Sharif Digital Repository

This research proposes a Bayesian model selection framework using the stochastic filtering for rapid Bayesian identification of structures under seismic excitations. Structural identification after an earthquake at a regional scale entails a high computational effort. For rapid damage detection on a regional scale, using simplified and low-cost structural models is preferred over complex finite element models, due to the large amount of information needed for finite element modeling of numerous structures within a region as well as the high computational cost of such models. Timoshenko beams, shear beams, and shear buildings are examples of simplified structural models used in this study to... 

Today, global warming is one of the main concerns of human society. Many factors contribute to global warming and air pollution. Air pollution in the metropolis cities has influenced human life. Vehicles are considered as one of the major sources of air pollution. Vehicle air conditioners bring conform to passengers, but they increase fuel consumption. Increased fuel consumption results in the production of pollutants and air pollution. In this study, the ejector cooling system is proposed as a cooling system of a car air conditioning system, and its performance is studied. To this aim, first, an ejector cooling cycle equivalent to the compression cooling cycle is designed. The ejector is... 

Recent stringent HC and CO emission regulations are because of increasing consciousness of the perilous influences of exhaust emissions. The chief attempt to pass the standards is to decrease the emissions during cold-start, due to catalytic converters are not efficient until they arrive a light-off temperature. It has been discovered that 50% to 80% of the controlled HC and CO emissions are sent out from tailpipe of automotive during the cold-start. Therefore, in order to minimize the cold-start emissions and fast light-off of catalytic converters, it is important to understand the catalytic converter characteristics and techniques for rapid warm-up catalyst. This thesis describes a... 

Economical strategy of developed countries imposes to improve energy efficiency and a rational renewable energies usage in the buildings. Ground source heat pumps are one of the most important tools in the way moving toward this goal. This study focuses on studying the effect of applying different refrigerants in the direct expansion ground source heat exchangers. In order to compare the performance of the ground source heat pumps using different refrigerants, a specific methodology is presented and implemented. First on this study, the thermal performance of a geothermal borehole filled with both CO2 and a zeotropic mixture of CO2 and R32 (20/80) is studied and the quality, temperature, and... 

The integration of renewable energy sources introduces several issues including islanding operation. Therefore, Islanding phenomenon should be detected by a fast and reliable islanding detection method. In this thesis an intelligent-based approach is proposed to detect islanding state for Photovoltaic (PV) and Doubly Fed Induction Generator (DFIG) units. Decision tree classification algorithm is chosen as weak classifier and by Adaptive Boosting (AdaBoost), detection accuracy is improved. 16 features are employed to construct feature vectors. Because of intermittency of renewable electricity generation, different states for PV and DFIG generation are assumed. Probable events are simulated... 

Hydrogen can serve as a green alternative to fossil fuels and contribute to improving environmental conditions. In this context, reducing the cost of hydrogen production is of fundamental importance. It is necessary to examine the impact of influential environmental parameters on hydrogen production cost reduction. In this study, a relationship for optimizing hydrogen production in two scenarios, with constant anode pressure and variable cathode pressure, as well as both variable anode and cathode pressures, has been presented. Furthermore, the effect of various parameters, including temperature, pressure, proton exchange membrane thickness, and solar cell efficiency, on hydrogen production... 

In order to improve the performance of structures against earthquake loads, engineers believe that both minimizing the rigidity and maximizing the ductility; can lead to minimization of the energy input of the structure. However, the minimized energy shall be depreciated as much as possible in different stories so that the damage to the main and Irreplaceable structural members remains as low as possible.
Steel with high strength and ductility is relatively an ideal material for this purpose; however, the ductility level of this material is much higher than that is normally in use. In order to have a better utilization of the steel ductility, RBS (Ribbed Bracing System) was invented in... 

It is possible to unload a transmission line for a while. In line restoration voltage and current of the line will have some dynamic changes. So the apparent impedance of distance relay will have dynamic changes. These changes may cause some bad results including entrance of apparent impedance to the operational zones of distance relay and even relay tripping. Consequently if relay trips, the line restoration process will stop and may not be possible.
So we want an algorithm to distinguish line restoration from short circuit condition and block the relay. This algorithm must be able to stop blocking if there is any fault in the operational zones of the relay.
In this thesis an... 

Nowadays, according to environmental issues and fuel economy in internal combustion engines, the tendency to use of electrical and hybrid-electrical propulsions has become more than the past. On the other hand, still there are some problems like distance and charge time in electrical propulsions. Among them there are Hybrid-electric propulsions that have the benefits of two other propulsions. These propulsions are classified into three categories: series, parallel and series-parallel.Propulsion hybridization will change the cooling system. Internal combustion engine, electric motors, inverter and batteries operate at different temperature levels. So more than one cooling circuit with its own... 

Ultra-high temperature ceramics (UHTCs) are a class of materials that have melting points above 3000°C and include borides, carbides and nitrides of some transition metals such as ZrB2, ZrC, HfB2, HfC, HfN, TaC. These compounds are of particular interest because of the unique property combination such as high electrical and thermal conductivity, chemical inertness against molten metals or non basic slags, and good thermal shock resistance. Sintering of these compounds is very difficult due to their high melting point and utilization of sintering aids or new consolidation routes is necessary to achieve high density sintered bodies. In this research, phase evolution and kinetics of diffusion... 

Due to an increasing need for refrigeration systems and consequently increasing in electricity usage and greenhouse gases production, using ejector refrigeration systems would be a suitable substitution for conventional cooling systems. Main drawback of ejector refrigeration systems is their low coefficient of performance. The key component to improve the cycle performance is the ejector. Prerequisite of improving ejector performance is an accurate CFD simulation for predicting entrainment ratio. In this study, a two dimensional, axisymmetric, steady state, compressible flow CFD simulation of a supersonic ejector is presented. CFD results are validated with experimental data. Furthermore,... 

Because of some limitations, tourists can not visit all the attractions during their one or multiple-day trip. So, they need to select the best places worth to visit based on information that they gathered via the internet, magazines, tour guides, etc. Also, they should choose the best route to the selected place, considering its visiting time and ways conditions. Other factors such as visiting days/hours and the timetable for a place, entrance fees and the other limitations should be considered simultaneously. These requirements and questions are all discussed as a tourist tour plan problem in the field of operations research. In this research, different kinds of tour planning problems have... 

In the nuclear industry, gas centrifuges are considered of high importance for the purpose of uranium enrichment. Today, with advances in science and technology, the use of gas centrifuges for separating isotopes other than uranium, is so common. With respect to the use of conventional methods such as Pancake equation in calculating the velocity profile in centrifuges, it is needed that A^2=(MV^2)/2RT≫1 (M: Feed molecular weight; V: Peripheral speed of centrifuge; T: Mean temperature of feed; R: The universal constant of gases). While the molecular weight of the feed mixture gets lower, the A2 parameter gets closer to one. So, other methods for modeling the behavior of the gas in the... 

In recent years horizontal Ground Heat Exchangers (GHEs) has attracted a growing interest as heat source/sink for ground source heat pump systems. Horizontal GHEs initial installation costs are lower than the vertical ones; however, they require larger land area and more pipes. Therefore, it is necessary to reduce their required land area and pipe length by improving their thermal performance. In this study, a numerical modal based on 3-D simulation of GHE with computational fluid dynamics methods is developed. The model is used to evaluate the thermal performance and initial installation cost of horizontal GHEs. Four different types of horizontal GHEs: linear, spiral, horizontal and... 

Nowadays by fast growing the population and development of countries, the demand of energy is increasing rapidly. Solar energy is one of the most reliable and environment friendly source of energy. Photovoltaic modules (PV) are such a solar systems that is able to convert solar energy into electrical energy. However, some parameters such as increasing cell temperature and dust accumulation can reduce the PV modules efficiency. Increasing the cell temperature reduce the capability of electrical production of cells and dust accumulation is an obstacle for solar radiation absorption. As a result, in this research tempt to solve these problems by building a new device for PV modules. In this... 

The annual increase in electricity consumption has led to several problems, including greenhouse gas emissions and global warming. Refrigeration systems are one of the main electricity consumers in the world. Ejector refrigeration systems use waste heat from industries or renewable sources such as solar energy to create the cooling effect. One of the main problems with these systems is the inefficiency of the cycle by the change of the ambient conditions including temperature rise. In ejector vapor compression refrigeration cycles, the compressor increases the pressure to an intermediate pressure. and the rest of the pressure increase is provided by the ejector. These systems can provide the... 

Inlet air cooling is a simple and economical method to increase the power output of gas turbines. High-pressure fogging systems and mechanical chillers are two common methods. High water consumption, damage to compressor blades by water droplets, and inefficiency in humid climates are disadvantages of high-pressure fogging systems. Mechanical chillers have high electricity consumption and initial costs. In this research, an earth-to-air heat exchanger (EAHE) is introduced as a new method for inlet air cooling of gas turbines and is technically and economically compared with the two common methods in the long term in the climate of Tehran city. Temperature distribution in the ground is... 

Fault occurrence is an inevitable problem in industrial plants. These faults have numerous types. Some common kinds of faults are faults in actuators, faults in system dynamics, and faults in sensors. In many cases it is not possible to change or repair the broken part immediately. On the other hand, it is not reasonable to shut-down the whole system due to a minor failure. Therefore we should take a measure to have the best output possible in a faulty plant. In this thesis we have proposed a new static compensator by which we distribute the contribution of the faulty actuator among the other ones. At the end we evaluate the method by means of simulations  

Given a set of obstacles as an arrangement of geometric shapes in the plane, we would like to find a path from the initial point s to the target point t that crosses the minimum number of obstacles. In other words, the goal is to determine the minimum number of obstacles that need to be removed to exist a collision-free path between s and t.On one hand, this problem can be used for measuring the strength of barrier coverage which is a fundamental concept in wireless sensor networks (WSNs), and on the other hand, it has been considered as a robot motion-planning problem. The objective of barrier coverage is to guarantee that any path from the start point to the target point, will intersect at... 

Electrodeposition is an old, well known and conventional science surface modification method to improve the surface characteristics, decorative and functional, of a wide variety of materials. This science is considered in nanotechnology as a bottom-up method for fabrication of one, two and three-dimensional nanomaterials. A great variety of secondary components can be added to plating baths resulting in metallic matrix composite and nanocomposite coatings production. Low amounts of iron addition for alloying zinc coatings, significantly increases the corrosion resistance of this generally used metal economically. Superhydrophobic coatings on metallic substrates have shown, during the past...