Journal of Hydraulics
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Journal of Hydraulicsendaily1Fri, 22 Dec 2023 00:00:00 +0330Fri, 22 Dec 2023 00:00:00 +0330Optimal Estimation of Secondary Flow Coefficient in Compound Channels with Vegetated Floodplains
https://jhyd.iha.ir/article_154658.html
This study adopted the Shiono-Knight model (SKM) to estimate the lateral distribution of the depth-averaged velocity within rectangular and trapezoidal compound channels with emergent vegetation in floodplains. To implement the SKM, it was required to estimate the eddy viscosity coefficient, friction coefficient, and secondary flow coefficient. The present study estimated the friction coefficient using the Colebrook&ndash;White equation modified by Rameshwaran and Shiono for vegetated beds. An analysis of eddy viscosity models across compound channels indicated that the model was not sensitive to the eddy viscosity coefficient; thus, the eddy viscosity coefficient could be assumed constant across the channel. However, the negligence of the secondary flow in the model would lead to a significant error, and it was required to calibrate the secondary flow coefficient. Thus, this study used a genetic algorithm (GA) to develop equations for the secondary flow coefficient for different sections of the compound channel under two different approaches: (1) the approach of Abril and Knight (2004), who proposed constant values for the main channel and floodplains, and (2) the equations of Devi and Khatua (2017), which related the secondary flow coefficient to the relative depth and width ratio. It was found that the secondary flow coefficient was dependent on the relative depth and width ratio. As a result, the equation optimized based on the Devi-Khatua approach outperformed the Rameshwaran-Shiono technique in estimating the lateral distribution of the velocity, with a 10.2% lower error. This paper employed SKM to estimate the depth-averaged velocity within three compound channels of rectangular and trapezoidal cross-sections with a vegetated floodplain at small and large scales. To solve the SKM, it was required to calculate the friction coefficient, eddy viscosity coefficient, and secondary flow coefficient. The friction coefficient was calculated using the modified Colebrook&ndash;White equation. Several eddy viscosity models were adopted to implement the SKM. It was found that the eddy viscosity coefficient had no significant effect on the performance of SKM. The present study focused on calibrating the secondary flow coefficient as it played a key role in the flow simulation of compound channels using SKM. Two approaches were adopted to calibrate the secondary flow coefficient: (1) the approach of Abril and Knight (2004) and (2) the approach of Devi and Khatua (2017). The latter defines the secondary flow coefficient as a function of the relative depth and width ratio. The optimal secondary flow coefficient was obtained using a GA and experimental data for different geometric and hydraulic conditions. A comparison of the predicted and observed velocities demonstrated that the Devi-Khatua calibration method improved the predictive accuracy of SKM by nearly 10.2%. The secondary flow coefficient was found to be dependent on the relative depth and width ratio. It was calculated to be positive in both the main channel and floodplain, suggesting clockwise secondary flows. The difference between the observed and predicted velocities was larger in the floodplain than in the main channel, which could have arisen from flow complexities around vegetation.Laboratory 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 efficiencyNumerical Solution of the Discharge Coefficient of Trapezoidal Arced Labyrinth Weirs with Different Middle Cycles Using Flow 3D Software
https://jhyd.iha.ir/article_171427.html
In the present study, a three-dimensional hydraulic flow simulation was carried out on these weirs using Flow3D software and the modeling results were compared with the experimental results to study the discharge coefficient of trapezoidal arced labyrinth weirs. Moreover, these models were tested under laboratory conditions in a rectangular flume with a length of 12m, a width of 0.6m, and a height of 0.6m in clear water conditions. The results indicated that the numerical model data showed adequate conformity with the experimental model data. In general, the discharge coefficients in the results of the numerical model were 1.2 to 18.9% lower than the experimental model. The difference between the discharge coefficients in the numerical model and the experimental model increased with an increase in the arc radius. As a result, with the R/w1=5 and R/w1=15 radius ratios, the discharge coefficients of the numerical model were approximately 1.2% and 18.9% lower than the experimental model, respectively. One of the pitfalls of the existing conventional linear weirs is their low discharge capacity due to the limited width of these weirs. The use of labyrinth weirs is considered an efficient and cost-effective solution for increasing the flow rate. These weirs provide a higher discharge capacity for the same hydraulic head than direct weirs due to the increase in the crest length in a given width. The flow running over the weirs within the peak flood hours has to flow within a short period of time. Therefore, it seems necessary to build a weir structure with a high discharge coefficient. Labyrinth weirs are used for this purpose because the amount of flow running through them is larger than linear weirs (Falvey 2003).Labyrinth weirs are used as cost-effective technical solutions for controlling flow in different conditions such as in dam weirs. Labyrinth weirs may also be used to control discharge capacity, reduce channel water level slope, distribute water between irrigation channels, etc. (Neveen Sad and Fattouh Ehab 2017). The plans of labyrinth weirs are classified into three categories, namely the triangular, trapezoidal and rectangular plans. Most weirs are built with rectangular, trapezoidal, or isosceles plans to increase their performance and facilitate their construction (Crookston 2010). The discharge coefficient in these weirs is determined by various factors such as the weir water level, the walls angle, and the crest thickness and shape (Ghare et al. 2008). Dimensional analysis is among the basic methods for experimental research, which serves to determine the dimensionless ratios. In the first step of this method, the variables affecting the discharge of labyrinth weirs are identified and then the dimensionless parameters are determined based on Buckingham&rsquo;s theory, . After determining the dimensionless parameters, their effect on the discharge of the weirs can be studied to obtain satisfactorily rational results.The comparison of the experimental results with the results of the numerical model for the discharge coefficient of trapezoidal arced labyrinth weirs with different middle cycles and different arc ratios in Flow-3D software is presented in the following diagrams.As seen in figures (5), (6) and (7), the discharge coefficient decreased with an increase in the hydraulic head. In other words, the results of the experimental model show higher discharge coefficient values than the numerical modeling results in Flow3D. In figures (5), (6) and (7), the trapezoidal labyrinth weir has a hydraulic head ratio of 0.1 to 0.7 in the adhesion and complete aeration phase and from 0.7 to 1 in the partial aeration and suffocation stage. Moreover, the arc radius ratio of 15 has the highest discharge coefficient values as compared to the 10 and 5 ratios. In other words, with an increase in the arc radius ratio, the hydraulic efficiency of the weir increases along with its hydraulic efficiency. As seen in figures 6 and 7, with an increase in the hydraulic head, the difference between the discharge coefficients in the numerical and experimental models decreased. Moreover, according to these diagrams, with an increase in the arc radius, the difference between the discharge coefficients in the numerical and experimental models increased, which could be attributed to an error in the numerical model in detecting the small variations in the arc radius. In other words, in the numerical model, the discharge coefficient did not differ significantly from the arc radius variations, whereas in the experimental model, the effect of the arc radius on the discharge coefficient was more significant. A comparison of labyrinth weir discharge coefficients resulting from the numerical and experimental models revealed that the discharge coefficients of the experimental values are higher than the numerical modeling results. Besides, the labyrinth weir properly completes the four hydraulic stages in the experimental and numerical conditions, reflecting the proper hydraulic performance of the weir. When the weir is in the full aeration state, the weir is in the maximum hydraulic efficiency state. It is worth stating that when the weir is in the partial aeration condition, its hydraulic efficiency starts to decline. Finally, if it reaches the suffocation stage, the weir loses its hydraulic efficiency, the energy is maximized, the entire length of the weir crest is fully submerged, and thus the weir functions as an obstacle in the flow path. The energy loss is maximized when the hydraulic head is maximized. As a result, the nappes collide in the weir outflow keys, resulting in a drastic energy loss. From the quantitative viewpoint, in the weir with a radius ratio of R/w1=5, the numerical and experimental results satisfactorily overlap, and for hd/p&gt;0.2 in the two diagrams, they are fully in line. In the weir with the R/w1=10 radius ratio, the numerical model outflow discharge coefficient is 10.2 percent smaller than the experimental results on average. Besides, with the R/w1=15 radius ratio in the results of the numerical model, the discharge coefficients are approximately 18.9 percent lower than the experimental model. In general, with an increase in the weir arc radius, the difference between the flow coefficients in the numerical model and the experimental results increases.The inception point of flow aeration on a rough stepped spillway
https://jhyd.iha.ir/article_171428.html
Stepped ogee spillways are one of the most widely used types of dams that are used in most dam construction projects, including small and large dams. The inception point of aeration on these spillways is an important place in determining the range of single-phase and two-phase flow, which characterize the areas at risk of cavitation. In this paper, the effect of roughness on the location of the inception point of flow aeration (IPFA) on the stepped Ogee spillways was investigated. For this purpose, the surface of the steps of a laboratory model was covered with gravel with specific granulation. The result indicated that by roughing the surface of steps, the displacement of IPFA moves towards the crest (upstream) and the length of non-aerated area on the stepped spillways is decreased by about 15 percent. The results declared that there is a direct exponentially relation between flow rate and displacement IPFA. At low flow rates, most of the flow turbulence is due to the roughness created by the geometry of the steps, hence the role of surface roughness is negligible, while with increasing flow rate, its role in increasing the flow turbulence increases, and its effect on displacement of IPFA becomes obvious. At a given flow, the length of the non-aerated is decreased with increasing roughness.In this study, the effect of surface roughness of steps on the displacement of IFPA was investigated experimentally. To this end number of laboratory experiments were programmed. To investigate the objective of this study, a stepped ogee spillway in which its horizontal part of steps was covered by gravel with given grain size. The results declared that three factors including the flow rate, the roughness caused by steps dimension (ks), and the roughness of steps surface (ns) are effective in the displacement of IPFA. In this study, the change in the size of the steps and the longitudinal slope of the stepped chute on the displacement of IPFA has not been investigated because it has already been studied by other researchers. There is a direct exponential relationship between the discharge and the IPFA (length of the non-aerated area on the stepped ogee spillway). As the flow rate increases, the location of this point is transferred downstream exponentially. With the increase of flow, the role of roughness in IPFA displacement became clearer and the reason is the increase of its role in creating and increasing flow turbulence. On average, surface roughness can be about 15% effective in reducing the displacement of IPFA.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
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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
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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.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.Investigation 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 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.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.Design of Operation Strategy for Canal Structures
https://jhyd.iha.ir/article_178550.html
Simple operation strategies make the users capable of regulating standard gates, such as overshot and undershot gates. For complicated operation, a control algorithm must be used, almost always done by programming the control algorithm within a programming software and coupling it with a canal simulator. In this research, a new operation strategy was designed to regulate inline water structures in the Alborz canal in Mazandaran province (Iran). Simple operation strategies make the users capable of regulating standard gates, such as overshot and undershot gates. For complicated operation, a control algorithm must be used, almost always done by programming the control algorithm within a programming software and coupling it with a canal simulator. In this research, a new operation strategy was designed to regulate inline water structures in the Alborz canal in Mazandaran province (Iran). Simple operation strategies make the users capable of regulating standard gates, such as overshot and undershot gates. For complicated operation, a control algorithm must be used, almost always done by programming the control algorithm within a programming software and coupling it with a canal simulator. In this research, a new operation strategy was designed to regulate inline water structures in the Alborz canal in Mazandaran province (Iran). To this end, the classic proportional integral derivative controller was coded in the rules boundary condition, being called by HEC-RAS during the canal simulation. The HEC-RAS model of the canal was prepared designing a controller for each inline gate to regulate upstream water depth. Performance indicators and statistical indices were used for evaluation. The calibration results of the controller gains indicated that k_p is 5, 4.5, 3.5, and 5 for regulating gates 1-4, respectively. The k_i and k_d gains were also calibrated. The results showed that the designed model can simultaneously simulate the canal and regulate the gates successfully, obtaining maximum and average depth errors of 7.5% and about 1% which are quite acceptable. The adequacy was 1 in almost all cases, and the efficiency was more than 0.97 with equitable distribution.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%.