Sharif Digital Repository

One of the most important problems in using wind energy is the estimation of wind energy potential of a region with acceptable accuracy. To use wind energy and convert it to electrical energy it is necessary to study the economical aspects of wind farm installation, and to choose an appropriate wind turbine to be installed in a region. To do such a study and to choose approperiate wind turbine, annual energy output of different wind turbines should be estimated in that region. The porpuse of this thesis is to develop new methods to estimate annual energy production of a wind turbine by using some of the parameters of wind speed pattern of a region such as wind speed average, wind speed... 

As long as the wind power penetration is low, overall dynamic behavior of a power system is determined by the interactions of system synchronous generators, but introduction of large amounts of new wind generation can affect the power system behavior. In this research, the impact of large wind farms on the small signal stability of power systems is studied. Because constant wind turbines are not very conventional in today’s wind industry and the dynamics of full converter wind turbines are isolated from power system, in this study only the doubly fed wind turbines are considered. In this order, a novel index is introduced to analyze the impact of doubly fed wind farms on the damping of... 

First and second law analyses of the pulse tube refrigerator cycle are performed in the present thesis. In this respect, mass, momentum and energy balance equations are employed to derive the system of governing equations. Three models have been resulted depending on the employed theoretical model to analyze the pulse tube and thermal regenerator sections. In the first model, the tube section governing equations have been descritised and finite volume technique has been employed to solve the equations. In the regenerator a linear trend was assumed for the pressure and temperature to complete the solution procedure. To improve the regenerator model, harmonic approximation technique has been... 

Iran is a country with bright cultural and historical background, and rich natural resources. It is also one of the important oil and gas exporters with a special geographical situation. The world energy needs are increasing rapidly and that requires higher oil production. On the other hand, oil is Iran’s most important source of revenue and the country is highly dependent on oil export. Islamic republic of Iran’s (I.R.I) 1404 program is visioning the country to be the first producer of material in the region, the second producer of oil in OPEC, and the third producer of gas in the world. Although critical conditions can slow down the process to achieve the vision, implementing this vision... 

The aim of this research is to consider the effect of geometric changes on pumping performance of two phase gas-fluid flow in a vertical pipe. The idea is to inject a light gas to the bottom of a tube full of fluid so we will obtain an upward flow due to density differences. Potential benefits of this device are numerous such as dredging of river estuaries and harbors, sludge extraction in sewage treatment plant, water treatment and many others. There are almost four distinct flow patterns which occurs in the rise pipe, bubbly flow, slug flow, churn flow and annular flow that each of them require special conditions. heat transfer between two phases, phase changes, mass and volume rate... 

Civil disobedience, as a protest mechanism, is one of the important topics discussed in political philosophy. The background of this idea dates back to Henry Thoreau, and later John Rawls played a very influential role in its theoretical development. The aim of this thesis is to conduct a critical study of this idea, focusing on the issue of its justification. The emphasis on the justification is placed firstly due to its central position in the discussions of normative political philosophy and secondly due to the controversial nature of civil disobedience in opposing official legal procedures. To this end, we have first discussed the definition of civil disobedience in two traditional and... 

CO2 as a green house gas plays a significant role in the global warming and weather changes. Absorption by means of amine solutions is the main industrial technique for separating of CO2 from gas mixtures. Hazards associated with high temperature during solvent recovery, large size of equipment, corrosion, solvent degradation, and other reasons has made researchers to look for alternative processes such as adsorption. The aim of this study was to synthesis and modify the nano adsorbent for CO2 capture. To fulfill this purpose, various nano silica structures were synthesized and the amount of adsorption of each sample was determined. To investigate the performance capability nano_adsorbents,... 

In this work, the segregation of solids in 2D gas-solid fluidized beds has been investigated carefully doing DPM approach. In this regard, various types of mixing index reported in the literature were need. Lacey index was chosen to study to study the segregation for different conditions. Effects of jetsam concentration, bed aspect ratio, solids density, restitution coefficient, initial arrangement and operation pressure and temperature were investigated. It was found that for beds with the mixed initial conditions, with an increase in the superficial gas velocity, the mixing index decreases and then increases. In addition, the mixing index increases with an increase in the jetsam... 

In this study, a comprehensive 2D mathematical model has been developed for the simulation of physical and chemical absorption of carbon dioxide in hollow fiber membrane contactors in the presence of nanoparticles. The model were developed by considering molecular diffusion in radial and axial directions as well as non-wetting conditions. Carbon dioxide absorption was simulated from a gas mixture containing carbon dioxide and air, that flows in the shell. Also, absorbent containing nanoparticles flows in tube side and counter currently. Effects of presence of nanoparticles were modeled by taking into account two prominent mechanisms proposed in the literature for mass transfer enhancement in... 

The main objective of the present work was to improve the turbulence in single drops using ferrofluids (magnetic nanoparticles) in the presence of uniform and oscillating magnetic fields. In this regard, magnetite nanoparticles ($\mathrm{Fe_3O_4}$) were synthesized by co-precipitation method, characterized using DLS, FT-IR, XRD, VSM, and TEM, and their stability was checked by UV-Vis. The obtained results indicate the proper synthesis of nanoparticles with a mean diameter of about 20 nm and by coating their surfaces by silane that were well stabilized in the base fluid. In the numerical section, the governing equations of transport phenomena for a single drop containing magnetic fluids were... 

Understanding mechanical behavior of engineering materials plays an important role in prediction of material response and helps to analysis and design of engineering structures. In this thesis, behavior of polymer concrete (PC) with three different epoxy resin ratios, ordinary cement concrete (OCC), lightweight concrete (LWC), lime mortar soil (LMS), four various types of sandstone and granite was investigated under uniaxial and triaxial compression. In order to predict the mechanical behavior of aforementioned brittle materials, their behavior was simulated in terms of axial stress and volumetric strain versus axial strain. For computation of volumetric deformation and softening behavior,... 

Power distribution systems are experiencing restructuring owning to the increasing trend of integrating renewable energy sources as well as privatization in the network. In this regard, the dependence of power generation by renewable energy sources on meteorological characteristics would challenge the conventional procedures of operating the system. Respectively, while the expansion of renewable energy sources would facilitate supplying the demand loads locally; the issues associated with the uncertainty and variability of power generation by these units should be addressed in future operational schemes of distribution systems. This condition has resulted in the development of the...