shores from erosion caused by waves, have received very little attention in terms of bed armoring around the bridge piers.Therefore, the aim of the present research is to experimentally investigate the hydrodynamics of flow around a new element designed to protect the bed around bridge piers from local scour. The F-jacks, a concrete armor unit (CAU), is introduced and its role on flow characteristics is evaluated for the first time in this study. This concrete element is a new design of the A-jacks concrete model, with one leg and five branches on top, and the angle between the branches surrounding the leg and the central branch is 30 degrees to ensure minimum contact between the legs of the element and the sediment surface. The selection of a 30-degree angle for the branches of the F-jacks element is due to its similarity to the diameter of the bridge pier, to provide complete coverage around the pier.MethodologyThe experiments of this research were performed in a 7-meter long, 50-centimeter wide, and 0.0001 slope flume with a rigid bed. A wooden cylinder with a diameter of D = 45mm and the same height as the flume was used as a model for a bridge pier and installed at a distance of 4.5 meters from the beginning of the flume (to develop the flow). The water depth (h) in the experiments was constant and equal to 15 centimeters, the flow rate (Q) was 0.021 m3/s, and the flow regime was fully turbulent and subcritical.In order to understand the physics of flow in relation to three-dimensional velocity variations, a Nortek Acoustic Doppler velocimetry (ADV) with a frequency of 25 Hz and a sampling duration of 120 seconds was used. In order to evaluate the hydrodynamics of the flow around the protected pier with F-jacks units, three different placement patterns around the pier were considered: 1) a non-dense arrangement (P1), in which 24 F-jacks elements were placed next to each other around the pier, 2) a dense arrangement (P2), in which 22 F-jacks elements are interlocked around the pier, and 3) an SP arrangement, which refers to a situation where the single pier is placed in the central axis of the flume.In addition to the measurement grid on the vertical XZ plane, a set of measurements was taken on the horizontal XY plane at Z/h=0.47 for each of the three selected patterns. To ensure the development of the flow in the test area, normalized mean velocity component profiles were shown to follow a similar trend for two 4 and 4.3 meter-long sections from the beginning of the flume, and the velocity data conforms to the logarithmic law of velocity distribution that confirms the validity of velocity data for developed flow conditions. Also, to verify the accuracy and sufficiency of measurements in the developed flow region under investigation, the power spectral density (PSD) of time series for all three velocity components shows that the slope of the power spectrum agrees well with the Kolmogorov -5/3 law in the inertial sub range.Results and DiscussionContour and vector plots of the time-average streamwise velocity component (u ̅) indicated that when the F-jacks elements were placed according to the P2 pattern around the pier, the flow pattern around the pier changes completely. Where, in the upstream of the pier, the average velocity significantly decreased from the water surface to the bottom, indicating the growth of the minimum and weakening of the downflow and horseshoe vortices. In the downstream of the pier, the high-velocity flow region at rear the pier disappeared, and the flow turbulence was significantly reduced, and the region of flow recirculation in the wake of the pier completely disappeared.With the placement of F-jacks units around the pier, a strong upward vertical velocity (w ̅ ) is obvious around the pier compared to the single pier (SP pattern), which is stronger in the dense arrangement of the elements (P2 pattern). This factor refers to the positive effect of the presence of elements in reducing the growth of downflow (negative vertical velocity), reducing bed disturbances, and turbulence transfer away from the bed region in the wake area around the bridge pier.The streamwise and vertical components of flow turbulence intensity (u_rms 〖,w〗_rms ) significantly decreased with the placement of F-jacks units around the pier according to the P2 pattern. Where, in the near-bed region around the pier, the turbulence intensity decreased by an average of about 93% compared to the SP pattern, indicating the high ability of F-jacks elements in controlling and reducing flow fluctuations and turbulence in this region and diverting flow fluctuations towards the water surface and away from the bed.Comparison of Reynolds shear stress on XY plane at Z/h=0.47 for the three mentioned patterns revealed that -&rho;(u^' w^' ) ̅ in the SP pattern is approximately 95% higher than P1 and P2 patterns, at the vicinity of the bridge pier. Furthermore, the magnitude of -&rho;(u^' w^' ) ̅ has significantly decreased with the placement of F-jacks units as the P2 pattern around the pier.ConclusionThe laboratory results presented in this paper provide a new understanding of flow behavior details around the bridge pier model with a new design of F-jacks armor units surrounding it on rigid bed conditions. The overall conclusion of this study showed that when F-jacks units are placed densely (P2 pattern) around the pier, the flow turbulence in this area is significantly reduced.The Numerical Investigation of hydraulic condition on flip bucket spillways and effect of inlet flow and shape on it
https://jhyd.iha.ir/article_176701.html
IntroductionSince beginning of the dam construction industry, one of the challenges that engineers have always been involved with, is how to reduce the enormous energy of water when it overflows from dams for which, many plans and ideas have been presented so far. One of these ideas is to utilize the energy dissipater structures among which, the flip buckets are well-known. Since the flip bucket is one of the most important components of a dam, whose destruction disrupts the normal performance of the dam, the engineers have always tried to enhance the efficiency of this component by investigating into the hydraulic conditions such as pressure, depth and velocity. Accordingly, it is of paramount significance to comprehensively study the hydraulic performance and condition of the flip bucketsMethodologyIn this study, behavior of the fluid in the flip bucket of a dam has been modeled using Flow-3D software. The obtained results in Froude number, were compared with the data derived from an existing physical model. After determining the error percentage and selecting the turbulence model etc., using the continuity and motion equations in the fluid dynamics and finite volume method, a model was built and through a trial-and-error process, Froude numbers ranging from, 2 to 7 were chosen. The results pertained to the velocity, static pressure and depth were captured and compared with geometric characteristics of the bucket and incoming flow condition. To efficiently employ the results, the produced graphs were normalized using a similitude analysis. The comparisons have been made with the non-dimensional ratios of Froude number and x/r (x: distance from the bucket and r: bucket radius) in the middle as well as right and left sidesResults and DiscussionIn order to choose the turbulence model (K-&epsilon;, K-&omega; and RNG turbulence models were used to compare the results of various models according to previous studies), after analyzing and optimizing the computational error between the numerical and the physical models, the k-&epsilon; model with the minimum rate of error was selected as the best practice. It needs to be noted that the error rate of pressure, velocity and depth are 1.52%, 1.5% and 1.58%, respectively. The results indicated that the velocity changes along the length of the bucket, generally have a slight increasing trend and reach their maximum value at the end of the bucket. In addition, velocity changes have an inverse trend as the Froude number increase. Moreover, it was observed that the depth changes are almost constant along length of the bucket and reach their minimum value at the end and decrease with the depth as the Froude number increases. Pressure changes also have a decreasing trend along the length of the bucket and also, decrease with increase in the Froude number. The situation of the above parameters in the sides is generally similar to the middle axis, but with a greater intensityConclusionIt can be generally stated that the most vulnerable zone of the flip bucket is where 0.1&lt;x/r&lt;0.3 (i.e., the region where flow runs backs to the top) in great Froude numbers. This zone is the critical area of the bucket structure due to the decrease in pressure, both in terms of the possibility of cavitations and increasing velocities. Furthermore, it was found that rate of vulnerability in the sides is greater than the middle. Moreover, range of the pre-final Froude numbers of the flow passing through to the bucket, is the turning point of the flow hydraulic condition that needs to be considered while designing this structure.The Performance of Differential Evolution Algorithm for Leak Detection in Water Distribution Networks Considering The Uncertainty of Nodal Demands
https://jhyd.iha.ir/article_176702.html
Water supply networks are one of the most important urban infrastructures for supplying water. Considering that currently water wastage is a global concern and on the other hand the demand for water is increasing, this issue has made it necessary to manage the demand and modify the consumption pattern. One of the important components of non-revenue water is leakage in the water supply network, and leak detection is one of the necessary measures to reduce non-revenue water and manage consumption. In this research, an optimization formulation has been developed for the purpose of leak detection in water networks assuming the lack of information on the number of leaks and pressure measurement data, and the search problem has been solved with the differential evolution algorithm. The performance of the developed model has been investigated by defining different scenarios in terms of location, amount and number of leaks. First, the location scenarios were examined in terms of the number and amount of leaks, including one, ten, and twenty leaks at the same time, and then the developed model was implemented for location scenarios with an unknown number of leaks and the uncertainty of nodal needs. The results showed that the success of the model in the case of the certainty of the input data and the existence of a node is 100%, and by considering the hourly changes in the nodal demand and increasing the number of leaks up to ten and twenty leak nodes, the success rate of the model in finding the exact leak points is 95% and 94.5% has been obtained. In the scenarios where the number of leaks was considered unknown, the success of the model to find the number of leaks is 94%. The success of the model in the case of uncertainty of nodal requirements with the number of known leaks reaches 91% with the increase of leaks and 86% with the number of unknown leaks.Experimental investigation of the effect of transverse waves 1, 2 and 3 modes caused by cylindrical pier groups of the bridge on local scour
https://jhyd.iha.ir/article_177268.html
IIntroduction The passage of water through obstacles such as bridge piers in the river, dock piers in the sea, and piers of any other hydraulic structures located in an open channel causes the formation of a boundary layer upstream of the obstacles and the separation of flow lines in the downstream obstacles, leading to the formation of vortex flows. The overlap of the vortices created by each of the obstacles leads to the formation of surface waves whose propagation direction is perpendicular to the flow direction. Under special circumstances when the frequency caused by the vortex of the obstacles is equal to the natural frequency of the structure's oscillation, a resonance mode is created and transverse waves with maximum amplitude are formed along the flume width. The formation of transverse waves with maximum amplitude can affect the safety and stability of hydraulic structures including bridge piers. To this end, recognizing transverse waves can reveal the reasons for the occurrence of some phenomena. Most studies on transverse waves have been conducted in a flume with limited width and a few waves. Thus, by conducting experiments in a wide flume and creating more waves, this study aimed to investigate the effect of waves in different modes on the local scour around the cylindrical piers of bridge.Methodology The experiments were carried out in the Physical and Hydraulic Modeling Laboratory of the Faculty of Water and Environmental Engineering, Shahid Chamran University, Ahvaz, using a rectangular flume with a length of 16 m, a width of 1.25 m, a height of 0.6 m, and a zero slope with glass walls. The flume bed was covered with sediments with an average size of d50 = 0.7 mm. The experiments were conducted with cylindrical pier groups in three stages. The experiments in the first stage were carried out without sediments and the cylindrical piers were placed on a fixed bed without sediments. The first stage experiments aimed to measure the wave parameters (wave amplitude, wave frequency, and flow depth) in the resonance. In the second stage, the sediment experiments were conducted with the formation of transverse waves. After adjusting the water level and forming the desired wave, 4 hours of equilibrium time was considered. Then, the pump was turned off and the end weir was slowly opened. After the complete discharge of the flow, the topography of the bed was measured using a laser meter with an accuracy of 1 mm as 1&times;1 cm2. The sediment experiments were in the third stage with the removal of transverse waves (control experiments) which were performed to compare with the results of the second stage experiments. A glass sheet was used for this purpose. The glass sheet prevented matching the natural frequency of the channel and the frequency caused by the tier vortex. Results and Discussion To investigate the effect of transverse waves caused by cylindrical piers on the maximum scour depth, each scour in the experiment with transverse waves was compared with the corresponding experiment conducted without transverse waves. The results showed that in wave modes 1, 2, and 3, the maximum scour depth was greater in the case with waves than in the case without waves. The maximum scour depth in wave mode 1 experiments at Froude numbers 0.059, 0.057, and 0.055 was 71, 55, and 54 percent higher than the scour depth in the experiments without waves, and for wave mode 2, the maximum scour depth in the experiments with waves at Froude numbers of 0.117, 0.110 and 0.106 was 90, 76 and 66 percent higher than the maximum scour depth in the experiments conducted without waves. The maximum scour depth in the wave mode 3 experiments with waves at Froude numbers of 0.156 and 0.151 was 70 and 68 percent was higher than the scour depth in the experiments without waves. This study also examined the effect of wave mode on the maximum scour depth. The results indicated that with an increase in the wave number, the maximum scour depth increased in each discharge. On average, the maximum scour depth in wave mode 3 increased by 130 percent compared to wave mode 1 and by 43 percent compared to wave mode 2, and the maximum scour depth in wave mode 2 increased by 60 percent compared to wave mode 1. Also, the maximum scour depth in each wave mode increased with an increase in the wave amplitude, indicating the existence of a direct relationship between the wave amplitude and the maximum scour depth. In addition to the maximum scour depth, transverse waves also affected the scour volume, which was greater in the experiments conducted with waves than in the experiments without waves. On average, the scour volume was 4.3 times in wave mode 1, 3.5 times in wave mode 2, and 9 times in wave mode 3 compared to the wave-free mode.Conclusion The present study examined the effect of transverse waves mode 1, 2, and 3 on the local scour around the cylindrical piers of the bridge. The formation of transverse waves affected the scouring of cylindrical piers, and the maximum scour depth in the experiments conducted with waves was greater than in the experiments without waves. On average, the maximum scour depth increased by 60 percent, 78 percent, and 69 percent in the wave modes 1, 2, and 3 compared to the wave-free mode respectively. Moreover, with an increase in the wave number, the maximum scour depth increased in each discharge, with the maximum and minimum scour depths being found in wave modes 3 and 1, respectively. Overall, the changes in the scour volume followed the same trend as the changes in the maximum scouring depth. On average, the scour volume was 4.3 times in wave mode 1, 3.5 times in wave mode 2, and 9 times in wave mode 3 compared to the wave-free mode.A second order well-balanced and entropy consistent numerical scheme for one-dimensional shallow water equations
https://jhyd.iha.ir/article_176757.html
IntroductionThe shallow water equations are a set of hyperbolic balance laws that describe the behavior of water flow in shallow regions such as rivers, lakes, and oceans. Solving hyperbolic balance laws poses significant challenges due to the presence of non-conservative terms, shocks and discontinuities. Analytical solutions are limited to simplified cases, so numerical methods are often used to solve these equations. Numerical schemes that solve the balance laws must ensure the well-balanced property (Bermudez and V&aacute;zquez 1994), meaning the discretized numerical fluxes must exactly balance by the approximated source terms. These types of numerical schemes use upwind/flux splitting techniques to handle wave propagation and discontinuities. Such well-balanced approaches work well for supercritical or subcritical regions but are known to struggle when Riemann problem includes both (LeFloch and Thanh 2011), (specifically in trans-critical flows and hydraulic jumps). To address this, various treatments, such as entropy fixes, shock fitting techniques and etc., have been proposed. Notably, Akbari and Pirzadeh (2022) introduced a set of shockwave fixes to cure the numerical slowly moving shock anomaly. Their proposed approach has the advantage of accurately capturing the hydraulic jump. However, such scheme is only first-order accurate, as higher-order schemes continue to advance, it becomes necessary to extend such technique to more accurate high-resolution schemes.MethodologyA second order well balanced numerical scheme are designed for the shallow water equations using a semi-discrete MUSCL reconstruction. The first step in the semi-discrete finite volume method is to discretize the governing equations in space. For the one-dimensional shallow water equations, this involves dividing the computational domain into a set of control volumes and approximating the integral form of the conservation equations over each control volume. By considering the fluxes at the control volume interfaces and accounting for the source terms, a system of ordinary differential equations (ODEs) can be obtained. To ensure accurate and stable solutions, a second-order finite volume approach is employed for spatial discretization. The proposed approach is intended to exactly preserve all steady states of shallow water equations retaining the second order of accuracy. To achieve this, we extend a recently developed fully well-balanced scheme, called HLL-MSF, to higher-order of accuracy. To extend the first-order HLL-MSF scheme to second order with the same well-balanced property of the first order one, a MUSCL reconstruction approach with a suitable weighted technique is proposed. The weighted approach allows the numerical scheme to return to the first order scheme with shockwave fixes at hydraulic jumps or at trans-critical points. Appropriate flux limiters are also introduced to ensure the well-balanced property of the numerical scheme in smooth steady state cases. The method's accuracy and stability are attributed to these carefully chosen flux limiters and weighted coefficients. The final step in the semi-discrete finite volume method involves time integration to advance the solution in time. In this paper, the third order explicit Runge-Kutta method is chosen as the time integration scheme. By combining the second-order finite volume spatial discretization and the third-order explicit Runge-Kutta time integration scheme, the proposed finite volume method ensures higher-order accuracy in both space and time. Results and Discussion To verify the well-balanced property and the second order of accuracy of the proposed numerical scheme several numerical examples and benchmarks contain in the literature including both steady and unsteady cases are presented. For numerical experiments that have analytical or reference solutions, numerical errors are obtained using L1 and L&infin; norms. The first test case is devoted to the simulation of steady state at rest or the lake at rest situation. numerical errors show that the proposed scheme is exactly well-balanced in this case. The second test case is related to a smooth steady state of trans-critical flow over a bump. The proposed second order scheme is confirmed to capture the smooth steady state exactly (Table 1). We also conduct a trans-critical flow with hydraulic jump to see how the proposed scheme behaves when the solution contains a shock discontinuity. Unlike the traditional higher-order schemes which often use the pre-balanced shallow water formulation to achieve the exact conservation property on steady state cases at rest, the proposed second order scheme can capture both smooth and non-smooth (Hydraulic jump) parts exactly with no smears and oscillations (Table 1). A test case is also conducted to confirm the second order accuracy of the numerical scheme. Table 2. shows that the intended accuracy is clearly achieved. Finally, three numerical experiments are conducted in quasi-steady and unsteady conditions including slowly moving shocks over flat or discontinuous topography. The higher-order approximate solvers are known to achieve better accuracy for such flows than the first order counterparts. ConclusionIn this paper a second order well-balanced numerical schemes are developed for the solution of one-dimensional shallow water equations. The approach is able to model different regimes of the flow accurately. The advantage of the proposed scheme over existing higher-order schemes is the fully well-balanced and entropy satisfying properties in which all steady states solutions are exactly preserved.Experimental investigation of the effect of hydrographs with different skewness and duration time on temporal variations of scour around a single cylindrical pier
https://jhyd.iha.ir/article_178450.html
IntroductionFor a bridge pier in the flow path, a three-dimensional and complex flow pattern is formed around the pier leading to the formation of a scour hole around it. The development of the scour hole will cause the instability of the bridge pier and ultimately the destruction of the pier and the bridge. This problem becomes very important during the floods, when the flow in the river increases rapidly and has the highest potential of destruction. Most studies have investigated scouring in steady flow conditions. The maximum scour depth that occurs under a flood hydrograph can be much smaller than the equilibrium depth resulting from steady flow under peak discharge conditions (Kothyari et al., 1992; Lai et al., 2009). Therefore, the use of flood peak discharge for design can greatly overestimate the maximum scour depth compared to the actual flood conditions (Chang et al., 2004). Considering the importance of scouring investigation in the conditions of unsteady flow and the limited available studies in this regard, more research in this field is necessary. The purpose of this research is to investigate the effect of the time of the rising and falling limbs of the hydrograph, as well as the duration of the hydrograph on the temporal variations of scour depth and its maximum value around the cylindrical pier.MethodologyThe experiments were carried out in a rectangular flume with glass walls and a straight length of 10 m, a width of 0.74 m and a depth of 0.6 m in the Physical and Hydraulic Modeling Laboratory of Shahid Chamran University, Ahvaz. The test section in the flume was covered with uniform sand with an average size of d50=0.7 mm and geometric standard deviation &sigma;=1.3. In order to achieve the goals of this study, a total of 13 experiments were examined. In order to investigate the effect of the time of the rising and falling limbs of the hydrograph on the temporal variation and the maximum scour depth, a number of 6 hydrographs with a constant duration of 100 minutes and the ratio of the time to reach the peak (Tp) to the duration time (Td) of the hydrograph (skewness) equal to 0.1, 0.2, 0.4, 0.6, 0.8 and 0.9 were designed. Also, 7 hydrographs with Gaussian distribution and duration times (Td) of 10, 20, 45, 80, 100, 120 and 160 were simulated to investigate the effect of flood duration on scouring (Fig. 3 and Table 1). A hydrograph generation system was used to create unsteady flow in the flume. This system included a programmed inverter that was used to adjust the variable flow rate of the hydrograph. The inverter was connected to the pump on one side and to the electromagnetic flow meter on the other side and was run by a computer through a software.Results and discussionThe results of the temporal variations of scouring showed that scouring starts from the sides of the pier and reaches the nose of the pier over time, and finally, the maximum depth of scouring occurs in the nose of the pier. The results showed that the maximum scour depth in the hydrograph with a Gaussian distribution occurs after the peak time (about 10% of duration time) (Fig. 5). Investigating of the effect of the rising limb of the hydrograph showed that in hydrographs with similar duration, the time to reach the peak of the hydrograph has no effect on the maximum scour depth, but it has a significant effect on the temporal changes of shear stress and scour depth. By reducing the time of the rising limb of the hydrograph from 90 minutes to 10 minutes, the shear stress change rate increases 9 times and the scouring rate increases about 6 times. Investigating the effect of the falling limb of the hydrograph on the maximum scour depth showed that the effect of the falling limb on the maximum scour depth increases with the decrease of the time of the rising limb of the hydrograph. The results also showed that the maximum scour depth in hydrographs with skewness of 0.1, 0.2, 0.4, 0.6 and 0.8 is 51.35, 21.28, 12, 5.56 and 1.79 percent more than the scour depth at peak discharge, respectively (Fig. 6). It was also observed that in hydrographs with the same peak time but different duration time, the time of the falling limb is effective on the value of the maximum scour depth. With the increase of 9, 4, and 1.5 times the time of the falling limb of the hydrograph, the maximum scour depth increases by 30.23, 14, and 1.82 percent, respectively. Investigating the duration time of the hydrograph showed that the increase in the duration time increases the depth and dimensions of the scour hole around the pier. It was observed that the maximum scour depth for hydrographs with a duration of 20, 45, 80, 100, 120 and 160 minutes were 19.44, 38.89, 52.78, 58.33, 66.67 and 69.44% more than a hydrograph with a duration of 10 minutes, respectively (Fig. 7). In addition, the slope of the time variations of the scour depth decreases with the increase of the duration time due to the lengthening of the flow rate changes interval along the rising limb of the hydrograph (Fig. 8).ConclusionIn this study, scouring around a cylindrical pier was investigated under unsteady flow conditions. The results showed that for hydrographs with similar peak discharge and duration time, the time of the rising limb of the hydrograph has a significant effect on the temporal variation of shear stress and scour depth, but it has almost no effect on the maximum scour depth. In addition, it was found that by reducing the time of the rising limb, the influence of the falling limb of the hydrograph on the maximum scour depth increases. Investigating the results of the effect of hydrograph duration time on local scour showed that with the increase of hydrograph duration time, the maximum scour depth increases and the slope of temporal variations of scour depth decreases.Numerical analysis of flow field and flood risk in solid urban block street intersections
https://jhyd.iha.ir/article_178453.html
Floods can cause significant damage to goods and people, particularly in densely populated urban areas with high asset values. Flood risk is typically assessed using flow depth, flow velocity, and water level parameters (de Moel et al., 2009). Meja-Morales et al., (2021) investigated the impact of flow exchanges between a porous urban block and surrounding streets and found that porosity significantly affects urban flood flow characteristics. In another study, Meja-Morales et al., (2023) examined the effect of flow instability and open areas in urban blocks on key flood characteristics and reported that the instability level of incoming hydrographs greatly affects the volume of flood water stored in urban blocks. This research aims to evaluate the distribution of flow depth, velocity, and flow patterns in non-porous urban block streets by considering changes in stable inflow. The study seeks to understand multidirectional flow paths caused by the street network and develop a flood risk map for humans using Flow3D software. The validation results of the numerical model showed that the turbulence model had the highest correlation with the laboratory model, with a relative error of 3% and 6.8% for the velocity profile near the water surface and averaged velocity at depth, respectively. In all models, the right and upstream streets had the highest and lowest depth, speed, and human stability number, while the downstream street had the largest range of flood parameters, with 2 to 3 times the average speed and 3 to 4 danger zones for pedestrians. Increasing the flow rate at Inlet 1 for a constant flow rate at inlet 2 increased the flooding characteristics of the right and downstream streets while decreasing the speed in the left street. Conversely, increasing the flow rate at Inlet 2 for a constant flow rate at Inlet 1 increased the flooding characteristics of the left street, decreased the speed in the right and downstream streets, and had minimal effect on the flood characteristics of the upstream street.Investigating changes in coefficients of the non-Darcy flow exponential relationship within rockfill materials under different flow conditions
https://jhyd.iha.ir/article_178456.html
IntroductionAs we know, the calculation of hydraulic gradient is highly important in the analysis of steady flow inside rockfill materials. Binomial and exponential relationships are used to calculate the hydraulic gradient based on the non-Darcy flow velocity, and the binomial relationship is more accurate and efficient than the exponential relationship. Since it is necessary to use an exponential relationship in the two-dimensional analysis of non-Darcy flow in coarse porous media, in the past, researchers have provided relationships to calculate the coefficients m and n of the exponential relationship based on the coefficients a and b of the binomial relationship. In some previous studies, Vmax= 1 has been considered, even though the maximum flow velocity depends on the physical characteristics of the pebbles and the characteristics of the flow and is not necessarily equal to one. For this reason, in this research, by designing and equipping the laboratory and recording the laboratory data, the maximum velocity based on the values of a, b and Re of the analytical model of Ahmed and Sunada(1969) is proposed.As mentioned above, various researchers tried to calculate the coefficients of the exponential relationship using the values of a and b in the binomial relationship. One of the most important relationships is presented by George and Hansen (1992) as follows.n=(5a+6bV_max)/(5a+3bV_max ) (1)m=(5a+4bV_max )(4a+3bV_max )/(4(5a+3bV_max ) (V_max )^(n-1) ) (2)Further, by stating that in the coarse-grained porous medium, the slope of the energy line (Sf) is equal to the hydraulic gradient (i), it can be stated that one of the most important parameters in the investigation of the flow in the gravel medium in free flow and under pressure is the calculation of it is a hydraulic gradient. In this research, using the coefficients of the binomial relationship, we presented a solution to calculate the values of m and n in the exponential relationship with better accuracy. Therefore, considering that the exponential relationship is used in the two-dimensional analysis of the non-Darcy flow in porous gravel media, this can play a significant role in reduction of the error of hydraulic gradient calculation.MethodologyIn the current research, the laboratory data recorded in the hydraulic laboratory of the Faculty of Civil Engineering of Zanjan University were used. For this purpose, an attempt was made to design and set up a test device and perform tests on different gravel materials. Experiments were carried out in a laboratory flume with the ability to tilt, with dimensions of 1m&times;1m and a length of 15m, and the length of 2.2m of the mentioned flume is filled with rockfill. The walls of the flume are made of plexiglass, and to measure the piezometric height along the porous media, 23 piezometers are used on the bottom of the channel, which are arranged at certain distances from each other and along them. The water flow in the channel is created by a pump with a maximum flow capacity of 90 liters per second. In order to create a porous media, three types of rockfill materials with small, medium and large diameters have been used in the experiments. During the tests, to ensure a stable flow, the pump was working for about 10 minutes with the desired flow and after the stability of the flow, the desired parameters were measured. These parameters include the piezometric height at the location of 23 piezometers as well as the water depth at the location of each piezometer. Piezometric values are read using a calibrated table. The water depth was also measured and recorded directly by a ruler.Results and DiscussionSince the exponential relationship is only accurate for a certain range of Reynolds numbers and the user area recommended for this relationship by its providers is only non-quiet flow conditions, therefore, if the exponential relationship is used in the two-dimensional solution of the equations, there will be a large error will enter the calculations. To avoid this problem, various researchers have tried to convert the binomial relationship into an exponential relationship. If the minimum flow velocity Vmin and the maximum flow velocity Vmax in the conversion area of the binomial relationship is in the form of an exponential relationship. In order to convert the two mentioned relations, relations (1) and (2) can be used. According to the conducted tests, in most cases, Vmin is considered zero and Vmax value is assumed to be equal to one, while the maximum flow velocity depends on the physical characteristics of the pebbles and the characteristics of the flow and is not necessarily equal to one. Therefore, Vmax can be calculated from the following relationship according to Ahmed and Sunada's(1969) analytical model and the definition of the Reynolds number as Re=&rho;Vd/&mu;.V_max=Re_max a/b (3)By using relations (1), (2) and (3), it is possible to take advantage of the accuracy of the binomial relation and the practical property of the exponential relation in the two-dimensional analysis in porous media.If relations (1) and (2) are used in the calculation of the coefficients of the exponential relationship of steady flow in gravel materials, the average relative error between the calculated and recorded hydraulic gradients in the laboratory assuming Vmax=1 (according to previous research) in fine gravel materials, medium and coarse are calculated to be 21.95%, 22.98% and 21.97%, respectively. While if relation (3) is used (the solution presented in the current research), the average relative error values of the hydraulic gradient are equal to 11.39, 14.69 and 19.72%, respectively.ConclusionIn general terms, by using relations (1) and (2) and using the relation proposed in the present study instead of Vmax=1, the average values of the relative error of the hydraulic gradient in fine, medium and coarse rockfill materials have decreased to 10.56, 8.29 and 2.25%, respectively, which indicates the high accuracy and efficiency of the proposed solution.Keywords: Non-Darcy flow, exponential relation, binominal relation, rockfill, hydraulic gradient.Simulation of the effect of dune lee slope on hyporheic flow characteristics
https://jhyd.iha.ir/article_178549.html
AbstractIntroduction: Rivers are complex systems in which different chemical, biological, and physical processes occur in it. When the flow moves along the river, there is an exchange between the surface flow and the subsurface flow. The hyporheic zone is a saturation zone below the riverbed, which plays an important role in many biological and chemical processes. Residence time is the most important characteristic of the hyporheic zone. Because the chemical and biological reactions that occur inside the sediments depend on the time at which flow paths remain in the bed for a while and then return back to the surface flow. Hyporheic exchange is the mixing of surface and subsurface flow just beneath the river bed. Such exchanges can be caused by the presence of different bedforms in the river. Dunes are one type of river bed that can be observed in straight, meander, and braided rivers. The pressure gradient between the upstream and downstream of a dune leads to hyporheic exchanges. The wavelength, amplitude, and slope of the lee side and stoss side can affect the rate of exchanges. In the present study, the effect of the dune lee side slope at angles of 10, 20, and 30 degrees on the characteristic of the hyporheic zone (i.e., residence time, exchange flow, and hyporheic depth) has been investigated numerically.Methodology: The FLOW3D software is used for the numerical simulation of surface flow. The simulation domain consists of a flume with 2.7m length, 0.1m width, and 0.3m height. The model running time was 120 seconds for surface flow simulation, which, with the passing of this time, the flow in the channel becomes stable. The pressures along dunes are introduced as a Dirichlet boundary condition on top of the groundwater model, i.e., MODFLOW. Then, the effect of the dune lee side slope at angles of 10, 20, and 30 degrees on the characteristic of the hyporheic zone (i.e., residence time, exchange flow, and hyporheic depth) has been investigated.Results and Discussion: The results show that the maximum and minimum pressure occurred on the stoss side and the crest of the dune, respectively. By increasing the dune lee side slope, the distance between the maximum and minimum pressure is reduced, the depth of hyporheic exchange decreases, and the exchange rate and residence time increase. Also, for all three angles, with a constant ratio of the subsurface to surface flow, the depth of hyporheic exchange increases with the increase of the hydraulic conductivity to the dune length ratio (K/A). Increasing the velocity of the subsurface flow causes the subsurface flow to dominate the surface flow and the flow in the subsurface flow moves towards the surface flow. As a result, by increasing the ratio of subsurface flow velocity to surface flow velocity, the exchange flow increases, and the depth of hyporheic exchange decreases.Conclusion: The results show that as the lee side slope increases, the residence time, and exchange flow increase, and hyporheic depth decreases. Also, by increasing the hydraulic conductivity, the hyporheic exchange depth increases, but by increasing the subsurface flow velocity and the porous media thickness, the hyporheic exchange depth decreases.Evaluation the effect of depth and flow velocity on the particle size and shape of surface sediments of sandy rivers using image processing methods
https://jhyd.iha.ir/article_178551.html
One of the important challenges in investigating the hydraulic, morphological and ecological behavior of rivers is to accurately determine the geometrical dimensions of river bed particles. The information extracted from the grain size curve of river bed particles has many applications in the field of river engineering, such as modeling of sediment transport, changes in sediment deposition or river bed erosion, and changes in river morphology (Hasannejad Sharifi et al., 2015).Nowadays, despite the fact that determining the granularity of the bed particles and the boundaries of rivers is important, the removal of sediments from the natural environment leads to disturbing the sedimentary bed and causes changes in the river system (Sadeghi and Qara Mahmoudoli, 2013). Therefore, it is very important to use a method that can calculate the results of granulation with less cost and quickly. Image processing methods are known as new method have been taken into consideration in order to increase rapidity and accuracy, along with the method of field measurement of granularity.Methodology: In this research, by examining the morphological and sedimentary conditions of the rivers of the Zanjan province, as well as the ease of access, Zanjanrud river was selected as the study area. Then three cross-sections for sampling with frame dimensions of 20&times;20 cm were determined from the bed of Zanjanrud river and after photographing the surface of the samples, painting by spray paint in order to identify the surface grains, sampling was done from the determined sections. The samples were taken to the laboratory and the sieve test was performed. Then, in the laboratory environment, each of the samples was arranged in a metal frame with dimensions of 20&times;20 cm and was installed in a channel with a length of 8 meters and a width of 20 cm. By applying the conditions of stagnant water at three depths of 4, 8 and 12 cm and water flow with different depths and velocities, the samples were re-photographed and the grain size curve were obtained by Image J and Hydraulic Toolbox softwares.Results and discussion: Based on the results of Sieve, in sample A, almost 85% of the particles have a diameter equal to and less than 31.7 mm. In sample B, almost 85% of the particles passed through the sieve of 1.38 mm. In sample C, more than 97% of the particles passed through the 38.1 mm sieve. According to the classification system of the United States, the sediments of all three sections of Zanjanrud are gravel. Also, according to the results, it can be seen that the standard deviation of the samples is less than 2, the uniformity coefficient is less than 4, and the sorting coefficient is less than 2, which shows that the examined samples are almost uniform. In sample A, atdepth of 8 cm, the average relative absolute error values were obtained similar to those at depth of 4 cm. In sample B, the average error value of the fine grains is the same \coarse-grain. The reason for this can be due to the low value of the standard deviation of this sample compared to the other two samples. The average error value at depth of 8 cm was found to be 14% for fine grains and 12% for coarse grains. In sample C, similar to sample A, the average error value in the fine grains is less compared to the coarse grains.The average relative error at depth of 8 cm was found to be 9% for fine grains and 14% for coarse grains. Results showed that Image J software has better performance than Hydraulic Toolbox software in determining the particles granulation curve of the Zanjanrud river.The effect of flow velocity and depth on the K values of the index diameter of 50% showed that at depth of 4 cm, the average values of K in samples A, B, and C are 1.01, 1.19, and 1.08, respectively. Also, at depth of 8 cm, the values of K for samples A, B, C are equal to 1.05, 1.12, and 1.11, respectively, and at depth of 12 cm,there are equal to 1.08, 1.18, and 1.13, respectively. According to these results, it can be seen that the K values of sample A are lower than the other two samples in all three depths of 4, 8, and 12 cm. At depth of 8 cm, the K values of sample B at different velocities coincide approximately with those of sample. Also, the K values of sample C at two depths of 4 and 12 cm are lower than the K values of sample B. The average K values of the 50% index diameter at three depths of 4, 8, and 12 of sample A are 1.01, 1.05, and 1.08, respectively (with an average value of 1.046); the mean K values of sample B are 1.19, 1.12 and 1.18 respectively (with an average value of 1.16) and also the mean K values of sample C are 1.08, 1.11 and 1.13 respectively (with an average value of 1.1) (with a total average of 1.1 for all three samples).Conclusion: In most of the hydraulic flow conditions, the granulation curve obtained by Image J software is close to the sieve granulation curve. In contrast, the Hydraulic Toolbox granulation curve is significantly different from the sieve curve and the curve of Image J software. The flow velocity and flow depth does not have a noticeable effect on the K values of the index diameter of 50%.Investigating the effect of operational parameters of a semi-industrial hydro-cyclone on the efficiency of Granite and Marble stones wastewater treatment
https://jhyd.iha.ir/article_189761.html
IntroductionThe use of modern methods of recycling effluent with high treatment efficiency in compare to the traditional methods (the use of sedimentation ponds) is of great importance. One of the modern methods of treating these effluents is the use of filtering presses. A newer method is using hydro cyclones as a result of centrifugal hydrodynamic forces for separating solid particles from the effluent, e.g., stone powder in the current research, (Naderi et al.2019). In this regards, many researches have been done in the field of separation of two different phases of fluid using hydro cyclone in different hydraulic conditions and geometric parameters.Materials and methodsMaterials used in researchThe materials used in this research were solid particles in the wastewater of the stone cutting factory of Mahmoudabad industrial town of Isfahan. The resulting slurry was collected in the factory and after drying and separation was used for the experiments. In this study, Granite and Marble stone powder with a density of 2750 and 3020 kgm-3 and a particle diameter distribution less than 600&micro;m was used. Also, the effect of hydraulic parameters such as flow division ratio (under flow discharge to inlet flow discharge), wastewater weight concentration and inlet pressure on hydro cyclone performance with a cyclone diameter of 140 mm in the separation of Granite and Marble powder stone from wastewater was investigated.Design of experiments Experiments were designed by Design Expert.10 software with response level method (RSM). In conducting experiments, first, a solution of Granite and Marble powder stone with the desired concentrations (0.64 to 7.36% by weight) in a volume of 20 liters was prepared in a tank, and then this solution was circulated to the hydro cyclone by pressure with a centrifugal pump.In each experiment, inlet perssure and overflow pressure were recorded using pressure guages and the volumetric flow rate from overflow and underflow was measured. Samples of overflow and underflow were taken with a specified volume and then stored and dried in an oven at 105&ordm;C for 24 hours. The residual dry mattter mass was measured from the overflow and underflow samples, and the solid particle separation efficiency was computed from Eq. (1):E=M_u/M&times;100 (1) In this Equation, Mu is mass per unit volume of Granite and Marble stone powder inside the underflow (grl-1); M is total mass per unit volume of examined Granite and Marble stone powder in hydro cyclone inlet (total overflow and underflow; grl-1) and E is the efficiency of separation of solid particles from the feed. Results and discussionInfluence of operating parameters of weight concentration of the feed (Cw), inlet pressure of the hydro cyclone (Pi), and the Ratio of outlet flow) under flow) from the discharge to inlet flow to the hydro cyclone (Rf) on the efficiency of the examined hydro cyclone is given in the form of Eq. (2) for Granite powder stone and Eq. (3) for Marble powder stone. (2) Efficiency=93.16-1.01R_f-4.36C_w+10.01P_i+0.04R_f C_w-0.04R_f P_i+0.96 C_w P_i+8.12E-003*〖R^2〗_f -0.08*〖C^2〗_w-2.41* P_i &sup2; (3) Efficiency=116.26-2.11R_f-9.13C_w+6.22 P_i+0.11R_f C_w+0.17R_f P_i+1.22 C_w P_i+5.54E-003*〖R^2〗_f+0.12*〖C^2〗_w-2.55* P_i &sup2; In order to validate the obtained model, two normal probability diagram comparing the predicted data of the model with the real values were used. The results showed that with decreasing flow distribution ratio, particle separation efficiency increases, also separation efficiency decreased with increasing inlet pressure, and with increasing effluent concentration.ConclusionIn this study, the effect of hydraulic parameters including flow separation ratio, inlet pressure and feed concentration was investigated on the performance of a semi industrial hydro cyclone. The analysis of the results using Response Surface Methodology (RSM) showed the effectiveness of the statistical method for obtain the optimum operational condition of the examined hydro cyclone. Based on the RSM method, the highest separation efficiency was obtained 86 and 88%, for Granite and Marble powder stone respectively. Key words:Flow ratio, Hydro cyclone, wastewater treatment, Separation efficiency.Developed Three-dimensional model for extract stage-discharge relationship in straight multi-stage compound channels
https://jhyd.iha.ir/article_189762.html
Developed Three-dimensional model for extract stage-discharge relationship in straight multi-stage compound channelsABSTRACTIntroductionIn natural rivers and certain urban channels, when flood events occur, the flow diverts from the main channel and inundates the surrounding floodplains. These particular configurations are termed compound channels. Floodplains can exhibit both symmetrical and asymmetrical patterns. Depending on geometric factors, lateral slope, and differences in elevation, multiple floodplains can manifest on each side of the main channel. These intricate structures are known as multi-stage compound channels. Multi-stage compound channels not only possess enhanced flow conveyance capabilities compared to simpler classic compound channels but also their second or third floodplains may offer prospects for recreational utilization or landscape enhancement within urban settings. Historically, the examination of flow parameters and the computation of conveyance capacities for compound sections were carried out using conventional methodologies, such as divided channel methods and traditional flow resistance equations like Manning, Chezy, Darcy-Weisbach, and others. However, these approaches often disregarded the momentum exchange arising from interactions between the main channel and floodplains, as well as the impact of secondary flows. Consequently, the estimated flow rates for compound sections tended to be higher than actual values. Sellin (1964) played a pioneering role in acknowledging the interaction between the main channel and floodplains, laying the groundwork for subsequent investigations into the evolution of conventional techniques. In contrast to the extensive research on classic compound channels, multi-stage compound channels have received limited attention and exploration in the scientific literature.MethodologyIn this research, a numerical solution of the Navier-Stokes equations using the finite volume method and The RNG k-&epsilon; turbulence model has been employed to simulate various hydraulic characteristics of multi-stage compound channels. These characteristics encompass the three-dimensional flow pattern, distribution of transverse velocity, secondary flows, turbulence energy, and the stage-discharge relationship. The RNG k-&epsilon; turbulence model is adept at reproducing rotational flows and large vortices, addressing the limitations of the standard k-&epsilon; model in representing non-circular channels at corner locations and rotational flows.To verify the validity of this mathematical model, laboratory data obtained from a channel with a three-stage asymmetric rectangular compound section (Singh, 2021) were utilized. The experimentation carried out in a channel featuring a main section width of 0.445 meters. On one side of the main section, two floodplains of widths 10 and 20 centimeters were established. The bed of the main channel was constructed using glass, while the bed of the first and second floodplains were covered with a uniform layer of syntetic grass to introduce channel roughness.The channel itself is 20 meters in length, with a longitudinal slope of 0.003. The total height and width of the channel are 0.5 and 0.745 meters, respectively. The bankful height is set at 0.0425 meters. The flow rate within this channel varies between 20 and 60 liters per second.Results and discussionOverall, the comparison of the three-dimensional model's computational results with experimental data in terms of the positions and values of maximum and minimum velocities indicates the satisfactory accuracy of the proposed mathematical model in this study.The turbulence intensity and momentum exchange at the interface between the first and second floodplains are lower compared to the interface between the main channel and the first floodplain. This discrepancy is attributed to the greater velocity difference at the interface plane of the main channel and the first floodplain. The influence of secondary currents at the main channel and first floodplain interface diminishes as the water level rises. However, significant secondary currents persist at the boundary between the first and second floodplains across all investigated relative depths. This underscores the significance of flow dispersion in contrast to convection in the second floodplain, particularly in cases of shallow relative depths.The highest flow velocity is observed at the midpoint of the main channel, inclined toward its right wall, situated far from the channel bed and close to the water surface. The computed transverse profiles of stream-wise velocity are satisfactorily accurate in both the main channel and floodplains (especially the second floodplain). Nevertheless, the modeling error is relatively notable at the interface of the main channel and the first floodplain. Predicting flow discharge for this channel using the mathematical model yields an average error of approximately 3.9% and a maximum error of 6.2%.ConclusionDue to the lack of experimental data on height and width variations of the second floodplain and their impact on flow characteristics, expressing the effects of these conditions is challenging. Further research involving precise laboratory measurements is required to comprehensively understand the influence of these changes.Considering that one of the applications of multi-stage compound channel is in urban areas and the first floodplain has a smaller width and is designed with the aim of increasing the channel conveyance capacity, and the second floodplain is intended to beautify the urban landscape and use it as a recreational and tourism environment. Therefore, it usually has tree vegetation. In addition to creating high shear stresses in the bed of the second floodplain, this causes high energy loss and a significant decrease in the conveyance capacity of the multi-stage compound channel. Therefore, it is recommended to design rivers or manmade flood control channels in the urban areas in the form of multi-stage compound channels so that the first floodplain is to be significantly increase the conveyance capacity of the channel and the second floodplain is for urban and public landscapes. This provides nearby people to escape from the danger zone during severe urban floods.Key words: finite volume method,quick method, RNG K-&epsilon;, multi-stage compound channel, stage-discharge relationshipInvestigating the use of variable coefficients of Forschheimer's relation in the analysis of unsteady flow in porous media
https://jhyd.iha.ir/article_190054.html
Introduction In Coarse-grained porous media, the size of particles and pores causes complications in the flow behavior, in a way that the flow has no layered state and the Darcy relation loses its validity. In these cases, the hydraulic gradient velocity relationship is nonlinear. The coefficients of the relationships have been examined by different researchers. Surface water relations, also known as Saint-Venant relations, are among the best computational tools governing free surface water flows. Equations mentioned above were first used in 1871 by Adbemar Barre de Saint Venant in order to analyze unsteady flow with a free surface, and afterwards many researchers investigated and estimated the characteristics of free flows as well as flow in porous medium by using these equationsThe main purpose of this research is to investigate characteristics of steady and un-steady flow in porous environment. By calculating the velocity values at each point and plotting the velocity graph against the hydraulic gradient, the coefficients of Forschheimer's binomial relation were obtained for each of the discharges. By examining the changes of these coefficients, linear relationships were obtained for the changes of the coefficients against the flow rate changes.Methodology In this study, the tilting laboratory channel of the Faculty of Civil Engineering of Zanjan University was used. In order to create a porous environment, 1.2 meters of the length of the channel has been selected and separated by two net separators. (Fig 1). The grading of pebbles used in this research is presented in Figure 2. Also, their physical characteristics are given in Table 1. The experimental program of this research was carried out in two sections of steady and unsteady flow. In the steady part, water flowed with 10 different flow rates from 8.51 to 20.62 L/s. By arranging the coefficients and the flow rates and plotting them against each other, a function can be derived to calculate each of the coefficients a and b based on the flow rate. The graphs in Figure 4 illustrates these functions. In the next part of the tests, the hydrograph in Figure 5 was passed through the porous media..Saint-Venant's equations were considered as governing equations and were solved using the method of characteristics. The equations were solved once by using fixed values and the other time by using the functions of Forschheimer coefficients.Results and DiscussionThe Saint-Venant equations for the problem were solved once by using the average values of the coefficients of Forschheimer's relation and again by using the functions of these coefficients. By solving the equations, the velocity and depth values and hence the flow rate at any moment and at any point of the porous medium were calculated. Table 3 shows the calculated flow rate error for two solution modes. In this table, the minimum and maximum values of the input hydrograph are compared with their corresponding values in the hydrograph at the point of 6 cm. Checking the error values shows that the calculated error of the maximum flow rate (which occurred at the peak of the hydrograph) in the case of constant Forschheimer coefficients is 13.36%, which is about 3 liters per second more than the actual hydrograph. In spite of this, there is only 2.16% error in the calculation hydrograph with variable coefficients of maximum discharge. This is also important in the minimum of hydrograph. So that the error value in the calculation hydrograph with fixed coefficients has 22% error (minimum of the hydrograph occurs at the beginning), while the corresponding value for the calculation mode with variable coefficients is only 1%.As can be seen in Fig 9, the calculated profile is approximately always a little lower than the observed profile and the difference between these two profiles maximize at the time of the hydrograph peak, and then the difference decreases again as the discharge decreases.Table No. 4 shows the percentage of the relative error for the observed and calculated flow profiles at different times. As mentioned, the maximum error among all times and all points is observed in 400 seconds and at the terminal point of the profile.Conclusion The results of the numerical solution in two cases of fixed and variable coefficients show that the percentage of relative error in the maximum and minimum discharge for the case of fixed coefficients is much more than the case of variable coefficients.The results indicate that the maximum discharge go smaller as we move along the medium and also occurs at a later time.The investigations determined that the average calculation error of the depth at the times of 100, 300 and 600 seconds is 4.88, 8.05 and 9.93 percent, respectively. Keywords: porous media, Forschheimer's Relation, Unsteady Flow, Saint-Venant Equations, Method of Characteristics.Laboratory and Numerical Investigation of Hyporheic Exchanges in Sand Mining
Pit
https://jhyd.iha.ir/article_190055.html
Introduction: River materials such as sand are widely used in the construction industry due to their accessibility, texture, and suitable particle size. While sand mining is essential for economic development and infrastructure projects, it can have significant adverse effects on river ecosystems. Therefore, It is crucial to implement sustainable mining practices and enforce regulations to mitigate these effects. When a river is diverted for sand mining, it can result in the loss of natural river features that promote hyporheic exchange. These features include meanders, riffles, and pools, which create flow patterns that allow water to infiltrate into the sediment and exchange with the groundwater. The hyporheic zone is the area just beneath a river where water and nutrients exchange between the river and groundwater. Sand mining pit can disrupt the hyporheic zone by altering the channel morphology and reducing the connectivity between the river and groundwater. As a result, the exchange rates of oxygen, nutrients, and other substances between the river and groundwater can be reduced, affecting the overall health and functionality of the river ecosystem. In this study, the effect of different sand mining pit lengths and upstream water depths on the characteristics of the hyporheic zone is investigated. Additionally, the numerical results of surface and subsurface models are calibrated with laboratory observations. Methodology: Experiments were conducted in a flume with a length of 7 meters, width of 1 meter and height of 1 meter. The velocity of the water was measured using an Electromagnetic Current Velocity Meter with an accuracy of 0.5 cm/s. Sediments with an average diameter of 2.3 mm, falling within the recommended range of previous studies, were filled in the channel (Rovira et al., 2005; Wu and Wang, 2008; Mori et al., 2011). Trapezoidal-shaped sand mining pits with a height of 0.1 m were constructed in the middle of the flume, and their lengths varied. The range of dimensions for the mining pits was determined based on previous studies conducted by Lee et al. (1993), Barman et al. (2019), Jang et al. (2015), and Haghnazar et al. (2019). The objective of the study was to investigate the impact of the length of the mining pits, the water depth, and different discharges on the hyporheic exchanges. The experiments were carried out in eight scenarios. In scenarios E1 to E4, the upstream water depth was 0.061 m, and the pit lengths were 0.25 m, 0.5 m, 0.75 m, and 1 m, respectively. In scenarios E5 to E8, the pit lengths were the same as before, but the water depth was increased to 0.101 m. To simulate the surface flow on the sand mining pits and the subsurface flow in the sediment, Computational Fluid Dynamics software was utilized (Cardenas and Wilson, 2007a, 2007b, 2007c; Chen et al., 2015). Anasys Fluent software was used for simulating the surface flow, while Comsol software was used for simulating the subsurface flow (Bear, 1972; Cardenas and Wilson, 2007a, 2007b; Trauth et al., 2013).Results and discussion: For the calibration of the surface model, the observed and simulated water surface elevation and the surface flow velocity were compared. RMSE for the free surface elevation in the E4 scenario was found to be 0.002 m, indicating a good agreement between the laboratory and numerical model. The comparison of vertical velocity profiles also showed a close match between the simulated and experimental velocities. It demonstrates the model's capability to simulate flow behavior and can be utilized for simulations related to similar scenarios. Additionally, injecting dye into the bed and comparing the simulated streamlines with the laboratory results were done to assess the accuracy of the subsurface model. Analysis of dye paths in the laboratory demonstrated that the simulated streamline pattern closely follows the pattern observed in the laboratory, it further indicates that the numerical model is capable of accurately representing the flow dynamics. It appears that increasing water depth has a significant impact on pressure values and the maximum pressure gradients. Additionally, the length of the pit also affects hyporheic exchange, with longer pits resulting in decreased exchange. the percent of hyporheic exchanges for the depth of 0.061 meters ranged from a maximum of 9.612% in E1 scenario to a minimum of 6.133% in E4 scenario. Also, the percentage of hyporheic exchange decreases with increasing discharge. Similarly, for the depth of 0.101 meters, the maximum percent of hyporheic exchanges was 10.003% in E5 scenario, while the minimum was 6.171% in E8 scenario. The E4 and E8 scenarios exhibited the highest dimensionless penetration depth and residence time, while E1 and E5 had the lowest values. The increase in water depth also led to an increase in the dimensionless penetration depth. It shows that at shallower depths, turbulent eddies may influence the flow field, resulting in shorter residence times and particle penetration. Regarding residence time distribution, the histogram analysis revealed a log-normal distribution for the E1 and E5 scenarios, while a Generalized Extreme Value Distribution was obtained for the other scenarios.Conclusion: In this paper, the effect of different lengths of sand pit mining and different depths of water was studied by analysis of surface flow and exchange with the subsurface flow. The results showed that increasing the length of the pit was found to decrease hyporheic exchange, indicating an inverse relationship between pit length and dimensionless hyporheic exchange. This suggests that longer pits may have reduced interaction between surface and subsurface flows. On the other hand, increasing the depth of water in the tested pits was seen to increase the dimensionless hyporheic exchange. This means that deeper water levels enhance the exchange between surface water and subsurface flow. The average maximum dimensionless penetration depth decreased as the pit length decreased, ranging from 1.66 to 2.66. This indicates that shorter pits may have limited penetration of particles into the subsurface. The range of hydraulic gradient values at a depth of 0.061m was observed to be between 0.10386 and 0.10644 meters, while at a depth of 0.101m, the range was between 0.10517 and 0.10645 meters.Multi-objective optimization of stepped spillways in order to reduce the design costs and maximize the energy dissipation (case study: Sarooq reservoir spillway)
https://jhyd.iha.ir/article_190056.html
Introduction: Considering that dams are one of the most important water storage resources in water projects, therefore, proper construction and operation management of them is one of the most important responsibilities of water resource managers. One of the important parts in the construction of any dam is the design of the dam spillway, which is responsible for discharging excess water from the reservoir to downstream in case of floods. Destruction or inefficiency of spillways causes severe damage to the dam or even causes its complete destruction, that is why the design and construction of this part of the dam is very important. Among different types of spillways, stepped spillways, in addition to passing excess water from the reservoir of dams, are also a structure that consumes flow energy. Until now, in the studies carried out in this field, the optimization of stepped spillways has been considered as a single objective, which usually aims to optimize, minimize construction costs or maximize energy consumption in these spillways, and rarely optimize the dimensions of spillways with Taking into account the two factors of cost and energy consumption has been considered simultaneously. Therefore, in this study, for the first time, a multi-objective optimization model has been developed by benefiting from the capabilities of the improved version of the dragonfly optimization algorithm for the design of stair overflows with the aim of minimizing the volume of concrete used and increasing energy consumption.Methodology: In the design of the stepped spillway, the discharge parameters (Q) and the horizontal length of the overflow (L) are among the most important input parameters, which are determined based on the initial studies of topography and hydrology and are considered constant during the design. According to the purpose of the present research, an optimal combination of effective parameters in the design of a stepped spillway, including slope, width, height of the spillway, water pressure on the spillway, and step height, should be determined in a way that leads to the highest energy consumption and the lowest design costs with By-law restrictions should be taken into account. In the current research, the objective function, which consists of decision variables, should simultaneously provide the maximum amount of energy consumption and the minimum volume of consumed concrete, while satisfying the constraints and hydraulic conditions of the design problem. For this purpose, the dragonfly optimization algorithm, which is one of the powerful algorithms of collective intelligence methods, and was first proposed by Mirjalili.This algorithm is inspired by the group and social behavior of dragonflies in nature. Dragonflies usually live alone in the wild and only act in groups for hunting and migration. The basis of the dragonfly optimization algorithm to find the optimal answer is their two crowding behaviors. In this way, based on the static behavior, the members of the algorithm population are divided into smaller groups and search the problem space, then based on their dynamic behavior (exploitation phase), they determine the optimal answer with more members.Results: The spillway of Sarouq Dam, located in West Azarbaijan province, was selected as a case study in this research to evaluate the developed model. In the first part, the problem of optimal design of the stepped spillway of Sarouk Dam was investigated as a single-objective problem with the aim of maximizing the amount of energy consumption. The purpose of redesigning Sarouk dam spillway was to provide an optimal design for a stepped spillway instead of the existing flat spillway with the aim of maximizing energy consumption downstream of the dam. In all the optimal models provided by IDA, the consumption of water energy has increased significantly. According to the report of Hosseini, 2019, the amount of energy consumption at the foot of the existing spillway of Sarouk Dam is equal to 23.41, which the use of the stepped spillway in the present research increases it for the flow rates of 560.2, 776.9, and 422 cubic meters per second, respectively. 71.32, 65.72 and 74.74 percent. According to the main goal of this article, in this section, the new and improved algorithm based on the dragonfly algorithm has been used to optimize the multi-objective overflow of Sarouk Dam by considering the amount of concrete pouring and the amount of energy consumption as objective functions. The results shown that, using the multi-objective optimization approach for the design of stair overflows leads to the presentation of different types of designs with different implementation costs and energy consumption rates. Therefore, using the multi-objective optimization approach has led to the production of many answers, which allows the employer to design the overflow according to the budget he has.Conclusion: In this research, using the improvement of a new metaheuristic algorithm called the dragonfly algorithm, a single-objective model was developed with the aim of maximizing energy consumption, and another multi-objective model was developed with the objectives of minimizing the construction costs of the stair overflow. The developed models were used for the optimal design of Sarouk Dam spillway. The use of the improved Dragonfly multi-objective optimization algorithm to minimize construction costs and increase energy consumption showed that the multi-objective optimization approach can provide a set of answers that is a great help to the employer in order to achieve an economic plan based on the budget. availableComparative analysis of construction costs of urban drainage network in different hydraulic simulation methods: a case study in Ghaderabad County, Fars Province
https://jhyd.iha.ir/article_190057.html
Introduction In this research, the comparison of different routing methods and their impact on the hydraulic characteristics and dimensions of storm water conveyance pipes and the construction cost of different options is investigated. For this purpose, the rainfall-runoff simulation model (SWMM), is used for routing. Qaderabad city is taken into consideration as a case study with the aim of implementing different simulation options. The purpose of this study is to compare the construction cost of different hydraulic simulation options.Methodology In general, in SWMM model, the routing of the flow in the pipe and conduit is governed by using the one-dimensional Saint-Venant equation. The Saint-Venant equation is solved using the implicit finite difference method. Different options are available in this model including steady flow, Kinematic wave, Diffusion wave and fully dynamic. All methods are considered in this study to gain a better understanding of the each methods on outputs and construction expenses as well.Results and Discussion After setting up the model, the simulation was conducted in the selected return period with four mentioned simulation option methods: Dynamic, Diffusive, Kinematic and Steady flow. Subsequently, the dimensions of the pipes were determined. The construction cost of each flood routing method was calculated and compared with each other. The dimensions of the conduits were selected according to the dimensions of the concrete pipes available in the market and the existence of sufficient freeboard. Hence, no flooding was expected to occur in the nodes. Generally, the outputs of two fully dynamic and diffusive methods were similar showing the minimal effect of inertia term. How ever the results were quite different for other two methods. The first two methods yielded shallower depths leading to smaller dimensions and lower construction costs whereas all momentum terms were included. Another comparison between flow depth, discharge, time to hydrograph peak were also conducted. Construction costs were calculated using TAKSA software. The results suggest that applying fully dynamic simulation, despite more computational costs, puts the engineers on the safe side with lower construction costs. Conclusion The average dimensions of the conduits used in the main conveyance pipeline were the same in the dynamic wave method and the diffusive wave method; But compared to the kinematic wave and uniform flow method, it was at least 9.8% lower. The dynamic wave method and the diffusive wave method had the same construction costs due to the same dimensions of the pipes used. However, the construction costs of these two methods were 55.7% lower than the kinematic wave method and 54% lower than the uniform flow method. Moreover, the construction costs of the kinematic wave method were 2.2% higher than the uniform wave method.Keywords: Flow routing, rainfall-runoff model, SWMM, urban flooding, TAKSAExperimental Investigation of the Threshold Submergence in Combined Throat Flumes
https://jhyd.iha.ir/article_190058.html
IntroductionThere are generally two main methods for measuring fluid flow in open channels. The first method involves measuring the average velocity and cross-sectional area and multiplying them to calculate the discharge. The second method involves creating a controlled depth using a structure and establishing a direct relationship between the depth and flow rate (known as the stage-discharge relationship), where the flow rate can be directly determined by measuring the depth (Potter et al., 2012). Flow passing through a structure for measurement is categorized into two main types: free or modular flow and submerged or non-modular flow. Since the hydraulic behavior of these structures differs under free and submerged conditions, determining the boundary between these two flow states is essential. The threshold of each structure represents the boundary between these two flow states. So far, no studies on this topic have been specifically for flumes with combined cross-sections. Therefore, this research aims to cover this subject. This study aims to experimentally investigate the threshold of submergence in trapezoidal-rectangular and triangular-rectangular combined cross-section flumes. For this purpose, the submergence threshold of these flumes is examined for various flow rates and geometries. Additionally, empirical relationships for both proposed flume types have been developed after dimensional analysis and non-dimensionalities of influential parameters for engineers to use in the design phase. Finally, the submergence thresholds of these two types of flumes are compared.MethodologyThe experiments in this study were conducted on horizontal and rectangular flumes with dimensions of 20, 0.6, and 0.5 m for length, width, and height. The flumes have a closed water flow system, and an end gate to control of downstream depth. In this research, different models of flumes were tested at various flow rates. In total, 170 experiments were performed for the trapezoidal-rectangular flume, and 101 experiments were conducted for the triangular-rectangular flume in the threshold submergence state.The effective parameters on the threshold submergence of a trapezoidal-rectangular flume include geometrical parameters, fluid characteristics, and gravity acceleration. The geometric parameters are the height of the flume P, the amount of floor opening a, and the width of flume B. The angles of upstream and downstream transitions are not considered because they are fixed. Fluid-related parameters include dynamic viscosity &micro; and specific mass &rho;. Another parameter affecting the flow in open channels is the acceleration of gravity g. Also, the parameters related to the flow, including the upstream depth h, and the downstream depth ht, are effective variables on the threshold submergence. By using Buckingham's &Pi; theory, choosing the parameters &micro;, g, and h as repetition variables, and using the theory of incomplete self-similarity (Barenblatt, 1987), finally, two Eqs. (1) and (2) are as follows.h_t/P=(h/B)^m f_1 ( a/B,Z) (1)h_t/P=(h/B)^m f_2 ( Z) (2)where m is a numerical constant that is determined based on experimental data.Results and Discussion The results indicate that although the ht/B index shows a consistent increasing trend, it effectively fails to differentiate between flows with different heights. The ht/h index demonstrates that this index does not exhibit a consistent trend compared to the h/B parameter. Therefore, based on the analyses conducted in this study, ht/P was considered a suitable threshold index for both types of flows under investigation.The index increases as the height of the flume increases for all three triangular prism side lengths (5, 10, and 15 cm). It is worth mentioning that the changes for low h/B ratios are negligible, and the difference between different flume depths increases with an increase in this ratio, especially for structures with side lengths of 10 and 15.The results show that with an increase in this parameter, the threshold submergence index decreases, indicating an increase in the sensitivity of the flow to the upstream depth. For a specific flow height and discharge, the upstream depth of the structure decreases with an increase in the parameter a. Therefore, the upstream energy of flows with higher opening ratios is lower, resulting in their submergence at an earlier stage.Similarly, similar to the trapezoidal-rectangular flow, in this type of flume, with an increase in height, the threshold submergence index increases, and the flume submerges later.Equations (3) and (4) demonstrate the threshold submergence index for the combined trapezoidal-rectangular and triangular-rectangular flumes. The results show that more than 80% of the data have an error of less than 5%. The provided empirical equations have achieved satisfactory accuracy in estimating the experimental results.h_t/P=4(h/B)^(1.1) 〖(a/B)^(0.088) (Z)〗^(0.096) (3)h_t/P=1.443(h/B)^(1.254) (Z)^(1.29) (4)Conclusion The investigation of various dimensionless parameters has shown that the ratio of the downstream depth to the flume height (ht/P) is a suitable indicator for the threshold submergence for both types of flumes. In both types of flumes, as the flow depth increases, the threshold submergence index also increases, indicating a decrease in the sensitivity of the flume to the downstream depth. The study of the effect of the trapezoidal base on the threshold submergence index has shown that as the base width increases, the threshold submergence decreases. A comparison between the two types of flumes has shown that in low flow rates, the triangular-rectangular combined flume reaches the threshold submergence earlier than the trapezoidal-rectangular flume. In contrast, in high flow rates, the opposite is true. Statistical analyses have demonstrated that the proposed relationships accurately predict the experimental results, with over 80% of the predictions having an error of less than 5%.Fractal assessment of time series of density currents in flume
https://jhyd.iha.ir/article_190059.html
Density currents formed due to the difference in density, however small, with the surrounding fluid. In addition, even if this density difference exists in the layers of a fluid, this type of flow formed. These currents are a type of two-phase currents that have special and different characteristics compared to normal single-phase currents. Hydrological and hydraulic phenomena known as chaotic, non-linear, dependent and sensitive systems to the change of the initial conditions and the temporal and spatial scale of the study. For this reason, any processing of hydrological time series has a direct effect on the chaotic behavior and the way the system responds to hydrological models and network forecasting.The experiments carried out in the hydraulic department of Shiraz University and a flume of 8 m length, 35 cm width and 60 cm height used. Flume has the ability to tilt. A source of 1000 liters containing thick sediment flow used. A number of 12 experiments conducted in such a way that the powder of passing rock classified from sieve No. 80 used as suspended sediment material to create a dense flow, which has a specific weight of 2650 kgm-3 and an average settling speed of 0.0106 mms-1 and an average diameter of particles. It is 0.0074 mm. The density of water is 998.7 kgm-3. Three channel slopes of 1, 2, and 3 percent and two density current inlet flow rates of 50 liters per minute and 90 liters per minute used. The density of the thick flow tank is 1005 kgm-3 and 1008 kgm-3, and the height opening under the sliding inlet valve is 1 cm. Fractal dimension is a decimal number that fractal objects are something between Euclidean and topological shapes. A fractal curve is a curve with an infinite self-similar component. This analysis based on the box counting method, which is a smart and simple method to implement. The fractal dimension obtained by calculating the number of non-overlapping boxes with the size required to cover the fractal curve.A general study of fractal indices such as scale factor diagrams, generalized fractal dimension and singularity spectrum shown in Figure 5 for the time series of dense flow velocity in all models at a distance of m5 from the inlet valve. The highest fractal dimension with a rate of 1.459 related to test number 5 and the lowest fractal dimension related to test number 7 with a rate of 1.22. The highest range of &alpha; corresponds to test number 3 with a rate of 3.04 and the lowest corresponds to test number 12 with a rate of 0.087. The lower this range is from the rate of 3.04, the more its multifractal degree decreases and the trend of the system is more towards single fractal patterns. When the inlet flow rate changes from 50 liters per minute to 90 liters per minute, the fractal dimension of the speed time series decreases by 2.2%, and the amplitude and angle &alpha; decrease by 53.5% and increase by 3.9%, respectively, and the tendency of the system With the increase of the input flow rate, it tends towards single fractal. Also, in the technical spectrum charts, with the increase of the input flow rate from 50 liters per minute to 90 liters per minute, the technical spectrum chart tends from full symmetry to right symmetry, in other words, with Increasing the flow rate, the exact fractal diagram that created from self-similar elements tends towards a single fractal, which is sensitive to small changes in the flow rate caused by increasing the flow rate of this factor.The generalized fractal dimension decreases with increasing flow rate and flow concentration, and it shows that the phenomenon is less sensitive to high concentrations and flow rates, and the flow behavior is dependent on the initial conditions. When the input density changes from 1005 kgm-3 to 1008 kgm-3, the fractal dimension of the velocity time series decreases by 4.2% and the amplitude and angle &alpha; decrease by 9.7% and increase by 9.8%, respectively. The rotation reduced by 6.7% and the Dq changes reduced by 1.5% and its graph is milder.Discharge-Level laboratory investigation of the flow passing through the composite structure of sharp crested triangular with multiple orifices
https://jhyd.iha.ir/article_190060.html
Structures such as weirs and orifices, their main function is to measure the flow rate and regulate the water level. The combination of weir and orifice structure has been noticed in the last decade. When there is a flood, by placing several orifices with a certain number and dimensions in the lower part of this weir, it is possible to pass more discharge. In this laboratory research, the percentage increase in discharge rate and changes in water flow in each of the models designed by changing the number and dimensions of orifices in the sharp-crest triangular weir with multiple orifices have been estimated. In the present research 19 weirs with square orifices were designed in five cases from one to five orifices and in dimensions of two to five centimeters and one weir without an orifice was designed as a control test. The results of this laboratory research showed that for a fixed control level, while the same level remains constant, due to the change in the number of orifices or the dimensions of the orifices, the flow discharge has increased. The results of examining the amount of flow rate changes (difference between the flow discharge resulting from the overflow-orifice test and the flow discharge resulting from the overflow without orifice) have shown that in each test sample, with the increase of each orifice created on average by two liters per second and per one increase of every one centimeter in the size of the orifice adds 2.3 liters per second to the water flow discharge. In the best case, for a combined overflow with a change in the size of the orifice from three to four centimeters in a fixed control level, it has the highest percentage of passing flow and is 57%. On the other hand, in the best case, by increasing the number of orifices from three to four apertures in a fixed control level, this percentage increase has reached approximately 42%, and it shows the superiority of these two combined models compared to other tested models.Hydraulic Model Calibration of a Laboratory Water Distribution Network Using Hydraulic and Water Quality Measurements
https://jhyd.iha.ir/article_190120.html
In the realm of hydraulic modeling for water distribution networks, the calibration process plays a pivotal role. Calibration involves precise adjustments to align a model with observed data. However, when the measured data is scarce, the calibration process becomes challenging. In such cases, laboratory models prove valuable for simulating real-world conditions. Variability in parameters like pipe dimensions, length, roughness coefficients, and nodal demand as well as nodal elevations often leads to disparities between computer-based model outcomes and reality. Despite extensive research on computer-based models, laboratory water distribution network models and their calibration have received relatively limited attention due to the challenges and costs associated with them. In this study, a laboratory model of a water distribution network was constructed and subjected to hydraulic calibration. Roughness coefficients and minor head losses within the network were determined using a meta-heuristic method. Then, pipe roughness coefficients for polyethylene pipes were assessed and compared with values from scientific references. In the following, hydraulic validation of the network was conducted using the water quality simulation of a conservative substance. This approach illustrates the level of concurrence of flow ratios in the network pipes between the model and reality.The laboratory network was made of PE40 and consists of a square looped system with 1-meter pipe lengths, employing a 1000-liter tank to maintain a constant water head. This research was conducted in three stages. In the first stage, network calibration was performed using piezometric pressure and output flow data. Roughness coefficient and pipe minor head loss coefficients were selected as decision variables. The objective function was defined to minimize the total weighted difference in piezometric head and discharge between the model and reality. In the second stage, validation was performed based on pressure and output flow data. In the third stage, the network's hydraulic validation with respect to pipe flow rates was performed through the modeling of a conservative substance. This is because the dissolution of a conservative substance occurs solely due to mixing at nodes and flow division, allowing it to represent the correspondence of flow ratios in network pipes between the model and reality. In this research, pressure data was recorded using piezometers, and salt concentration was calculated using TDS (Total Dissolved Solids) sensor. After performing the optimization, a value of 0.008 was obtained for the Darcy-Weisbach friction coefficient (ɛ), This value aligns well with the assumption of new pipes in the network, in agreement with previous research (e.g., 0.050 by The Plastics Pipe Institute, 2008, and 0.070 by Padilla et al., 2013). Also, values of 1.20 and 0.89 were obtained for the minor loss coefficients of 0.5 and 1-meter pipes, respectively. Furthermore, the optimized minor loss values effectively reflect differences attributed to the number of connections in the 0.5 and 1-meter pipes, falling within recommended scientific ranges. Notably, unlike previous field studies, this research uniquely focuses on a laboratory model.After hydraulic calibration and validation using pressure and output flow data, further validation was conducted using the water quality model. The saltwater solution was injected at a specific point in the network, and the TDS quality parameter was measured at the two points in the network. Subsequently, utilizing the TDS values and the established relationship between TDS and salt concentration calculated in the laboratory, the salt concentration at the location of two sensors was determined. It's worth mentioning that the network's water supply contained dissolved solids. Subsequently, initial and injection concentrations were applied to the model and, the simulation was performed. A comparison of salt concentration results at two sensor locations revealed an 8.5% error in the first experiment and 2.5% in the second, confirming excellent agreement between the laboratory and computer-based network hydraulic model.Experimental study of skimming flow on the stepped spillway in the non-aerated area using PIV
https://jhyd.iha.ir/article_190121.html
Understanding the flow behavior over stepped spillways has been the subject of many previous studies. Most of the studies conducted on stepped spillways have been in skimming flow conditions and the aerated parts of the spillway. Also, many of these results have been the result of observing the flow behavior on the side of the spillway, and there is still no complete view of the flow behavior in the depth of the spillway. The present study investigates the skimming flow behavior on a short and wide stepped spillway in a non-aerated area. For this purpose, the image processing technique called particle image velocimetry )PIV( has been used to process the movement path, velocity, and behavior of the flow and analyze it in the side sections and depth of the spillway. In a few previous studies, the more detailed behavior of the skimming flow has been investigated. The results of these studies have defined some of the characteristics of two sub-regimes of the skimming flow regime. However, the behavior of the sub-regimes mentioned by the researchers was mostly described as laboratory observations. This article takes a closer look at this issue. Also, in this study, it was shown that the flow behavior in the areas above the pseudo bottom line is almost similar to different cross-sections, but in the areas under the pseudo bottom line, the flow behavior experiences significant changes, so that its effects on the velocity profiles are quite evident., , , , , , , , , , , , , , , , , , ,, , , , , , , , , , , , , , , , , , ,, , , , , , , , , , , , , , , , , , ,, , , , , , , , , , , , , , , , , , ,