Sharif Digital Repository

Study of the structural flexibility of large-scale wind turbine components on aeroelastic performance is important under the existence of critical atmospheric conditions. Prediction and control the critical deformations, identifying maximum local deformation and modeling the forces involved, are required. Aeroelasticity analysis is a suitable method for studying the coupling effects of wind turbine aerodynamics, dynamics and structures. This research has been done by modeling wind turbine components including blades, hub, nacelle and tower, taking into account aerodynamic couplings, dynamics and structures. Considering the large scale of reference wind turbine, nonlinear equations have added... 

High swirl combustors with circulative structures in the flow field, have a highly flame stability with a wide range of operating conditions. In this study, Sharif Gas Turbine Model Combustor (SGTMC) which is a double high swirl burner, was investigated experimentally and numerically. In experimental studies, SGTMC with different settings of swirlers is investigated in terms of flame lean blow-out(LBO), wall temperature, the exhaust gas composition and pollutant and also flame geometry parameters. Setting of burner are changed by variations in air fraction between inner and outer air inlets or swirlers’ vanes degrees and flow rotation directions. The results indicate that the concentrations... 

In line with the energy policies of the country, which is based on the development of the natural gas system, the natural gas transmission sector has also had a significant expansion during this period, especially in recent years. On the other hand, the promotion of energy efficiency has been a major issue in energy policies and programs. Therefore, the necessity of expanding and developing the rational use of energy has been considered more than ever. The use of energy recovery technologies will be an effective step in this regard. Owing to the wide expansion of gas pressure regulating stations in Iran and the high potential losses in pressure relief valves, substituting an expansion... 

Considering the continuous growth of renewable energy sources in electric grids, the importance of utilizing simple, generic, and upgradable models for different network stability studies is increasing. In recent years, generic and standard wind turbine models for transient and short-term frequency and voltage stability studies have been developed. In this regard, researchers are still working on promotion of the generic models, especially to expand them for unbalanced transient studies, improve the transient response, and include inertia response. In this thesis, different methods for generic modeling of wind turbines are surveyed and the development procedure of WECC and IEC generic model... 

In this dissertation, two parts of research has been conducted. First, with the aim of minizing the fluctuations of power output of wind farms and the need for energy storage system, optimization of wind farm (WF) layout has been studied. Deployment of battery energy storage system (BESS) is a viable option to alleviate the inherent power fluctuation of wind farms. In this thesis and based on the power spectrum density (PSD) theorem, it is hown that the WF layout affects not only the total harvested energy but also the level of power fluctuation, which in turn influences required capacity of battery energy storage system (BESS) needed to mitigate the inherent power fluctuation of the wind... 

Low effiencies of equipments and lack of forecasting heat integration in some oil regions are the reasons of primary energy losses in these regions. Also there have been difficulties in providing electric power demands in regions separate from the state electricity network which is a barrier in front of exploiting all the potentials of the region. This research introduces a model that can lead to selection of optimal configuration of equipments and units in order to establish a CCHP system that answers variable electric, heating and cooling demands ensuring a safe margin of power generation. The model simultaneously has the ability to select between existing and new installable equipments.... 

The lubricating oil is commonly used to cool down the moving parts of turbine gas systems. In many applications, this oil is cooled down using a recirculating water circuit. The water is then cooled down using an air-cooled heat exchanger. Any deficiency in aerothermodynamic design of such heat exchanger would result in high temperature of gas turbine moving parts such as bearings. Obviously, this mal-performance has adverse effect on the lifetime of these parts and their maintanence aspects. Since the good performance of air-cooled heat exchanger has numerous advantages for the performance of related gas turbine unit, it is mandatory to design these heat exchangers in minimum sizes and... 

Wind turbines have been the subject of many researches in recent decades. Optimization and continuous improvement of these systems play a decisive role in the development and exploitation of wind farms. Wind turbines can be studied from several aspects such as structure, dynamics, aerodynamics, electricity and control. In this research, robust power control of the wind turbine has been studied with emphasis on accurate 2 DOF mechanical and aerodynamic modeling. Aerodynamic coefficients of the turbine have been calculated using the numerical methods and the effect of this numerical modeling has been studied in comparison with the analytical methods on the turbine power control. Several new... 

Offshore wind energy is widely recognized as a renewable energy source that has the potential as a global energy source. Although the use of coastal wind turbines has been successful, it has been challenged in terms of visual, acoustic and environmental impacts. In addition, in terms of technology, it is difficult to achieve high levels of energy from coastal wind resources due to low annual average speed; Therefore, the wind energy industry is trying to make more use of the deep-water wind resources. However, before developing these types of deep-water turbines, economic challenges and technical problems must be resolved. Mooring failure is one of the major issues in the design of offshore... 

In this thesis, a new wind turbine scheme based on Electrically-Excited Synchronous Generator (EESG) and diode-bridge rectifier is proposed and developed. This new scheme is mainly based on the idea of generator excitation current employment as a means of wind turbine control. That is why the new scheme is called Excitation Controlled Synchronous Generator (ECSG) wind turbine. The most important aspects of the proposed ECSG wind turbine scheme are cost-effectiveness, simplicity and higher reliability, as well as higher efficiency. Considerable cost reduction for the converter unit of ECSG wind turbine is so important since costly converter has been one of the main challenges of the... 

Nowadays, science and technology, once again, lead approach to renewable natural resources to access energy due to fossil resources restrictions. Growing need for energy, being concerned about exhaustion of fossil resources, environmental pollution caused by burning fossil materials, climate warming and the greenhouse effect and etc. are obvious evidences of aforesaid fact. On the other hand, oceans and seas are large reservoirs of energy which comes from sunlight, geothermal resources, Earth's rotation and gravity by means of mechanical and hydrothermal processes. During the years, many ideas were conducted to achieve and mine the mentioned enormous energy potential of the oceans and seas.... 

Over the last decades the attention of the most modern countries about usage of wind has grown due to the recent crisis of energy. This renewable energy source offers a cost effective solution for electricity production. Wind energy is the best candidate among other sources due to wind turbines technology reliability. In order to gain maximum power from wind turbines, their size becomes relatively large, which creates more complexity in their repair and maintenance, furthermore Wind turbine downtime is outside the expectations, which is more costly than corrective maintenance, therefore in order to minimize sudden downtimes and related huge maintenance, a reliable monitoring technique must... 

Thermodynamic analysis of a system is a method for recognizing the type of energy transmission between system and surrounding environment. It also helps to find how macroscopic properties of the system change during this process. This analysis is based on first and second laws of thermodynamic. The first law expresses conservation of energy and inspects quantity of energy transmission but doesn’t evaluate quality of energy. The second law expresses quality of energy and the ability of doing work. The analysis that uses both of the laws is named exergy analysis. By exergy analysis the place of useful energy losses in the system can be determined. In this research the exergy analysis of... 

Axial compressor design is a very complex and expensive process. In general, for design and development of a new axial compressor, manufacturing companies usually intend to employ an existing and successful axial compressor as an starting point and modify and upgrade it. In this regard, dimensional scaling is a common method for derivative axial compressors. The goal of dimensional scaling is to get a different capacitywhile minimizing the development time and cost. In this thesis, theNASA eight stage transonic axial flow compressor is chosen as the base model for dimensional scaling to lower and upper size of its original dimension. The scaled compressor is analyzed with a quasi 2-D code.... 

An improvement of thermal efficiency of modern gas turbines is achieved by increasing turbine inlet temperatures. One of the methods of turbine cooling is to form a film layer on the external surfaces of the blades, so that they can work at high temperatures. Most of the studies concentrate on flat plate geometries with injection through slots or rows of holes. Turbine blade surfaces usually have curvatures which seem to alter the flow field significantly on the film-cooled surfaces. However, there are few reports which investigate the effect of curvature on three-dimensional jet flow injected into the turbulent boundary layer over a curved surface. The surface curvature and the blowing... 

Recently, the brushless doubly fed induction generator (BDFIG) has been proposed to be used in wind turbines due to variable speed operation with fractionally size power electronic converter and without brushes and slip rings. In this thesis, for the first time, LVRT capability of BDFIG has been assessed regarding the grid codes and several approaches have been suggested for improving it. Firstly, the steady-state performance of the BDFIG in different operating modes has been investigated and required tests have been performed. In addition, a new operating mode named as "double cascade mode" has been introduced. The fault-on performance of BDFIG has also been studied by means of torque-speed... 

Nowadays, the use of gas turbines with low capacity have acceptance in large quantity. This type of gas turbines with a capacity of approximately 5-200kW are known as microturbines. This type of turbines due to the existence of limitations on increasing of turbine inlet temperature and compressor pressure ratio has low efficiency compared to the turbine with high capacity. Therefore the use of a recuperator in the cycle is necessary. Optimum design of heat recuperator has important effect on improving of gas turbine cycle efficiency. In this project for optimum design of heat recuperator, the effect of recuperator on gas turbine cycle efficiency is studied. By determining geometric... 

This thesis consists of three main chapters. The first chapter is about describing principles about offshore wind turbine, principal concepts. This chapter also explains about advantages and disadvantages of installing wind turbine at offshore fields, and economical aspect of this kind of wind turbine farms. In the second chapter,anumerical method is used to investigate a SeaStar tension leg platform offshore wind turbine response behavior in parked condition. This code considers nonlinearities due to changes in tension of tethers. Wave forces are calculated adopting the Airy wave theory. Furthermore, shear turbulent wind is exerted on tower, with maximum speed 30 m/s on the hub. Since surge... 

Gas turbine is one of most widely used in power plants to generate electricity or mechanical power options in the industry , which is having its own advantages and disadvantages . if the turbine use simple , efficiency is generally below 33%. . After installing and employ , these turbines produce efficiency less than their nominal amount . The methods no change in structure exist that increase the efficiency or power of the turbine to acceptable level .In this thesis, gas turbine and to improvement performance methods has been studied . gas turbine with the methods are simulated to obtain the effect of each method in different environmental conditions . Economic sensitivity analysis... 

Rapid growth in energy consumption and environmental concerns over conventional power generation technologies has increased the need for alternative energy sources. Kinetic hydropower has been available for decades, however, despite its minimal environmental impact, commercialization has been limited. The main purpose of the first part of this thesis is investigation of flow properties near the convergent-divergent nozzles with various geometries. Two parameters that studied include variation of drag force on body and mean velocity of water flow in middle cross section. In the second part, we studied a horizontal marine current turbine (which its geometry is taken from a NREL wind...