جستجوی مقالات مرتبط با کلیدواژه « stepped spillway » در نشریات گروه « عمران »

Stepped spillways are one of the types of weirs used in waterway systems. This structure is used to discharge measurement, energy dissipation, and water aeration. Due to engineers' tendency towards environmental sustainability and not manipulating natural landscapes, porous spillways made of stone in the form of gabions are a suitable alternative to impermeable concrete spillways. These spillways have technical, economic, environmental, and hydraulic priorities compared to conventional concrete stepped spillways. Porous spillways are a suitable alternative to the usual concrete spillways in water transmission and distribution systems due to their high hydraulic and technical performance on the one hand and negligible negative environmental impact on the other hand.In this research, the hydraulic performance of the porous stepped spillway under free flow conditions has been investigated in a laboratory manner. This research investigates the effect of different variables including flow rate, upstream blockage, and porosity, on the discharge coefficient of the porous spillway. The materials used in the porous spillway were selected from four gradations between 1.13 and 4 cm with a uniformity coefficient close to 1. Each porous spillway was tested for seven blockages between zero and 100%. Also, the results were compared with a solid stepped spillway model with and without blockage. In the following, it has been extracted to present the empirical relationship of the discharge coefficient in these spillways under blockage conditions, using the dimensional analysis of effective dimensionless parameters under free flow conditions.Finally, in the final part, based on the dimensional analysis, two empirical relationships are presented using SPSS and GEP (gene-expression programming) for calculating the free flow discharge coefficient for porous stepped spillways.The results showed that the free flow discharge coefficient increases with the size of the filling material. The percentage increase in discharge coefficient for porous stepped spillways is approximately 34 to 230% higher than that of solid spillways. Unlike solid spillways, whose free flow discharge coefficient increases with increasing the flow rate, in porous stepped spillways, the trend of free flow discharge coefficient changes in low flow rates is downward. With an increasing flow rate, it gradually becomes horizontal and then increases with a slight slope. As the blockage increases, the flow coefficient in the porous stepped spillway gradually decreases. In blockages above 80%, the flow coefficient of the porous stepped spillway is insignificantly different from the solid stepped spillway. In the solid stepped spillway, in the percentage of obstructions below 80%, the obstacle does not affect the free discharge coefficient. The presence of blockage upstream of the porous stepped spillways sometimes reduces the discharge coefficient by more than 70%. The extraction of empirical relationships based on the GEP meta-heuristic model has higher accuracy than those extracted from the nonlinear multivariate regression using SPSS. The average error of the relation of the GEP porous stepped spillway free discharge coefficient was 4%, and the nonlinear multivariate regression model was 7%.

Energy dissipation in stepped spillways is one of the primary goals of such structures. In this study, the accuracy of the artificial neural network (ANNs) method, the adaptive fuzzy neural inference model method based on the trained firewall optimization algorithm (ANFIS-FA) and the gene expression programming method (GEP) in estimating the energy loss of skimming flow regime on stepped spillways has been studied. Also, by performing sensitivity analysis, the importance of input parameters in predicting energy loss for each of the three mentioned methods has been investigated. For this purpose, 154 series of laboratory data have been used. The input parameters for each method include the hydraulic jump Froude number, the Drop number, the number of steps, the pseudo bottom slope and the ratio of the critical depth to the height of each step.. The results show that all three methods had a higher ability to predict energy loss than classical methods for estimating energy loss based on conventional regression methods. The accuracy of the ANFIS-FA (with) method is slightly higher than the GEP (with) method. The accuracy of the neural network is slightly lower than the above two methods.However, the highest accuracy obtained is related to the multilayer perceptron neural network with 3 hidden layers with the number of 12, 8 and 7 nodes in each layer, respectively. In all three methods, the most effective parameter is the waterfall number and the least effective parameter is the pseudo bottom slope.

A stepped spillway is a hydraulic and cost effective measure to dissipate the energy of large water flow over the spillway. Due to some limitations in stepped spillways, this study is intended a plan to increase and improve the effectiveness of energy depreciation. For this purpose, the effect of the wedge-shape elements on the velocity and pressure changes over the steps, water level and energy dissipation at downstream the stepped spillway are evaluated. In this regard, several forms of wedge elements are studied with changes in wedge arrangement and the rate of discharge by using numerical model of Flow-3D, and the appropriate models from the aspect of the most energy depreciation are selected and studied in the laboratory. In the laboratory, 25 experiments were performed on 5 physical models.Numerical and experimental results show that the addition of wedge elements on the stepped spillway has reduced the velocity and water depth at downstream of spillway to about 80% and 30%, respectively, and the energy dissipation over the stepped spillway increased by about 2.7 times. Also, by drawing the distribution profiles of pressure on the edge and the floor of steps, it was observed that the negative pressure in the horizontal section turned into a positive pressure. Also negative pressure in the vertical section decreased up to 96% and positive pressure increased about 2 times. As well as, by increasing the density of the elements, the results that increase the energy dissipation are more remarkable.

In the present research, the effects of different turbulence models and cavitation phenomenon in the stepped spillway of Siah Bisheh dam was investigated using the FLUENT model. Three standard K-Epsilon, Renormalization Group (RNG) K-Epsilon, and K-Omega turbulence models were employed for minimum, maximum, and flood discharge flows of 150, 170, and 203 cm3/s, respectively. The numerical method was validated by simulating a laboratory spillway, by which an appropriate consistency was observed. Also, the results showed that the probability of the cavitation phenomenon was more likely for a discharge flow of 203 cm3/s downstream of the stepped spillway area of the Siah Bisheh dam. Therefore, an appropriate aeration system can be utilized in suitable locations to reduce the probability of cavitation by decreasing velocity in the desired areas. Moreover, the cavitation index changed at each point of the spillway by changing the turbulence model type. Therefore, choosing the turbulence model to investigate the cavitation is of great importance. For example, the maximum velocities created in the investigated models with a discharge flow of 150 cm3/s for standard K-Epsilon, RNG K-Epsilon, and K-Omega turbulence models were 1.34, 2.32, and 1.32 m/s, respectively. The standard K-Epsilon and K-Omega models were very similar in all discharge flows and the results of the RNG K-Epsilon turbulence model were different from the other two models.

One of the most prominent features of the stepped spillway performance is the considerable loss of energy during it compared with other types of spillway. Considering this feature, obtaining a more detailed view on the energy dissipation parameter and, finally, increasing its amount has been the focus of most studies related to this type of spillway. For this purpose, using a Flow-3D model, the effect of pitched steps (steps with hole) on the velocity and pressure variations, water height at downstream and energy dissipation has been investigated. As well as the appropriate model of the most energy dissipation in the laboratory was developed and studied. Numerical and experimental results show that pitched steps reduces the velocity to about (82-69%) and reduces the water height at the downstream by up to 33%, and the energy dissipation is increased to about 4 times. According to the pressure distribution profiles at the vertical edge of the step, it was observed that the amount of negative pressure in the vertical wall decreased by about 82%, and the positive pressure was approximately increased by 3 and 4 times. The negative pressure on the floor of the steps is turned into positive and the positive pressure near the edge is increased due to the presence of the hole. Also, the results showed that the error rate of the studied parameters in the numerical and experimental models was very low and acceptable, indicating a good fit between numerical and experimental data.

One of the major challenges in dam engineering is the design of the discharge flow of the stepped spillway. The rate of energy dissipation in downstream currents is higher than that of skimming currents. To achieve this goal, the discharge and skimming slope of the spillway must be low, which makes it economically efficient and applicable. For this reason, in the design process of spillway discharge, flow is assumed to be skimming. In this study, after validation of the Flow-3D model, the discharge flow of the Siah Bishe spillway was simulated. For validation, the values of the flow-Ashle curve were evaluated, and the root means square error of 5.07 was obtained. According to the results of numerical simulation, the flow must be at least 17 m3/s for the discharge. As the flow rate increases, the flow will discharge and move into the state of transient flow, which will continue to flow with 37 cubic meters per second. Finally, for values of more than 60 cubic meters per second, the flow is definitely skimming.

Realization of the advantages of a higher degree of energy dissipation have created an increasing interest in stepped spillways. This study using a three dimensional, 1:50 scale, physical model was conducted to investigate the impact of variation downstream channel width of the converging stepped spillways with a curve axis. For this purpose, the converging stepped spillway with a curve axis was constructed and tested in four ratio of downstream channel width to spillway width ( ) ranging from 0.214 to 0.286. The results of the experiments indicated that in the converging steeped spillway by increasing total upstream head, the discharge coefficient will go up for each of the width ratio ( ) and before submergence stage for the spillway, the discharge coefficient is independent of downstream channel width variations. By contrast, when the spillway was submerged, there is a decrease in the coefficient of discharge can be caused by tailwater submergence and it causes the differences in the discharge coefficient for each of the widths ratio ( ). Also, the obtained data demonstrates that as increases, the flow depth and static pressure decreases at the bottom and the toe of the spillway model. Moreover, it was observed that as discharge increases, the energy dissipation decreases for all models, but model with higher ratio of lead to reduce more energy dissipation in higher discharge. In addition model with width ratio of due

In this paper one of the newest meta-heuristic algorithms named Gravitational Search Algorithm (GSA) is used to optimal design of stepped spillway with minimizing cost. Generally, dam construction projects classify as expensive projects in which the related high costs should be reduced. Dams consist of different structures. One of these structures is energy dissipater structure. Generally, different structure such as spillway have been used for energy dissipation. Here, stepped spillway is considered as an energy dissipater structure. Therefore, GSA is used here for optimizing the excavation and concrete costs and reducing the final costs of this structure. With the use of MATLAB software for GSA coding, the Tehri dam in India is considered here as a case study and the construction cost is reduced using GSA so that all of the hydraulic constraints will be satisfied. In the following, the obtained results of GSA are compared with the results of Genetic Algorithm (GA) and Vittal and Porey (VP) approach. Comparing the results of VP approach with two used algorithms indicates that when the spillway has four steps, the results of GA and GSA are improved respectively 6% and 7.6% than the results of VP and the results of GSA are improved 1.8% than the results of GA.

In recent years, research has shown that as a good strategy for energy dissipation of spillway in stepped spillway have been considered. The design goals of stepped spillway can be used to increase the intensity of energy dissipation during spillway and thus reduce the dimensions mentioned stilling basin. Therefore optimum design of spillway on maximum energy dissipated main goal in this research. The dimensions of the spillway is considered as variables based on differential evolution algorithm and Firefly algorithm and also the combination of two algorithms for optimum design is variables. By increasing the flow rate is reduced relative energy dissipation and optimum height of the steps increases. In this study, three different inlet flow 422 (m3/s), 560.2 (m3/s), and 776.9 (m3/s), were used. The results showed that, for example, in  three  flow the energy dissipation during the horizontal steps of 200 meters by combining the algorithm, respectively, for the three flow is 79.29%, 78.47% and 68.47%.

Scouring is one of the issues that is important in the design of various types of hydraulic structures. One of these structures is a stepped spillway. The aim of this study is to evaluate the similarity between the profiles of scour holes downstream of the stepped spillway. To do so، results of 67 experiments in two different experimental models were used; these results were in a wide range of particle Froude number، the stilling basin length، downstream depth، sediment particle size distribution and two different slopes of stepped spillway. In this study، 5 different lengths of stilling basin، from 37 cm to 120 cm، were used. Also، the range of utilized discharge was from 8. 43 lit/s to 88. 95 lit/s. Duration of the tests were selected to be 6-hours، 8 hours، 12 hours and 24 hours and، in total، 834 scour profiles and approximately 85000 points to were used derive required relations and to performother analyzes. Based on the experiments results، the similarity between scour-holes located in downstream of stepped spillway was analyzed. In this process، two methods were used to make the profiles dimensionless. Based on statistical parameters، best method was selected and similarity of downstream profiles were shown. Relations that predict maximum scour depth، the distance from maximum depth to the end of the stilling basin and volume of transported sediments are developed based on the dimensionless parameters in different time periods. Furthermore، impact of different parameters on the geometry of scour holes were studied. When the Froude number increases، while all other parameters are constant، the dimensions of the scour-hole increases. When the stepped spillway slope increases، the dimensions of the scour-hole decreases and، moreover، when the tail water depth increases، while all other parameters are constant، a deeper hole with longer longitudinal distance forms. Overall، 8 cross section profiles under different conditions were taken. These profiles indicate transverse development of the scour-hole، in addition to longitudinal development.

Many investigations have been performed in order to increase the efficiency of energy dissipation over the spillways. In this study, the chute was roughened by means of the dentate blocks that were made of Teflon with new geometric shape and configurations. The experiments were carried out at three slopes, under six discharges and five dentate blocks configurations. Based on the laboratory results, it was concluded that the roughness geometry influences the relative energy loss. It was also found that using mix arrangements and selecting different sizes among roughness elements can increase the value of relative energy loss. Finally, it was observed that the dentate blocks spillway caused an extra 21% reduction in energy dissipation compared to the stepped spillway which is widely utilized to dissipate the energy.