جستجوی مقالات مرتبط با کلیدواژه « هیدرولیک جریان » در نشریات گروه « آب و خاک »

Management of irrigation networks has always been one of the most important issues in the agricultural sector, and the use of modern valves and structures for controlling and adjusting the water flow is very important in irrigation channels. Water level control structures are used in irrigation canals to imple-ment delivery methods (Naghaei and Monem 2013).
Gates are one of the most used water structures in distribution canals that are used to transport and deliver water to consumer or to control the flow rate or water level. Determining the relationship governor on these structures can improve the performance of open canals and therefore prevent water loss. Lopac gate as a water level adjustment structure has recently attracted attentions and its performance in applied and practical areas of irrigation channels in different countries is accepted. The gate can be opened along the flow direction and can regulate upstream water level for various dis-charges by adjusting the gate opening angle (Oad and Kinzli 2006). So far little studies have been done on these types of gates. Some studies have examined hydraulic conditions of the flow passing through rectangular Lopac gate and presented the discharge equation as well as its coefficient in free flow and submerged conditions. In the present study, an experimental investigation has been conducted on new type of Lopac gate called elliptical lopac gates. This type of gate, which is a combination of rectangular Lopac gates and elliptical sharp edges have good function in passage of rubbish, foliage of trees and sediments along with the flow. We constructed and installed an elliptical Lopac gate as well as a rectangular Lopac gate at the laboratory scale to control and compare performance of both types of gates. The test were conducted for 5 opening degrees and for 5 discharge. Then, discharge equations of the elliptical Lopac gate in free flow condition with the help of buckingham pi theorem were presented with appropriate precision of Mean Absolute Percentage Error (MAPE = 4.44%).Also, changes in the energy flow dissipation crossing of Elliptical Lopac gate and Rectangular Lopac gate were studied and compared.

Taking water from rivers is one of the most important topics in hydraulic engineering. One of the problems associated with most intakes is the accumulation of sediments in intake entrances. Failure to control the sediment's entering the intakes results in its transfer into irrigation channels and their establishment that creates many problems due to sediment transport or its settlement in various parts. Due to the development of computing systems as well as unmeasurable complexities of water flow and sediment in laboratory models, using numerical simulations can be very effective and substantial in hydraulic investigation of such flows. Flow passing through the lateral intakes and channel junctions is usually turbulent. Turbulence is one of the most important features of the flow pattern in a bend which influences a lot of processes occurred in rivers including erosion, sediment transport, bed morphology, and shape of natural channels. Investigating the kinetic energy of flow turbulence in open channels due to the maximum shear flow of the bed and the scouring of the floor is very important and can be considered for prediction of bed topography. The accumulation and sedimentation in water intake and reduced intake efficiency is one of the problems that arise in most intakes.

Therefore, in the present study, the sediment controlling structure, a skimming wall, was used in front of the intake. Then, the three-dimensional flow in sedimentary bed around the intake entrance was simulated by Flow3D model and results were compared with experimental model. In this research to increase intake efficiency and control the amount of sediment entering the intak, two structural skimming wall in front of the intak and spur dike on the opposite shore it is used. In the research using three-dimensional flow field numerical model FLOW3D around 60 ° lateral intake located on the direct path was solved numerically and counters velocity and turbulence kinetic energy is drawn. The experiments conducted and results were compared with the numerical model. Flow hydraulic and dynamics in front and inside the intake is studied. Velocity vectors inside the intake, in both longitudinal and lateral directions were compared with experimental results.

In the absence of structures, inside the main channel, the flow separation width at levels close to the bed is broader than the higher levels. However, by installing skimming wall in front of the intake, the flow separation close to the substrates carrying more sediment is reduced and it is increased on the surface that has less sediment. It also allows less sediment into the intake. In the absence of structures, the surface flow lines in the intake tend to the right wall and the bottom flow lines tend to the left wall. The width of separation zone on the surface is broader than the one on the floor. In presence of skimming wall structure or both skimming wall and spur dike, the flow lines near the bottom tends to the channel center. In addition, the zone with stagnant flow on the left side of intake is broader at the bottom than on the surface. In all three cases, the maximum longitudinal velocity and the maximum resultant velocity have occurred at the beginning of the intake inlet in its left corner. The maximum transverse velocity has occurred in the intake center. In these figures, there are areas with secondary vortex flow on downstream and the left of the intake.

The results showed that by adding the structure of the spur dike in the main channel, the velocity in the main channel is 1.5 times compared with the other two cases. and the area inside the intake also affects. Also, the tip of the axis of the velocity vectors is displaced to the intake. As a result, In the back area of the spur dike, the longitudinal velocity decreases and there deposition. Comparison of the distribution of the maximum kinetic energy of flow turbulence at two different depths indicates a 50% increase in the maximum kinetic energy of turbulence in the upper layer compared to the lower layer.

This study investigated the effects of non-structural methods, as practical alternatives for upgrading the operational performance of the irrigation canal. To fulfill this objective, a hydraulic flow simulator model for the Nekoabad irrigation network's main canal was developed, calibrated and then, using two performance evaluation indicators, the adequacy and dependability of water distribution were evaluated. To evaluate water distribution improvement in each one of the non-structural solutions, daily water distribution planning; according to each solution was provided in MATLAB and linked to a simulated mathematical model. To determine the effectiveness of each approach, spatial analysis of changes insecure distribution (sufficient and sustainable) of agricultural water from upstream to downstream of the irrigation network, was done in GIS. The obtained results indicate that the adequacy of surface water distribution was improved 10-11% and 9-7% in the first and second non-structural alternatives, respectively. Besides, the dependability of surface water distribution shows about 13-15% within the application of the alternatives. The results reveal that the second alternatives, fulfilling appropriate water distribution along with the middle and downstream canal reaches, show a more or less good performance.

Rivers has long been regarded as one of the most basic human water supplies. If the topography, a morphology, water requirements conditions, etc. allow water to be transferred to gravity, the use of the dike can have a significant impact on the flow rate and the sediment input to Intake. Dike design needs to consider several parameters such as position, length, type, etc. Using a good design can increase the input flow rate and reduce the sediment entering it. In this study, to evaluate the dike impact on flow hydraulic conditions in the Intake with different situations, 30, 45, 60 and 90 degrees two simple L-shaped dikes in the upstream and downstream Intake and for five inlet flows (0.7, 1.12, 2.84, 5.04 and 6.23 Lit/s) were considered in the laboratory flume made by the author as a physical model to simulate the flow of the basin; then different effects of the dike on the hydraulic flow were studied. The results of the tests showed that the L-shaped dike in the upstream and downstream Intake in the internal arc flume increased the inflow flow rate into the Intake. Also, the best angle of deviation for the maximum flow entered the Intake angle of 60 degrees.

Riverine wetlands are waterbodies that are located at lowlands alongside rivers and are inundated during floods or recharged by aquifers. In order to identify and locate suitable sites for wetlands, the hydrological properties including watershed physiography, river discharge and its temporal (seasonal) variation as well as groundwater table fluctuation should be studied. Continued population growth and urgent need to conservation, rehabilitation and expansion of natural and valuable environments such as wetlands which support environmental services required by human should be strongly considered for sustainable development. The aim of this study is to assess utilization of biological capacity of rivers to restore the riverine wetlands in order to improve the biological and ecological conditions of the country’s wetlands.
In this research, the potential of Tajan River within the Sarakhs county, was identified considering presence of the streamside tree cover, specific ecotourism capacity, specific bird watching capacity, appropriate morphology of the river and inundation characteristics of floodplains. Creation of riverine wetlands alongside the Tajan River can play an important role in flood mitigation through storing of precipitation induced surface runoff. To this end, all factors affecting on delineation of proposed wetlands boundaries including geomorphological and geological, hydrologic, hydrodynamic, economic, social and developmental characteristics of the Tajan watershed were investigated. During field survey from the study area, on the basis of predominant condition from biodiversity, species, ecological, hydrologic and hydraulic point of view, four sites were determined as suitable for riverine wetlands within the watershed. Then, the cross-section of each of these sites have been surveyed and measured in detail in order to assess their morphological and hydraulic characteristics.
On the basis of flow Hydraulics and river morphology studies, two out of the four selected sites which are located within the Sarakhs’ Jahanbani Forest, due to low velocity of flow and high width of river in these river reaches were assessed as suitable for implementation of vegetation and wetlands restoration measures. Analysis of monthly discharge data of Polekhatoon- Kashafrud hygrometry station in recent years, indicates that the Tajan river flow is nil or negligible during warm months. Therefore, to supply water for the suggested wetlands, it should be relied upon floods and annual discharges from their upstream sub watersheds.
The annual discharge of the Tajan river at one of the suggested sites for the riverine wetlands within the Sarakhs’ Jahanbani Forest was estimated about125.9 MCM. This site due to its high potential for tourism and high diversity of birds can be exploited from various perspectives if tourism activities are developed in the region.

Abstract: The present research investigate experimental the head loss of flow energy throw the semi cylindrical wire-gates. The effective parameters on the studied system in forms of dimensionless parameters obtained by using Buckingham’s theory. The experiments were conducted in a rectangular flume with the length of 8m, width of 0.282m and height of 0.3m in Soil Conservation and Watershed Management Research Institute, using physical models with diameters 70, 120 and 160 mm in height of the opening between 0 until radius and differently discharging. The ratio of cylindrical structure diameter to channel width (D/B) was in the range of 0.25 to 0.57 and the Froude number was in range of 0.08 to 0.55. The results shows that in all angles which structure sets, dimension less parameter Hf/H cases curvature upstream and downstream with increasing Froude number and dimensionless parameter H/P increases, so that coefficient in both cases curvature upstream and downstream with increasing water depth upstream and dimension less parameter H/P Linearly decreases. Constant a (H/P) and Froude number, a dimensionless parameter Hf / H when the curvature is upstream semi cylindrical wire-gate due to the gradual contraction of flow lines and thus decrease the input is less than the curvature is downstream structure. Moreover, the result shows that in addition to the angle of semi cylindrical curvature to horizon line, structure diameter was affected on head loss amount.

Because of the fairly simple equations for accurate flow measurement and controlling the water level, weir and gate method is more useful than the separate weir, gate and partial flume methods. Since the flowing water in the channel always contains sediment particles and floating debris, they are deposited at the gate inlets and behind the weirs which reduces the size of the channel in the structure range and which reduces some problems such as neighboring land flooding due to overflow of water from the channel banks, threatening the structure stability and reducing the measurement accuracy. Using a combination of weir- gate model, in comparison with other conventional devices, will make it possible to get the actual conditions closer two main hypotheses derived from the relations and accurately measure the discharge coefficient. In this model, the deposited materials are easily passed through the gates and the suspended debris are easily passed over the weirs. One of the combined weir- gate structures is semi cylindrical weir- gate structure. Regarding about the form of the combined weir- gate structures, it has some advantages , including simple design, sediments and floating material flow, high flow discharge coefficient compared with other replaceable structures and its being economic. Semi Cylindrical gate turning around center Axis, for reason of rotation the center becomes Conversion to wire, wire gate with opening with different height.
The experiments were conducted in a rectangular flume with the length of 8 m, width of 0.282 m and height of 0.3 m in Soil Conservation and Watershed Management Research Institute. In this research, PVC pipes were used as semi cylindrical gate structures. The experiments were conducted for three diameters 70, 120 and 160 mm with height of the opening between zeros until radius, angles zero, 30, 45, 60 and 90 degree and differently discharging. Experiments were performed at a discharge limit of 2-27 l/s. In order to decrease turbulence of the flow, the gate was installed at the end 4 m of the flume. The ratio of cylindrical structure diameter to channel width (D/B) was in the range of 0.25 to 0.57 and the Froude number was in the range of 0.08 to 0.55.
Coefficient discharge of semi cylindrical structure and then dimensionless parameters of [H/P], [a/H], [ /H] and [Fr] against the discharge coefficient in the studied gate opening between zero until radius were investigated. According to result with decrease dimensionless parameter of a/H, discharge coefficient increased, So that the maximum Coefficient discharge rate of angle 90 degrees and minimum angle 0 degrees. Also in a constant of a/H for the curvature of the downstream and upstream, with increasing the diameter of semi cylinder, discharge coefficient remains and has no change, shows that changes in diameter of semi cylinder have no significant impact on discharge coefficient. With increasing H/P for both curves upstream and the downstream, discharge coefficient increased. Also in a constant of H/P for the curvature of the downstream and upstream, with increasing the diameter of semi cylinder, discharge coefficient remains. With constant of angles with increasing Freud for all angles, both the curvature of the downstream and upstream, /H decreased. Also in a constant of Freud and angles, with increasing the diameter of semi cylinder, /H remains. According to the result, discharge coefficient of semi cylindrical gates varies, in Experimental limit, from 0.45 to 1.45 which is more than that of sluice gates reported by the USBR. One of the reasons, this is ascribed to this is the difference between the amount of entrance, head loss in this structure, because when the flow approaches cylindrical gate, due to curvedness of the wall upstream, a gradual gathering of flow lines gives the aerodynamic method to entrance section, thus decreasing resistance against the flow and entrance head loss and increasing discharge coefficient. However, in sluice gates the vertical wall in entrance section is conducive to fast gathering of flow line, thereby increasing resistance against flow, increasing entrance head loss, and decreasing discharge coefficient relative to a semi cylindrical method.
The results showed that increasing Froude coefficient and decreasing the a/H (ratio of gate opening to upstream water depth) dimensionless parameter decrease, respectively increase the discharge coefficient and decrease head loss in all aspects of structural alignment. Within addition by increasing the H/P dimensionless parameter (ratio of upstream water depth to structure diameter) discharge coefficient increased. Results showed that the maximum and minimum values of discharge coefficient are related respectively to 90 degree and 0 degree angle.

Soil erosion by water is one of the most widespread forms of land degradation and it has caused many undesirable consequences in last decades. On steep slopes, rill erosion is the most important type of erosion, which produces sediment and rill flow. It can be also considered as a vehicle for transporting soil particles detached from upland areas. Recent studies indicate that soil detachment rates are significantly influenced by land use. It is also known that there is a major difference between detachment rates of disturbed and natural soils (Zhang et al., 2003). Plowing rills especially in steep slopes increases sediment production. Sun et al. (2013) reported that the contribution of rill erosion in hill slope lands in china was more than 70%, which was approximately 50% of total soil erosion. In addition, measured soil loss is statistically related to hydraulic indicators such as slope, water depth, flow velocity, flow shear stress and stream power (Knapen et al., 2007). This study aims to evaluate the effects of hydraulic variables (shear stress and stream power) on spatial-temporal soil detachment rate. The focus is on the plowing rills in hillslope areas under wheat dry farming cultivation.
The study area is located in hilly slopes with the slope of 22.56% under dry farming wheat cultivation at 60 km of west of Shiraz, Iran. Top-down conventional plowing was carried out in order to create 10 meters furrows. Slope and cross sections of rills were measured throughout the experiment at 1 m intervals by rill-meter. Water was added to the top of the rills for 10 minutes and inflow rates were 10, 15 and 20 L min-1. Hydraulic parameters such as shear stress and stream power were calculated measuring rill morphology and water depth. Flow velocity and hydraulic radius along the different rill experiments were also calculated. Sediment concentrations were measured in three equal regular time and distance intervals (measurement points (MPs)), they were considered to calculate sediment detachment rate in different times and sections of each rill experiment for spatial and temporal soil detachment rate evaluation. One-way analysis of variance (ANOVA) was employed to test the significance of differences of sediment detachment rate among different treatments.
The results showed that the maximum values of shear stress and stream power were 14.07 Pa and 10.29 Wm-2 and the minimum values were 7.41 and 2.77 respectively. This research also indicated that changes in longitudinal profile of these hydraulic parameters along the rills affected the soil detachment rate values. Obtained average, minimum and maximum of the soil detachment rate were determined as 0.09, 0.02 and 0.22 kgm-2s-1, respectively. Due to Detachment-Transport Coupling mechanism, there was a significant difference between the initial and following MPs (P

Accurate design of Spillways as one of the main parts of dams is an important issue in the stability and safety of dams. Determining the characteristics of flow hydraulic by using physical models is too expensive and time-consuming. In this study, two-dimensional flow over ogee spillway was simulated by solving Poisson functions of stream and pressure using the Finite Element method and analyzing k-ε turbulence and volume of fluid models in Finite Volume technique. Also a comparison was made between the results of numerical models and measured values in order to investigate the accuracy of the models in calculation of water free surface profile and flow velocity. The average relative error in velocity calculation using Finite Element and Finite Volume approaches was obtained 2.09% and 0.93%, respectively. The corresponding values for free surface profile were obtained 1.25% and 0.72%, respectively. The results showed that the Finite Volume approach had better performance than the Finite Element method in modeling flow hydraulic over the ogee spillway.