Evaluating the Effect of Downstream Channel Width Variation on Hydraulic Performance of Arched Plan Stepped Spillways

In the present study, a 3D physical model with a scale of 1:50 was developed based on the Germi-Chay dam. The model was used to assess the impact of downstream channel width variation on the efficiency of arched plan stepped spillways. Four ratios of downstream channel width to spillway crest width (Wch/W) were considered which range from 0.214 to 0.286. The hydraulic parameters such as water surface profile, static pressure, discharge coefficient, energy dissipation, and stage-discharge were assessed for each model. Results of the experiments indicated that the values of the discharge coefficient increased with increasing the upstream head values before the submergence state occurrence. However, in this state, the downstream channel width variations had no significant impact on the discharge coefficient. On the other hand, with spillway submergence, influence on discharge coefficient was observed when width variations occurred. Observations showed that an increase in the width ratio caused a decrease in static pressure. In addition, the results of the submerged state clearly showed the effect of the width ratio variations on energy dissipation. For a particular discharge, the highest width ratio led to minimal energy dissipation. Results revealed that the most efficient model was when Wch/W?=?0.286. This model was the only one that successfully passed the probable maximum flood discharge in the maximum allowable height (5 m).

     

Applications of soft computing techniques for prediction of energy dissipation on stepped spillways

In this study, numbers type of soft computing including artificial neural network (ANN), support vector machine (SVM), multivariate adaptive regression splines (MARS), and group method of data handling (GMDH) were applied to model and predict energy dissipation of flow over stepped spillways. Results of ANN indicated that this model including hyperbolic tangent sigmoid as transfer function obtained coefficient of determination (R ² = 0.917) and root-mean-square error (RMSE = 6.927) in testing stage. Results of development of SVM showed that developed model consists of radial basis function as kernel function achieved R ² = 0.98 and RMSE = 2.61 in validation stage. Developed MARS model with R ² = 0.99 and RMSE = 0.65 has suitable performance for predicating the energy dissipation. Results of developed GMDH model show with R ² = 0.95 and RMSE = 5.4 has suitable performance for modeling energy dispersion. Reviewing of results of prepared models showed that all of them have suitable performance to predict the energy dissipation. However, MARS and SVM are more accurate than the others. Attention to structures of GMDH and MARS models declared that Froude number, drop number, and ratio of critical depth to height of step are the most important parameters for modeling energy dissipation. The best radial basis function was found that as best kernel function in developing the SVM.

     

Predication of discharge coefficient of cylindrical weir-gate using adaptive neuro fuzzy inference systems (ANFIS)

Settlement of sediments behind weirs and accumulation of materials floating on water behind gates decreases the performance of these structures. Weir-gate is a combination of weir and gate structures which solves them Infirmities. Proposing a circular shape for crest of weirs to improve their performance, investigators have proposed cylindrical shape to improve the performance of weir-gate structure and call it cylindrical weir-gate. In this research, discharge coefficient of weir-gate was predicated using adaptive neuro fuzzy inference systems (ANFIS). To compare the performance of ANFIS with other types of soft computing techniques, multilayer perceptron neural network (MLP) was prepared as well. Results of MLP and ANFIS showed that both models have high ability for modeling and predicting discharge coefficient; however, ANFIS is a bit more accurate. The sensitivity analysis of MLP and ANFIS showed that Froude number of flow at upstream of weir and ratio of gate opening height to the diameter of weir are the most effective parameters on discharge coefficient.