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

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

In the past, various methods have been proposed to control beach heel scouring.  For shallow rivers (such as mountain rivers), various types of overflows are used.  Therefore, the development of scour in cross-vane and w-weir structures for coastal protection was investigated in this study.  The results showed that by installing a w-weir structure in a 90-degree position compared to a 30 and 60-degree position, a 37.9% and 19.7% reduction of scouring was observed, respectively.  Also, by installing the cross vane structure in the 90-degree position compared to the 30 and 60-degree position, a 35.4% and 21.2% reduction of scouring was observed, respectively. With increasing width (L / B) (ratio of the width of structure to the width of flume), the w-weir structure decreased from 1.5 to 2, scour rate of 7.9%.  Also, with increasing width (L / B) (ratio of the width of structure to the width of flume), the cross-vane structure has decreased from 1.3 to 1.7, and the scour rate has decreased by 4.7%. The w-weir structure had an average of 7.3% less scouring than the cross-vane structure.

Estimation and prediction of scouring around the piers play a significant role to design these structures since with increasing dimensions of scour hole, stability of the pier is threatened; as a result, the structure may be destructed. In this study, scour hole in the vicinity of twin and three piers is estimated by using fuzzy c-means clustering of ANFIS (ANFIS-FCM) network technique. To do this, firstly, the parameters affecting scour hole around twin and three piers including Froude number (Fr), the ratio of the pier diameter to the flow depth (D/h), and the ratio of the distance between the piers to the flow depth (d/h) were detected. Subsequently, seven ANFIS-FCM models were defined by means of these dimensional input parameters. It should be stated that 70% of the experimental data were utilized to training the models and 30% of the rest were applied to testing. Next, the superior ANFIS-FCM model and the most important input parameter were introduced by implementing a sensitivity analysis. The premium model as a function of all input parameters simulated the scour values with a reasonable accuracy. For instance, the correlation coefficient (R), the scatter index (SI), and the Nash-Sutcliff efficiency coefficient (NSC) are respectively computed to be 0.988, 0.106, and 0.976. Furthermore, the Froude number was considered as the most important input parameter. Lastly, a computer code was introduced so as to simulate the scour hole around the twin and three piers.

Today, abutments disrupt the normal flow of rivers and cause scouring and erosion of sedimentary materials around them, creating holes and resulting in much damage every year. Researchers have proposed various methods to reduce the power of water erosion. One of the essential methods in this regard is creating slots in abutments. Since the expansion of the scour hole endangers the stability of the bridge structure, this study examined the effect of slot dimensions in the support on the scour hole dimensions. The findings demonstrated that the presence of slots in abutments effectively reduces the dimensions of scour holes. With the slot, the volume of the scour hole can be reduced by up to 50%. Furthermore, as the relative speed of scouring increases by 75%, the depth of the scour hole also increased up to 140%. An increase in slot depth leads to a decrease in scour hole depth of up to 85%.

With the advancement of science, human societies use transmission pipes to transport water and other fluids from the bed of seas, rivers, streams and natural drains. If pipelines pass through rivers and seabeds on their way, great care must be taken in their design. The main purpose of this study is to investigate the effect of the insertion depth of the shield on the pipeline scour at different distances of the pipe from the bed. This study was carried out in a flume with the length of 10 m and the width of 30 cm. Experiments were conducted under clear water condition (u/uc=0.95). Uniform sediment with a median diameter of one millimeter (D50=1 mm) was considered. In this research, a PVC pipe with an external diameter of 2.5 cm was used. The distance of the pipe from the bed (G) was considered based on a coefficient of the pipe diameter (0, 0.25, 0.5, 0.75, 1). Also, the insertion depth of the shield (Dw) was selected according to a coefficient of the pipe diameter (0, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75 and 2). The results of the experiments showed that in the case that the shield was not used, with the increase in the distance between the pipe and the bed, the maximum scour depth under the pipeline decreases.

Scouring at the place of submerged pipelines under the effect of eddy currents around the pipe passing through the riverbed leads to the settlement and failure of the pipeline as well as the penetration of the fluid passing through the pipe into the stream. Therefore, efforts to reduce these risks and their effects are always the attention of researchers and engineers. In the current research, scouring and sedimentation around the pipe and its surrounding bed under the effect of a protective plate at different positions and heights have been investigated and analyzed using Flow-3D. A comparison of the simulation results of the present research with the laboratory results showed that the used numerical model with the statistical index R2=0.96 has an acceptable ability in simulating the mentioned phenomenon. Also, the results showed that by installing a plate with a height of H=1.25D (D is the diameter of the pipe) and at a distance of 0.5D downstream of the pipe, the scouring depth under the pipe decreases by 60%, and also the average level of the bed in the upstream area increases by 82%, which is the most optimal state among different downstream positions. The optimal state of the plate in the upstream corresponds to the height of H=0.75D and at a distance of 1.5D, which not create scouring, and the average level of the bed between the pipe and the plate in the upstream has increased 4.9 times compared to the state without the plate.

The ecosystem and equilibrium of rivers can be significantly affected by the river bank erosion which can also limit the human access to the rivers. Groyne is an important river restoration structure that prevents bank erosion through deviation of flow from the river banks to the main channel. From the permeability aspect, these structures can be classified into three types of permeable, impermeable, and bandal-like ( hybrid type which includes permeable and impermeable types ). Moreover, these structures can be categorized to straight, T-shaped, and L-shaped configurations. This research aims to investigate the local scour around a new type T-shaped bandal like groyne. The total number of 66 experiments were conducted through a straight flume ( 12 m length, 0.6 m width, and 0.6 m depth ) under non-submerged and clear water conditions. T-shaped bandal like and T-shaped impermeable groyne structures were fabricated in three web to wing length ratios of 0.5, 0.75, and 1. Also, three upstream to downstream wing ratios of 0.5, 1, and 2 and the permeabilities of 33%, 50%, and 60% were selected for the T-shaped banal like structure. The experiments were carried out at the flow discharge of 6 Ls-1, 9Ls-1, 12 Ls-1 and 15 Ls-1 in the presence of the T-shaped impermeable groynes and the T-shaped bandal-like groynes. It was revealed that, increasing the structure permeability resulted in decreasing of the maximum relative scour depth. Under 33%, 50%, and 60% permeabilities of the T-shaped bandal-like groynes, the maximum scour depth was decreased by 63%, 78%, and 83%, respectively compared to the T-shaped impermeable groynes. Moreover, it was observed that the maximum relative scour depth was increased by the average of 46% as for the greater values of structure length. The maximum relative scour depth was also increased for the greater values of flow discharge. It was found that there is no relationship between the maximum scour depth and the ratio of upstream wing length to the downstream wing length of groyne. Based on the results, the permeability and length of the groynes and the flow discharge are among the factors affecting local scouring around T-shaped bandal-like groyne. The significant decrease in the relative scour depth in T-shaped bandal-like groynes compared to T-shaped impermeable groynes indicates that the T-shaped bandal-like groynes have better performance than the impermeable ones in scouring control, structural stability and river bank protection.

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.

In free overfall spillways, waterfalls over the crown of the spillway almost vertically and impacts the downstream bed of the dams. Due to the high velocity and energy of the flow which impacts the erodible downstream bed, it may cause scouring close to the foundation of the dam and consequently threaten the stability of the dam.

In this study, artificial intelligence methods were used to estimate the scour depth of slope control structures with sharp-crested weir due to the complexity of the phenomenon. Three models including neural network, adaptive fuzzy neural system, and support vector machine (SVM) were used as artificial intelligence or black-box model to solve the problem..

The results showed that artificial intelligence methods are more efficient than conventional experimental methods in estimating the depth of downstream scours of slope control structures with sharp-crested weir. Using more parameters in the input of artificial intelligence models does not increase the accuracy of these models. It is because of increasing errors as a result of using more parameters in these models. In estimating the downstream scour depth of slope control structures with the sharp-crested weir in both calibration and validation stages, an adaptive fuzzy neural system model is up to 20% more reliable than the artificial neural network model and up to 8.5% than the support vector machine model.

Due to the importance of the topic in the fluid transfer industry, the way of pipelines across the width and bed of the rivers has been considered especially in recent decades. In practice, the passage of pipelines through meandering rivers and river bends is unavoidable. In this research, local scouring of buried and semi-buried pipe in 90-degree mild bend under different scenarios was investigated. The results of this research can help the functioning of rivers and their interaction with structures in the river such as buried and semi-buried pipelines, predicting the amount of water washing around them and using its results in the design and placement of these pipelines.

The laboratory model on which the scenarios of this research are based includes an arc-shaped channel located in the hydraulic laboratory and physical models of the water science and engineering department of Razi University. In this arc-shaped flume, the length of the upstream span is 5.4 meters, the length of the downstream span is 4.5 meters, the inner radius is 1.6 meters, the outer radius is 2.1 meters, the height is 0.6 meters, and the floor width is 0.5 meters. In order to check the correct functioning of the physical model and to trust its results, an experiment was conducted without the presence of the pipe buried in the bend. In this experiment, the flow descent number equal to 0.32 and sediments with a uniform grain and a diameter of 0.85 mm and a thickness of 15 cm were placed in the flume bed. After conducting the test for 6 hours and not observing the movement of the bed load, the pump was finally turned off and after the complete drainage of the flume, the bed profile was measured.

The effect of the placement angle of the repeller pipe relative to the mild arc (θ) on the scouring pattern
The results showed that by placing the pipe in the repulsive state, the amount of scour after the pipe and under the pipe has increased compared to the attracting state. According to the placement angles, it was observed that in repulsive mode, with the increase of the placement angle of the pipe in the bend, the amount of scouring after and under the pipe has increased. The effect of the placement angle of the attracting pipe relative to the mild arc (θ) on the scouring pattern In the absorbant state, it was observed that by approaching the beginning of the arc and reducing the placement angle of the pipe due to the non-alignment of the flow direction with the pipe direction, the amount of scour after the pipe decreased, but the process of scouring under the pipe was observed as in the repulsive state.The effect of pipe placement depth on scouring pattern By increasing the depth of pipe placement, it was observed that the effect of the pipe on local erosion has decreased; Even in some simulation scenarios, the placement of the pipe in the depths with the ratio of the placement height to width of the channel of 0.06 buried pipe has no effect on the local erosion. It can be concluded that at depths equal to or greater than The ratio of placement depth to channel width is 0.06, the effect of local scouring caused by the buried and semi-buried pipe is minimal, and as a result, it causes the least damages.

The results showed that by placing the pipe in the repulsive state, the amount of scour after the pipe and under the pipe has increased compared to the attracting state. According to the placement angles, it was observed that in repulsive mode, with the increase of the placement angle of the pipe in the arch, the amount of scouring after and under the pipe has increased. However, in the absorbiant state, it was observed that by approaching the beginning of the arc and reducing the placement angle of the pipe due to the non-alignment of the flow direction with the direction of the pipe, the amount of scouring after the pipe decreased, but the process of scouring under the pipe was observed as in the repulsive state.

One common method for Blank River protection and restoration is use of Spur dikes. Spur dikes either in the forms of group or single, depending on their permeability is classified an permeable and impermeable. Spur dikes restore flow pattern and prevent erosion of river banks. This leads to stability and immovability of river. However, they have some disadvantages; on installation they require drying river and erosion around their structure causes destruction (Anonymous, 2002, 2003) and (Anonymous, 2010). Due to the mentioned disadvantages use of spur dikes will be halted and use of vane, which has a higher environmental compatibility, is suggested. This study aims to introduce “composite structure”; a new structure with a combination of a Spur dike with different permeability and a single vane. The main aim of this study is to increase the amount of sediment transported behind the structure by water flow produced by the vane in the combination structure.

One of the structures that is widely used for training the rivers and channels is groyne. From past time, application of the groyne indicates the wide advantages of these kind of structures. One of the important issues in the design of groynes is the local scour phenomenon in the nose due to changes in flow pattern and presence of strong vortices. In recent years, most research has been based on open and impermeable groynes, and most have been done in laboratory. Therefore, in this study, the scour and 3D flow pattern around the T-shaped gabion groyne were simulated using Flow-3D numerical model and turbulence model (k-ω) and compared with the experimental results. The results showed that the model (k-ω) has better agreement with the experimental results in predicting the maximum scour depth and flow pattern around the T-shaped gabion groyne. So that the location of scour and the maximum depth of scour obtained from numerical simulation are close to the experimental results. Increasing the body permeability also has a significant effect on reducing turbulence, eddy and transverse velocity.

Due to scouring problems in impermeable spur dikes, which compromise structural strength and stability and as a result repair and maintenance costs increase, an alternative method of scouring is needed to protect the river bank. In this area, bandal-like structure can be used. This structure is a combination of an impermeable spur dike and a permeable spur dike. The upper part is impermeable causes the upper half of the flow run towards the center and the inner wall and the lower part is permeable enabling the lower half of the stream passes through it (Rahman et al., 2003a, b). The lower part causes the flow to slow down and reduces speed, and because the flow near the bed has a higher concentration, it leads to settling sediments in the downstream of the river near the coast. On the other hand, because of the flow through the lower half, the power of downstream flows are reduced compared to the impermeable spur dike and the horseshoe vortices are vanished. Therefore, the scouring rate in the bandal-like structure is less than the impermeable spur dike (Zhang et al., 2010; Teraguchi et al., 2011b)Regarding that the scouring rate, the bandal-like structure is less than an impermeable spur dike therefore, its use has been suggested by some researchers. Since the sedimentation rate behind the bandal-like structure is less than the impermeable spur dike, in the present study, a new structure called the wedge bandal-like is proposed to enhance the sedimentation of the bandal-like. Wedge bandal-like structure is constructed of a bandal-like structure and a repellent impermeable triangular spur dike. The purpose of using this structure is to use both the advantages of the bandal-like structure as well as the benefits of repellent impermeable triangular spur dike, for deviation of flow and sediment transport to the back of the structure and sedimentation. Both structures cause the secondary flow of the surface to move towards the outer arc before moving to the outer shore down the bottom and practically shore the coastal tail into middle areas.

Spur dikes are structures that constructed for protection of the river walls against the erosion. Spur dikes are generally built perpendicular or at an angle to the river bank or revetment, protruding into the watercourse. The effect of the geometrical characteristics of the hockey spur dikes on formation developing of scour hole has been rarely studied. Spur dikes. The current study aims to evaluate the effect of the length of the hockey spur dike on the formation and development of scour hole and comparing with that effect in L-shaped spur dike. In this direction, all experiments were done in clear water conditions using the spur dikes in length of 8 cm and 12 cm and in a laboratory flume. The results asserted that the dimensions of the scour hole and the length and thickness of the sedimentary hill were increased by raising the length of the spur dike. However, this increment was lower in hockey spur dike than the L-shaped spur dike. The maximum depth, area and the volume of the scour hole were also increased by raising the length of the spur dikes. This increment in-average was equal to 57.5 and 67.7 per cent in L-shaped spur dikes and equal to 33.3 and 42 per cent in hockey spur dikes for two different lengths of spur dikes. Furthermore, no scouring was observed in downstream section of the hockey spur dikes near the wall. Therefore, the dimensions of the scour hole around the hockey spur dike was lower than those in the L-shaped spur dikes.

Among the approaches to reduce flood damage is to reduce the flow rate near the shore by spur dikes. The study first simulated the transfer of sediment and scour around series spur dikes in an experimental model using Flow 3d software. According to the comparison results, one can observe a good match between the results of the numerical and experimental models that the error rates of MAPE around the first spur dike, for U/Ucr ratios were, 0.75, 0.85 and 0.95 and were 9%, 13.79% and 14.10%, respectively. Then two protective spur dikes with various lengths (10 and 20 cm) were used in canal upstream and the effects of the presence of these two protective spur dikes simultaneously on the scour around the main spur dike were examined. In modeling done, increase in U/Ucr depth increases the maximum spur dike depth, so that with increase in U/Ucr by 26% (from 0.75 to 0.95), the increase in the maximum depth of the first spur was 51%, in the second spur dike 4 times, and in the third spur dike 116%. When the protective spur dike couple with various lengths is used simultaneously, and then these two protective spur dikes simultaneously drastically reduce the effect of the flow intensity to the wall and nose of the main spur dike. Moreover, the maximum depth of scour around the

Local scouring that occurs due to human construction of structures in the course of rivers flow can lead to erosion of the river's bottom and threatens to change the natural flow of the river. One of the indirect methods of reducing scouring is the use of protective structures.

In this research, the effect of protective sheet length on the scour depth reduction of cylindrical base was investigated.

The results of the experiments showed that the laying of protective plates could reduce the scour depth to 69.50%. Also, the best relative length (the length of the protective plate to the width of the bridge base, L / b) of the protective plates is equivalent to one, and with the increase in the length of the protective plates, the effect of the plate length on the scour depth reduction was reversed, so that reducing the scour depth for the relative length of 5.0 and 2 are respectively, 50% and 60% more than the control (without protective plates), and in all experiments, the relative depth of scour has increased with increasing the flow rate.

Scouring depth due to dam break flows as one of the important engineering problems can be investigated numerically by means of an appropriate multiphase model. Smoothed Particle Hydrodynamic (SPH) model is a Lagrangian Mesh-free based method that has been introduced to solve such complicated flows.

A Multiphase version of this model is modified in this study to predict scouring depth after dam break flows. At first, the introduced model is validated via comparing the results with experimental data and it is confirmed that the model can well predict turbulent multiphase flows. Then, the performance of a scour protection structure with different length and heights is simulated against dam break flow to find an optimum geometry for this structure.

Based on the results, it is concluded that the effect of structure height on scour reduction is more sensible than the effect of structure length. In contrast to the structure length, a small edge at the end of the protective structure can efficiently decrease the final scoured depth. However, there exists an optimum height with the best performance. A too high scour protection structure can even result in a higher scouring depth than an unprotected case. Therefore, it is necessary to use a protection structure with an appropriate height and the introduced model can be utilized as a helpful tool to check the required performance of this structure.

The main problem downstream of hydraulic structures, such as weirs, is scouring and movement of bed materials.  The piano key weirs (PKW) is one the types of weirs. Due to the fact that the geometric shape of the weir affects the condition of the downstream scour, therefore in this study, the downstream scouring of the piano key weirs with a trapezoidal geometric shape is studied. In this paper, the scour profile and the rate of change were compared with the change in the lateral wall angle of the weir.

For this purpose, four experimental models of this type of weirs were made and these models were tested in a laboratory flume at different flow rates. Also, to investigate the effect of tail water depth on scour profiles, one of the models was investigated at three different tail water depths.

The results of scouring characteristics showed that in trapezoidal piano key weirs, the maximum depth of the hole is created under the output key and by increasing the discharge and decreasing the tail water depth, the geometric dimensions of the scour hole increase in trapezoidal models. Also, in trapezoidal piano key weirs, by increasing the side wall angle of the weir, the geometric dimensions of the scour hole are reduced. In all flows, by increasing every 3 degrees of the side wall angle of the piano key weir, maximum scour hole depth on average, 5%, Spatial position distance, maximum scour hole depth and scour hole span length, respectively, and it decreases by 8% and 3% on average. Also, when Frd>65% is, this difference becomes insignificant and there is not a significant difference in the shape of the scour hole for PKW models.

Predicting the extent of local scouring downstream of hydraulic structures has been one of the topics of interest to researchers in recent years. In this research, downstream scouring of a trapezoidal piano key weir under changes in the hydraulic conditions of the flow and the height of the flow drop passing through the weir in a channel with a length of 10 meters and a width and height of 0.75 and 0.80 meters in the hydraulic laboratory of Water Engineering Group. And hydraulic structures of Tarbiat Modares University of Tehran have been studied. Uniform and non-sticky sediments with an average diameter of 2 mm in length and width of 3 and 0.75 m downstream of the piano key weir were used. All experiments were performed under free flow conditions. The results showed that the maximum occurrence of scour depth with increasing flow drop height is farther away from the weir. The maximum scour depth increases with increasing flow drop height. Scouring in the transverse middle of the bed is less than its walls. Increasing the height of the flow drop is accompanied by more changes in the topography of the bed.