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Showing 24 results for Weir
Numerical Investigation of Guide Walls Geometry at the Entrance of Dam Spillway (Case Study: Karun-3 Dam)
M. Sadeghi, T.o. Naeeni, F. Kilanehei, M. Galoie,
Volume 26, Issue 3 (12-2022)
Abstract
One of the most important hydraulic structures in a dam is the spillway. The design of the ogee spillway crest is based on the lower profile of the free-flow jet passing through the sharp-crested weir. When the downstream ogee spillway profile for the design discharge conforms to the lower profile of the free-jet passing through the sharp-crested weir, the pressure on that surface of the spillway becomes zero. In this study, the design of the ogee spillway was performed initially based on both two- and three-dimensional numerical modeling and then compared to the USBR standard method. The comparison of the final numerical and analytical results showed that although the vertical two-dimensional outputs were completely in agreement with the USBR standard profile, the three-dimensional profiles were different because in this model, guide walls were not considered. According to the analysis, if the flow entering the spillway is parallel to its axis, the lower profile of the sharp-edge spillway will be in complete agreement with the standard profile. Since, the design of guide wall geometry for ogee spillways is carried out using physical modeling which iteratively revises during a high-cost trial and error procedure, this research based on the case study of the spillway of Karun-3 dam has been tried using numerical modeling. The closest geometry to the geometry of the overflow guide wall was obtained which creates the least difference in transverse velocities. In this way, the design of guide walls can be done with more accuracy and low cost in comparison to physical modeling.

Comparison of Hydraulic Efficiency of Arched Non-linear Weirs in Plan Using GEP and SVM Neural Networks
M. Majedi Asl, T. Omidpour Alavian, M. Kouhdaragh, V. Shamsi,
Volume 27, Issue 3 (12-2023)
Abstract
Non-linear weirs meanwhile economic advantages, have more passing flow capacity than linear weirs. These weirs have higher discharge efficiency with less free height upstream compared to linear weirs by increasing the length of the crown at a certain width. Intelligent algorithms have found a valuable place among researchers due to their great ability to discover complex and hidden relationships between effective independent parameters and dependent parameters, as well as saving money and time. In this research, the performance of support vector machine (SVM) and gene expression programming algorithm (GEP) in predicting the discharge coefficient of arched non-linear weirs was investigated using 243 laboratory data series for the first scenario and 247 laboratory data series for the second scenario. The geometric and hydraulic parameters were used in this research including the water load (HT), weir height (P), total water load ratio (HT/p), arc cycle angle (Ɵ), cycle wall angle (α), and discharge coefficient (Cd). The results of artificial intelligence showed that the combination of parameters (Cd, H_T/p, α, Ɵ) respectively in GEP and SVM algorithms in the training phase related to the first scenario (Labyrinth weir with cycle wall angle 6 degrees) were respectively equal to (R2=0.9811), (RMSE=0.02120), (DC=0.9807), and (R2=0.9896), (RMSE=0.0189), (DC=0.9871) in the second scenario (Labyrinth weir with a cycle wall angle of 12 degrees) it was equal to (R2=0.9770), (RMSE=0.0193), (RMSE=0.9768), and (R2 = 0.9908), (RMSE = 0.0128), (DC = 0.9905), which compared to other combinations has led to the most optimal output that shows the very favorable accuracy of both algorithms in predicting the coefficient the Weir discharge is arched non-linear. The results of the sensitivity analysis indicated that the effective parameter in determining the discharge coefficient of the arched non-linear Weir in GEP and in SVM is the total water load ratio parameter (HT/p). Comparing the results of this research with other researchers revealed that the evaluation indices for GEP and SVM algorithms of this research had better estimates than other researchers.

Experimental Study of discharge - head Flow Rate Relation through Combined Structure Sharp Crested Rectangular Weir with Multiple Square Orifice
S. Barani, M. Zeinivand, M. Ghomeshi,
Volume 27, Issue 4 (12-2023)
Abstract
In this study the effect of orifice number and dimensions in combined structure sharp crested rectangular weir with multiple square orifice was investigated. For this propose, some experiments in different flow rate, different orifice number and dimensions were done. The results showed that by different orifice numbers and dimensions, flow discharge increased at the same upstream flow head. This increasing trend was observed in all numbers and dimensions of the investigated experiments. The analysis of the quantitative results showed that by increasing the number of orifices, the discharge rate through the combined structure of weir-orifice was increased on average 2.06 liters per second and by increasing each centimeter of orifice dimensions, the discharge was increased by 2.82 liters per second. Also by calculating the percentage of flow rate increase, it was observed that by adding the orifice number, it increases by 18.7% and by increasing the size of the orifice by one centimeter, the flow rate increases by 28.1%.

Laboratory Investigation of the Effect of Wall Slope on the Discharge Coefficient of Trapezoidal Arced Labyrinth Weirs
M. Majedi Asl, T. Omidpour Alavian3, M. Kouhdaragh,
Volume 27, Issue 4 (12-2023)
Abstract
Weirs of the labyrinth have some advantages including the high coefficient of the irrigation of weir and the low fluctuation of water when the flow passes over the crest of the weir. In this research, the flow rate coefficient has been investigated by changing the weir geometry in terms of wall slope, arc cycle angle, and nose length change in the upstream and downstream of each cycle of the trapezoidal arc labyrinth weir. A total of 240 tests have been performed on 16 different physical models in a channel with a width of 120 cm and a narrowing of 20 cm from each wall. All models have been compared with the control model (normal labyrinth weir) (80A). The results showed that the 80B weir with an arc cycle angle of 20 degrees and without wall slope has a better performance than other weirs. Also, the weir with an arc cycle angle and a wall slope of 20 degrees in a divergent form (D20B) in the area (Ht/P) <0.31 has a better performance than other weirs with an arc cycle angle of 20 degrees, and after this area, the weir with a wall slope of 10 degrees has performed better in divergent form (D10B). In weirs with different cycles at an arc cycle angle of 20 degrees, the labyrinth weir with 5 cycles (N5) has performed better up to the point (Ht/P)=0.36. Also, at the maximum point, the difference is 13 and 17%, respectively, compared to the 4-cycle and 3-cycle weirs.

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