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

The purpose of the design of energy dissipaters is to dissipate part of the kinetic energy of the inflowing flow in order to return safely the flow to the downstream channel or river and prevent scour below spillways, chutes and sluices. However, surveys show that despite the numerous researches, there is a lack of research on the comprehensive study of hydraulic performance of stepped spillway with curve axis under downstream transition channel slope variation. Therefore, in this study, several physical models of curve axis stepped spillway with converging training walls were made and the impact of downstream transition channel slope variation on the hydraulic characteristics of this type spillway was assessed.

This study was conducted with the aim of investigating the hydraulic performance of stepped spillway with curve axis under downstream transition channel slope variation. The experiments were carried out in a rectangular flume with length of 15 m, height of 1 m and width of 2 m. The experiments were performed at different discharge rates from 0.015 to 2.1 times the design discharge and the physical model was tested under four different transition channel slopes of m=0, m=1:33, m=1:30, and m=1:27.

The results of the experiments indicate that in the converging steeped spillway with downstream transition channel slope variation, by decreasing slope of transition channel, the discharge flood in the maximum head allowed will go up. Also, it is find that in the range of H/Hd = 0.7, the discharge coefficient in the stepped physical model for all transition slopes was less than the smooth USBR model and in the range of 0.7 < H/Hd < 1. 3 there was a good consistency with the USBR model. However, with increasing the total water head, due to the spillway submergence the discharge coefficient for all transition slopes showed a descending trend and the spillway efficiency decreased in compared with the standard USBR ogee spillway. Moreover, the results showed that the models with slope of 0 and 1:33 are two models which can pass the probable maximum flood discharge in the maximum allowable height successfully But, the model dimension of physical model with downstream transition Channel slope of m=1:33 is smaller than that of m=0.Therefore, model with slope of m=1:33 can be selected as the most efficient model.

General qualitative and quantitative results of the present study are summarized as the fallowing: 1- In the converging stepped spillway by increasing total upstream head, the discharge coefficient will go up for each of the transition Channel slope (m) and until the downstream flow is at either supercritical or critical stages, the discharge coefficient is independent of variation of transition Channel slope. By contrast, at the submergence stage for the spillway, the difference in the discharge coefficient can be due to tailwater submergence occurring in the spillway. 2- Energy dissipation over converging stepped spillway decreases with increasing the discharge ratio, but model with smaller amount of transition slope (m) lead to decline more energy dissipation in higher discharge. 3- The model with slope of m=1:33 can be selected as the best model due to it’s ability to pass the probable maximum flood in the Maximum allowable head.

Proper design of the factors effective in hydraulic performance of drip-tape irrigation systems appropriate to the field and crop conditions is the key for their success. For this purpose, two important and sensitive parameters are lateral spacing and emitter spacing. Lack of correct selection of these two parameters affects the drip-tape irrigation system performance and it has a significant impact on the cost of implementing such irrigation systems. To investigate the effect of the lateral and emitter spacing on winter wheat yield, its components, and water use efficiency, a factorial arrangement experiment with two factors based on randomized complete block design was conducted at the Soil and Water Research Institute Station, Karaj, Iran. The investigated factors included lateral spacing (at 30, 45, and 60 cm) and emitter spacing (at 10, 20, and 30 cm). Results showed that in most of the studied indices, the 20 cm emitter spacing in different lateral spacing was the superior treatment. The results showed that, although the 30 cm lateral spacing led to the highest yield, but based on the results of economic analysis, the highest economic performance for a wheat field could be achieved at 45 cm lateral spacing, which could be adopted by farmers.

The ogee spillway with a curve axis has a longer crest length than the spillway with linear crest. Therefore, in a specific reservoir water level, it can discharge higher flow rate compared to a straight one and due to this reason is preferred in applicable plans. In this study, physical model of Germi-Chai spillway which include an ogee crest with a curve axis and converging training walls was constructed in scale of 1:50. The SCWMRI Soil Conservation and Watershed Management Research Institute, has led a research effort on it. For each of the convergence angles, including 60 and 90 ̊ in both symmetrical and asymmetrical situations, flow characteristics such as discharge, water surfaces, depths and distributions of pressure were investigated in the downstream channel of the spillway. Experiments conducted in varying flow discharge from 30% to 177% of  design discharge. Based on visual observation, at the toe and the end of straight portions of the spillway face, due to converging training walls, interference streamlines occurred which led to generate a rooster tail phenomenon. It was observed that in the convergence angle of 90°, rooster tail had been witnessed up to slightly more than 118% Qd. However, it saw nearly 147% Qd in 60° convergences. Moreover, it should be emphasized that due to asymmetric angles, closest wall to the rooster tail had more static pressure.

One of the appropriate procedures to increase discharge capacity of spillway in dams, particularly when increase of overflow width is not possible, is using labyrinth spillways. Due to the fact that a considerable portion of costs of dams is allocated for construction of spillways, the search for methods to optimize these structures becomes important. In the present research, the Cuckoo Search (CS) algorithm has been used to find the best geometry of the trapezoidal labyrinth spillway. For this purpose, concrete volume of the spillway was considered as objective function. Aslo, the spillway design considered different hydraulic constraints. Optimal parameters of this algorithm were selected by performing sensitivity analysis. Then, CS was run randomly for 15 iterations. The coefficient of variation and convergence speed obtained from random runs for the proposed algorithm were equal to 0.00001 and 1000 iterations, respectively. Finally, minimum value of the objective function of the proposed algorithm was compared to the results obtained from spillway design and the results of Genetic Algorithm (GA) and Differential Evolution (DE) proposed in the previous studies. It was found that the proposed spillway dimentions using CS resulted to 38.91% less concrete with respect to the real prototype. In the proposed model, other than reduction of the spillway concrete volume, the overflow discharge of the spillway was increased. On the other side, concrete volume reduction obtained by CS was 12% less than classic optimization algorithms (GA and DE). Considerable decrease (more than 1/3) in the volume of concrete in the proposed spillway indicates high ability of CS in solving the problems of optimizing spillways and the necessity of using it.