مجله هیدرولیک
سال هشتم شماره 1 (بهار 1392)

Adequate determination of dam overtopping risk by considering random variables uncertainty is an important issue in the design of earthfill dam. Therefore, ignoring these uncertainties cause overestimation or underestimation of dam height. Uncertainties of rainfall and flood have more effect on overtopping risk. In this study, flood hydrograph was generated by considering uncertainness of rainfall and rainfall-runoff parameters with using developed model named RPG (Rain Pattern Generator) and HEC1 models. In addition, overtopping risk of Jamishan dam was estimated by using the Monte Carlo simulation (MCs). The effect of main variables such as spillway width, dam height and normal water level on risk of dam overtopping was evaluated by considering related variants. Results show that average variation rate of dam overtopping risk was 0.03 based on unit variation of spillway width. Also average variation rate of overtopping risk was respectively 3.1 and 1.56 based on unit variation of normal water level and dam height. Therefore, variation of flood control volume is more effective on risk of dam overtopping than spillway capacity.

This paper introduces a metaheuristic optimization model for pipe networks on the basis of the notion of dynamic threshold. At first, the problem cost function, constraints and the procedure for coupling the hydraulic simulation model to the optimization are developed. Then, a simple version of binary genetic algorithm is exploited to solve the problem which is equipped with the dynamic threshold method as one of the optimization operators. By means of this operator, as the optimization progresses, the problem decision space is gradually contracted according to the search history. This increases the chance of finding the global optimum design as the search space is more and more condensed by the dynamic thresholds. The proposed scheme is then applied against two benchmark examples upon which, the method is investigated and compared with the previous studies. The results show that the incorporation of the dynamic threshold into a simple genetic algorithm can make it computationally efficient as well as more promising in finding the global optima.

In this paper the measurement of flow pattern along the mixing layer bounding a separation zone using SPIV is peresented. Furthermore, spatial characteristics of the mixing layer have been visualized using uranine dye injection and UV light method. Results of the measurements showed that the maximum turbulent kinetic energy and Reynolds stress occur where the mixing layer characteristics changes.Immediately downstream of the side obstacle the power spectral density of the turbulent fluctuations agrees well with -5/3 slope which is indicative of the 3D turbulent flow. By going downstream, the turbulent energy of the low frequency fluctuations decreases by -3 slopes. This shows that 2D flow structures are dominant. At the reattachment zone, the energy distribution for most of the frequencies decreases by -5/3 slope again. In this part, the turbulent flow generated by the bed friction is responsible for three dimensionality of the turbulent flow. Interaction of two separation zones changes characteristics of the temporal flow structures inside the mixing layer.

The shallow mixing layer bounding a separation zone is a prominent but poorly understood hydrodynamic feature. To investigate characteristics of the separated shallow mixing layer generated by a single side obstacle, experimental measurements were obtained by means of high resolution surface particle image velocimetry (SPIV). Results indicate that unlike the free shallow mixing layers and also mixing layers bounding a deep circulation zone, the velocity profiles are self similar just in a short distance downstream of the groyne and also near the reattachment region. Furthermore, growth of the width of the mixing layer with downstream distance shows a two-phase development. The firstphase is exponential until a distance about 3.5L, where L is the abutment length, followed by a second-phase characterized by a linear pattern. The growth rate of the first stage is higher than the second phase.

Stilling basins are used for dissipation of kinetic energy downstream of hydraulic structures such as drops, weirs, chutes and gates. In this study hydraulic jump characteristics in presence of a submerged vane was evaluated in a flume, 12 meters long, 0.4 meters wide and 0.4 meters high. The heights of vanes were 1.1, 2.2, 3.3 and 4.4 centimeters and they were located in front of the flow with an angle of attack of 10, 20, 30 and 90 degrees. Sixty four experiments with upstream Froude numbers in the range of 3 to 8 and four different discharges of 15, 20, 25 and 30 liters per second were used in this study. Results show that use of submerged vanes can decrease length and downstream depth of hydraulic jump up to 25 and 10 percent, respectively. The bed roughness under this condition increase the bed shear stress 12 times higher compared to smooth bed and this condition occur for the vane with 4.4 centimeters hight and angle of attack of 90 degrees.

Flood routing is considered to be one of the most significant issues in many water engineering projects. Hydraulic flood routing methods particularly in branched rivers and rivers with unknown intermediate basin are commonly used because of their high accuracy compared to hydrologic methods. These methods need providing cross sections and bed slopes at all reaches of the flow path which requires a lot of time and budget. On the other hand, hydrologic methods such as the Muskingum method are very simple and require much less data and time. The Muskingum method is one of the common hydrologic flood routing methods of rivers. In order to apply this method for a certain reach, two basic parameters have to be determined. These parameters are functions of the river specifications and usually are estimated by using trial and error combined with a curve fitting technique. The method is quite simple but it is restricted to single reach problems. In this study, a method is proposed in which the calibration (parameter estimation) is performed by using the genetic algorithm, which is capable of solving complicated problems including more parameters. The proposed method is applied for single and multiple reach problems in addition to a river with lacking data of the intermediate catchment hydrograph. In all applications, comparisons of observed and computed outflow hydrographs indicate satisfactory agreements.