Effect of air injection pipe position on local scour reduction around the cylindrical bridge pier with experimental investigation
Mahshad
Afsharpour
Hydraulic Structure Department. Faculty of Water Science Engineering. Shahid Chamran University of Ahvaz,
author
Seyed Mohsen
Sajadi
Hydraulic Structure Department. Faculty of Water Science Engineering. Shahid Chamran University of Ahvaz,
author
seyed mahmood
kashefipor
Shahid Chamran University
author
Mahmood
Shafaei Bajestan
Hydraulic Structure Department. Faculty of Water Science Engineering. Shahid Chamran University of Ahvaz,
author
text
article
2020
per
Extended Abstract Introduction Local scour is one of the main factors of the destruction of bridge piers in rivers before the life expectancy of these structures. One of the newest indirect methods for reducing the erosion and scour around the bridge piers is the air injection method which is based on counteracting with downward flow to create such conditions to prevent or reduce the flow impact on the bed and the destruction of bridge piers. Tipireddy and Barkdoll (2019) studied the effect of air injection in controlling bridge pier scour. The results of this study showed that the maximum scour depth decreased with increasing air injection rate until the ratio of air outflow velocity from the pores to flow velocity was 57.1 and then increased. The performance of air injection to reduce bridge pier scour has been investigated in only one study, considering all parameters except constant air outflow rate. The main objective of this study was to investigate the effect of air injection on reducing bridge pier scour considering the number and the location of injection pipes. Research Methodology Experiments were carried out at the Hydraulic Laboratory of the Faculty of Water Engineering, Shahid Chamran University of Ahvaz in a flume with 10 m long and 0.74 m wide and 0.6 m deep. The bottom of the flume was covered by sediments with a mean diameter of 0.7 mm with a standard deviation of 1.21 indicating uniform sand. All experiments were performed in four Froude numbers of 0.18, 0.2, 0.22, and 0.24 at a constant depth of 15 cm under clear-water conditions. To reach these conditions, the flow depth was adjusted so that the ratio of flow velocity to the critical velocity is less than 95%. In order to determine the appropriate time for the experiments, a 12-hour test at a Froude number of 0.2 was performed and it was observed that about 90% of the scour occurred in the first 3 hours. In order to create an air injection system, porous pipes were selected with an internal diameter of 4 mm. Each pipe had 24 pores with a diameter of 2.2 mm at fixed intervals mounted on the upstream half of the pier and two ends were connected to the air compressor for injection. Experiments were carried out at air injection rate of 100 lit/min and in 7 different number and position of aeration pipes on the pier. The pipes were mounted in three general modes: one pipe, two pipes and three pipes. The installation level of the pipe on the pier was considered as three heights of 1/3h, 1/2h, and 2/3h from the bed. Results and Discussion A number of four control experiments (without the air injection system) was first performed at four specified Froude numbers. A total of 28 experiments were performed in the presence of the air injection system at the air injection rate of 100 lit/min. The aeration pipe at on the upstream half of the pier provides some protection for the sediments against the horseshoe vortices. Effect of aeration pipe position on scour depth and scour development around bridge pier To investigate the effect of the position of the aeration pipe on the pier, the pipes were installed in single-pipe mode at three different heights on the pier and in the simultaneous usage of two pipes, the pipes were installed in three modes at the same three height. The transverse expansion of the scour hole for the bridge pier were plotted in two general modes using a single aeration pipe and two aeration pipes in four Froude numbers. In single-pipe mode, the maximum decrease in the scour hole depth in front of the bridge pier (25.5%) was observed at the pipe installation depth of 5 cm beneath the bed and for Froude number of 0.18. For the use of two pipes with the same injection rate and similar hydraulic conditions, the maximum decrease in scour depth of 11.8% occurred when the pipes were installed at depths of 7.5 and 10 cm beneath the bed. Effect of aeration pipe on scour depth in scour development around bridge pier In order to investigate the effect of the number of pipes on the scour depth, the transverse expansion of the scour hole around the bridge pier was plotted in three general modes: single pipe (three mode), two pipes (three modes) and three pipes (one mode). The results showed that the lowest efficiency was observed to the state of the three pipes and the efficiency is to the one state.. Effect of Froude Number on Scour Depth and Scour Expansion around Bridge Pier The shape of the relative scour depth was plotted against the Froude number for the use of an aeration pipe. The results showed that there is a direct relationship between the scour hole depth and the Froude number and the scour hole depth increases with increasing Froude number. Conclusion In this study, the effect of air injection system on the scour pattern and sedimentation around the bridge pier under clear-water conditions in a straight flume was experimentally investigated. All experiments were performed with four Froude numbers of 0.18, 0.2, 0.22, and 0.24 and 7 different numbers and installation levels of the aeration pipe at air injection rate of 100 lit/min. The results showed that aeration structure in the flume reduced the scour depth around the pier. The reduction of the scour depth at the front of the pier in the single-pipe test was 25.5% with an installation level of 5 cm, Froude number of 0.18, and air injection rate of 100 lit/min. The results of comparisons made to investigate the effect of the number of aeration pipes on the pier showed that the three-pipe mode had the lowest efficiency. This system reduced the volume of scour hole around the pier. Therefore, it can be concluded that the application of this structure can be an appropriate alternative in comparison with the commonly used protective structures, therefore, further studies are suggested.
Journal of Hydraulics
Iranian Hydraulic Association
2345-4237
15
v.
3
no.
2020
1
14
http://jhyd.iha.ir/article_107770_8bc08c9a480c6093ec97a2a5bb3a3488.pdf
dx.doi.org/10.30482/jhyd.2020.223209.1446
Accuracy assessment of RS-based DEMs in flood inundation mapping of different morphological types of rivers
Amir Mohammad
Arash
MSc. Student of Hydraulic Structures Engineering, Department of Irrigation and Reclamation Engineering, University of Tehran, Karaj, Iran
author
Mehdi
Yasi
Associate Professor, Department of Irrigation &amp; Reclamation Engineering,
University of Tehran, IRAN
author
Asghar
Azizian
Assistant Professor of Water Engineering, Department of Water Engineering, Imam Khomeini International University, Qazvin, Iran
author
text
article
2020
per
Introduction Flood is one of the most devastating natural hazards that causes significant losses and damages. Flood inundation maps are initial requirements for river floodplain management and eliminating flood risk in integrated flood management plans. Surveyed topography datasets, together with bathymetry data, were utilized to construct the river terrain for flood inundation mapping, however, such data is rare. Therefore, for tackling this challenging issue, DEMs as an accelerator and free of charge datasets, are widely used in flood modelling. The recent advancement of GIS and RS technologies enabled scientists to benchmark high-accuracy DEMs, such as LIDAR (Light Detection and Ranging), which perform as excellent as driven DEMs from surveyed topographies, for flood modelling. Despite the reliability of these finer datasets, the limited coverage of world and the exorbitant price of provision has forced experts to utilize coarser-resolution DEMs rather than these higher-resolution DEM sources. As a result, the accuracy of open-access and free of charge DEMs used in flood modelling in the data-sparse rivers should be investigated broadly, unless the lower-resolution DEMs hinder flood modelling results by incorrectly reproducing river terrain. In this study, three sets of widely used open-access DEMs’ performance in flood inundation mapping and estimating hydraulic parameters of four various rivers are assessed thoroughly. Methodology In this paper, three sets of free and accessible 30m resolution DEM resources (ALOS, SRTM, ASTER) of four various sorts of rivers in Iran will be utilized as HEC-RAS geometry input file. In short, this study consists of 5 main steps: 1) Creating surveyed topography maps with 1:1000 or 1:2000 scales 2) Generating GDEM by interpolating topography maps obtained from the prior step 3) Determining channel geometry and extraction of cross-sections by operating GIS-based DEMs and GDEM in HEC-GeoRAS extension on ArcGIS 4) Flood modelling of the rivers by geometry input files produced from step 3, plus US and DS boundary conditions and design flow of the rivers 5) Assessment of DEMs’ performance in estimating hydraulic parameters based on efficiency measures, such as Root Mean Square Error (RMSE), Mean Absolute Difference (MAD), Mean Absolute Percentage Error (MAPE), Relative Error (RE) and F-statistics. 6) Investigating the relation among the accuracy of DEMs and morphology characteristics of various Iran rivers, namely Sojasrud in Zanjan province, Taleghanrud in Alborz province, Gorganrud in Gorgan province and Sarbaz in Sistan-Baluchistan province of Iran. Results and discussion The river geometry derived from ALOS DEMs were more identical to surveyed cross-sections. According to previous studies, ALOS DEMs captures the more accurate depicting river bathymetry data, the higher performance of this dataset in flood modelling is expected. However, all of these GIS-based DEMs were unable to present the Gorganrud river geometry data. Apart from the better representation of river geometry, the ALOS DEMs dataset is superior to ASTER and SRTM DEMs datasets in terms of fairy prediction of hydraulic parameters (water extents and water surface elevation). For instance, ALOS had the least RMSE (2.3-8.6 m) in predicting flood extent compared to the rest. Moreover, the higher value of F statistics (approximately 80%) proves that this model presented the flood inundation map with the highest agreement. Reversely, the RMSE of ASTER, the least accurate model, in flood extent estimation was from 2.8 to 15m. Identically, the predicted flood pattern map of these rivers using ASTER leads to the more significant discrepancy with the F-statistics of 68% at most. The SRTM performance in generating flood inundation map was better than ASTER and less accurate compared to ALOS (maximum value of 78% in F-statistic was recorded). The accuracy of DEMs in stimulating WSE of the mountainous rivers was similar to each other, and it was higher than predicted WSE of lower-slope rivers. Moreover, the estimated WSE using ALOS led to less disagreement with the benchmark values, whereas the operation of ASTER and SRTM for this purpose resulted in overestimating. Although the Relative Error of these DEMs in predicting Gorganrud river flood WSE was almost 5%, the MAPE of whole DEMs was 1% within all cross-sections in the rest of the study rivers. Conclusion The accuracy of flood inundation mapping is highly dependent upon its geometry input file. The high-resolution DEMs, including LIDAR dataset, are often used due to their accuracy, still in most of flood inundation mappings projects, coarser-resolution DEMs are operated owing to their accessibility and free of charge datasets. It is critical to evaluate the influence of these DEMs on hydraulic outputs. In this research, various open-access DEMs configurations were operated in four various rivers located in different regions of Iran. The results reveal that the ALOS DEM dataset is superior to ASTER and SRTM DEM datasets in terms of a better representation of river geometry and fairy prediction of hydraulic parameters (water extents and water surface elevation). For instance, the higher percentage of F statistics (approximately 80%) proves that this model presented the flood inundation map with the highest agreement. However, the maximum values of F-statistics of SRTM and ASTER were nearly 78% and 68%, respectively, showing the flaws of these models in flood extents mapping. The efficiency of all DEMs datasets in estimating WSE of the rivers was excellent, but Gorganrud river is an exemption. The Mean Absolute Percentage Error of these DEMs for estimating WSE, which was under 1% within the majority of cross-sections, was not meaningful. Consequently, ALOS is particularly potent in accurately hydraulic modelling. Additionally, the remote-sensing based DEMs are more applicable in wide and (or) straight river reaches than narrow and meandering rivers. It would be better if DEMs are modified in advance to reduce the level of disparities in flood modelling. In this line, there are several modification methods led to lowering this predictable errors, such as using GCPs (Ground Control Points) or merging cross-sections with DEMs to create an integrated surface.
Journal of Hydraulics
Iranian Hydraulic Association
2345-4237
15
v.
3
no.
2020
15
31
http://jhyd.iha.ir/article_111209_13517a869bdb625a8110a6dfeae63be4.pdf
dx.doi.org/10.30482/jhyd.2020.231744.1460
Introducing Two-Dimensional Hydraulic Simulation as a Technique for Estimating the Time of Concentration
Fatemeh
Esmailmanesh
MSc Student of Irrigation and Drainage, Jahrom University, Fars, Iran
author
Masih
Zolghadr
گروه مهندسی علوم آب دانشکده کشاورزی دانشگاه جهرم
author
Mohammad Rafie
Rafiee
Department of Water Science and Engineering, Faculty of Agriculture, Jahrom University, Fars, Iran
author
text
article
2020
per
Introduction Time of concentration (TC) is the time in which a water parcel travels from watershed divide to its outlet. Time of concentration is also the most important factor in selecting design discharge for an area, since the most severe floods are those caused by rainfalls with durations equal to the concentration time of a watershed. Time of concentration is necessary in the studies of water resources management, flow volume and discharge estimation, design of spillways and hydraulic structures, development of flood predicting models, flood alert systems, river management and drainage projects and many other water related studies. There are various empirical methods for calculation of concentration time. The focus of this study is to simulate the water parcel to calculate the time of concentration with a two-dimensional hydraulic model (HEC-RAS 5.0.7). To the knowledge of the authors this method has never been applied for estimation of time of concentration. Methodology: Currently there are two main methods to evaluate the time of concentration; applying empirical formulas or applying graphical methods with requires flood hydrograph and corresponding rainfall hyetographs. Due to the differences in the accuracy levels of empirical methods in different areas, along with the unavailability of graphical methods in most of the watersheds, this study aims to estimate TC, using the basic definition of time of concentration which is the travel time of a water parcel from basin divide to the outlet. Two-dimensional HEC-RAS model was used to navigate the runoff flow in the main channel of a watershed from the farthest hydrological point to the outlet. Besides, 48 different empirical equations were gathered from the literature and used to estimate the time of concentration. In order to validate the numerical method and the empirical formulas, the actual concentration time of the flow is measured by salt solution tracking. Then, the comparison of the measured data with the results of the numerical and experimental methods is made, using the percent of error index. Ali Abad watershed of Fars province has been considered as a case study due to the appropriate data availability and the possibility of various measurements as described in the following sections. Results and discussion Results showed that only 5 methods indicate relative errors less than 20% of which 4 belong to the empirical formulas (8% of the total empirical methods) and one to the numerical simulation. The NRCS is also a well-known equation in which runoff flow in a watershed is divided into three parts: sheet flow, concentrated shallow flow and open channel flow. Flow velocity is estimated by the Manning's relation in the reach according to this method. This method’s accuracy is about 82%. In order to run the two-dimensional model, DEM of the area with 10 meters’ accuracy was used to define the bathymetry. Manning roughness coefficient was also calibrated for model tuning. Over ally the best results were obtained from the hydraulic simulation when applying bank-full discharge equal to 3.53 cms so that the error of this method was limited to 3%. Hence, it is wise to accept the computational costs of a two-dimensional hydraulic simulation to predict the time of concentration instead of empirical formulas, Since the results might be used to construct costly hydraulic structures. Conclusion: Different methods of concentration time estimations were evaluated and compared with the actual concentration time obtained by salt solution tracing in Aliabad watershed of Fars province. Two-Dimensional simulation of the water parcel from the basin divide to the outlet was also performed by HEC-RAS 5.0.7. The results indicated that among empirical relations, the concentration time value obtained from the Simas and Hawkins equation is much closer to the actual value and is considered as the best empirical equation for Aliabad watershed. This equation involves river length and slope, watershed area and surface storage. Following Simas and Hawkins, equations developed by SCS, SCSlag, Yen and Chow, and NRCS gave closest estimations to the actual concentration time, respectively. However, the results of hydraulic simulation show the most accuracy depending on water parcel definition. That is because, the two-dimensional model takes the topography, local slope, roughness and geometry of the water body into account and is a reliable technique to estimate the time of concentration in any desired location. Nevertheless, for empirical relations it is necessary to realize the limitations of each method and compare it with the study area. Hence, it is recommended to apply hydraulic simulation instead of empirical formulas to estimate the time of concentration. Also, with the measurement data, the results of this study can be used as a criterion for measuring concentration time in similar hydrological studies.
Journal of Hydraulics
Iranian Hydraulic Association
2345-4237
15
v.
3
no.
2020
33
45
http://jhyd.iha.ir/article_111273_cce0815f62b7b31f90aeb1b5794b94d4.pdf
dx.doi.org/10.30482/jhyd.2020.232604.1462
Experimental Study of Hydraulic Parameters in Density Current Due to Channel Constriction
mohammad
hosseini
Department of Civil Engineering, Najafabad Branch, Islamic Azad University, Najafabad, Iran.
author
mohammad hadi
fattahi
Department of Civil Engineering, Najafabad Branch, Islamic Azad University, Najafabad, Iran.Department of Civil Engineering, Marvdasht Branch, Islamic Azad University, Marvdasht, Iran.
author
Saeid
Eslamian
Department of Civil Engineering, Najafabad Branch, Islamic Azad University, Najafabad, Iran.
Department of Water Engineering, College of Agriculture, Isfahan University of Technology, Isfahan, Iran.
author
text
article
2020
per
Introduction Density currents are stratified flows caused by density differences between the inflow and the still water. The inflow could be moving under, through, or over the reservoir water depending on the density of each. The stratification is caused by differences in temperature, the presence of dissolved materials, or the presence of suspended solids. If the presence of suspended sediment in the inflowing water is the main or only cause of stratification, the density current is known as turbidity current. When turbidity currents enter a reservoir, they plungebeneath the fresh water traveling down the slope. If the turbidity current reaches the dam, it may be vented through the low-level outlets, thus preventing the deposition of sediment in the reservoir. There are many studies in the literature regarding the transport mechanism and characteristics of density currents Methodology The Hydraulic Laboratory of Shiraz University, Iran, was used to conduct density current tests. The intended flume is related to hydraulic single-phase open channels, which is transformed into a density current flume by modifying and adding accessories. Flume length is 8m, width 35cm and height 60cm. A 1000 liter tank containing sedimentary turbidity current was used by a 2-inch outlet pump with a maximum passing discharge of 35 m3/hr. A flow meter was used to control the density current inlet. The flume was filled with water using a pipe connected to a 20000 liter water tank. During the experiment, the inlet valve of this tank is disconnected and a 500 liter regulating water tank connected to the pump is used to control the water table in the flume. The channel has sloping capability. The velocity measured by a 2D electromagnetic flowmeter, a product of UK’s Valeport Company with a precision of ±5 mm/sec. The flowmeter includes a data logger and sensors to transmute measured current velocity and discharge time series, etc. to the computer for further analysis. A number of siphons with a diameter of 5 mm suction tube were used to remove the sediment. The tubes connected to the siphons were located at 10 points along with the direction of current depth, through which the average current concentration was measured. An experiments were performed on 3 model samples. Model 1 is a simple, sloping flume without obstacle. In model 2, the flume has a decreased section and continuous constriction at 4.5 m, which is the passing section of the half of channel. In model 3, the flume has a local constriction in 4.5 m, and the passing current through the sides is 10 cm. All records were conducted at 5 m distance from the channel. The parameters of velocity, concentration, and thickness of density current were measured at the desired position. Results and Discussion In the inner region below the maximum velocity, drag on the lower boundary is the main controller parameter, and the proper expression for the velocity profile is a power law distribution as follows in stratified currents. For the whole experiment, the variation of the coefficient n is almost large and varies from 3.027 to 5.33 in different experiments. High variation of this coefficient can be due to the effect of the shear in bed on the velocity profiles, and the coefficient α ranges from 0.13 to 0.84. The value of β coefficient also ranges from 1.185 to 1.758 in all experiments. From the general comparison of all the conditions for the dimensionless velocity profiles in wall region, the best coefficient n is equal to 3.86, which shows a high correlation of 0.878, and for the jet region, the best coefficient α and β are 0.412 and 1.343, with a correlation coefficient of 0.92. Subsequent density current velocity increases and its concentration decreases by creating a constriction and this is due to the accumulation of current behind the obstacles. The constriction also causes an average increase of current velocity by 2.26 times, and the concentration of accumulated current behind the obstacles increases by 1.45 times. The Richardson criterion and the sediment trap efficiency were used in order to correlate accumulation of sediment with the hydraulic parameters of density current, the Richardson number is reduced with increasing trap efficiency, and the correlation coefficient is well established by 0.83 value in all the test modes. On average, about 29.8% from sediments of density current is accumulated behind obstacles for two models with all different states. Conclusion The dimensionless velocity profiles in the upper edge of current show greater dispersion due to the non-permanent behavior of the current in this region. The maximum current velocity in the wall region is greater than the jet region. The best coefficient n is 3.86 for dimensionless profile of velocity in wall region, which shows a high correlation of 0.878; the best coefficients α and β are 0.412 and 1.343, respectively, with a correlation coefficient of 0.92 for the jet region; the best coefficient α is 0.1 for the dimensionless profile of concentration in wall region; and the best coefficients β and γ are 1.15 and 0.8, respectively, with a correlation coefficient of 0.94 for the jet region. Also, the effect of local and continuous constriction showed that the constriction increased the velocity of density current by 2.26 times, and also increased the concentration of current sediments behind obstacles by 1.45 times, and trap efficiency rate of sediments was 29.8%.
Journal of Hydraulics
Iranian Hydraulic Association
2345-4237
15
v.
3
no.
2020
47
59
http://jhyd.iha.ir/article_113304_b5313de0d2b3047e2e5452fb77b09770.pdf
dx.doi.org/10.30482/jhyd.2020.240969.1470
Experimental Study of the Discharge Coefficient in Side Weirs with the Piano Key and the Rectangular Labyrinth Crests
saeid
jeddi
Department of Civil Engineering, Faculty of Engineering, Bu-Ali Sina University, Hamedan, I.R.IRAN
author
jalal
sadeghian
Assistant Professor, Department of Civil Engineering, Bu-Ali Sina University, Hamadan, Iran
author
Bahram
Rezaei
Assistant Professor, Department of Civil Engineering, Faculty of Engineering, Bu-Ali Sina University, Hamedan, I.R.IRAN
author
text
article
2020
per
Introduction: The weirs or spillways are the oldest and the most important hydraulic structures. They have several applications such as evacuation of excess water flow due to floods, control of water level in the reservoir, flow distraction, reducing river erosion and measurement the flow discharge. The side weir is one of different type of spillway which used to control the flow level, diversion and flood damage prevention in dams and hydraulic structures. Also, the side weirs can be divided to the linear and nonlinear crest. Nonlinear weirs come in a variety of forms, such as Labyrinth weir and Piano Key weir. They are used to increase the length of the crest and their discharge capacity where there is length limitation for constructing the weir. Due to importance of the discharge coefficients in the side weirs with the Piano Key and the Labyrinth crest shapes, in the present work a vast range of experimental studies were performed on those types of weirs with different height and geometries. The results of experiments are then used to compare the Key Piano side weir with the Labyrinth one. Methodology: The experiments were carried out 10 m flume at the Bu-Ali Sina University, Civil Engineering Department. A simple rectangular cross section was selected with almost 10 m long, 0.60 m wide and 0.60 m height. The Rectangular Labyrinth and Piano Key weirs experimental models are made using 5mm Plexiglas material in 3 cycles, and 4 heights of 5 cm, 10 cm, 15 cm and 20 cm. The side weirs models had 57 cm length and fixed in the wall opening near the flume end. Since in this research the flow condition is the spatial varied flow, the De Marchi relationship and dimensional analysis have been used to investigate the discharge coefficients in the Piano Key weirs and the Rectangular Labyrinth weirs. Results and Discussion: The study shows that in general, in the Rectangular Labyrinth weir, by increasing weir height the weir’s capacity and consequence the discharge coefficient increases. For example in Rectangular Labyrinth weir with 20cm height the discharge coefficient is almost 34 %, 7.3 % and 14.1 % bigger than that for weir with height of 5 cm, 10 cm and 15 cm respectively. Also, a comparison between the 5, 10 and 15cm weir, with the 20 cm height weir, reviled that the weir efficiency has increased by 35 %, 7.8 % and 14.5 %, respectively. Meanwhile, in the Rectangular Labyrinth weir with heights of 5 cm, 10 cm, 15 cm and 20 cm by increasing Ht / P from 0.95, 0.66, 0.46 and 0.32, respectively, the weir efficiency decreases significantly and its performance get close to linear weir. Also comparing to the Piano key weirs with 5 cm, 10 cm and 20 cm heights, in the weir with 15 cm height, the averaged discharge coefficient increased by 9.3 %, 5.5 % and 9.2 %, respectively. The results of experiments on the Piano key weir shows that by choosing 15 cm as the weir height, the average weir efficiency increases by 9.5 %, 3.5 % and 9.4 % respectively ( to compare with 5 cm, 10 cm and 20 cm weir ). Also according to the experimental results on the Piano key weir with 5 cm, 10 cm, 15 cm and 20 cm height, by increasing the Ht / P ratio from 0.88, 0.6, 0.44 and 0.35 values, the weir performance also get close to linear weir and the weir efficiency reduced considerably. In rectangular Labyrinth weir and Piano key weir, the interference of the flow shedding blades causes a weir at the end of the outlet keys, which is the beginning of a significant decrease in the weir efficiency; and as the interference of these shedding blades increases, the weirs flow gradually deviates from its original function and acts as a linear weir. Conclusion: For the weir with specific value of Ht / P ratio, the smallest weir has the highest discharge coefficient and the lowest discharge capacity. Previous study on the Labyrinth and Piano key weirs indicated that when the weir axis is perpendicular to the flow direction, the efficiency of the Piano key weir is much more than that for the Rectangular Labyrinth weir. However, for side weirs where the weir axis is parallel to the flow direction the Rectangular Labyrinth weir shows better efficiency and performance to compare with the Piano key weir. The Type A Piano key side weir performs better than the Type C Piano key side weir.
Journal of Hydraulics
Iranian Hydraulic Association
2345-4237
15
v.
3
no.
2020
61
74
http://jhyd.iha.ir/article_113426_efff8140344a237e6a52dc14003b8abf.pdf
dx.doi.org/10.30482/jhyd.2020.242322.1471
Numerical Simulation of Dense Discharges from 30o Submerged Inclined Jet in Free and Bed-Affected Conditions
Mohammadmehdi
Ramezani
Babol Noshirvani University of Technology
author
Ozeair
Abessi
Babol Noshirvani University of Technology
author
Ali
Rahmani Firoozjaee
assistant professor, Babol Noshirvani University of Technology
author
text
article
2020
per
Introduction: Human population growth and industrialization have led to an increase in freshwater demand all around the world, specifically in coastal areas. The conventional resources of freshwater (e.g., rain, rivers, lakes, etc.) do not meet this demand; hence finding new resources of freshwater besides preserving and the optimal use of the available freshwater resources is strictly considered recently. During the last decades, the desalination of seawater by removing salt from the roughly unlimited supply of seawater has emerged as a new source of freshwater in coastal zones. One of the major by-products of desalination plants is the effluent with higher salt concentration than the feeding water, called brines. Disposal of the produced brine into coastal bodies has raised serious concerns due to its potential to cause negative impacts on the marine environment, especially on the benthic communities. The disposal of brines is typically done through a single inclined nozzle or multiport diffuser that laid on the seafloor far enough from the coastline. So far, many different studies have been performed on dense jets to find the optimal angle of the inclination. The generally accepted design practice recommends a 60° angle as the optimal angle. However, the terminal rise height associated with this angle is relatively high. Consequently, smaller angles are more appropriate for shallow coastal waters. This paper investigates geometrical and mixing characteristics of 30° inclined dense jets in free and proximate to bed conditions through simulating two numerical series. In the first series, nozzles are placed well above the bed in terms of y_0⁄d to act like free jets. In the second series, the distance of nozzles to the lower boundary has reduced to observe the possible effect of proximity to bed on dense jets behavior. Methodology: The governing equations of the present problem are continuity, conservation of momentum, and tracer advection-diffusion equations. These governing equations are solved using an open-source finite volume model named OpenFOAM. The buoyantBoussinesqPimpleFoam solver, which is a transient solver for buoyant, turbulent flow of incompressible fluids, is modified within the OpenFOAM to solve the governing equations of the present problem. Moreover, the realizable k-ε model and the Boussinesq approximation are employed for turbulent closure and buoyancy effects, respectively. Results and discussion: The major geometrical characteristics of dense jets, including the centerline trajectory, the location of centerline peak, the terminal rise height, etc., are presented. The centerline trajectories are in acceptable agreement with previous analytical and experimental studies. They are generally symmetrical; however, a slight asymmetry was observed in the boundary-affected cases. The other geometrical characteristics in all cases are in good agreement with previous data. The mixing and dilution characteristics were also studied through cross-sectional concentration profiles. It is observed that the present simulations predict the dilution at the return point significantly conservative. The buoyant instabilities on the inner edge of flow are also evident in the mean concentration profiles. Conclusions: Ocean outfalls are the most widely used method for brines disposal. Therefore, predicting the flow behavior along the near field region (a short distance from the nozzle tip) is vital. The review of the previous studies showed that the literature is rich in this field. Several investigations, experimentally and theoretically, have been reported for predicting the brine flow through surface and submerged discharges into both stagnant and flowing waters. There are also commercial models developed for this purpose, which work based on simplifying assumptions for the governing equations. Recently, thanks to progress in computer performance, the use of numerical methods to solve physical problems has become possible for engineering purposes. The discharge of brines, as with many other engineering flows, are physically complicated and fully turbulent, so requiring robust and accurate modeling. In the present paper, a numerical study was reported for inclined dense jets at the angle of 30o. Two series of simulations were performed. In the first series, the nozzles were placed far from the bed. While in the second series, the nozzles were placed in a close distance to the bed. The aim was to investigate the possible effects of proximity to bed on dense jets behavior. The locations of the terminal rise height and impact point, as well as the dilution at the return point, were determined. The simulations predict trajectory data in free jets with reasonable accuracy, but dilution predictions are conservative in comparison to previous analytical and experimental studies. Comparisons between two numerical series showed discharging 30° inclined dense jets in a close distance to the bed in the cases that in this study were examined had no appreciable effects on neither the geometrical characteristics nor mixing and dilution characteristics.
Journal of Hydraulics
Iranian Hydraulic Association
2345-4237
15
v.
3
no.
2020
75
91
http://jhyd.iha.ir/article_113797_5ae0b4fe1a32bbf7703b9e0fd723f85b.pdf
dx.doi.org/10.30482/jhyd.2020.228141.1454
Resilience analysis under simultaneous failure of pipes in water distribution network (Case study in one of the cities of Khorasan Razavi)
mansoureh
atashi
PhD student in Hydraulic structures, Department of Water Science and Engineering, Ferdowsi University of Mashhad, Mashhad, Iran
author
Saeed Reza
KHODASHENAS
Professor
author
Ali Naghi
Ziaei
Water engineering, agriculture faculty, Ferdowsi University of Mashhad, Mashhad, Razavi Khorasan Province
author
Raziyeh
Farmani
Associate Professor, Department of Engineering, University of Exeter, Exeter, UK,
author
text
article
2020
per
Water distribution systems (WDS) are the crucial component of urban infrastructure that play a critical role in delivering sufficient water to users with acceptable pressure, volume and quality. Occurrence of a pipe failure may interrupt service, undermine system performance and ultimately lead to consumer dissatisfaction. More serious condition occurs when several pipes in the system fail simultaneously. Nowadays, the threat of accidental or man-made disruptions motivates water utilities to plan risk mitigation works and to improve the preparedness for extreme events. Pipe breaks increase with aging infrastructure, natural disasters such as earthquakes and man-made disruptions. Three criteria; reliability, resiliency and vulnerability have been used to assess the performance of the water distribution system (Hashimoto, Stedinger, and Loucks 1982). The resilience capacities are absorptive, adaptive and restorative that a system needs to be able to respond to perceived or real shocks (Francis and Bekera 2014). Butler et al. (2017) defined the resilience in WDSs as “the degree to which the system minimizes level of service failure magnitude over its design life when subject to exceptional conditions”. Failure modes in WDSs can be broadly categorized into structural failure and functional failure (Mugume et al. 2015). Response to pipe failure can indicate system resilience to loss of structural connectivity (Butler et al. 2014). Todini (2000) proposed a technique based upon the definition of resilience index that emulate both reducing the cost and preserving a capability of the system to overcome failures while still satisfying demand and pressure at each node. Diao et al. (2016) proposed the Global Resilience Analysis (GRA) as a methodology that focusses on the response to system failure modes. Using GRA, the whole range of performance strains resulting from any stress magnitude can be evaluated.In GRA, the model of pipe failure mode (stress on the system) is modified by changing the pipe status to closed for three hours during peak consumption (Diao et al., 2016). In this paper, the numerical code of the GRA method for NET3 network is evaluated and the resilience of water distribution network is examined separately from the main transmission lines. Then, the pressure-based algorithm for the above method is assessed. then the resilience of the real water distribution network in Iran is examined. Based on the inquiry from the water and wastewater company, and considering the diameter of the network pipes, the failure time of the pipes in the consumption peak (12-18) is considered to be an average of 6 hours. Finally, the critical network pipes are identified and the resilience analysis of the network is examined if these pipes are protected. - Methodology In this paper, the GRA approach is adopted to evaluate the system resilience under different pipe failure modes (Diao et al. 2016). The possible failure modes were modelled with increasing the stress magnitude and estimating the corresponding strains (Johansson 2007). Different combinations of pipe failure are considered as stress magnitude and ratio of unsupplied demand to total demand is defined as strain magnitude. Due to huge number of possible combinations (a system with N component and m simultaneous failures has ∑n!/m!(n-m)! potential failure scenarios), it is not possible to model every conceivable scenario for each system failure magnitude (Sweetapple et al. 2018). For any given stress magnitude, an appropriate affordable number of failure scenarios must be determined. Where the total number of scenarios (TNS) is determined as follows (Diao et al. 2016). EPANET2 hydraulic solver is used to determine the hydraulic and water quality conditions in a pressurized WDS (Pathirana 2010). As a demand-driven model, EPANET2 determines the nodal pressures by considering the specified demand at nodal points (Rossman 2000). To illustrate actual supplied water to customers in abnormal conditions, the available nodal demand is expressed as a function (Eq. 2) of nodal pressure head (Wagner, Shamir, and Marks 1988). - Results and discussion Figure 4 shows the calibration of code with results (Diao et al. 2016) for the Net3 distribution network. The results of the code above 95% correspond to the results (Diao et al. 2016). In figure 5 the resilience of Net3 for two approaches (i.e., whole network (WN), and network without CRP (NWCRP)) are compared. The GRA showed that Net3 encountered complete failure due to simultaneous failure of the four main CRPs. Whereas excluding these pipes caused the failure of 12 pipes lead to the same results. The maximum and average network supply shortage were 36% and 12% higher than the whole network model. The supply shortage for all combinations of CRP failures in the peak demand period (18-20 pm) is presented in figure 7. In figure 8 the resilience of real water distribution network for three approaches (i.e., network without CRP1 (NWCRP1), and network without CRP2 (NWCRP2)) are compared. If the resilience of the main transmission lines is examined separately from the total distribution network, the resilience of the network will increase in three modes of maximum, average, and minimum by 72, 23, and 14%, respectively. The results showed that if ten critical pipes were protected, network resilience would increase by an average of 20 percent.(fig.9) - Conclusion Resilience analysis is critical to the presentation of emergency schemes in distribution networks before a crisis occurs. Based on resilience analysis, the distribution network can be fully identified and the critical elements of the network can be identified. One of the network components that is considered in resilience analysis is the failure of part or all of the different pipe combinations. In this study, after testing the resilience analysis model in the NET3 study network, the model was implemented for a real water network in Iran. Accordingly, by reinforcement of the main lines, the efficiency of the real network will increase by a maximum of 72%. Because this network has the only major source , with a single failure of the pipes, it reaches 100% of the water supply. The resilience analysis of other network pipes also shows that if the network's ten critical pipes are protected, the network's resilience will increase by an average of 20%.
Journal of Hydraulics
Iranian Hydraulic Association
2345-4237
15
v.
3
no.
2020
93
105
http://jhyd.iha.ir/article_113902_bbef3faed0ca77e83d679d0cff92c240.pdf
dx.doi.org/10.30482/jhyd.2020.235645.1464
Experimental Study on the Effect of Discharge and Tailwater Depth on Bed Topography Downstream of a Piano Key Weir
Aram
Ghafouri
Tarbiat Modarres University
author
Massoud
Ghodsian
Tarbiat Modarres
author
chonoor
abdi
Tarbiat Modarres University
author
text
article
2020
per
سرریز غیر خطی کلیدپیانویی در مقایسه با سرریز خطی ضمن آبگذری بیشتر، ساختاری به نسبت ساده دارد و سازهای اقتصادی است. مزیتهای دیگر سرریزهای کلیدپیانویی عبارتند از: دبی بر واحد عرض عبوری از سرریز را تا 100 مترمکعب بر ثانیه بر متر افزایش میدهند، دبی عبوری از این نوع سرریزها حداقل 4 برابر سرریزهای معمولی (خطی) است، باعث افزایش ظرفیت مخزن میشوند و از لحاظ اقتصادی مقرون به صرفهتر بوده و هزینه نگهداری کمتری دارند. این ویژگیهای سرریزهای کلید پیانویی، آنها را به سازههای کارآمدی تبدیل کرده است. تمامی آزمایشها در یک کانال مستطیلی به عرض 75 سانتیمتر، با کف فلزی، دیوارهی شیشهای و ارتفاع 80 سانتیمتر واقع در آزمایشگاه هیدرولیک گروه مهندسی آب و سازههای هیدرولیکی، دانشگاه تربیت مدرس تهران انجام شد. جریان آب از یک مخزن زیر زمینی به وسیله یک پمپ با حداکثر دبی 85 لیتر بر ثانیه تامین میشد. مخزنی به عرض 05/2 متر در بالادست از طریق یک تبدیل به کانال وصل شده است. تنظیم عمق جریان در کانال به وسیله دریچه تعبیه شده در انتهای کانال انجام میشد. سرریز کلیدپیانویی مورد نظر در فاصله 1 متری از ابتدای انحنای کانال نصب و آببندی آن انجام شد. تمامی آزمایشها با سرریز در شرایط جریان آزاد انجام شد. در پاییندست سرریز، لایهای از رسوبات یکنواخت با قطر متوسط 64/1 میلیمتر، انحراف معیار هندسی 24/1، ارتفاع 5/42 سانتیمتر و طول 2 متر قرار داده شد. در این تحقیق سرریز کلیدپیانویی نوع A ذوزنقهای شکل، از جنس ترموپلاستیک (فیلامنت رایج PLA) با ضخامت 2/1 سانتیمتر استفاده شد. هر سرریز دارای 6 کلید (3 کلید ورودی و 3 کلید خروجی) و عرض 75 سانتیمتر (هم عرض کانال)، طول تاج (B)و ارتفاع خالص (P) به ترتیب 50 و 20 سانتیمتر میباشد. دبی جریان با دستگاه دبیسنج ثبت میگردید. آزمایشها با سه دبی 03/0، 04/0 و 05/0 متر مکعببرثانیه و پنج عمق پایاب از 08/0 تا 18/0 متر انجام شد. در طول آزمایش عمق آبشستگی و پروفیل بستر در دیواره سمت راست و سمت چپ کانال، با استفاده از عکسبرداری با دوربین اندازهگیری و ثبت میشد. در انتهای هر آزمایش با خاموش کردن پمپ آب، جریان آب به صورت تدریجی کاهش یافته و از کانال خارج و زهکشی آن صورت میگرفت. سپس توپوگرافی کامل بستر با استفاده از دستگاه برداشت توپوگرافی لیزری با دقت 1 میلیمتر اندازه میگردید. در این شکل x فاصله طولی از دیوار پاییندست سرریز و y فاصله عرضی از دیوار سمتراست کانال است. فواصل نقاط برداشت پروفیل بستر در محدوده حفرهی آبشستگی 3 سانتی-متر و در پاییندست آن 5 سانتیمتر بود. با توجه به منحنی تغییرات زمانی عمق آبشستگی پاییندست سرریز برای دبیها و عمقهای پایاب مختلف مشاهده گردید که که قسمت اعظم آبشستگی در دقایق اولیه آزمایش رخ داده و سپس نرخ آبشستگی به طور قابل ملاحظهای کاهش مییابد. همچنین مشاهده میگردد که با افزایش عمق پایاب، عمق آبشستگی در پاییندست سرریز روند کاهشی دارد. زیرا افزایش عمق پایاب، کاهش ارتفاع ریزش جریان و در نتیجه کاهش سرعت جریان برخوردی به پایاب را به همرا دارد. در نتیجه از قدرت تخریبی جریان کاسته شده و عمق آبشستگی کاهش مییابد. همچنین مشاهده میگردد که بیشترین عمق آبشستگی در تمام دبیها در دیواره سمت راست و کمترین عمق آبشستگی در دیواره سمت چپ رخ داده است. همچنین مشاهده می-گردد که با افزایش عمق پایاب در دیواره سمت چپ شاهد افزایش 2 درصدی عمق آبشستگی و در دیواره سمت راست حدود 5/21 درصد کاهش آن هستیم. با توجه به توپوگرافی بستر پاییندست سرریز کلیدپیانویی روشن است که تغییرات ایجاد شده در بستر تابع مقادیر دبی و عمق پایاب است و بسته به عملکرد و شرایط هیدرولیکی جریان، موقعیت عمق ماکزیمم و گستردگی این حفرهها در عرض و طول کانال متغییر است. همچنین مشاهده میشود حفرهی آبشستگی پاییندست سرریز، نسبت به محور طولی کانال تقارن ندارد که به دلیل اثرگذاری کلیدهای ورودی و خروجی بر روی جهت جریان خروجی از روی سرریز میباشد. البته میتوان گفت الگوی کلی آبشستگی در شرایط مختلف تقریباً مشابه است. تغییرات حداکثر عمق آبشستگی در پاییندست سرریز، در حدود 8/5 تا 8/8 برابر عمق آب روی سرریز میباشد. با توجه به این شکل روشن است که موقعیت وقوع حداکثر عمق آبشستگی نیز تابع دبی و عمق پایاب است و در فاصلهی 15 الی 27 سانتی-متری از پاشنهی سرریز اندازهگیری شده است. نتایج آزمایشگاهی نشان داد که بیشترین کاهش تراز بستر یا آبشستگی در پاشنه سرریز، در تمامی دبیها در حالت کمترین عمق پایاب (8، 5/9 و 11 سانتیمتر)، رخ داده است. زیرا در عمق پایاب کمتر، جریان با سرعت بیشتری به پایین دست برخورد میکند و در نتیجه در این حالت مقدار آبشستگی و کاهش تراز بستر بیشتر است. همچنین در حالت عمق پایاب کمتر، به علت آشفتگی بیشتر جریان، تغییرات عرضی بستر بیشتر است. با توجه به پروفیل طولی بستر در میانهی کانال در حالت بیشینه و کمینه آبشستگی مشاهده میگردد که روند تعییرات بستر در تمامی آزمایشها تقریباً مشابه است بطوریکه در پاشنهی سرریز آبشستگی رخ داده و با فاصله گرفتن از سرریز، آبشستگی بیشتر شده و در انتهای کانال تغییرات جزئی مشاهده میگردد. همچنین مشاهده میگردد که با افزایش عمق پایاب، عمق آبشستگی کاهش یافته، محل وقوع حداکثر عمق آبشستگی از پاشنهی سرریز دورتر میشود و گسترش طولی حفره افزایش یافته است. حفرهی آبشستگی در جهت محور طولی کانال تقارن ندارند. این حفره از دو بخش تشکیل شدهاست بخش اول که به دلیل وجود انرژی جنبشی ناشی از جت به پاییندست کشیده شده و بخش بعدی به علت جریانهای برگشتی به سمت بالادست کشیده شده است. بخش اول به دلیل قدرت جت جریان، قسمت اعظم این حفره را در بر میگیرد، مشاهده گردید که در تمامی آزمایشات حفرهی آبشستگی به سمت پاییندست توسعهی بیشتری داشته است. با مقایسهی این آزمایشها مشاهده میشود که با افزایش عمق پایاب از میزان پیشروی حفرهی آبشستگی، به سمت پاییندست کاسته شده است. مقادیر طول بالادست حفره آبشستگی بین 3/6 و 4 و مقادیر طول پایین دست حفره آبشستگی بین 2/13 تا 6/20برابر عمق جریان روی سرریز اندازه گیری شده است.
Journal of Hydraulics
Iranian Hydraulic Association
2345-4237
15
v.
3
no.
2020
107
122
http://jhyd.iha.ir/article_113651_2e790152ab6c8b5e12a7fa960dcb796d.pdf
dx.doi.org/10.30482/jhyd.2020.236770.1465