JOURNAL OF DAM AND HYDROELECTRIC POWERPLANT
Year:2016 | Volume:3 | Issue:8 |Papers Count:6

Nowadays, using oblique arms and columns in the structure of large hydrogenerators has many advantages such as thermal expansion without large mechanical stresses, foundation load reduction, oval air-gap prevention, and etc. Therefore, in this paper the use of oblique columns in the stator-frame of a large hyrogenerator in comparison to a traditional structure (i.e. stator-frame with radial columns) is investigated for the first time by developing a Finite Element inhouse program. The use of this inhouse software reduces the time of modeling of complex structures of large hydroelectric power generators and heavy analysis of commertial softwares significantly, and helps to develop a preliminary design and structural analysis of this type of generators. In this paper, the effect of number, dimensions, and angle of oblique columns on foundation loads and structural deformation in stator-frame are described and the optimum values are obtained. The results of this study show that, the application of oblique column technology has significant advantages in reducing foundation forces, reducing the natural frequencies, and uniform structural deflections.

Inaccuracy in earth fill dam’s analysis is one of the most important reasons of breaking this huge structures. assuming soil saturated only and disregarding time in rapid drawdown analysis cause errors in results of analyses that this article discuses about them. In this article Gulak earth fill dam has been modeled in three situations named saturated only, saturated-unsaturated with linear and nonlinear functions and the results show that modeling dam in saturated only situation not only effects on seepage results, but also causes about 25 percent error on safety factor of dam. In the fallowing this result achieved that by using nonlinear functions for permeability and vol.water content and choosing required parameters for van genuchten equation from laboratory result accuracy of analyses increases about 13 present than using a linear function. Also In rapid drawdown analysis to avoid shocking to the model, by using a transient analyze, drawdown of the reservoir was modeled as a process depending on time and results show that disregarding the time in rapid drawdown of reservoir analysis cusses about 4.8 percent error that this error increases to 13 percent by reducing drawdown rate.

Nowadays application of negatively buoyant jet as a known remedy for dilution of brine generated at desalination plants and effluents from industrial units is quite common. The initial momentum of the jet together with the buoyant force induced due to the density difference between the jet and the ambient fluid entrain the ambient fluid into the jet and dilute the effluent.This paper focuses on the experimental study of negatively buoyant jets at low densimetric Froude numbers, namely values between 3.44 and 11.35 in a co-flow. Total 36 tests for discharge angles of 30, 45, 60, 75, 90 and 115 degree with respect to horizontal is performed under three jet to ambient flow velocities between 6.33 and 20.92. Variables include three length scales relating to the jet trajectory including maximum penetration depth, horizontal distance of the nozzle to the point of maximum penetration depth and the horizontal distance from nozzle to the impact point. Empirical equations are derived for the geometrical length scales in terms of the densimetric Froude number, velocity ratios and discharge angle. The results are applicable to the design of submerged outfalls in shallow streams.

Nowadays, the evaluation of reliability and availability is one of the most important criteria in all engineering sciences. Due to the increasing of dependency of the life into the electrical energy, the availability of power system is very important for consumers. To achieve this issue, each of the main components of the power system must have adequate reliability. In this paper, reliability evaluation of the pumped storage plants using Markov process is carried out.For this purpose, at first an overview of the structure and the usage of the pumped storage plants is presented. Then, the main concepts of the Markov process model are reviewed and the appropriate model for reliability evaluation of a pumped storage plant is presented. Using the presented model and according to existing equipment, various indicators of reliability and also the possibilities of failure mode, full and half capacity of the plant are reported and sensitivity analysis is carried out to evaluate the effect of repair and failure rates of equipments on reliability of the plant.

Internal erosion and seepage in earth dams is known as a major parameters of dam break and investigation on these phenomena is of important issues in monitoring and surveillance of dams. Numerical modelling of seepage in dams’ body and determining the highest level of seepage line (phreatic) is one of the finest remedies in this field. Thereafter, in this research natural element meshless numerical model (NEM) along with the Sibson’s interpolation was used for simulating seepage through the body of Droodzan dam. At first, in order to validating the NEM, simulation of flow in an embankment obstacle was done. After ensuring about the accurate operation of the numerical model, seepage simulation in the Droodzan dam’s body was applied and the results were checked with the observation data of dam’s piezometers. Regarding an average less than 5 for the relative error, the accuracy of the NEM can be concluded. Findings of the study confirm the inexistence of interior erosion or piping in the dam’s body as far as the internal drain of the dam is working properly.

For optimal management of water resources in a catchment it is important to estimate the amount of water within a catchment by hydrological modeling. Hydrological modeling is very crucial in arid and semi arid areas because of limited water resources in these areas. In this study, the problems of hydrological modeling in these areas have been investigated and particularly is focused on effective rainfall. Then, a method is proposed to calculate effective rainfall and hortonian flow in a catchment. A hydrological distributed model, BTOPMC, is utilized and its performance is compared before and after applying modified hortonian flow formulation. Nash-Sutcliffe and volume error are the criteria used to calculate the model performance. Results have shown that applying modified equation for hortonian flow in BTOPMC have improved Nash-Sutcliffe and volume error about 12% and 10%, respectively that reflects its favorable impact on estimation water amount in a catchment by using BTOPMC.