s.a.a. salehi neyshabouri

A compound open channel is composed of the main channel and flood plain. In experiments with compound open channel conducted to ensure that the flow is uniform and fully developed, it is necessary to study the distribution of discharge in the main channel and flood plains. The purpose of the present study is to investigate the effects of channel inlet condition on flow uniformity by considering distribution of discharge in channels with length to flood plain width ratio lower than 35 (needed for fully developed flow condition) by analyzing the flow field and turbulence parameters. For this purpose, particle image velocimetry method has been used in a rectangular compound open channel. To provide correct measurement of secondary velocities, using a non-intrusive method such as particle image velocimetry is completely essential. The results of this study show that in short compound channels with the same screen installed in the main channel and flood plain, there is significant mass transfer from the flood plain to the main channel until the end of the channel length. It was found that in this case, a considerable downfall occurs for the maximum velocity position in the main channel. However, with a supplementary screen installed in the flood plain, in addition to the typical screen, expected conditions are established similar to the fully developed compound channels. In this condition, the time-averaged streamwise velocities vary considerably in the flood plain along the spanwise direction. On the other hand, in short compound channels with the same screen installed in main channel and flood plain, the streamwise velocities do not change significantly along the flood plain width duo to the imperfect interaction of main channel and flood plain. These observations express that to provide correct distribution of discharge, a supplementary screen should be installed in the flood plain of the compound channel.

Water quality is crucial to the development and management of water resources. Therefore, maintaining water quality, especially freshwater, which constitutes the major human consumption for a variety of drinking, agricultural, and industrial uses is important. Water quality is reduced by various natural and anthropogenic factors. One of the most common and important processes that reduces the quality of water resources is the influence of saline sea water on surface water. Seawater infiltration is a natural process due to the difference in the density of seawater from fresh water. Seawater is denser than fresh water because of the presence of minerals such as salt. The higher density of seawater causes it to be submerged under freshwater and, on the contact surface, seawater penetrates into the freshwater wedge. Salt water intrusion of sea toward the river caused a decrease in the quality of fresh water which makes it useless for utilizing in agricultural, industrial, and drinking and led to obliterating this fertilized plain upon its infiltration into the surrounding land. In order to reduce these negative effects through hydraulical control of salt water intrusion, we need to know about the efficacious mechanism of this issue. Thus, this study using ANSYS Fluent for modeling salt water intrusion on the surface water examined influences of changing in the sea water density and the water level of river on the measure of salinity intrusion. Also, air bubble curtain system as an alternative to preventing salt water intrusion was investigated. Results showed that sea water density and the water level of river had direct relationship with salinity intrusion, which means that upon an increase in the sea water density or the water level of river, salt water intrusion will increase, vice versa. Therefore, penetrating salinity increased by 86% with an 0.2% increase in saltwater density and was decreased %45 by decreasing %19 at river water level. Air bubble curtain system by creating impeding bubble between salt and fresh water is an appropriate solution for preventing salt water intrusion.

Sediment transport is one of the most basic and important characteristics in river hydraulics and bed morphology. The prediction of sediment transport path in rivers and also artificial laboratory channels is absolutely complicated, and mostly conducted with semi-empirical methods. In such cases, the Lagrangian method is essential for exploring the physics of individual sediment particles. The investigation of the flow pattern in the compound channels originated from 1960s and followed by the exploration of turbulence structures of overbank flows. However, studies on the characteristics and processes of sediment transport in the compound channels are rarely conducted. For completion this gap, in this experimental study, the rolling and sliding motions of individual bed particle in the floodplain of a rectangular compound channel have been experimentally investigated. Specifically, the mechanical parameters of particle motions such as velocity and acceleration are investigated. In this regard, different statistical distributions, especially Gaussian or normal distribution, are employed to introduce the properties of bed sediment motions in the floodplain.

The experiments were conducted in the hydraulic laboratory of Tarbiat Modarres University in a straight open channel with length of 10 m, width of 1 m and height of 0.7 m (Fig. 1). The laboratory flume is a wide rectangular channel with a compound section (Fig. 2), where the side wall and bottom of the channel are made of glass. The main channel is 0.4 m wide and the floodplain is 0.6 m wide. To control the water depth, an adjustable weir was used at the end of channel. The discharge at the inlet of the channel was controlled using a regulating valve downstream of pump and measured by an electromagnetic flow-meter. The hydraulic conditions of the experiments are summarized in Table 1. According to the calculations, the Reynolds and Froude numbers are 28000 and 0.34, respectively. Therefore, the flow in the compound channel in the present study has turbulent and subcritical regime. The flow depths in the floodplain and main channel are 5 and 20 cm, respectively. To capture high quality images from bed particle motions in short intervals, a camera with the speed of 24 frames per second and FullHD resolution was used (Fig. 3). To improve the quality of images, the floodplain and main channel bottoms were coated with black color in the measurement zone. Moreover, for detection of particle trajectories, the measurement zone was regularly meshed by the perpendicular lines with the distance of 10 cm. Several projectors were applied at different angles for illumination of the measuring plane. The spherical bed particle characteristics of the present study are mentioned in Table 2. Particle tracking were conducted at the distances of 5, 20, 40, and 50 cm from the floodplain side wall (Fig. 4), and repeated about 20 times for each one.

Chi-Squared test were used to determine the appropriate distribution to describe the longitudinal and transverse velocity and acceleration of individual particles (Fig. 5). Also, skewness and kurtosis of data series are employed to investigate the fitness of velocity and acceleration data to the normal distribution (Eqs. 2 and 3). The skewness values for the particle longitudinal and transverse velocities are always close to zero and their kurtosis values are close to 3, in the case of sediment release at 20 cm from the floodplain side wall. This indicates that the particle longitudinal and transverse velocities follow the normal distribution. However, kurtosis of longitudinal acceleration diverges from 3, and consequently, does not follow normal distribution (Table 3). The averaged longitudinal and transversal velocities of the sediment particles increase, approaching to the interaction zone (Fig. 6). Also, the standard deviation of longitudinal and transverse velocity and acceleration values increase with the increase of distance from the floodplain side wall (Fig. 7 and 8). Kurtosis of streamwise and spanwise velocity and acceleration of sediment particles increase far from floodplain side wall (Fig. 9), duo to the uniformity of particle motions in the interaction zone. The linear relationship between the average particle velocity and flow shear velocity indicates that there is a good agreement between the results of the present study and previous researches.

The results of this study show that the sreamwise and lateral velocity and spanwise acceleration histograms of spherical particles in the floodplain far from the interaction zone, could be fitted to the normal distribution. While the kurtosis of histograms increases considerably, approaching to the junction. The histogram of streamwise acceleration does not fitted by normal distribution. The histogram kurtosis of velocity and acceleration is enhanced approaching the interaction zone.

Nowadays, \ design/rehabilitation of \ urban \ stormwater \ drainage systems has become a challenging issue due to more frequent severe floods in urbanized areas. These severe floods may cause significantly crucial social problems as well as financial damages. Also, regarding considerable advance in soft computing, optimization \ frameworks can \ provide a valuable \ computational \ tool for storm management. In the present study, using NSDE (Non-dominated Sorting Differential Evolution) \ algorithm and EPA-SWMM (Environmental Protection Agency - Stormwater Management Model) software, a coupled numerical and multi objective optimization model was developed to rehabilitate eastern part of Tehran metropolis drainage system. Not only is this part of Tehran Stormwater Drainage System (TSDS) the biggest drainage network of TSDS, but also its eastern part is dealing with a significant lack of capacity. In this direction, different mitigating strategies including combinations of relief tunnels and/or storage units were evaluated and optimal rehabilitation strategies were suggested according to minimizing conflicting objective functions of costs and flooding. For this purpose, formerly suggested rehabilitation solutions introduced by Mahab Ghodss consulting engineering company have been evaluated and extra relief tunnels considered to enhance their performance in relation to reduce volume of flooding in the network. Therefore, the total number of four different layouts of rehabilitation strategies have been assumed in order to rehabilitate eastern part of TSDS. Results have revealed considerable reduction of costs with respect to previous rehabilitation proposals for the study area stating the desirable performance of proposed coupled numerical and optimization framework of the present study. Moreover, regarding application of storage units in upstream of the network, although these units reduced rehabilitation costs significantly compared to other strategy by reducing length of required relief tunnels, relief tunnels slightly outperformed than upstream storage units in relation to the flood volume reduction. It seems possible to enhance the performance of storage units by relocating them.

The design of stilling basin always corresponds to the fact that the length of the jump should be restricted to the length of stilling basin. Baffle blocks are hydraulic structures, installed in the basin in order to stabilize the jump and reduce the length of the jump. Flow under the condition of submerged hydraulic jumps with baffle blocks could be observed as two regimes: The deflected surface jet (DSJ) and reattaching wall jet (RWJ). The formation of each regime relates to different factors, such as block shape and location, submergence factor, block size, and Froude number of entrance flow.In this article, a numerical study was conducted to investigate the influence of some parameters, including blocks height and shape, the distance of blocks from a gate and the distance between the blocks, on the length of submerged hydraulic jump with baffle blocks. The FLUENT software has been used for 3D RANS simulation. Twenty models with different geometrical conditions according to the mentioned parameters were created. It was observed that for DSJ regime, the length of the submerged hydraulic jump is reduced more than 40% based on the distance of baffle blocks from sluice gate. It means that, it can be expected to see more reduction in length of the jump as the blocks are installed closer to the gate. However, for RWJ regime, the decrease of the length is limited to less than 14%. So, due to this considerable difference between the operations of these two regimes, the noticeable point is that all the conditions should be in the way so that the flow occurs as a DSJ regime. In addition, it can be concluded from the results that increasing the height of blocks more than the thickness of entrance jet cannot make any effective change in the length of the jump. Furthermore, it was observed that using baffle wall (i.e., a continual wall which spreads along the whole width of a channel), instead of baffle blocks in the same condition, increases the length of the submerged hydraulic jump. The reason is that the vortices that are formed due to submerged jump's conditions become more intense as the baffle wall deflects the whole jet into the surface. Thus, in this situation vortices have more impact on the flow.

Using structural and nonstructural measures for flood damage reduction is a long-standing problem in water resources planning and management. In present study، an algorithm is presented to optimal design of flood mitigation measures in the watershed scale by simulation based optimization approach. To do so، the numerical model of MIKE-11 was used to calculate the risk of death and the physical damages of flood scenarios under different combinations of structural and non-structural flood mitigation measures. The numberdeath depends on the flood characteristics (the intensity of hazard) obtained by run of numerical model in each round، the vulnerability of population and the vulnerability of properties in flood-prone areas. Each of flood mitigation measures changes one of these three factors and affects on the number of death in flood events. As likewise، each measure may affect on physical damages by altering the magnitude of floods or vulnerability of land uses. In fact for a flood scenario، the physical damages in each combined option are computed using the change of geometry of rivers in model and its boundary conditions or modifying the damage-elevation curves or both. The numerical model was coupled with the NSGA-II multi-objective optimization model to provide the optimal Pareto front solutions considering two conflict objectives of minimizing the investment costs and the potential flood damages in the watershed. Finally، the presented model was applied for a small watershed in the center of Iran as a case study and the optimal trade-off solutions were calculated for different flood scenarios. Results showed by application of presented approach the investment costs may decrease several times and at the same time potential flood damages are minimized. Using a numerical model in the structure of proposed framework provides a flexible tool to consider the interaction of different measures in different reaches of watershed. For example model can dynamically predict in which rivers there is a need to build dam and what is the optimal height of dams in various branches to prevent the synchronizing the flood peaks of branches or detention dams with which measures must be applied to minimize the total cost and flood damages. For the study area، flood wall option just proposed by flood warning option in obtained optimal designs. This shows “flood wall” option to reduce damages on properties with “flood warning” option to reduce the loss of lives is an effective flood mitigation strategy for the study area. Also، if the investment level is low، the application of two non-structural measures of “waterproofing” and “watershed management measures” have a priority than the other measures for the study area. Using the obtained trade-offs، for each level of funding، decision makers can assign the optimal combined option considering the decision criteria.

With the aim of investigating the distribution of wall shear stress in an open channel with a rectangular cross section and a smooth bed, an accurate needle type probe has been developed and after verification, it has been used for shear stress measurement in various cases of open channel uniform flows. In this instrument, capacitive type pressure transducers with 0.1 Pascal accuracy and 100Hz sampling rate were used to measure pressure fluctuations. Measured bed shear stresses are compared with the result of available analytical models and CFD simulations using FLUENT code for instrument verification. Variations of the measured local bed shear stresses at channel centerline with respect to channel aspect ratios, mean bed shear stresses and the lateral distribution of local bed shear stresses compare favorably with the previous experimental and analytical results and with the results of the present numerical simulations. Experimental measurements and numerical simulations show that the secondary currents affect the distribution of side wall shear stress more than the bed shear stress. Because of the presence of the alternate low-high velocity zones at the near bed region, the lateral distribution of the bed shear stress exhibits an oscillatory pattern.

Submerged vanes are plane structures placed on river bed with an angle to the approach flow which cause secondary flow. They are used to reduce sediment entrainment to water intakes structures. The vane’s geometric parameters affect the flow pattern around the vanes. Numerical solution of the three-dimensional Reynolds-Averaged Navier-Stokes equations for turbulent flows around submerged vanes placed in front of the intake in curved channel with 180° bend using the Fluent software in order to identify the optimum vane’s angle and height and the last vane position is the aim of this paper. The results of numerical model are compared with available experimental data. Investigations show that the optimum angle of attack for the first vane is 20° to approach flow and the optimum ratio of the vane height to the flow depth is 36%. Also the last vane position just off the downstream corner of the intake is recommended.

Spur dikes are used for preventing river banks erosion. The flow and scouring pattern around the spur dikes used in the outer bank are complicated especially when spur dikes are used in the bends. This is mainly due to the interaction between the flow pattern associated with the spur dike and the helical currents in the bend. In this paper result of experiments on scour around a T shaped spur dike and the effect of spur dike location on the amount of scouring and the effect of curvature of bend on the variation of bed topography are reported. Experiments were conducted in a re-circulating rectangular channel having 0.6 m width, 0.7 m height with different values of radius of bend to centerline (R/B=2,3,4). The main channel consisted of a 7.1 m long upstream and a 5.2 m long downstream straight reaches. A 90 degree channel bend was located between the two straight reaches. The bed and sides of channle were made of glass supported by metal frames. Natural uniform sediment with median size d50 =1.28 mm was used with a thickness of 0.35 m and covered the whole length of channel. Experiments were conducted for 25 l/s discharge. Results show that when spur dike installed at section 75 degree, the amount of scour is maximum. Also, by increasing the curvature of bend the amount of scour increases. But the lateral development of scour hole decreases.

Flow is affected by both the pressure gradient and the centrifugal forces in the bend of rivers and their interaction leads to secondary flow. In this study the flow field and scour in a 90 degree bend were experimentally measured. Experiments were carried out in a channel with mild curvature. A three-dimensional Acoustic Doppler Velocimeter (ADV) was used for measuring the flow field. Also, a laser bed profiler was used for measuring the variation of bed topography. The results show formation of a main secondary flow in the bend and another second secondary flow near the outer bank. The direction of the second secondary flow is opposite to the direction of the main secondary flow. This flow pattern is evident from the middle sections of the first half of the bend up to the end of the bend. The results of flow pattern and bed scour were also addressed. In addition, the vortices in the bend, the changes in the secondary flow and the vortices and the scour pattern at the outer bank and sedimentation at the inner bank are investigated.

A two-dimensional numerical model, based on solution of the Reynolds-averaged navier-stokes equations with k-eand EASM (explicit algebraic stress) turbulence models, is presented to describe' the free surface water flow over bed topography (dune) in open channels.The model application indicates insufficiency of k-e turbulence model for simulation of flow over dunes (because of separation and streamline curvature). In this case, algebraic stress model that is economic method for calculating stresses can do better. Therefore, an explicit version of it (Wallin and Johanson 2000) is used All of the differential equations are solved with a finite volume method in a nonstaggered grid. The geometric shape of sand dune is simulated by introducing a general non-orthogonal curvilinear coordinate system.The numerical results were compared with the available experimental data reported by Mierlo and Ruiter (1988) and general agreement was observed. Detailed calculations indicate improving prediction of turbulence characteristics and length of separation zone by EASM model.

In this paper the bed evolution in channel bend under different hydraulic conditions is presented. Experimental tests were conducted in 180 channel bend with movable bed. In each test the bed level at various sections were measured. Experimental results showed that in all experiments, the point bar was formed in the first half of the inner bank and scour hole was formed in front of the point bar. At the outer bank, in the second half of the bend, the point bar was formed in the inner bank and some scour holes were formed in the outer bank. The position of these scour holes was found to be dependent on Froude number. By increasing the Froude number, these positions are shifted toward the apex of the bend. Verification of bed level in cross sections shows that the slope of bed increases as the Froude number increases. In this study, a relationship is presented that predicts the transverse bed profile.Also, the velocity measured in section with maximum deposition show the existence of secondary flow only in some parts of channel cross section due to the lateral balance between the upslope force induced by the helical circulation and the down slope gravitational force in the lateral direction. The oscillatory manner of the bed evolution result from oscillatory manner of depth averaged velocity across the channel.

Three-sided spillways are used in dams as well as in irrigation networks, and water and wastewater Treatment plants. In this study, the effect of some major parameters on hydraulic behavior of flow in a three-sided V-shaped spillway and its side channel was evaluated using a physical model. The effect of changes in the end-sill height, the distance of the end-sill from the beginning of the side channel, and the side channel slope with different discharges were studied. Flow pattern and pressure fluctuations in the channel were considered as an indication of the flow behavior. Results showed that the end-sill height had the greatest influence on the intensity of pressure fluctuations and flow behavior in the side channel and increase in the end-sill height, decreased pressure fluctuations. Results also indicated that the location of end-sill from the beginning of the side channel, did not have considerable influence on pressure fluctuations. Moreover, increase in side channel slope up to about 3 percent decreased pressure fluctuations. However in slopes beyond 5 percent, pressure fluctuations increased again. Negative bed slopes decreased pressure fluctuations in the side channel considerably. It was also concluded that increase in flow discharge improved the flow condition in the side channel.