نشریه سد و نیروگاه برق آبی ایران
پیاپی 9 (تابستان 1395)

Rubber dams are hydraulic structures that are constructed on rivers which are cheaper than similar structures. In this research, rubber-dam modeling was performed by 3 different pressures inside the tube (1.5 to 3 KN/m2) and 3 discharges (1.5 to 5.5 lit/s) by Flow-3D software. A rubber dam, located on an open channel, was verified using an experimental model. The correlation coefficient resulted from fitting numerical model results and physical quantities, was 0.9357, which represents high accuracy of the numerical-model results. Maximum discharge coefficient was about 0.46 in discharge of 5.25 lit/s and pressure of 3 KN/m2. It was revealed that 100% increase in internal pressure of the tube leads to 5% increase in discharge coefficient. While, the same amount of discharge increase will lead to an increase of more than 25% in discharge coefficient. The H/Dh parameter was recognized as one of the effective factors on discharge coefficient. The modeling results showed that 31% increase of this parameter will increase discharge coefficient by 70%. Also, effective factors on flow velocity through the rubber dam were evaluated.

The safety of concrete gravity dams as massive structures is very important issue. In complex situations, the stability analysis of concrete gravity dams is not possible by conventional software, so should other methods be used. In this study, taking into account various parameters in the dam and foundation contact, the factor of safety using the finite elements with strength reduction method is determined. In this method, the strength parameters are reduced until the instability starts. By this method the sliding stability of three different dams has been investigated. In the first model the geometry of the dam-foundation contact is horizontal; the second has unconventional contact geometry. In the third model there are two instability mechanisms. In this case, dam can slide on the horizontal surface of the contact or the instability can occur in the foundation beneath the dam. It should be noted that the stability of the last two models cannot evaluate by the conventional stability analysis. However, using the proposed method their stability safety factors can be accurately determined.

This study has been conducted to evaluate the effect of mechanical properties of materials of isolation layer to improve the seismic response of gravity dam. To achieve an innovative solution in the present study, a soft layer is assumed to be attached to the upstream face of the dam. This layer which partially absorbs the incident pressure waves from the reservoir is referred to as the isolation layer. Due to the finite thickness and geometry of the concrete dam, the reflected waves from the downstream face of the dam and the dam-layer interface may slightly alter the equivalent value of the wave reflection coefficient at the upstream face of the dam.The Koyna dam is modeled as a case study to indicate the effect of isolation layer on seismic response of gravity dams.
A flexible layer attached to the upstream face of dam and the upper level of foundation under different thickness and height is considered. The response of un-isolated dam is compared with an isolated dam under various condition. Consider to obtained results, it is revealed that the isolation layer can have the reducing effect on responses of dam model because of damping the induced hydrodynamic pressure due to earthquake.

Generating discrete fractured network (DFN) at the base of geometrical and physical characterizations of discontinuities is one the most important methods to study the discontinuity system effect on rock mass. In this paper characterizations of 639 discontinuities surveyed in powerhouse cavern of Rodbar Lorestan project have been studied by scanline and areal sampling methods. Based on the processes and corrections of bias types, one bedding and three joint sets were existed in the site. The tectonic activities and direction of principal stresses have caused differences in trace length and spacing characteristics and the probability distribution function of joint sets based on their genetic types. The calculated average trace length by scanline and areal method are very close for one joint set and for the other one the difference is 26%. The density differences between circular and rectangle sampling windows for joint sets J1 and J2 are 7% and 15%, respectively. The differences between actual and apparent intensity in circular sampling for joint sets J1 and J2 are 12% and 14%, respectively. Meanwhile, the volumetric intensity calculated by various methods have shown that the calculation of this characteristic is very difficult in the field.

The main endeavor in this paper is to study on 32 fundamental Iranian dams and investigating efficiency scores and also ranks of placed powerhouse on them by using data envelopment analysis and stochastic frontier analysis methods in 1393. Applying copula technique in the stochastic frontier analysis is an advantage to our study between similar activities. EMS and MATLAB programs have been used to evaluate efficiency of centers by any models. To have a unique result, we use the average of scores by four models in any center and it is seen that Sefidroud has been selected the best efficient center and also Taleghan is in the last order. Also for comparing results of the mentioned four models, we use correlations which are based on ranks of the hydroelectricity centers in every model. The minimum compatibility is between results of BCC and SFA-Clayton models which is 63.86% and the maximum compatibility is between results of standard SFA and SFA-Clayton models which is 99.41%. Meanwhile compatibility between results of CCR and BCC models is 72.10%.

In this paper after simulating a dam with GeoStudio software, the place of phreatic curve, intersection it with the downstream slope, the drop before the core and also passing through it, were analyzed and the results were compared with Rezk's experimental solution. Also, the effect of changes in the water level of the reservoir, the relative value of the different permeability and changes of the slope of the upstream and downstream on the phreatic curve have been analyzed. The results of this research show that phreatic line with the relative value of the same permeability is not dependent on the value of the permeability. Also, the relative value has been assumed (kc/kd) = 0.1, in Rezk's experimental solution, which has a 25% error. We have reduced the error to less than 3% with the extension method of Rezk in the lower Permeability ratios. In this case, Rezk's experimental solution and the results of finite element method show excellent agreement. Also it was determined that the error rate changed by changing the geometry of the dam so that the error decreased from 43% to 25% by reducing the slope of the upstream.