جستجوی مقالات مرتبط با کلیدواژه ": آبشستگی" در نشریات گروه "مهندسی آب"

Protection of the downstream of culvert outlets against scour process, as a water conveyance structure, is a highly significant issue in design of culverts. In this study, the effect of bed litter length on downstream scour depth is investigated. For this purpose, experiments were carried out on the laminate with different lengths. According to the results, the particle landing at 22%, 33% and 66%, respectively, and the landing at particle landing of 2.5%, respectively. 15%, 20%, and 40% decreased particle depth by 20%, 25%, and 31%, respectively, indicating that bedding has a positive effect on decreasing downstream scour depth. The scour for the flooring considering the length of the layer showed that the scour depth decreases with the increase of the layer length due to the constant landing number.

In this laboratory study, the longitudinal changes of the flooring to the depth of the downstream scour of Calvert (square calvert shape), the changes in the length of the flooring to the depth of scour downstream of the calvert are discussed. For this purpose, experiments were performed on the floor with different lengths. According to the results, 22%, 33% and 66% were observed in particle 2 landing, 15%, 20% and 40% in 2.5 particle landing, respectively, and 20% and 25% in particle 3 landing, respectively. And reduced scour depth by 31%. This showed that changes in floor length and characteristics have a positive effect on the scour depth downstream of Calvert. Therefore, all these results have been studied in the laboratory environment and are real numbers and have been taken on a small scale.

Bridges are among the most important and most prolific river structures ever used. The three commonly used methods to deal with the scouring phenomenon around the bridges are to place the piers in a lower level than the depth of the erosive pit, to reduce the power of the vortex produced around the base, to use the shrub protection cover, or to use a collar, gaps, or submerged plates around the base bridges. Submerged plates are structures that are installed at the bottom of the river with an angle to the main stream and to prevent river erosion, rivets and base structures of the water and waterway reformation and morphology of the bed, which produces a secondary vortex and Changing the flow pattern in the river bed and, consequently, changing sediment transport and erosion. In this research, the effect of square cross-sectional diameter and the effect of submerged panels on scouring are investigated using SSIIM software.

The scouring mechanism at the abutment is very similar to the pier of a bridge; such that the decrease in current intensity near the upstream of the abutment, a vertical pressure gradient is created, this pressure gradient moves downwards to become the initial vortex, the size of which expands with the development of the scour cavity (Melville, B.W. 1997).The bridge pier near the abutment causes deepening of the scour near the support (Hong, S. 2005). However, the scouring depth is determined prominently by the scouring of the abutment and that this value may be greater than the scouring depth of a pedestal alone (Nyarko, K., & Ettema, R. 2011; Karami et al., 2017).The length of the abutment has an essential effect on its scouring depth, such that by doubling the length of the abutment, the scouring increases by about 18 times and decreases with decreasing abutment distance (Arab and Zomordian 1393; Anjum Rooz et al., 2017).In the present study, we applied FLOW-3D to build a numerical model to investigate the effect of changing the piers' distance from the abutment on the scour depth and scour rate around the two piers.

Flow-3D is one of the most potent applications in computational fluid dynamics. This research makes applications to solve the mean Navier-Stokes equations of time (Reynolds equations) using the finite volume method under a rectangular grid on the base of the Eulerian theory.The flow continuity equation is written as Equation 1. FLOW-3D calculates the load transport of each sediment type, including bedload transport, separately. FLOW-3D calculates the load transport of each sediment type, including bedload transport, separately. The dimensionless form of the bed load transfer rate in terms of n is written by Equation 2, in which dn is obtained from Equation 3.We used the laboratory results obtained from the research conducted by Hosseini et al. (2016) to validate the numerical model and adopted the study undertaken by Khosronejad et al. (2012) to model the pier scour. A rectangular channel with a length of 6 meters, a width of 1.21 meters, and a height of 0.45 meters; was used to model the bridge pier and abutment. ‎Fig. 2 shows the rectangular channel a pier and abutment placed in, and Table one describes the model configuration.

For the three-dimensional simulation of flow, the geometry of the field was discretized into a fine mesh. ‎Fig. 2 shows the boundary conditions assigned to the numerical model. Then, three turbulence models, K-ɛ, RNG, and LES have been investigated to compare the maximum scour depth in the rectangular channel for a flow rate of 0.052 m3/s, and their results are shown in Table 3.The results indicate that the LES turbulence model can estimate the maximum scour depth for the bridge pier and the abutment. Although the LES turbulence model takes more time to run, it is more accurate and presents a scouring pattern similar to the following laboratory sample justifying the computational costs. The maximum scour depth at the bridge abutment estimated by the LES model is about 74% of the measured value, while its maximum scour depth measured at the bridge's pier is 87%.‎Figs 3 and ‎4 illustrate the bed changes around the abutment and the bridge pier for the numerical and laboratory model. Comparing the bed changes and the location of maximum scour depth for the numerical model of pier and abutment and results of laboratory models shows that the numerical model has a good capability in simulating bed changes and local scour around each of the abutment structures and bridge pier.Comparison of scour time development resulting from numerical models around the abutment and bridge pier with laboratory models, ‎Fig. 6, shows that 70% of the maximum scour depth in the abutment area occurs in 20% of the initial scour time, which is relatively consistent for both numerical and laboratory models.Examination of substrate changes, ‎Figs. 7-‎11, shows that a deep scouring depth occurred for the abutment and at the upper-right edge of the forehead. And by reducing the pier distance from the abutment in the models, the maximum scours depth around the pier, and abutment structures have undergone significant changes.

Comparing the scour pattern and the location at which the maximum scour-depth for pier and abutment resulted by the numerical model with experimental, shows that the numerical model procured using FLOW-3D can well simulate bed changes and local scour around the bridge pier and abutment. Furthermore, increasing the relative velocity of the flow, strengthening the eddy currents around the pier and abutment, consequently arising the scour depth; as the relative velocity increases by 10%, the scour depth increases by about 50%. Moreover, when the distance from the base to the abutment decreases, the scouring depth around the rectangular abutment increases.

Scouring is the erosion around structures that occurs due to complex eddy currents and creates a pit around the supporting foundations of structures (Melville, 1997). Depth of scour plays a vital role in 1) the degree of the potential destruction of flow around the structure and 2) designing the dimensions of the foundation of structures in the path of water flow. Therefore, determining the mathematical relationship between scour depth and affecting parameters (Barbhuiya and Dey, 2004) and understanding the scour mechanism around bridge piers, and accurately estimating scour depth for more and better protection of bridge piers against this phenomenon (Breusers et al ., 1997) is of great importance. Numerous comprehensive studies have been performed since 1953 to identify the effect of various factors on scouring rate and determine its estimation methods (Laursen and Toch, 1953; Shen et al., 1966; Garde and Ranga-Raju, 1985; Melville, 1995).To date, researchers have studied the effect of geometric and hydraulic parameters (Sturm and Sadiq, 1996; Kouchakzadeh and Townsend, 2000; Jordanova and James, 2003) and effective vegetation Young et al., 1993; Amir et al., 2018) on scouring, but the simultaneous effect of changing the length of abutments and vegetation on the amount of middle pier scour has been less considered. Therefore, in this study, the amount of scour around the middle pier of the bridge in compound sections in case of simultaneous change of abutment length and vegetation has been investigated.

Normalized parameters significantly deepen the understanding of various physical phenomena and allow the results of limited experiments to be applied to different situations. In this study, the maximum scour depth  was selected as the primary variable and expressed as equation ‏(1) in terms of effective parameters. Then, considering the parameters  as iterative variables, using Buckingham p-theorem, equation ‏(1) was written as a dimensionless relation ‏(2). Because the amount of channel slope, unit weight of sediments, uniformity coefficient and average diameter of materials, velocity and depth of flow, and length of bridge pier are constant in all tests; normalized parameters  and Froude number were removed. By simplifying and combining other parameters, dimensionless relations for degree of scour depth and volume were obtained as equations ‏(3) and ‏(4).A trapezoidal laboratory channel made at the Water Research Institute, ‎Fig. 1, was used for the experiments. The central pier of the bridge around which the scour was examined has a square cross-section with sides of 4 cm. Abutments on both sides of the channel were provided in 8, 16, and 24 cm sizes. Vegetation was studied using non-submerged cylinders in diameter and length of 1 and 20 cm respectively applied in rows in areas of ​​1, 2, and 4% of the floodplain area. ‎Fig. 2 shows the image of the laboratory channel. Experiments were performed in two time intervals of 3 and 8 hours to obtain equilibrium time and maximum scouring.

A total of 9 experiments were performed in which the depth and volume of scouring were determined. To name each experiment, the vegetation and abutment length were marked respectively with V and A. For example, V%1A80 refers to an experiment with 1% vegetation and an abutment of 80 mm length.‎Fig. 3 shows the changes in the longitudinal profile of the bed after scouring in different conditions of vegetation and the length of the abutment. Increase in the abutment length increased the height of material accumulation in all experiments. Increasing the percentage of vegetation leads to an increase in the volume of material accumulation in all samples due to increased bed roughness and turbulence of the flow and enlargement of the scour cavity. Also, it is observed that with increasing the percentage of vegetation and the length of the abutment, the length of scouring (after the hole in the direction of flow) increases.‎Fig. 4 shows that the depth and volume of scouring increases with increasing vegetation percentage. The highest scour volume occurred in 4% vegetation (the densest vegetation condition studied), which results in 9.2 cm and 7031 cm3 for experiments V%4A160 and V%4A240, respectively. The lowest scour depth and volume values were related to 1% vegetation and V%1A80 test, which are 4.1 cm and 766 cm3, respectively. Increasing the vegetation from 1 to 2% and from 2 to 4%, the scour depth at the pier of the bridge (with length and width 4 cm and 8 cm abutment length) increases by 14 and 57%, respectively, i.e., the scour volume, respectively increases 3.2. And 1.9 times.As the relative length of the abutment increases, the rate of deflection and the intensity of the flow in the main channel increase, after which the amount of scouring around the middle pier increases. As the percentage of vegetation in the floodplain becomes denser, the bed roughness increases, and the flow rate in the main channel increases, causing more scouring around the middle pier of the bridge (‎Figs. 5 ‎and 6).

This study investigates the effect of flood vegetation and abutment length on the scouring depth and volume in a compound channel. This study shows that with increasing the percentage of vegetation, the scour depth at the pier of the bridge increases, and with increasing the length of the bridge abutment, the depth and volume of the scour increases. By the way, vegetation and abutment length percentages are the most influential parameters in creating scour depth and volume in which the former has more effect.

The flow and drainage structures are widely used in irrigation and drainage networks due to their simple and relatively precise relationships. The flow causes the return of water and consequently increases the flow cross section and decreases the speed and also creates suitable conditions for sediment deposition and waste in the water, which is considered as a disadvantage of this structure. With the accumulation of sediments upstream, the flow conditions are changed and the accuracy of the extracted relationships is reduced to estimate the discharge. By combining the flow and valve, it is possible to reduce the problems and disadvantages of using each one alone and at the same time use their advantages so that the depositable materials behind the flow and accumulator in the hatch entrance pass through the substructure. Rhine, the combined behavior of spillway flow with jet out from under the hatch, creates different conditions downstream of such structures and causes scour changes downstream of this. The overall purpose of this study was to investigate the effect of valve opening rate on scouring rate in the case of discharge through the combined structure, upstream head height using flow-3D numerical model.The results show that by reducing the opening of the valve, the height of the water on the structure increases and causes the scour depth to increase. Also, by increasing the flow rate over the spillway and under the valve and the height of the upstream water, the maximum scour depth increases.

Studies on hydraulic structures, especially around the bridge bases, show that one of the main causes of bridge destruction is the local turbulence of the flow. In order to be economical and reliable design, you have to get the maximum depth of deflection around the bases. Estimating the maximum depth of scouring with the purpose of determining the depth required for bridge bridges is necessary, as otherwise it may lead to bridge collapse. SSIIM software is used in this study, which takes into account the flow and sediment equations in a three-dimensional fashion. In this software, the flow field is obtained from the Navier-Stokes equations and the K-ε turbulence model, and then, using the nondetective solution of the deposit field and the continuity equation, the ground level changes are calculated around the bridge's base. Comparison of the results shows that the scour depth increases with increasing height, and if the angular gradient exceeds a limit, then the destruction of the wall of the scouring cavity is accompanied.

Local scouring around the bridge piers is one of the causes of their destruction. Therefore, in order to reduce and control this phenomenon, extensive research has been done and solutions in this regard have been presented. These solutions consist of two parts, direct and indirect, which in this study by defining scenarios, reviewing both methods and their simultaneous impact was done. In this study, the method of using cable, which changes the flow pattern around the base, was considered as an indirect and groundwater method that causes the flow lines to deviate from the substrate, as a direct method. Therefore, different states of the foundation, in front of the base, behind the base and the cable around the base with relative steps equal to 0.33, 0.5 and 0.67 in clear water conditions were investigated. According to comparative experiments, the use of a waterfront in the front results in an average scouring depth of 15 to 20% less than a footstool in the back of the base. Therefore, in general, according to the diagrams, it can be concluded that the combined use of cable and groundwater has reduced the scour depth and is accepted as a method of reducing the base scour depth.

Studies on hydraulic structures, especially around bridge piers, show that one of the main causes of bridge destruction is local turbulence. In order to have an economical and reliable design, the maximum scouring depth around the foundations must be achieved. Estimation of the maximum scour depth is necessary in order to determine the required depth for the bridge piers, because otherwise it may lead to the destruction of the bridge. In this research, SSIIM software has been used, which considers flow and sediment equations in three dimensions. In this software, the flow field is obtained from the Navier-Stokes equations and the εK-turbulence model, and then, using the non-permanent solution of the sediment field and the continuity equation, the floor level changes around the bridge pier are calculated. The results of this study show that the numerical model used, which is one of the three-dimensional models available to engineers, predicts acceptable values ​​in flow simulation, calculation of free surface and calculation of bed topographic changes in the river. In some places the speed calculation error increases, but the model is able to model the distribution of velocity and rotational currents well. From the presented models, it was proved that under the same conditions, the scour around the square and cylindrical base is more than the rectangular base.

Local scouring is one of the most important phenomena and factors in the destruction of the bridge bridges, which was studied in order to reduce the destructive effects of this phenomenon using the experimental model and the effect of the combined stone and chipping of the submerged plates in this study. In this research, a laboratory model of a cylindrical base group of 5 cm in diameter and a stone of china with grains of 1, 1.5 and 2.5 cm in diameter, and submerged plates in numbers (2, 4 and 6) of a plate of 10 × 15 in a flume An experimental laboratory and a landing number (0.25, 0.22 / 0.20 / 0.2) were tested and analyzed. The main objective of this study was to investigate the combined effect of Chinese stone and submerged panels on reducing the scour depth of the group The bridge is a cylindrical bridge and, using Buckingham's dimensional analysis, the parameters The results of this study showed that by increasing the diameter of the stone and the number of submerged plates, the percentage of the depth of water washed to the diameter of the base was significantly reduced. Which was found to be the highest for bases 1, 2, 3 (69%, 72%, 74%) and the lowest values (49%, 50%, 57%), which showed that by increasing the flow rate of erosion Also increased.

Protection of the downstream of culvert outlets against scour process, as a water conveyance structure, is a highly significant issue in design of culverts. In this study, the effect of bed litter length on downstream scour depth is investigated. For this purpose, experiments were carried out on the laminate with different lengths. According to the results, the particle landing at 22%, 33% and 66%, respectively, and the landing at particle landing of 2.5%, respectively. 15%, 20%, and 40% decreased particle depth by 20%, 25%, and 31%, respectively, indicating that bedding has a positive effect on decreasing downstream scour depth. The scour for the flooring considering the length of the layer showed that the scour depth decreases with the increase of the layer length due to the constant landing number.

Withdrawal of water from subsurface and surface sources There are always problems when using the water transfer method and hydraulic and hydrological rules, the most important of which is closing the mouth of your catchment and catchment channel. One of the methods of controlling sediment entering the lateral catchment is the use of submerged plates. Submerged plates are small pieces of different genders that are placed at a low angle to the flow (10 to 30 degrees), which creates a vortex flow perpendicular to The direction of flow in the bed layers compresses the water and causes the plate and tea to fall down in the bed sediment. It is created to create a channel for the passage of sediments downstream. In addition to reducing their performance, scouring around the plates changes the hydraulic conditions and more sediment enters the reservoir. Examining its amount in selecting the optimal shape increases both the life and efficiency of the plate and more sediment control. Numerical construction with CCHE 2D software for 5 geometric shapes of submerged plates in four landing numbers 0.45, 0.55, 0.6 and 0.66 based on the laboratory work of Davoodi et al. (2015) is simulated with the difference that in addition Rectangular shape 4 Modified shapes are also examined that the purpose of measuring the amount of scour around these plates in order to identify the effect of modifying the geometric structure in reducing scour that plates B3 and then B4 had the best performance.

This research investigates changes in the length of the apron on the scour depth of Culvert downstream. So the experiments were conducted on the apron with different lengths. Results of the study revealed that the depth of scouring has reduced in particle Froude 2 to 22%, 33%, and 66%; and apron in particle Froude 2.5 to 15%, 20%, and 40%; and in particle Froude 3 to 20%, 25%, and 31%, respectively. It shows that length changes and characteristics of apron have positive effects on the scour depth of Culvert downstream.

Bridges are the vital components of each country’s roads. Economic studies of the road construction show that the road bridges allocate much cost to it and due to the delicate structures of their system; they have great vulnerability as well. Therefore the detailed design of the various components of the bridge should be considered further. Erosion and transport of bed material is separated from it by a process called scouring. Occurrence of scouring around the bridge piers is one of the main reasons for the defeat and destruction of bridges and their instability. So it is important to provide methods to control and reduce this phenomenon. In the present study, the modeling of non-submerged plate’s perpendicular to the water flow has been expressed in upstream of the cylindrical pier using software SSIIM. Reducing the depth of the scouring hole was observed in these pages, and has a great influence around the bridge pier