جستجوی مقالات مرتبط با کلیدواژه « Numerical Simulation » در نشریات گروه « آب و خاک »

Labyrinth weirs have always received special attention compared to linear weirs due to the increase in flow capacity through the increase in width. The number of 23 models was simulated using Flow-3D software to investigate the effect of various factors such as changing in the height of the dam body, changing the height of the weir apexes (weir height), the discharge passing over the weir, and the effects of different angles of the weir apex in the plan on the amount of bed erosion in the downstream of Labyrinth weir was studied. Validation of the numerical simulation results with the experimental model indicated a very good agreement between the numerical simulation and the experimental values. This reduction in the weir with an apex angle of 60 degrees is more than other models and the scour depth is reduced from 31 to about 90%. Also, the amount of flow traversability in this type of weir is more than other models, which made the weir with an angle of 60 degrees to be introduced as the most optimal weir in investigating the efficiency of the weir and the reduction of scouring compared to linear models, 45 and 90.

Flood plains of rivers play a significant role in the transfer of flood discharge. In this research, the vertical distribution of the longitudinal and transverse flow velocities and the amount of discharge passing through different sections of the main channel in flooded meandering rivers under the effect of the change in floodplain width and relative depth were investigated. Because the fact that the width of the floodplain is constantly changing along the river's path, in this article, from the four meandering compound channels with floodplain widths of 3.3, 4.31, 5.32, and 6.33 meters and three relative depths of 0.26, 0.35 and 0.45 were used. The results of the numerical simulation showed that with the increase in the width of the floodplain, the value of longitudinal and transverse flow velocities decreases and these changes in the transverse and longitudinal flow velocities are more noticeable due to the change in the width of the floodplain in the middle sections and above the overflow depth of the main channel, so that with the increase 92% of the width of the floodplain, the value of the maximum transverse and longitudinal flow velocity in the middle section decreases by 21% and 25%, respectively. Also, according to the results of this research, with a 92% increase in the width of the floodplain, the average flow velocity and discharge through different sections of the main channel will decrease by 24% and 33%, respectively.

Erosion and sedimentation in river arches cause problems in river structures. Therefore, the pattern of flow and transport of sediments in the open channels of meandering River has attracted the attention of river engineers. Since the flow field in the bends of rivers is three-dimensional, therefore, in the last few decades, the prediction of changes in bed level and changes in the location of banks with the help of computer programs has been given more attention.In this study, using SSIIM software, topographical changes of meandering channels with sinus generator and moving bed have been modeled, and bed level changes have been studied under different conditions. For this purpose, solid beaches Natural rivers are principal resources of water and energy. Design and operational management of natural rivers needs a complete knowledgement of mechanics of flow pattern and sediment transport. The complex three-dimensional flow characteristics inriver bends reveals the necessity of using a three-dimensional numerical model.The numerical model used in the present study is called SSIIM, an acronym for Sediment Simulation in Intakes with Multi block option. In this study, in the first step, SSIIM is applied to investigate the characteristics of turbulent flow in a Sine-Generated channel with 70-degree angle, the rectangular cross section of width B =40cm and fixed bed. In addition, a comparision has been also made between the turbulence models, the flow characteristics such as Longitudinal and transverse velocity, Water level and bed Shear stress has been considered. The results have been validated with laboratory data. The results show that SST-k-ω model has better consistency with experimental data than k-ε model. Also distribution of bed shear stress depends on Froude number although secondary flow is independent. Furthermore, distribution of bed shear stress and secondary flow is dependent on the width to depth ratio. For b/h<8, another circulation cell occurs near the outer bank.In the second step, to investigate the variation of channel bed subjected to steady flow, Channel with movable bed has been employed. Comparison of results show good agreement between computed and measured bed topography. Finally, the effective parameters including interval time step, grid size, Froude number, width to depth ratio and meandering angle has been investigated. Results show that by increasing the Froude number and the ratio of width to depth point bar and point pool gradually migrate downstream channel. Whereas by increasing meandering angle, point bar and point pool moving Upstream.

Hydraulic jump is used for dissipation of kinetic energy downstream of hydraulic structures such as spillways, chutes, and gates. In the present study, the experimental measurements and numerical simulation of the free hydraulic jump by applying Flow-3D software in six different conditions of adverse slope, roughness, and positive step were compared. It should be noted that two turbulence models including k-ε and RNG were used for numerical simulation. Based on the results, simulation accuracy using the RNG model was more than the k-ε model. The statistical indices of NRMSE, ME, NS, and R2 for comparing the water surface profile were obtained at 34.3, 0.0052, 0.995, and 983 for the application of the RNG model, respectively. Also, using the RNG model, the values of these indices for the velocity profile were obtained at 14.92, 0.127, 0.9982, and 962, respectively. In general, the error of the simulated water surface and velocity profile were obtained at 5.31 and 12.4 percent, respectively. Moreover, the maximum error of the numerical simulation results of D2/D1, Lj/D2, and Lr/D1 was ±12, ±12, and 16%, respectively. Therefore, the use of Flow-3D software with the application of the RNG turbulence model is recommended for numerical simulation of the hydraulic jump in different situations.

Due to the increase in population and the need for water supply, preservation and protection of surface water and groundwater resources has been considered by governments. One of the pollutant sources in rivers is entering salinity from groundwater into the river, that in this research is considered as distributed (non-point) sources. The goal is to identify the salinity intensity, location and length of sources by measuring the temporal distribution of concentration in one observation point. For this purpose, the inverse solution of advection-dispersion equation in the river was employed using the simulation-optimization approach. MIKE11 numerical model was used to simulate flow and transfer of salinity in the river, and genetic algorithm was employed for optimization. In the proposed model, considering only one observation point with some measured intensity data for recovering several sources, unknown location and length of the sources, in addition to their intensities is the most significant advantage of the present study. The model verified by using hypothetical examples, 40 km section of the Karun River and also by applying five and 15 percent noise to the observation data. The results confirm the ability of the model to recover the specifications of several distributed sources using only one observation point. With five percent of noise in the observation data, all three specifications of sources can be recovered with the desired accuracy. While at 15 percent of noise, the accuracy of the model in recovering the location and length of sources was decreased. Also, to recover the specifications of each source, employing only three points of the measured data in the ascending part are sufficient.

In this paper, the ability and performance of two unsaturated soil constitutive models are compared. One constitutive model is in the context of classical plasticity, and the other constitutive model is in the context of generalized plasticity. The selected models consider the effect of water retention curve on the unsaturated soil behavior. First, a program in FORTRAN language is written for each constitutive model. In the next step, the written program is validated with the experimental results. Finally, eight different suction-stress paths are modeled to identify the strengths and weaknesses of the constitutive models. The results showed that both models could simulate the loading at constant suction, increasing the yield stress and decreasing the soil deformation with an increase of suction. In drying–wetting cycles, the variation of the yield stress of the Sun et al., 2007 model is less consistent with experimental data than the variation of the yield stress of the EBSZ model, and Sun et al., 2007 Model cannot simulate some important properties of unsaturated soils. The EBSZ model cannot simulate a sudden volume reduction (failure) under decreasing suction in unsaturated soils. Using the EBSZ model in the deformation analysis of unsaturated soil may not be reliable.

One of the most important hydraulic structures in a dam is the spillway. The design of the ogee spillway crest is based on the lower profile of the free-flow jet passing through the sharp-crested weir. When the downstream ogee spillway profile for the design discharge conforms to the lower profile of the free-jet passing through the sharp-crested weir, the pressure on that surface of the spillway becomes zero. In this study, the design of the ogee spillway was performed initially based on both two- and three-dimensional numerical modeling and then compared to the USBR standard method. The comparison of the final numerical and analytical results showed that although the vertical two-dimensional outputs were completely in agreement with the USBR standard profile, the three-dimensional profiles were different because in this model, guide walls were not considered. According to the analysis, if the flow entering the spillway is parallel to its axis, the lower profile of the sharp-edge spillway will be in complete agreement with the standard profile. Since, the design of guide wall geometry for ogee spillways is carried out using physical modeling which iteratively revises during a high-cost trial and error procedure, this research based on the case study of the spillway of Karun-3 dam has been tried using numerical modeling. The closest geometry to the geometry of the overflow guide wall was obtained which creates the least difference in transverse velocities. In this way, the design of guide walls can be done with more accuracy and low cost in comparison to physical modeling.

Geometric and morphological characteristics of each river are its main characteristics by which the management planning of the basin and the conservation of natural resources around it is done. Estuaries are formed at the mouth of rivers in a border area between sea and land. Deformation of estuaries due to sedimentation and erosion changes the pattern of river flow. In this research, the hydrodynamic model (HD) is used to calculate the flow rates and velocity and the sediment transport model (ST) is used to calculate the suspended load and bed level. The results of the hydrodynamic model showed that the maximum speed at 17 km of Shalmaneh station (beginning of the third interval) is approximately 4.7 m /s. This value decreases to about 1.5 meters per second as we approach the end of the estuary. Due to the importance of the role of floods in bed changes, the model was implemented using the 25-year flood discharge of Shalmanrood River (355 cubic meters per second) for a period of one year. After that, the river route was divided into three parts and the behavior of Shalmanrud river was studied according to the deformation created in the sections of each part. The maximum amount of sediment in the first part is 0.41 m in non-flood condition and 1.1 m in flood condition. In the second part, sedimentation increases and in non-flood state reaches 0.8 meters and in flood state reaches 2 meters. In the third part, the amount of sediment will be more than the first and second parts. The maximum amount of sediment in this part is 0.53 m in non-flood condition and 1.4 m in flood condition.

The study of annual damage statistics due to floods in Iran and the world shows the extent of flood damage to natural and human resources in different regions. Determining the flood zone of rivers in order to protect national resources and reduce flood damage provides the possibility of protecting the river from encroachment and the construction of any unauthorized facilities in it. Therefore, in the present study, the capability of numerical models in simulating the flood zone of rivers was evaluated in the range of Azarshahr Qushqura river and the two-dimensional hydraulic model HEC-RAS 5.0.7 and one-dimensional HEC-RAS model were compared. Changes in the hydraulic characteristics of the flood flow including depth and velocity of the flow at different cross sections of the models were evaluated. The results showed that the water surface level (flow depth) of the two-dimensional model HEC-RAS compared to the one-dimensional model had the lowest error as compared to other hydraulic parameters of flood flow. The two-dimensional HEC-RAS model showed the highest error rate in the flow velocity parameter in comparison to the one-dimensional model. The results indicated that two-dimensional HEC-RAS model V5.0.7 determined the surface of the flood zone 12.46 % more than the one-dimensional HEC-RAS model. The confirmation of the resulting zones on the current state of the river and comparison with the river aerial photo of 1346 indicated the higher accuracy of the two-dimensional HEC-RAS model in estimating the flood zone of the river.

Study of separation zone is so important in right-angled three-branch or four-branch open channel junctions. Some effective parameters in this case are inlet discharge ratio and flow depth which in this research the effect of inlet discharge ratio and weir height ratios (flow depth) on flow pattern and dimensions of separation zone has been simulated numerically. Investigation of numerical results showed that k-ω model well validated with experimental results and had good agreement, so that simulation error was less than 20%. Dimensions of separation zone in main and side channels were directly proportional with the inlet discharge ratio. Also as increases of height ratio of outlet weirs, flow depth increases and separation zone dimensions decreased. According to the analysis of numerical results, dimensions of separation zone in vertical direction, of the channel bed to water surface increased, so that for discharge ratio 0.6 and height ratio of outlet weirs 0.377, length of separation zone at the channel bed, 0.1 m up the bed and water surface was about 60 cm, 75 cm and 85 cm, respectively. So of the water surface towards the channel bed, length of separation zone decreased about %29.

High kinetic energy of supercritical flow formed from spillways as well as middle and bottom outlets of the dam body are commonly considered a water jet. This flow type in interaction with the erodible bed can endanger the stability of structures located in its path. The main purpose of this study is to assess the mechanisms of flow and scour due to simultaneous operations of wall and impinging jets. To this end, the flow pattern and the scouring process has been simulated by Flow3D. First, the numerical model results are validated against experimental data. Then the velocity vectors, secondary currents due to the collision of water jets, and the geometric parameters of scour (e.g., scour depth, scour length, and ridge height) are investigated at various stages from the beginning of the scouring process to the equilibrium. The results of the flow pattern analysis indicated that by the collision of water jets, a single clockwise rotating vortex is formed at intersection of the jets. The latter vortex leads to further erosion of a sediment bed. Flow separation occurs at the top of the ridge due to the accumulation of the eroded sediments at the downstream of the scour hole over time. A counter-clockwise vortex is generated at the upstream of the ridge as a result of the flow separation. Investigation of the scour mechanism demonstrated that the highest scouring propagation rate occurs during the early stages of the scouring process.

In this study, the turbulent flow field in rectangular channels with side weir is simulated using the FLOW-3D software. To verify the modeling results, the experimental measurements obtained by Hager (1982) are used. Also, for simulating the flow turbulence the standard k-ε and RNG k-ε turbulence models are used. The numerical modeling results show that the RNG k-ε turbulence model has more accuracy. According to the modeling results, the RMSE and R2 values for the standard k-ε turbulence model are calculated 0.005 and 0.969, respectively. Meanwhile, these values for the RNG k-ε turbulence model are estimated 0.004 and 0.971, respectively. Also, analysis of the numerical results indicates the acceptable accuracy of the numerical model in predicting the experimental results. For example, the RMSE and correlation coefficient values for the mentioned model are calculated 0.004 and 0.971, respectively. Subsequently, the effects of the side weir inlet length on the flow pattern are investigated. For this purpose, three different numerical models with weirs with lengths of 1m, 0.7m and 0.5m are defined. According to the modeling results, by decreasing the inlet length the side Froude number value along the side weir decreases. In contrast, by decreasing the side weir inlet length the maximum value of the flow field pressure for the model with a inlet length of 0.5m is predicted. In other words, the maximum pressure values for the models with side weirs with lengths of 1m, 0.75m and 0.5m are calculated 271pa, 286pa and 317pa, respectively.

Investigating and understanding river change issues is one of the important factors in sediment hydraulic sciences and river engineering. These studies can be done with the help of physical, mathematical models, or both, but due to financial and time constraints, mathematical models are more general and often used. In this study, the GSTARS model was used to investigate erosion and sedimentation and select the most appropriate function in 12.5 km in length from the Talar river in Mazandaran Province. Simulation using the 55 sections taken in 2006, the daily flow data of the hydrometric station of the Shirgah, located at the beginning of the rich and characteristics of the river sediment, was done. The calibration and validation of the model with cross sections taken in 2012 showed that Yang's sediment transport equation has the highest correlation with reality and can be used to predict river change. The amount of sediment depleted from the case study using the Yang equation is estimated at 8590 tons per year. Also, the study of longitudinal profiles of the river with different sediment transfer functions showed that the study reach at the end range has an erosion trend and is not capable of sand and gravel mining.

In this research, a three-dimensional numerical model has been developed to simulate the flow pattern at lateral intake in 180-degree bend. Due to the curvature of flow boundaries and computational grid, the three-dimensional Navier-Stokes equations are solved in nonorthogonal and nonstaggered curvilinear coordinates, and given the complexity of the flow conditions, the k-ω model for low Reynolds numbers is used to solve turbulence terms. The equations are discretised by the finite volume method and the central difference and power law algorithm are used to discretise the diffusion and convection terms, and the stable semi-implicit (SIMPLEC) is used to couple the flow and pressure field. Also, to increase the efficiency of the model, one block with variable domain has been used to simulate both channels (main and intake). The developed model was first validated in two tests of flow in 180-degree bend and the lateral intake in a straight flume. Then flow pattern at the lateral intake in 180-degree bend for 45-degree diversion angle in the establishment angle of 40-degree was simulated and compared with the available laboratory data. The average modeling error in the main channel and intake was about 7.3% and 19.7%, respectively, which is acceptable compared to the results of other commercial models.

In this study, an Analytical program has been conducted to identify the behavior of of amplitude aquifer to different water turbulence and find a relationship for optimal groundwater abstraction of this aquifer. The geographic information system is first used to process geological, hydrological, and hydrogeological data, and then the MODFLOW-2000 code is used to simulate the flow. After the initial simulation, the hydraulic conductivity parameter in a stabilized steady situation (April 2005) and in a unstable situation (2004-2005) The hydraulic conductivity parameter and the discharge coefficient, in particular, were measured. Then, for a period of 18 months, with the data of 2012-2013 and for the optimized parameters, the validation test was performed. Two different management scenarios for a 102-month period were defined to predict groundwater level fluctuations and the effect of water pumping from the domain aquifer. The results of the numerical model analysis show that if the aquifer is operate with the current situation, the sharp drop in water in the aquifer and the gradual drying of the aquifer will continue in the future, so that the maximum and minimum drop limit of observation wells number 5 und 3 is respectively 12/20 meters and 1.70 meters. Of course, lowering the discharge pumping rate will improve this situation. Therefore, considering that the range amplifier is fully developed, the power supply-pumping diagram was drawn. The results show that by using the nutrition-pumping diagram, the water level can be controlled to a certain extent by considering economic and environmental issues and the areas of aquifer that are close to the aquifer (trava boundaries) are affected and the wells operating in this area have the least effect on the drop in water level.

Utilizing adjacent piers is one of the cost reduction factors in bridge construction. The impact of turbulent flow around piers on each other, piers distance and the amount of scouring in the adjacent piers are of great importance. In this research, it is tried to present a convenient and efficient combination of adjacent piers in order to reduce the amount of scour by analyzing the placement of these piers in two different shapes and various distances from each other and its impact on the amount of local scouring and the bed erosion pattern. Numerical simulation is done by FLOW3D software. Designed models for two cylindrical and combined shapes of piers in two specific placements, side by side and tandem, and in 6 different distance between the two piers for each state, totally 26 simulation models were simulated and investigated. It is found that the scouring depth increases significantly by decreasing distance between piers which creates a wider obstacle against the flow and water jet between the piers. The flow depth is decreased by increasing this distance and the adjacent piers have no impact on the amount and pattern of scouring in S=4D and higher distances away from each other and the most suitable distance was obtained at S=2.75D. In the tandem cases, it was found that the piers distance does not have any impact on the amount of scouring at the upstream and just the middle part experiences quantitative changes in the bed level; this impact is low by decreasing the distance and obvious by increasing the distance. All the mentioned items are correct in the combined pier, but the amount of scouring shows reduction.

Side weirs are installed on the side wall of main channels. By reaching the flow to the side weir, the exceeded flow falls from the side weir crest and is directs to the side channel. The flow within the channels with side weirs is considered as spatially varied flow. In this study, the three-dimensional flow in a rectangular channel with side weir was simulated by the FLOW-3D software. For simulating the turbulence of the flow, the standard and RNG turbulence models were used. According to the modeling results, the accuracy of the RNG turbulence model was higher than that of the standard model. Furthermore, the Volume of Fluid (VOF) model was used for estimating the variations of the flow free surface. In the study, the velocity was predicted with an acceptable accuracy. Also, the MARE values for the longitudinal, transverse and vertical components were estimated 0.480, 0.468 and 3.519 percent, respectively. Then, the effects of sharp and broad crested weirs on the characteristics of the flow field in the main channel along the side weir for three different models with width of 0.01, 0.05 and 0.15 m were investigated. According to the numerical modeling results, by increasing the width of the side weir crest the shear stress value in the vicinity of the side weir crest increase significantly.

In this paper, using a 3D numerical model, the flow pattern at lateral intake was simulated. A three-dimensional finite volume model with standard  was developed to solve turbulence equations. In order to simulate the main and diversion channels, only one block with varied domain arrays was used. The Reynolds-Averaged Navier-Stokes (RANS) equations are solved in a curvilinear non-orthogonal coordinate system with collocated grid. Pressure correction algorithm of SIMPLE and convection schemes of Power Law are applied to the model. In addition, for velocity-pressure coupling; the Rhie and Chow method were used. Experimental data obtained from laboratory study is utilized to verify the model computations. The flow pattern at lateral intake with one-block numerical method was modeled. The numerically modeled results show acceptable agreement with the measured data and demonstrate the capability of the developed numerical model.

 The concentration changes of suspended load along the river reach and the contributing factors are of importance for hydraulic and environmental engineers. The first step to calculate the concentration of suspended sediment load is determining the flow hydraulic characteristics along a river reach. Although most of flow in nature are unsteady, the quasi-steady flow condition was considered to be simple in this study and the water surface profile along the river reach with irregular cross sections was calculated by standard step-by-step method. In order to calculate suspended sediment load under non-equilibrium condition, the advection-diffusion equation with source term was numerically solved. In the present sediment model, ten discretization methods, five relations for calculating capacity of suspended sediment load, eight relations for diffusion coefficients and eight relations to calculate particle fall velocity were used and their effects on suspended sediment distribution along 18480 m of Gharasoo river were investigated.

 The HEC-RAS model output was used to calibrate the present hydraulic model. The models were run with the conditions as same as Manning roughness coefficient and river geometry conditions. The results showed that the calculated water surface profile along the river reach by two models are completely overlapped each other. In other words, the present model has a very good accuracy to predict the water surface profile in the river reach. As most commercial 1-D models (same as HEC-RAS) only consider the equilibrium condition  for sediment  transport and the bed or total load sediment, comparing the results of present sediment model with them seems not to be reasonable. Therefore, to validate the present suspended sediment model and finding the best method of discretization, an especial shape concentration hydrograph was introduced to the present model as input hydrograph and the model was run when the source term has been deleted deliberately.  The volume below the input concentration hydrograph and calculated hydrographs in different cross sections was compared to each other. Comparing the hydrographs showed that the maximum error in calculating the volume of concentration hydrograph with the input hydrograph was 0.029% implying that the model satisfies the conservation laws as well as reliable programing. Among ten discretization methods, the best method for discretization of the advection-diffusion equation was Van Leer's method with the least error compared to other methods. After validating the model, effect of five relations for calculating capacity of suspended sediment load was investigated. The results showed that using the Wife equation estimated the amount of suspended sediment higher than other equations. The Toffaletti equation also estimated suspended sediment load lower than other equation. Among eight particle fall velocity formulas, Stokes relationship estimated the fall velocity larger than other equations. Hence, the Stokes equation application decreases the possibility of suspending the sediment particles. However, employing Van Rijn and Zanke relationships resulted in a greater suspended sediment load distribution along the river reach. Among eight relationships for diffusion coefficients, Elder and the Kashifipour - Falconer equations exhibited the lowest and the highest amount of diffusion in the concentration hydrograph, respectively. Furthermore, the calculated suspended sediment concentration under non-equilibrium conditions was 11.7 % higher than that under equilibrium conditions along the river reach.

 Most 1-D numerical models only simulate the bed and total loads sediment transport under equilibrium condition while sediments are transported under non-equilibrium conditions in nature. Sediment transport under non- equilibrium conditions may be greater or lower than the equilibrium condition known as the capacity of sediment transport. In this research, a numerical model was developed to simulate the suspended sediment transport in a river reach under non-equilibrium conditions. The amount of suspended sediment concentration was calculated for each sediment grain size. The results showed that the distribution of suspended load along the river reach is not significantly sensitive to the fall velocity relations while the type of sediment transport equation affected the suspended sediment transport concentration. The concentration of suspended sediments for non-equilibrium conditions was also 11.7% higher than the concentration of sediments in equilibrium condition.

Generally, intakes are used for conveying and diverting the flow within main channels and rivers. In this study, a flow field was simulated using FLOW-3D software. In addition, the flow free-surface variations were predicted using the Volume of Fluid (VOF) scheme. The flow turbulence was estimated by standard k-ε and RNG k-ε turbulence models. For instance, the MAE values for standard k-ε and RNG k-ε models to simulate the free surface profile were computed 0.166 and 0.201, respectively. The modeling results showed that the numerical model simulated the flow field with an acceptable accuracy. For example, the RMSE, MAE and R values for the simulated flow free-surface variations were calculated 0.164, 0.158 and 0.997 percent, respectively. Then, the effects of four flow division angles (30, 45, 75 and 90 degrees) on flow field pattern were considered. Regarding the modeling results, the highest depth-averaged velocity was obtained for the model with 45-degree. Among the models with division angles of 30, 45 and 75 degrees, the maximum shear stress was predicted for the model with 45-degree.