Sharif Digital Repository

People’s interaction and their impressions on each other has been one of the specifications of the societies; which has been studied and are used in various ways for widening the circle of thoughts and introducing the concepts. Low cost of the use of this method and feasibility of controlling the sensitivity about the considered issue (and some times the source of the issue), are the advantages of this advancement. This issue has also had numerous usages in the marketing and business. In this thesis an approximate algorithm has been designed for extracting the structure of the network, diffusion rate and the effective nodes in the network. This algorithm is... 

With the increasing number of applications in internal combustion engines, environmental impact and air pollution caused by emissions has been much attention. Natural gas is a promising fuel for limiting pollution laws in many countries. The use of fuel with a higher ratio of hydrogen gas to carbon pollution reduction motor. In this context and with regard to development policy and also due to the diversity basket NGV fuel, fuel injection, has been modeled analytically and numerically in a direct injection engine. In this study, an analytical model for spray injection fuel delivery and is dissolved. The resolution of the method of separation of variables is taken. The effect of the nozzle... 

Today, oscillating heat pipes play an undeniable role in energy recovery due to their high thermal capacity. Studies show that the working fluid plays a more effective role in improving the performance of the oscillating heat pipes. In this study, a model is proposed to determine the optimal concentrations of Fe3O4-MWCNT/DI Water hybrid nanofluid based on NSGA-II multi-objective optimization algorithm. The Thermophysical properties of the fluid have been optimized to obtain the concentrations that provide the highest thermal conductivity and specific heat capacity and the lowest dynamic viscosity and density for hybrid nanofluids. Then a number of these concentrations¬ have ¬been selected... 

Due to the wide application of plate-fin heat exchangers in various industries such as the petrochemical industry, aerospace industry, air conditioning systems, separation and liquefaction of gases, especially natural gas, boiling, condensation, and transportation industries, proper design of these heat exchangers is necessary. Most of the previous researches in the field of heat exchanger modeling has been done in single-phase mode. The two-phase modeling has been performed, often thermodynamically, and the effects of turbulence and surface tension have been ignored. Thus, in the present study, numerical modeling of the two-phase plate-fin heat exchanger is presented. In this project,... 

- Pulse-compression is one of the spread spectrum techniques that allows a radar to simultaneously achieve the energy of a long pulse and the resolution of a short pulse. The long pulse band-width is increased by phase or frequency modulation, then this modulated long pulse is compressed by matched filter of the receiver. A simple class of pulse-compression waveforms is Binary phase-coded pulse that uses rectangular sub pulses. When the transmitted signal encounters a moving target, the performance of radar degrades due to Doppler frequency shift of received signal. Binary codes have high side lobe levels for long Codes, so to solve this problem the Quadriphase-coded pulse that constructed... 

The potential of phase change process in liquids at microscale has been a favorite for the scientists to fabricate this type of micropumps. To hold unidirectional flow in microchannels usually nozzle-diffuser arrangement is used. Due to the existence of difference in pressure drop in the nozzle and diffuser sections, one can see unidirectional flow through diffuser direction. The objective of this article is to analyze analytically the thermo-hydrodynamic behavior of the Isopropyl Alcohol (IPA) bubble of a phase change micropump. Considering the simultaneous effects of hydrodynamic and thermal characteristics of the bubble in the bubble generation chamber, and temperature-saturation... 

One of the most important environmental problem across the world is global warming due to increase in greenhouse gas concentration in atmosphere. The main objective of this thesis is to try to find some ways that lead to stop or decrease, increasing trend in greenhouse gas emission, espicialy CO2. The investigation of the sources of emission of CO2 and proposed methods to decrease the rate of the emission, reveals that sepration of CO¬2 from combustion products and its storage is the only promising solution of this problem. The common feature of all propsed methods for elimination of CO¬¬2 from combustion gas, is the presence of a separation step. The addition of this separation step to... 

Transmit waveform plays a significant role in active sensing systems. High speed and off-the-shelf processors, digital arbitrary waveform generators, and solid state transmitters have paved the way for an increased capability to adapt the transmit signal and the receive fil-ters with respect to (w.r.t.) the illuminated environment. In this thesis, we have considered the waveform design problem for different scenarios, in two parts. Firstly, we have con-sidered the problem for the extended target model in single-input single-output (SISO) radars. There, we have assumed known target impulse response (TIR) with an unknown reflection factor and found the waveform corresponding to the optimal... 

Natural gas liquefaction is a gas refrigeration technology, which enables the export of natural gas worldwide, in liquids formed and stored at very low temperatures. In this project, a plate-fin type of heat exchanger, which is used for liquefaction of natural gas (mainly methane) at very low temperatures, has been investigated. The most important and effective part of this gas refrigeration cycle is the cold box heat exchanger. The cold box consists of two or more floors in which some sorts of fins are installed in each floor. In this simulation, the three-sream heat exchanger is designed in such a way that the input temperature of the natural gas is about 200 K and the output is 145 K at a... 

Tubular sections and consequently tubular joints in construction of steel structures in the form of space frames is widely used in ground and marine structures, including offshore jacket platforms. The passage of part of the life of the existing offshore platforms has caused cracks in various parts of the joints of these structures due to various reasons, the most important of which is fatigue. In this thesis, by adopting numerous numerical studies and validations with some cited experimental papers, the principles governing the proper buckling behavior of tubular members focusing on the conventional geometries of Persian Gulf platforms as well as the behavior and local flexibility of... 

One of the most important parts of vehicles and most of mechanical machines is power transmission system, especially the Gearbox used in them.In order to optimize the use of energy, especially fossil fuel, researchers are looking for new mechanisms to refine the operation of vehicles and other machines.One of the mechanisms which absorbed researcher’s attention during recent years is the Continuously Variable Transmission. By using these gearboxes which are replaced with older samples, we can have the continuous range of aspect ratio between two constant values. This important property causes the decrease of the use of fuel.In recent decades many manufacturers have used different kinds of... 

Airlift pumps are widely used in numerous industries for different applications such as transmission of viscous fluids (heavy hydrocarbons of oil), pumping of corrosive liquids and so on. In general, parameters which affect the efficiency of an airlift pump can be classified into two major groups. The first group is the designing parameters such as the diameter of the upriser pipe or the submergence ratio. The second group is the operation parameters such as diameter of the bubble, inlet pressure of the gas and so on. One of the designing parameters which can have an effective influence on the performance of an airlift pump is the non-constant diameter of the upriser pipe, which can be... 

Nowadays, due to expansion of the cities, growth in population and developments in technology, energy demand has increased extremely. Therefore responding this increased demand is a great challenge in political and economical management of all countries. Thus in recent years, cogeneration has become so popular between experts in the energy field because of its great efficiency and performance. The goal of this research is to design a controller based on a model which can predict the behavior of the cogeneration system. This controler is called “Mode Based Predictive Controller”. It utilizes the system in such a manner which has the lowest operation costs. This goal is obtained via modeling... 

Two phase cross flows around a body have seldom been studied until now and considering these flows can play a significant role in long-term reliability and safety of industrial systems. In this paper flow regimes, drag coefficient and void fraction around different cross-section prisms were considered. To achieve this aim, main equations of flow have been developed for investigation of drag coefficient in air-water two phase. Our numerical analyses were performed by a designed and written CFD package which is based on Eulerian-Eulerian approach. Geometries, which have been studied in this article, are: circle, rectangle and triangle, for different aspect ratio and leading edge angle,... 

Multiple Input Multiple Output (MIMO) radar is an emerging technology which has attracted many researchers recently. The problem of beampattern design of a MIMO radar in uniform arrays and with the covariance based method of point targets has been investigated by many papers so far. In this thesis it is desirable to consider this problem in non-uniform arrays. Many authors have designed the transmitted beampattern by means of designing the cross correlation matrix of transmitted signals elements, but in this paper optimizing the locations of transmitted antennas will be done as well as cross correlation matrix of transmitted signals to achieve a better results  

Double channel and coreless induction furnaces are used extensively in many processing industries due mainly to their good heating efficiency, high production rate, clean working environments and relatively low operating costs. The study of heat transfer treatment and evaluation of the heat losses of these furnaces becomes an important issue in melting industries. In this dissertation, a heat transfer analysis will be performed for an induction furnace and heat losses by conduction, convection, Eddy-Current and Hysteresis in a furnace structure, and radiation from the body of a specific induction furnace will be modeled considering the symmetry of the furnace chamber. The models presented in... 

Detecting of coherent structures in bidirectional vortex combustion chamber is the original aim of this project. For this aim a numerical simulation is performed by using OpenFOAM, open-source CFD software. Also influence of fuel nozzle places in formation of coherent structures is analyzed. Effects of combustion in these structures and differences in cold and hot flows are analyzed too. There are papers that present influence of coherent structures in vortex burners and other applications, but based on reviews that are performed in this work, it seems that influence of coherent structures have not seen in bidirectional vortex chambers. So it can be one of innovations of this work. Swirl... 

Phosphating is one of the most procedures as a final surface treatment or pre-treatment (lubrication and Infrastructure color) is done on ferrous and nonferrous alloys. Phosphate coating on the wire drawing, increase speed of drwing, increase die life, increased resistance to abrasion caused by the friction reduction, reduced maintenance costs and improved surface appearance are combustible and conditions. The aim of this study was to evaluate the effects of variables such as temperature, pH bath, the coating bath components concentration on coating properties and optimize calcium zinc phosphate coating on steel wire, for better lubrication and decrease friction in the wire drawing process....