نشریه سد و نیروگاه برق آبی ایران
پیاپی 5 (تابستان 1394)

The high penetration of wind and solar resources and uncertainties in electricity generation from these kinds of DERs may cause problems in the operation of microgrids based on renewable energies and decreases the reliability indices. Implementation of high response generations such as hydro generation is one of the solutions to reduce the uncertainties. This paper presents a method for modeling a microgrid based on hydro, wind and solar generations. Reliability indices of the microgrid are calculated in presence of the lines connecting the microgrid to the upstream network. To demonstrate the effectiveness of the proposed method, detailed simulation results are presented and analyzed for 5 case studies.

In the elbow of morning glory spillway, the occurrence of cavitation is expected due to the high velocity and head, separation and pressure drop because of the geometry of curve. Hence, morning glory spillways are one of the most talented cases for the occurrence of cavitation phenomena. In this study the possibility of cavitation occurrence in the spillway’s elbow due to the hight change of vertical shaft is considered by using numerical modeling. To model the flow, “FLOW3D” software is used. It is investigated that numerical results are vwey near to experimental results. The pressure distribution for different length of vertical shaft by different rates of flow was evaluated. Later, the possibility of the cavitation occurrence was analyzed by obtaining the cavitation index. The results show that changing vertical shaft’s length, has a meaningful effect on the pressure values and cavitation index. The pressure increases by increasing the length of vertical shaft and the cavitation danger in reduces. Moreover, the pressure on the spillway’s elbow is increased by increasing the rate of flow.

The regenerative pump is a rotor-dynamic turbomachine capable of developing high pressure rise at low flow rates.In this paper, the CFX software is carried out to investigate the performance of a regenerative pump considering the modification in blade and casing geometry. For this purpose, the blade shape changes to the bucket form. In this study, the fluid flow is considered steady-state and frozen rotor technique is used. For the turbulence modeling, realizable k–ε model is chosen which is suitable for complex shear flows involving in rapid strain, swirl, vortices and locally transitional flows. Results of the numerical simulation show that the modified blade angle to achieve the maximum efficiency is about 40 degree. The performance curves of the new designed pump extracted from CFD simulation, have been compared with the experimental results of regenerative pump with radial blades. Results show that the efficiency of the pump with bucket-shape blades and new casing with central core is improved relative to radial blades one. Also, the head coefficient and the number of the flow rotations increases while the flow coefficient decreases. The turbulence intensity decreases during rotation of fluid using central core in the casing and as consequent turbulent losses is reduced.

One of the most important problems in water resources management is the optimal operation of reservoirs. In this research, a metaheuristic algorithm called Water Cycle Algorithm (WCA), has been developed in MATLAB software, with the purpose of optimal allocation strategies of a multi-reservoir system (Golestan and Voshmgir dams) located at Gorganrood Basin (North of Iran), for a five year period (from 2007-2008 to 2011-2012). Firstly, the performance of the developed model was investigated through several standard test functions. Next, the developed model is applied for monthly operation of Gorganrood multi-reservoir system. The objective function was defined as the “minimization of the total deficit for the study period”. In order to investigate the performance evaluation of the developed model, two criteria of reliability (temporal and volume) and vulnerability have been used. The results of the developed model were compared with Gravitational Search Algorithm (GSA) and standard operation policy (SOP). WCA,GSA and SOP models were capable to supply 97.73, 85.26 and 76.78 percent of Golestan dam water demand, respectively. For the Voshmgir dam, the mentioned methods could supply 97.06, 89.31 and 68.29 percent of water demand, in same order. The results revealed that WCA model was the best in optimal operation of a multi-reservoir system, among other studied models.

The main objective of load frequency control (LFC) is to return the steady-state frequency error to zero. Frequency aberrance from the nominal value and supplying active power consumers are the main reasons of the change of water entered to turbine. In this paper the state equation and transfer function of the load-frequency control with hydro-turbine is described. Small signal stability together with the effects of parameters such as inertia constant, water starting time and constant speed on the dynamic behavior of the power system have been investigated. Also, the application of transient droop compensation (TDC) in response to water turbine by eigenvalues analysis and behavior dynamic simulation of the power system is shown. Also, using transfer function, PID controller for load-frequency control in power system is designed and the change of the gain controller is investigated. The simulation results reveal that the response of the proposed controller is better than the response of the conventional integral controller.

This paper presents a finite element model to get a reliable estimation of the effect of sediment inertiaon seismic performance of concrete gravity dams considering interaction effects. The equivalent fluid assumption is used to show the sediment behavior. Water is assumed as compressible, inviscid fluid with small amplitude displacements and the dam is modeled as an elastic solid. Due to the complexity of a dam­reservoir-foundation system, the finite element method is an efficient tool for studying the dynamic response of concrete gravity dams in which the different boundary conditions can be simulated more appropriately. In order to seismic analysis, a computational procedure for two-dimensional finite element analysis of system subjected to seismic excitations is developed using Ansys software. The analysis is carried out in time domain considering dynamic excitations. Newmark time integration scheme is developed to solve the time­discretized equations which is an unconditionally stable implicit method. To demonstrate the effect of sediment on seismic performance of concrete gravity dams, the response of Pine Flat dam due to El Centro ground motion is presented as a case study. The model was analyzed and compared with the cases in which the reservoir is assumed without sediment and with 20% volume of sediment. Obtained results show the amplification effect of sediment on seismic response of model.