Sharif Digital Repository

Design of optimal controllers for nonlinear systems and even for linear systems is one of the most important parts of the control science. In optimal controller design, our aim is to maximize or minimize some kind of cost function associated with that particular problem. Such cost functions are usually combining the overall control effort, system’s energy, or some other important specifications of the system. Explicit solution for linear quadratic controllers exists under some mild conditions such as stabilizability of the system. The solution is in the form of a full state-feedback law. But in practical problems, we may not have access to all of the system state variables. The problem can... 

Micro/Nano science has obtained enormous applications in aerospace engineering especially in the propulsion system of micro/nano satellites. The satellite attitude control is a vital part of every space mission. Different thruster systems have been already suggested and utilized to achieve this important mission correctly. Considering the future perspectives of space missions for small satellites, the development of micro/nano thrusters has been attracted more attention since the last decades. The scope of this research is to analyze hybrid hot/cold laboratory supersonic micro-thrusters especially for the micro-satellite implementations. The ultimate goal of the current research is to... 

Analysis and design of power systems are challenging due to ever increasing dimension of the system and also the nonlinearities involved in the system. The conventional approach is to use linear analysis tools and then investigate the nonlinear impacts by the means of computer simulations. This requires great deal of trial and error and it is not always a timely approach. In this project, we initiate a comprehensive nonlinear analysis for a single-machine infinite-bus system by studying a Hopf bifurcation in its dynamics. We use results of our nonlinear analysis to study how a capacitive compensation such as TCSC works. Subsequently, we design a nonlinear controller for a PSS to have... 

In the present study, the process of recycling spent lithium batteries by co-precipitation method has been investigated. The process of regeneration of lithium batteries by co-deposition method consists of four stages. In the first stage, the cathodic material is separated from the aluminum foil using NMP solution, and then the cathodic material is heat treated at a temperature of 700 degrees. In the second stage, using sulfuric acid and hydrogen peroxide, the cathode material is leached at 60 ° C, pulp density 55 g / l, time 100 minutes, sulfuric acid concentration 3.25 M and volume percentage of hydrogen peroxide. 10% More than 99% of lithium, nickel, cobalt and manganese are leached. In... 

A control strategy for islanded (autonomous) operation of a microgrid consisting of two Distributed Generation (DG) units is proposed in this thesis. The DG units are connected together in a radial configuration. Each DG unit utilizes a voltage-sourced converter (VSC) to interface to its dedicated load. The DG units and the loads are to operate in the islanded mode of operation. To provide autonomous operation for the microgrid, voltage and frequency of the loads should be regulated. The proposed control strategy utilizes (i) an internal oscillator for frequency control in an open loop manner and (ii) a decentralized servomechanism controller to regulate the load voltage. The microgrid is... 

Disturbance rejection is one of the most important criteria that should be considered when designing control systems. The problem has been widely investigated and studied when the parameters of disturbance signal is known. However, there are still ongoing researches in the field when the parameters of disturbance signals are uncertain and/or varying with time. In some applications the disturbance signal can be modelled by special dynamics, e.g., step type disturbances with unknown magnitude, sinusoidal disturbances with unknown magnitude and frequency, and damped sinusoidal disturbances with unknown magnitude, frequency and damping factor. In such cases, an adaptive scheme for estimating the... 

The problem of LQR design based on full state feedback is solved completely in the subject of Optimal Control. So far, however, despite the fact that use of output feedback in many applications of Control is desirable or even necessary, designing optimal controllers using output feedback in general does not seem to have received much attention in the existing literature. Of course, special cases of designing simple controllers using analytical or numerical-analytical methods do exist in the literature. A new algorithm for tuning an optimal controller (P, PI, PID, etc) for a low-order system without delay, and also in the presence of delay, has been introduced in this thesis using the LQR... 

Increase of sensitive customers to power quality has raised concerns in industries regarding requirements of quality power supply. Uninterruptible Power Supplies (UPSs) are known as efficient tools in providing reliable power supply to sensitive customer. However, in a UPS, getting a desired output requires appropriate structural implementation and successful output voltage control. On the other hand, due to the increase in sensitive loads in customers, the output power range of UPSs has increased. Consequently, design and producing high power UPSs is not economical. In addition, tendency to have high reliability power supplies disrespect of their physical locations has moved researcher... 

In this thesis we evaluate VIC hydrological model’s simulated soil moisture and discharge at Saghez synoptic station, located at ZarinehRood sub basin, Urmia Lake basin in three time periods to overcome observational and satellite data scarcity in the basin. All the input files for this macro scale semi-distributed model chose from satellite data. With a multi-objective calibration algorithm called NSGA-II and utilizing Nash-Sutcliffe (NSE) and R2 as objective functions for discharge calibration and correlation coefficient and RMSE for soil calibration, the model results evaluated. As where as we didn’t have access to observational soil moisture data, we utilized SMAP satellite soil moisture... 

The microstructures of stainless steels consist of an austenitic matrix with almost continuous network of primery carbides.This class of steel had replaced the traditional super alloys with a reduction in costs and has similar properties under conditions of creep, which is one of the principal degradation mechanisms leading to failure in service at elevated temperaturs , therefore, their mechanical properties such as tensile strength and creep resistance are particularly important in hot deformation. Recently the effects of temperature and aging time on static strain aging in worked stainless steel have been investigated. In this study the deformation behavior of HP-series austenitic... 

The notable share of housing sector in GDP (approximately five percent) shows this sector’s relation with macroeconomic activities. On the other hand, House as an asset leads housing sector to be affected by monetary and fiscal variables. A dynamic panel data was used in this study to evaluate the relations between housing sector and some macroeconomic variables in metropolises of Iran. As results show, in long term growth of liquidity, GDP per capita and sharp ratio have positive effects, and land per capita has negative effect on housing price in metropolises of Iran. Price increases have not been equal in different cities. Inequality of land price between metropolises and between... 

In this research, an Index of Iran informal economy in response to the government interventions in credit, labor and product markets is stimated by EMIMIC model. To do this, first these interventions are measured using principal components analysis. In the model, the variables GDP and employment are used as indicators and taxation rates, government distortions in credit, labor and product markets, government expenditure, per capita income, unemployment and inflation as causes of the informal economy. We conclude these government interventions have affected Iran informal economy and their influence is more than indirect interventions influence such as taxation. The estimated index of Iran... 

With altering natural state and increasing impervious surfaces, traditional urbanization leads to deteriorating the environment and water catchments. During the years most efforts in order to control the urban runoff outflow, have been focused on quantity; and awareness about improving water quality has been raised just in the last few years and, which emphasizes on pollution source control. Standard water quality sampling methods are time consuming, expensive and because of sampling in broad geographic areas, difficult; however modeling is a more efficient way in assessing water quality and as worries about non-point source pollution grows, different kinds of models have been used to... 

The role of government in economy has been a controversial subject in economics. Lately, there has been some fundamental change in evaluating this subject. One could mention two of these as 1) realizing the importance of micro-founded macro model for evaluating policy, and 2) taking into consideration the rent-seeking behavior of politicians. In this research, a general equilibrium in a micro-founded macro model will be discussed and then in political economics framework, the effect of government on this equilibrium will be investigated. Only the redistribution role of government has been considered. First, the model in which a benevolent government is seeking optimal policy is Discussed.... 

Gini coefficient is the most prevalent index for the measurement of inequality and is usually extracted by means of nominal variables based on income or expenditures of households. In this study we have extracted more accurate Gini coefficients. By using the raw data of Households Budget Survey (HBS) and STATA software, a special CPI for each household of the sample is extracted. Subsequently nominal expenditures are deflated by these special CPIs, and at last, Gini coefficients are extracted from real expenditures. Our findings indicate that in recent years, extracted Gini coefficients are remarkably higher than prevailing ones.
 

This paper investigates the behavior of the Y-shaped bracing system. Because of the special type of eccentricity in this system, the behavior of the frame is strongly dependent on the geometrical changes of the braces. So that even in the elastic region, it shows the geometrically nonlinear behavior. The amount of eccentricity is very effective on the nonlinear behavior of the frame. Also the ratio of cross sections of the bracing members has a very important impact on the expected performance of the frame. The results show that this system tolerates large displacements, and can act like a base isolation system. Firstly, using a two-dimensional accurate modeling related to the geometrical... 

The Overstrength, Ductility and the Response Modification Factor (R) for 70 steel X-braced , Inverted-V-Braced and Offcenter Bracing System frames were evaluated by performing pushover analysis of model structure with various stories (3,6,9,12&15 story) and span length (4,6&8 meter). Some result were compared with those from nonlinear dynamic analysis. According to the analysis result the R factors obtained from nonlinear dynamic analysis are 15% more than obtained from pushover analysis and R factors computed from pushover analysis were generally smaller than the values given in the design codes. R factors in Irregular structure in height are about 90% of R values in regular structure in... 

Maghemite (γ-Fe2O3) nanoparticles were produced after high temperature oxidation of gelatin-Fe3O4 nanocomposite, obtained from a common coprecipitation process of Fe2+ and Fe3+ ions in an alkaline medium in the presence of a gelatin protein as an effective mediator. Size, shape, surface morphology and magnetic properties of the prepared γ-Fe2O3 nanoparticles were characterized using XRD, FTIR, TEM, SEM and VSM data. The results revealed that primary, gelatin-Fe3O4 nanocomposite had been formed and next, the gelatin decomposition in furnace produced a spinel structure of γ-Fe2O3. The effects of furnace temperature and time of heating together with the amount of gelatin on the produced...