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fadaei--farzad
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Fuel management optimization based on power profile by Cellular Automata
, Article Annals of Nuclear Energy ; Volume 37, Issue 12 , 2010 , Pages 1712-1722 ; 03064549 (ISSN) ; Moghaddam, N. M ; Zahedinejad, E ; Fadaei, M. M ; Kia, S ; Sharif University of Technology
2010
Abstract
Fuel management in PWR nuclear reactors is comprised of a collection of principles and practices required for the planning, scheduling, refueling, and safe operation of nuclear power plants to minimize the total plant and system energy costs to the extent possible. Despite remarkable advancements in optimization procedures, inherent complexities in nuclear reactor structure and strong inter-dependency among the fundamental parameters of the core make it necessary to evaluate the most efficient arrangement of the core. Several patterns have been presented so far to determine the best configuration of fuels in the reactor core by emphasis on minimizing the local power peaking factor (Pq). In...
Study of self-diffusion in two binary solutions, glycerol-water and methanol-water using diffusion-ordered spectroscopy
, Article Scientia Iranica ; Volume 23, Issue 3 , 2016 , Pages 1175-1183 ; 10263098 (ISSN) ; Tafazzoli, M ; Sharif University of Technology
Sharif University of Technology
2016
Abstract
The concentration and temperature behaviors of the self-diffusion coefficient were analyzed in glycerol-water and methanol-water solutions using Diffusion-Ordered Spectroscopy (DOSY) experiment. Our results indicate that the self-diffusion coefficient dips with increasing concentration and decreasing temperature. The concentration behavior shows that there is hydrogen bond interaction between water and alcohol, which declines the self-diffusion coefficients of both in the aqueous binary mixtures. The self-diffusion activation energies were estimated 13.6, 29.4, and 32.8 (kJ/mol) for methanol and 24.8, 25.5, and 27.6 (kJ/mol) for water in the methanol-water solutions with 0.03, 0.10, and 0.20...
Evaluation of Dynamic Properties of Plastic Concrete Using Bending Disk Tests in Small Strain Range
, M.Sc. Thesis Sharif University of Technology ; Jafarzadeh, Fardin (Supervisor)
Abstract
Evaluation of the compression wave velocity (Vp ) and small strains elastic modulii of various types of plastic concrete specimens in unconfined and triaxial compression tests using piezoelectric transducers was performed in this study. Plastic concrete consists of aggregates, cement, water and bentonite, mixed at a high water cement ratio, to produce a ductile material. It is used for creating an impermeable cut-off wall for seepage control in highly permeable dam foundations. A plastic concrete cut-off wall acts essentially as a barrier to stop or reduce the groundwater flow. In this study the effect of specimen age, water-cement ratio, bentonite-cement ratio, confining pressure, wave...
Study of the Affecting Factors on the Stability of G-Quadruplex Structures
, Ph.D. Dissertation Sharif University of Technology ; Tafazzoli, Mohsen (Supervisor)
Abstract
We used spectroscopic techniques to study self-assembled structures based on nucleobases like G-quadruplexes and macrocycles. Also we used DOSY NMR technique to study hydrogen bonding network in alcohol solutions. First part of our results indicate thermodynamic stability and slow kinetic of G-quadruplexes in apolar aromatic solvents like toluene. Also our results show easy monitoring of formation of each K+ or Na+ complex by NMR, due to the low solubility of alkaline metal salts in apolar media and possibility to stop at any given time in order to control G-quadruplex yield. When combined with suitable functional units, these valuable attributes may be used for the noncovalent synthesis of...
Descriptive Modeling of Traffic Accidents of Urban Public Transport Drivers Based on Role of Drivers’ Behaviors, Attitudes and Perceptions
, M.Sc. Thesis Sharif University of Technology ; Nasiri, Habibollah (Supervisor)
Abstract
Drivers' behavior is an influential factor in more than 90% of driving accidents. Due to the increased traffic load due to the use of private cars, as well as traffic congestion restrictions for the use of private cars at large city centers, the use of public transportation means for transportation of goods and passengers in order to reduce traffic load is a very convenient option and it is sometimes necessary. Therefore, it is very important to examine the behavior and character of drivers of public urban vehicles in order to increase traffic safety. The purpose of this research is to present and develop a descriptive model that describes the behaviors leading to at-fault accidents for...
Maximizing non-monotone submodular set functions subject to different constraints: Combined algorithms
, Article Operations Research Letters ; Volume 39, Issue 6 , 2011 , Pages 447-451 ; 01676377 (ISSN) ; Fazli, M ; Safari, M ; Sharif University of Technology
2011
Abstract
We study the problem of maximizing constrained non-monotone submodular functions and provide approximation algorithms that improve existing algorithms in terms of either the approximation factor or simplicity. Different constraints that we study are exact cardinality and multiple knapsack constraints for which we achieve (0.25-)-factor algorithms. We also show, as our main contribution, how to use the continuous greedy process for non-monotone functions and, as a result, obtain a 0.13-factor approximation algorithm for maximization over any solvable down-monotone polytope
Optimization of Die Profile in Screw Extrusion Process for an Arbitrary Profile by Considering Viscoelastic Effects of the Material
, M.Sc. Thesis Sharif University of Technology ; Asghari, Mohsen (Supervisor)
Abstract
In this thesis, equations related to large deformation of a polymer were derived by considering viscoelastic effects. To express type of material behavior which includes elastoplastic and viscoelastic property at the same time, two-layer viscoplastic model was used. An axisymmetric model was used for modeling problem in finite element software. By derivation of parameters related to two layer model and entering them in finite element software and also entering other properties required to model the forming process, modeling was performed by special profile connecting input and output sections. Due to favorable properties of spline functions, profiles used in die geometry, were selected from...
Robust Control of Spacecraft Rendezvous in Halo Orbits in the Three Body Problem
, M.Sc. Thesis Sharif University of Technology ; Pourtakdoust, Hossein (Supervisor)
Abstract
The problem of spacecraft rendezvous on periodic orbits around the L_1Lagrange point of the Earth-Moon system is investigated. For this purpose, the nonlinear relative equations of motion are drived within the contex of the Circular Restricted Three Body (CRTB) problem. Subsequently, several types of rendezvous missionas well as control teqniques are considered for analysis and simulation. Application of different control approaches allows for partial verification as well as comparison of results achieved with various teqniques. The considered control approaches include optimal closed loop Linear Quadratic Regulator (LQR), nonlinear Feedback Linearazation (FL) as well as the nonlinear...
Solids Mixing Behavior in two Dimensional Fluidized bed with Inlet Jet Effect
, M.Sc. Thesis Sharif University of Technology ; Molaei Dehkordi, Asghar (Supervisor)
Abstract
In this study, the mixing and segregation of different mixtures of solid particles with various density or size in gas-solid fluidized beds have been investigated. In this regard, the integrated model of computational fluid dynamics and discrete particle method (CFD-DPM) were used. The soft sphere contact scheme and the linear dashpot-spring model were applied for to evaluate the contact forces. After validating the simulation results with experimental data from the literature, effects of an inlet gas jet were investigated by using some quantitative and qualitative mixing indexes. Effects of gas velocity, percentage of heavy particles, density and particle size ratio, initial arrangement of...
Direct Torque Control of Permanent Magnet Synchronous Machine Using Nonlinear Flux Observer
, M.Sc. Thesis Sharif University of Technology ; Tahami, Farzad (Supervisor)
Abstract
Direct Torque Control (DTC) is one of the vector methods to control Permanent Magnet Synchronous Machines (PMSM). In order to achieve an appropriate control in vector control methods, an accurate estimation of flux is indispensable. Flux estimation should be fulfilled in a wide speed range without considerable dependence on motor parameters. Prevalent flux estimation methods are based on integration of stator voltage which is not feasible in low speed, or performed based on assumption of decoupled equations on d and q axis which is not precise for applications with fast dynamic. Different flux estimation methods are investigated in this thesis with the aim of improving the flux estimation in...
Design and Implementation of a Soft Switched Bidirectional Charger for Vehicle-to-grid (V2G) Applications
, M.Sc. Thesis Sharif University of Technology ; Tahami, farzad (Supervisor)
Abstract
Due to the growing oil price and environmental considerations, tendency to use local and environmentally friendly energy sources has increased.Bidirectional transmission can be one of the key features of the smart grid,so the use of car battery connected to the grid as local energy sources makes sense. This can provide network stability, especially during peak load times. Vehicles connected to grid (V2G) is an electric vehicle or a plug-in hybrid electric vehicles can delivered the electricity to the grid. These systems require either two separate power electronic converters can be used for transmission in either directions or a two-way transfer charger. The aim of this project is to design...
Design and Implementation of a Soft-Switched Multiport Bidirectional Converter
, M.Sc. Thesis Sharif University of Technology ; Tahami, Farzad (Supervisor)
Abstract
In recent years, multiport bidirectional converters have been a center of attention in renewable energy systems. This research focuses on three-port bidirectional converters. First, series resonant bidirectional converter is precisely analyzed. This analysis includes sinusoidal, exact state space and small signal analysis through phasor concept. This converter can work in higher switching frequencies and higher power ratings in comparison with common DAB bidirectional converter due to its inductor impedance cancellation. To increase power rating a three-phase version is proposed which has reduced output filter capacitance. Then, three-port bidirectional resonant converter is proposed and...
Direct Speed Control of Permenant Magnet Synchronous Machine
, M.Sc. Thesis Sharif University of Technology ; Tahami, Farzad (Supervisor)
Abstract
Accurate and fast position controlling is an important issue in today’s industrial needs. Drives used for position control require fast dynamics on speed control. Cascade linear controllers have sluggish response due to bandwidth limitations on speed and current loop. These structures limit the dynamics above all in high power applications where the switching frequency is low. In this thesis, deadbeat direct speed control is proposed, which overcomes limitations by cascade loops resulting in high-speed control dynamics. This approach uses a model of the plant to generate the control signals. According to measured speed and currents, the controller specifies the best voltage vector in order...
Design and Implementation of High Efficient Charger for Plug-in Hybrid Vehicles with Power Factor Correction Feature
, M.Sc. Thesis Sharif University of Technology ; Tahami, Farzad (Supervisor)
Abstract
In this project the novel zero-voltage-switching topology for power factor correction bridgeless boost rectifier is proposed. By employing an improved ZVS pulse-width-modulation (PWM) switch cell, ZVS of all the main switches is achieved without additional current or voltage stress of main switches. Also for the auxiliary switch the zero-current-switching is provided. In all modes of opretion of this converter, the power path is provided by maximum two semiconductor so the conduction loss of converter is low as in conventional converter. With this features the efficiency of proposed converter is very high
Hybrid Modeling and Control of DC-DC Series Resonant Converters for Applications of Wide Range Power
, Ph.D. Dissertation Sharif University of Technology ; Tahami, Farzad (Supervisor)
Abstract
The subject of control and stabilization of dc-dc series resonant converter (SRC) is still a challenge in power electronics. The conventional controller design and stability analysis for this converter are based on the model which is derived using the sinusoidal approximation and averaging followed by linearization about an operating point. This model is not applicable to a SRC that operates below resonance especially in discontinuous conduction mode (DCM) because the sinusoidal approximation is no longer acceptable. However, a SRC may be purposely designed to operate in DCM. Therefore, it is essential to investigate the stability analysis and controller design using a more sophisticated...
Control of Quasi-Resonant Converters Using Model Predictive Control
, M.Sc. Thesis Sharif University of Technology ; Tahami, Farzad (Supervisor)
Abstract
DC-DC switching convertors are power electronic circuits that have various applications nowadays. Quasi-resonant convertors are a kind of these convertors that are of great interest due to their simple structure and soft switching. The goal of controlling these convertors is to achieve constant output voltage while varying the input voltage and the load by choosing a proper switching frequency. Classic controllers show drawbacks in the case of high input voltage and load tolerance, and this nonlinear behavior of the systems results in some practical challenges. In this thesis, nonlinear predictive controller for quasi-resonant Buck convertors is designed. Having designed the linear...
Control of Quasi-Resonant Converters Using Multiple Model Fusion
, M.Sc. Thesis Sharif University of Technology ; Tahami, Farzad (Supervisor)
Abstract
Nowadays, power electronics converters with pulse width modulation (PWM) are widely used in different power circuits. Operation of semi-conductive switches during on and off conditions causes switching dissipation and consequently decreases the efficiency of the PWMs. Recently, by increasing the required power for power electronics applications, quasi-resonant converters attract attentions. Quasi-resonant converters, by adding resonant circuits to the PWM converters causes the soft switching operation (switching with zero current or voltage) and decreases the energy loss. In conventional control methods of these converters, the nonlinear average circuit model is linearized around the...
Design of Electrical Drive for Steer-by-Wire Systems
, M.Sc. Thesis Sharif University of Technology ; Tahami, Farzad (Supervisor)
Abstract
Hydraulic steering technology has been used in vehicles for decades. Recently, a trend has been seen towards the use of electronic steer-by-wire systems that provide greater design flexibility by customizing the connection between the steering wheel and the steering mechanism. Steer-by-Wire systems (SbW) offer the potential to enhance steering functionality by enabling features such as automatic lane keeping, park assist, variable steer ratio, and advanced vehicle dynamics control. The lack of a steering intermediate shaft significantly enhances vehicle architectural flexibility. The task of a SbW system is two-fold: turning the steered wheels by tracking the hand wheel (HW) rotation and...
Wireless Power Transfer System Design using Selected Harmonic for Electric Vehicle Charging
, Ph.D. Dissertation Sharif University of Technology ; Tahami, Farzad (Supervisor)
Abstract
Long lasting portable power is an ultimate desire for electronic devices. The limited capacity of the batteries in addition to the heavy weight and extra costs are the main challenges of the batteries for energy storage in large electrical devices like electric vehicles. Wireless Power Transmission (WPT) technology can address these issues by providing online electric power for these portable devices. Furthermore, this technology can supply electric devices especially portable ones by eliminating cables and connectors with more reliability.The current research is focused on optimum design of the wireless power transfer system for electric vehicle charging applications. The optimization of...
Control of Three-phase UPS with Nonlinear Load Using Disturbance Observer Considering Transformer Concerns
, M.Sc. Thesis Sharif University of Technology ; Tahami, Farzad (Supervisor)
Abstract
Nowadays, non-linear loads comprise an important part of electrical grids. One of the most essential sources of nonlinear loads is switching power supplies, which mainly include power electronic rectifiers. When power outage occurs, Uninterruptible Power Supplies (UPS) must be able to supply these loads. The nonlinearity of the load has a significant effect on the Total Harmonic Distortion (THD) of the output voltage, which may not be easily reduced, especially in three-phase inverters. Furthermore, the presence of isolating transformers in these power supplies limits the control of harmonics and intensifies the nonlinear effects of the system.In this Master Thesis, a disturbance observer is...