جستجوی مقالات مرتبط با کلیدواژه « سرریز کنگره ای » در نشریات گروه « عمران »

Generally, labyrinth weirs pass more water compared to their equivalent rectangular weirs. Thus, these types of weirs are popular amongst hydraulic and environmental engineers. In this paper, for the first time, a novel artificial intelligence (AI) technique called "outlier robust extreme learning machine (ORELM)" is used to estimate the discharge coefficient of labyrinth weirs. The ORELM method has been proposed in order to overcome the difficulties of the classical ELM in predicting datasets with outliers. In this method, the concept of “sparsity characteristic of outliers” is used. Also, in this study, to verify the results of the numerical models the experimental measurements conducted by Kumar et al. (2011) and Seamons (2014) are employed. The experimental model established by Kumar et al. (2011) is composed of a rectangular channel with a length of 12m, a width of 0.28m and a depth of 0.41m. The weir is made of steel sheets and placed at an 11m distance from rectangular channel inlet. Also, Seamons (2014) experimental model has been set up in a rectangular channel with the length, width and height of 14.6m, 1.2m and 0.9m, respectively. First, the number of the hidden layer neurons initials from 5 and continues to 45 and the most optimal number the hidden layer neurons are taken into account equal to 5. In this study, the Monte Carlo simulations are used for examining the abilities of the numerical models. The main idea of this method is based on solving problems which might be actual in nature using random decision-making. The Monte-Carlo methods are usually implemented for simulating physical and mathematical systems which are not solvable by means of other methods. In this paper, the K-fold cross validation method is employed for validating the results of the numerical models. To this end, the observational data are divided into five equal sets and each time one set of these data is used for testing the numerical model and the rest for training it. This procedure is repeated five times and each test is used exactly once to train and once to test. This method increases the flexibility of the numerical model when dealing with the observational data, and it can be said that the numerical model has the ability to model a greater range of laboratory data. For instance, the maxim value of R2 is obtained for the K=4 case (R2=0.954), while for the K=5 case the values of RMSE and MARE are estimated 0.034 and 4.408, respectively. After that, different activation functions are evaluated in order to detect the most accurate one for the numerical model. Subsequently, six different ORELM models are developed using the parameters affecting the discharge coefficient of labyrinth weirs. Also, the superior model and the most effective input parameters are identified through a sensitivity analysis. For example, the values of R2, RMSRE and NSC for the superior model are calculated 0.943, 5.224 and 0.940, respectively. Furthermore, the ratio of the head above the weir to the weir height (HT/P) and the ratio of the width of a single cycle to the weir height (w/P) are introduced as the most important input parameters. Also, the results of the ORELM superior model are compared with the artificial intelligence models including the extreme learning machine, artificial neural network and the support vector machine and it is concluded that ORELM has a better performance. Then, an uncertainty analysis is conducted for the ORELM, ELM, ANN and SVM models and it is proved that ORELM has an overestimated performance.

Considering the importance of redesign of dams spillways to provide optimum dimensions, the hybrid meta-heuristic based approach of Particle Swarm Optimization (PSO), Gray Wolves (GWO) and Direct Search Optimization (DSO) were proposed. In this approach, the spillway volume, which indicates the amount of concrete and cost, is considered as the objective function and spillway height, number of cycles, apex length and angle of wall are considered as decision variables. By implementing the proposed model, based on the Ute dam labyrinth spillway data, the spillway optimal dimensions were determined and compared with the other studies result. The results represent the very good performance of the proposed approach in generating global optimal solution, and non-hybrid use of DSO algorithm is not recommended due to network size constraint, increased computational cost and failure to achieve optimal solution. The optimal dimensions led to concrete saving and reduction of costs to 64% compared to the existing dam design. Investigating the optimal dimension of trapezoidal labyrinth spillway indicates that increase the flow capacity of the spillway to 15760 cubic meters per second. Finally, the comparison of the optimal dimensions obtained with two trapezoidal and triangular sections showed that the optimal form for labyrinth spillway is triangular.

Weirs have important roles in dam safety in which they should spill floods with high return period. Designers generally enhance width of the weirs to increase their discharge capacity. This procedure involves topography as well as economic limitations. Here, arced weirs can be considered as an alternative. In plan view, arced weir is part of a circle that increases the crest length for a given channel width. This increases the flow capacity at a similar heads. Such structures are also recommended for modification and increasing the capacity of the existing spillways. Discharge capacity of labyrinth weirs is a function of flow height, effective crest length, height of weir and shape of the crest. Discharge coefficient is also a function of height of flow, height of weir, weir thickness and crest shape. In this study, hydraulic characteristics of arced labyrinth spillways are numerically investigated. Here, the effect of crest shape on the discharge coefficient of the labyrinth spillway is included. In the first step, dimensionless parameters affecting the performance of arced weirs are introduced using Buckingham π theorem. To analyze this problem, a commercially available CFD code; Flow 3D by Flow Science; was selected. Flow 3D is known for its ability to accurately tracking free surface using Volume of Fluid (VOF) method. A similar method called Fractional Area to Volume Ratio (FAVOR) is used to define labyrinth within the model. Also, Reynolds averaged Navier Stokes (RANS) equations are solved using a finite volume method. Besides, The Renormalized Group Theory (RNG) model was implemented for turbulent simulations. The laboratory data of Crookston and Tullis (2012a) is used to validate the numerical model. These researchers conducted experiments on physical modeling of the labyrinth spillways at the Utah Water Research Laboratory at Utah State University. Comparison of numerical simulations with those of experimental results validates the ability of this software to simulate the complex flow over labyrinth spillways with an acceptable accuracy. In this study, result of 16 geometry models was used to develop a hydraulic design and analysis formulation for arced labyrinth weirs. Discharge coefficient data for Half-Round, Quarter-Round, Sharp-crest and Flat-crest arced labyrinth weirs are presented for 6̊ ≤ sidewall angles ≤ 24̊ and various head water ratio (0.1≤ H0/P ≤ 0.9). The study has shown that half round crest shape could increase the discharge coefficient about 22% compared to other crest shapes. Also, the results show that factors such as local submergence and nappe interference near an upstream apex has a negative impact on performance of arced labyrinth weirs. The local submergence area is directly related to the flow head, crest shape and sidewall angle. For high head conditions, the local submergence may decrease the efficiency of a labyrinth spillway. Efficiency parameter is defined as the ratio of discharge of arced weir to that of liner weir with the same width. From efficiency curves indicates that reduce of sidewall angle can improve efficiency. As a result, the highest efficiency related to arced labyrinth spillway with sidewall angle (α = 6̊ ).

Labyrinth weirs are one of the most common structures in regulating water level and release of flow in irrigation channels and reservoirs of the dams without special operation. A major problem in the operation of these structures in water conveyance channels is sedimentation at the upstream of the weirs, which can affect the performance of these structures. In this research, the effects of changes in the geometry and upstream channel bed of weirs on the discharge coefficient of the trapezoidal labyrinth weirs was investigated experimentally. Experiments were performed for cases without change in channel bed level and 3 levels of channel bed changes at the upstream of weirs (30, 60 and 90 percent of weir height), and six geometries of trapezoidal labyrinth weirs under wide range of flow discharges. The experimental results showed that increase of the channel bed level up to 60 percent of the weir height did not affect discharge coefficients of the labyrinth weirs. However, by increasing the channel bed level to 90 percent of weir height, there was a decrease of approximately 14 percent in discharge coefficients of the weirs with respect to the case with no changes in channel bed level. The comparison of results indicated that because of increase in local submergence at the outlet cycles of the weirs, for upstream channel bed level smaller than 90% of the weir height, the discharge coefficients of the trapezoidal labyrinth weirs with smaller angle of apex cycles and larger length of cycles in flow direction was more than other geometries of the weirs. By increasing the upstream channel bed level to 90 percent of the weir height, the approaching flow velocity increases and most parts of flow, releases from apex of the cycles since it requires larger momentum to exit from the cycles. Therefore, for discharge coefficient of the labyrinth weirs with larger angle of apex, both the cycles and smaller length of the cycles in flow direction were more effective than other geometries.