جستجوی مقالات مرتبط با کلیدواژه « Shear Stress » در نشریات گروه « کشاورزی »

One of the structures for regulating the water level in the irrigation and drainage ducts is the lopac gates, which are proposed as a structure for regulating and controlling the flow level. In this study, a new design of this type of structure has been proposed in which the gates are placed next to each other in pairs, and they are called multiple lopac gates. The objective of this research is to investigate the effective hydraulic parameters of the proposed structure and compare it in a case where a gate is used under the same conditions. All the simulations were modeled with 3 amounts of opening 30, 45, and 60 degrees and at 3 flow rates of 20, 40, and 60 liters per second and using Flow3d software, in these simulations, the number of mesh cells is 1000000 and RNG turbulence model is used.  The results showed that the maximum shear stress was reduced by an average of 38% compared to the single gate mode in most tests at different openings and flow rates using multiple lopac gates, and the largest amount of this reduction was related to the opening of 45 degrees, and the flow rate is 40 liters per second with a value of 76%. Also, the forces acting on the gate at different flow rates and openings will be reduced by 150% on average. In the qualitative investigation of flow vortices, the investigations also showed that vortex range, length, and strength are reduced compared to the single gate mode when two gates are used, and the number of vortices increases compared to when a single valve.

A major part of the globe is made up of seas, rivers, underground waters and oceans, and from those places where a major part of the resources needed by humans comes from these methods and requires engineering constructions, coastal protection is important. . being high Development, sustainable, engineering and selection of the best protection method to organize and stabilize the coast, depend on the sea from the sea. Among the protection methods, we can mention coastal wall structures, which reduce the wave height from the beach by creating damping. In the current research, according to the performance of numerical modeling, laboratory results are used to check the efficiency of Open FOAM software and the k-o SST turbulence model in modeling the individual behavior of the body of the coastal Ivar structure. Considering different conditions in modeling, the total number of 10 tests, 5 in the case of coastal wall structure and 5 without structure in 5 different degrees (6, 7.5, 9, 10.5, 12 cm) and the same conditions (structure height 7.5 cm) was chosen to implement the program. The results showed that the forces have increased compared to the state without the structure, in other words, it can be said that the presence of the structure can be compared to the state without the structure in the depreciation of the experimental force. Since the change of forces to the structures is a function of the height, so it decreases with the increase in the amount of influence.

Packaging, transportation, and separation of agricultural products are among the processes that cause potential damage, losses, and increased waste, depending on the type of product. Therefore, determining the mechanical strength properties is one of the most important approaches to prevent mechanical damage. Using mechanical tests, such as compression tests, is a common approach to obtain information, but simulation methods can help determine a wider range of information, such as stress and strain distribution patterns in the fruit, at lower cost and higher speed. Quince (Cydonia oblonga), which like other fruits is susceptible to mechanical damage, is rich in various compounds such as flavonoids and phenolic acid, which contribute to anti-cancer, anti-inflammatory, anti-allergic, and antimicrobial properties. In this study, to determine the mechanical properties of quince, compression tests were performed on fruit specimens at a rate of 10 mm/min using a materials testing machine and supplemented by simulation using ANSYS software FEM. The results of the experiments and simulations showed that a viscoelastic model adequately describes the behavior of the fruit under quasi-static loading. The simulation results for loading rates of 5 and 20 mm/min showed that the specimen is subjected to higher shear and normal stresses at a rate of 20 mm/min. The minimum of shear and normal stresses is associated with the rate of 5 mm/min. According to the evaluation results, it is better to perform harvesting and post-harvesting of quinces in such a way that lower loading rates (5 mm/min) are applied to avoid losses as much as possible.

The main difference between compound sections and simple sections in channels is due to the velocity difference between the floodplain and the main channel. This velocity change ultimately causes changes in the shear stress distribution of the bed canal. The structure of flow turbulence in compound channels is complex due to the combination of boundary shear stress and Reynolds stress near the interface of the floodplain and the main channel .Due to the fact that the flow hydraulics in rivers, which are considered to be a type of compound channel, depends on their shape and the changes in canal shape are dependent on bed shear stress, determining the distribution of bed shear stress in rivers is also of great importance. In this study, the boundary shear stress distribution in compound channels has been simulated with 2 numerical models of Fluent and Flow-3D software and compared with real experimental data (Wallingford, England), as well as a comparison between the output results of the shear stress distribution in the compound section is also performed based on the YLM method. To verify the accuracy of the simulation results, 3 methods of determining the convergence (error parameter) have been used to compare the computational results with the experimental results. The results showed that there was a very good match between the results of the numerical models and the experimental data, and as a result, both software could calculate the shear stress distribution appropriately. Generally, the numerical results of fluent software were closer to the experimental data compared to Flow 3D software.

One of the effective methods to reduce the kinetic energy downstream of hydraulic structures are the aprons. The horizontal aprons is one of these structures in the river that are often used downstream of stilling basins. At the time of execution, the apron and the riverbed are at the same level but when there is a flow in the boundary between the connection of the river bed and the aprons, scouring occurs, which causes the destruction of the apron and there is a possibility of destroying other water structures. In this research, using Flow 3D software, different scenarios were simulated for five Froude values of 0.32, 0.3, 0.25, 0.2, and 0.15, three Manning roughness coefficients of 0.025, 0.02, and 0.014 per particle diameter of 1.8 mm for horizontal aprons. In this numerical model, the graph of scouring depth changes in relation to Froude numbers in different roughness coefficients, the effect of Froude numbers on the location of the scour hole for different roughness coefficients of the horizontal aprons, the shear stress changes in relation to the length of the horizontal aprons with different roughness coefficients and different Froude numbers, as well as Erosion changes with respect to the length of the horizontal aprons were calculated with different roughness coefficients and different Froude numbers.

The formation of bed form in alluvial rivers due to sediment transport has a significant effect on the hydraulic parameters of the flow such as bed shear stress. The formation of the bed form and its shape and geometry depends on the bed shear stress. Therefore, the relationship between bed form and flow parameters (such as bed shear stress) is complicated. In the present study; the effect of dune bed forms with different heights on bed shear stress has been investigated. Artificial dunes made by sand-cement mortar with a length of 25 cm and heights of 1, 2, 3, and 4 cm were used. In the tests of this research, flow discharge of 10, 15, 20, 25, and 30 l/s and bed slopes of 0, 0.0001, 0.0005, 0.001, and 0.0015 were used. The results showed that with increasing the relative submergence and Δ/λ, the bed shear stress increased in dune-covered beds. The formation of the dune bed form and the increase in its height leads to an increase in the bed shear stress. The bed shear stress in dunes with a height of 1, 2, 3, and 4 cm was, on average, 39, 80, 141, and 146% more than in plane beds, respectively. Moreover, form shear stress for dunes with a height of 1, 2, 3, and 4 cm was, on average, 27.37, 43, 57.11, and 58.74% of the total shear stress, respectively.

Sediment dams are built with multi-purpose goals including flood control, erosion, sedimentation and aquifer feeding. These dams, with the aim of controlling the sediment from transferring part of it to the reservoirs of the dams in the downstream, and by causing a delay in the surface runoff, they control a part of the flood and feed the aquifer of the area. Improper design or lack of optimal implementation of these structures causes the reduction of useful life and sometimes premature destruction of these structures. Evaluating the function and technical performance of such plans with the aim of improving and managing the system is of special importance. For this reason, in this article, a number of sediment dams implemented in Abdanan City of Ilam Province were investigated and evaluated. This research was conducted in the form of hydraulic simulation and comparison of the current situation with the conditions before the implementation of the project, in a section of the waterway about seven kilometers long. It should be mentioned that six stone and mortar dams have been built during the last decade. The results of the hydraulic simulation of the flooding of waterways and constructed structures showed that, based on the discharge with a return period of 100 years, the average overflow width of the construction dams is about 25% larger than the required value and the length of the stilling basin is about 40% less than the required value. In general, in all construction dams, the length of the stilling pond is not chosen correctly, so that the short length of the stilling pond has caused the hydraulic jump to leave the pond or to form at its end. Due to the high flow speed in the area of the hydraulic jump, erosion and destruction in the end zone of the calm pond has intensified, which has been extended to the upstream side and the main structure of the sediment dam. Based on the hydraulic simulation of the flood and the relative comparison of the results in the conditions before and after the construction of the dams, it was found that the constructed dams have a positive effect on the parameters of flow speed, flow strength and flow shear stress, which are all factors that aggravate erosion in the waterway. So that for discharge with a return period of 25 years, the speed, power and shear stress parameters of the flow have decreased by 23, 29 and 27%, respectively, during the research period. Therefore, the average reduction of these parameters locally and at the construction site of the six dams was estimated as 73, 85 and 82%, respectively. In general, according to the field visits and investigations, the implementation of the plan has been effective in controlling floods and sediments, and in case of annual protection and repair, its effects will be doubled.

Gates are Flow control structures used in irrigation canals. In the meantime, Lopac Gates have very efficient capabilities such as controlling and regulation the level of water upstream, automation, lower energy consumption than other types of gates (like sliding gate, radil gate) and the possibility of passing floating objects. Elliptical Lopac gate (ELG) are one of the new types of lopac gates that are intended to increase the discharge coefficient compared to other types of lopac gates. The present study was conducted with the aim of modeling ELG in five different elliptical ratios with sudden transition in the channel using Flow3d software. All models are considered in three discharges of 25, 35 and 45 liters per second and in three openings of 20, 30 and 40 cm and simulation has been done with RNG turbulence model. The final results showed that by increasing the elliptical ratio from 0.7 to 1.28, the energy consumption gates ​​will decrease from eight to 20 percent compared to the initial energy. In the study of floor shear stress, the results show that by increasing the elliptical ratio, the average shear stress decreases by 52 percent. In the section on flow vortices, the results show that in elliptic ratios greater than one, vortex currents and current deviation from the path are reduced and the flow rate decreases from 22 to 54 percent.

One of the complicated phenomena in sediment hydraulic engineering is scouring around bridge pier. Regard to three-dimensional and complicated flow pattern around piers, measuring some hydraulics parameters during the tests such as flow pattern, variation of bed profile and shear stress are difficult, in this situation application of numerical models in order to extract results and more detailed study is useful. Aim of this research is numerical modeling of flow pattern, variation of bed profile and scour depth and shear stress around rectangular pier using Flow 3D and applying the results to protect piers against scouring. Results showed, for aligned pier with flow, shape of scour hole and flow pattern were symmetrical, the side in contact with flow is high-pressure and the other side is low-pressure. As increase of pier angle, shear stress in front of the pier increased so that for pier with 10° angle with flow direction, shear stress was 0.55 N/m2. Also fluctuations of bed profile and water surface increased. Application of submerged vanes, changed scour pattern and moved sediment in front of pier which scouring was reduced. Increase of height and angle of submerged vanes improved their protective role. Base on the results of numerical model, after 30 minutes, scour depth in front of pier in aligned pier with flow and angle of submerged vanes 30°, in same level with bed, 1.25 cm and 2.5 cm on the bed, was 3.1 cm, 0.035 cm and +0.005 cm (on the bed), respectively. As increase of pier angle, performance of submerged vanes to control scouring in front of pier and in side of high-pressure wall decreased, but in side of low-pressure wall scouring compared with alone pier was less.

Rill erosion is an important form of water erosion on cultivated slopes. Rills are flow paths that are created by concentrated flow on hillslope and causes higher rates of soil loss. The amount and type of particles transferred through the rills or the selectivity of the particles may be affected by various factors, especially the flow rate. This study was conducted to investigate the rill erosion and the particle selectivity under the flow characteristics. Field experiment was done in a rainfed land with a slope gradient of 10% in the rills/furrows with 6 m in long under different flow intensities (2, 2.5, 3, 3.5 and 4) using a randomized complete block with three replications. Field measurements were performed using a flow rate of 3 lit min-1 at intervals of 5-min for 60 min. Rill erosion and the particle selectivity were determined along with flow characteristics for various flow intensities. Significant correlations were found between flow intensity and flow characteristics (velocity, shear stress and power), rill erosion and the selectivity of particles. With an increase in flow rate, flow characteristics increased in the rills and enhanced rill erosion as well as the selectivity of sand and clay, whereas the selectivity of silt decreased in the rills. Silt showed the highest sensitivity to selection by concentrated flow, so that flows with lower shear stress could erode it from the rills. Wholly, this study revealed that the flow rate is the most flow characteristics influencing rill erosion and the selectivity of soil particles.

The objective of this study was to investigate how the earth dam is destroyed due to the effect of upstream and downstream slope of the body in overflow conditions. Therefore, eight models were provided that each model is constructed from the embankment dam with different upstream and downstream slopes (1:1, 2:1) and the soil properties (Sc) on breach formation. The time and method of dam break for flood discharges were investigated. The results showed that the upstream side slope of the embankment dam has less effect than the downstream side slope on the scour process resulting from the phenomenon and by increasing the downstream side slope of the embankment dam, the amount of erosion in the scour hole increases 28 %. Then, using nonlinear regression, relationships were presented to estimate the output flow rate and the location of the waterfall. A to the erosion and formation of the waterfall inside the body of sticky earth dams, two main outlines of the great waterfall and a series of waterfalls were presented. Finally, the formation of these waterfalls due to the effect of shear stress created during sediment erosion relative to the critical shear stress of the dam constituents was investigated and evaluated. Considering the limitations based on shear stress, the formation status of the type and the leaching pattern of the body of the cohesive earth dams during the overpass were estimated. Then, a general plan was presented to predict the behavior of the overflow stream in homogeneous and sticky soil.

Study the soil erosion process, sediment transport capacity plays a vital role in the physical description of soil erosion processes. In recent years, researchers examining the sediment transport capacity under different laboratory conditions have shown that hydrodynamic parameters, especially shear stress and unit stream power have a significant effect on sediment transport capacity. Despite the studies, the effects of sediment size on sediment transport are still not well understood and considering that previous studies have been done in direct channel, the effect of longitudinal slope and transverse slope change by changing sediment particle size in composite channel is investigated and not well understood. Therefore, recognizing and investigating the factors affecting this case is of special importance in hydraulic science. One of the influential factors in the hydraulic and hydrodynamic conditions of floodplains is the lateral slope of floodplains. However, qualitative and quantitative study of the parameter requires the presentation of appropriate laboratory research methods. In this study, by aiming at the effect of lateral slope of floodplain on hydraulic and hydrodynamic conditions of flow, as well as the effect of granulation and hydraulic parameters on the amount of sediment output, an experimental design was presented to investigate this parameter. In this study, the effect of granulation and changes in hydraulic parameters in the combined flood section (with flood plain on one side of the main channel) was investigated. Two laboratory models of compound cross-section with the first model of the lateral wall slope of the flood plain zero and in the second model, the value equal to 50% was considered. In addition, in order to investigate the effect of longitudinal slope on the washed sediments, the longitudinal slope was changed in three steps: 0.002, 0.004 and 0.006. In order to investigate the effect of the average diameter of sediments on the scouring process, sandy sediments with a diameter of 0.9 and 3 mm were used during the experiments. By comparing the changes of hydraulic parameters (velocity, shear stress, ratio of main channel depth to depth of plain flood, discharge and Froude number) with changing sediment granulation, the results showed that by reducing the grain size and at zero transverse slope, the amount of hydraulic parameters increased. The results showed that increasing the longitudinal and transverse slope has a great effect on increasing the volume of leached sediments along the channel and by increasing these longitudinal and transverse slopes in the channel, more sediment transfer volume occurs. By examining the changes in shear stress and unit stream power against sediment transfer capacity, the results showed that with increasing the longitudinal slope and in the transverse slope of 0.5, the sediment transfer capacity has increased. As the shear stress increases at different longitudinal and transverse slopes, the sediment transport capacity increases. These findings indicate that the slope has a positive effect on shear stress. The results show that the transverse slope has a significant effect on the increase and change of shear stress with sediment transfer capacity and in the transverse slope of 0.5 and in different longitudinal slopes, increase in sediment transfer capacity is more and washed sediment increased. With increasing depth of flow in main channel to depth of flow in floodplain, more sediment is removed from the flume and the least amount of sediment washed is when the longitudinal slope is equal to 0.002, transverse slope 0.5, and median particle diameter is 3mm, occurring in discharge of 1.6 l/s. As the Froude number increases, the amount of sediment output will increase more when the size of the sediment particle decreases. Also shear stress varies in longitudinal and transverse slopes.

The maximum value of soil detachment due to overland flow is the soil detachment capacity. The present study aimed to evaluate the effect of particle size classes on the rill detachment capacity (Dc) in Saravan watershed (North of Iran). For this purpose, the variations of Dc have been measured on soil samples with three particle size classes (0-1, 1-2 and 2-3 mm) under laboratory conditions through a flume experiment at five slope gradients (4.1 to 38.3%) and five flow rates (0.26 to 0.67 Lm-1 s-1) with five replications. The results showed that the Dc in 2-3 mm class was significantly higher than the other particle size classes (p < 0.05). The unit stream power was found to be very accurate predictor of the Dc in forestland of Saravan watershed. Rill erodibility, which calculated by relationship of the Dc and the water flow shear stress, had the lowest value in 0-1 mm class. Overall, this study has confirmed that the particles with size larger than 2 mm on steep slopes are more susceptible to erosion and separation by surface runoff in delicate environment ecosystems, such as the Saravan Forest Park in Northern part of Iran.

Compound channels form the cross section of many rivers, especially in adjacent areas of residential and agricultural areas. Investigation of hydraulic behavior of compound channels is of great importance in floodplain control and river management plans. In this study, by modeling a concrete compound channel with Ansys Fluent software using k-ε turbulence model and VOF method, shear stress and average flow velocity in compound channel with divergent floodplains were determined for different divergence angles. Also, the boundary conditions for flow in the studied channel are defined as input mass flow rate, output limit as pressure outlet, solid boundaries as non-slip and rough wall and upper channel boundary as non-slip and rough wall. The modeling and comparison between the laboratory data and the results of the present study showed that the maximum velocity in the channel occurs with a divergence angle of 3 degrees and with increasing the divergence angle, the flow velocity also decreases. In addition to, maximum of shear stress in the compound channel occurs with a lower divergence angle; In other words, as the divergence angle of the floodplain increases, the amount of shear stress of the fluid also decreases.

Soil structures, despite their advantages over concrete structures, are considered as high risk structures. These structures face irreparable cultural, social and economic losses against conditions such as floods. The most common cause of earthen dam damage is the overflow phenomenon, which accounts for 59% of failures (Schmocker and Hager, 2010). One of the ways to increase soil resistance is to add mixed materials with high shear strength to the soil. In this research, nano materials were mixed at five levels with the soil used in the earth dam, and an increase of about 70% of the shear strength of the soil was observed as a result of adding 5% nanoparticles to the soil. Furthermore, other soil properties from the perspective of geotechnical science and soil behavior, when mixed with nanomaterials, were investigated. Hui and Yan(2013) In their research investigated the role of particle size in the destruction of earth structures. By examining non-cohesive soils with average particle diameters of 0.33, 0.4 and 0.62, they concluded that particle size, flow rate and water height behind the embankment have a direct effect on the demolition process  of earth dams.

Bed load transport modeling in rivers and channels with vegetation over bed and banks is important. On the other hand, the complexity of bed load transport through vegetation and shortcoming of previous studies, declare the necessity of developing new models. Therefore, in the present study, the pseudo fluid model in combination with bed shear stress and resistance equation was used based on stochastic method of bed load transport. The developed model uses new definitions for dimensionless parameters of flow intensity and bed load rate that include vegetation properties with fluid and sediments. The calibration and verification of model results with experimental results showed that the model with R2=0.91 and RMSE=8.2 have accurate capability in modelling bed load transport through vegetation. The parametric analysis of vegetation features and comparing the results with previous equations showed the reduction of 45 and 68 % in absolute mean error in Mayer-Peter-Muler (R2=0.45,  RMSE=231.9) and Parker (R2=0.75,  RMSE=91.9) models, which indicates the superiority of developed model and the presented framework can be used in hydraulic analysis of sedimentation engineering in rivers.

Accelerated soil erosion is the most important degradation factor of soil and water resources. Typically, soil erosion involves the detachment and transport of soil particles by rainfall, shallow surface flow or the interaction of these two factors. Therefore, understanding the motion threshold of sediment particles and temporal variation of sediment concentration in flow-induced can provide a detailed cognition of the processes inducing soil erosion and sediment transport and their eventual interactions. It is also important for increasing the accuracy of soil erosion models. In this study, the particle motion threshold and temporal variation of sediment were studied for a sandy sample at three slopes; 3.1, 5.9, 8.9% and-dunder three flow discharges of 4.78, 7.12 and 9.05 (×10-5 m2 s-1). This study was carried out in the laboratory conditions using a flume with 240 cm long by 40 cm width. The results showed that the Shields curve is not suitable for this study to determine the motion threshold. The threshold stream power of particle motion was determined 0.035 W m-2. Also, with increasing slope and consequently increasing stream power up to 0.05 W m-2, the erosion intensity increased and soil erosion changed from sheet erosion to rill erosion. The results indicate that the formation and development of rill erosion would be the main factor for soil loss and sediment production in hillslopes. Therefore, prevention of rill formation by strip croping, terracing and terrace farming is an effective strategy for soil conservation.

The control of speed and pressure oscillations along the stream, as two critical parameters in designing hydraulic systems, is vital since they have to be set within an acceptable range in order to prevent damages to hydraulic structures. Ead and Rajaratnam (2002) studied the hydraulic jump characteristics on the corrugated bed and calculated the thickness of dimensionless boundary layer to be 0.45. Pourabdollah et al. (2015) investigated the effect of roughness and adverse slope of the bed on the velocity profile and determined the mean shear force coefficient to be 11.5 times more than that of the classical condition. Fiorotto and Rinaldo (1992) stated that in hydraulic jump the pressure is oscillating around the mean pressure value, which is almost equal to piezometric head at each point. Also Lopardo and Solari (1980) determined the pressure oscillations equal to 0.084 for hydraulic jump at downstream of valve. Accordingly, although various studies have been carried out on hydraulic jump characteristics under different conditions, the simultaneous effect of end positive step, bed roughness and adverse slope on hydraulic jump characteristics have not yet been explored. Therefore, the aim of this study was to investigate the velocity profiles, flow surface and pressure oscillations in hydraulic jump within the stilling basin at defined conditions.