Sharif Digital Repository

In this thesis, a new approach is proposed for two-level optimal control of large-scale nonlinear systems. In this approach, by defining some parameters as coordination parameters the overall system is decomposed into several interactive subsystems, where the optimization problem redefines for each one of them. The obtained sub-problems which are in the form of standard optimal control problems with lower dimension are solved in the first level. To obtain the overall optimal solution, coordination of the first level solutions is performed in the second level. For solving the first level problems, the indirect gradient and Newton methods are used. The gradient method is applied in the first... 

Results showed that 9 factors of “Brand Equity”, “Product Quality”, “Service Quality”, “Service Recovery”, “Perceived Value”, “Relationship”, “Employee Satisfaction”, “Physical Environment” and “Distribution Channel” are most effective factors by researchers that have effect on customer satisfaction. Thus, the Macromodel of this research was designed based on these factors. Due to limitations and context of the research, “Service Quality”, “Service Recovery” and “Relationship” were chosen in the final model. Results of questionnaire showed that the 5 parameters of “Service Recovery Speed”, “Reliability”, “Responsiveness”, “Empathy” and “Seller-focused antecedents” was the most important... 

This study investigates consumers’ response to changing the household electricity meter from single stroke case to three stroke case. Existence of different prices in different hours during the day is the advantage of three stroke electricity meters compared to single stroke ones. Electricity bill data of 19,742 subscribers, in Tehran Interior Region 2, during the period 1387 to 1393, has been used to evaluate this policy. Subscribers who always use only single stroke electricity meters or three stroke ones are considered as the control group; and subscribers who have experienced electricity meter change during the period are considered as the experimental group. Changing electricity meters... 

Identifying fractional systems and designing controllers for these systems is one of the leading challenges due to their limitations. Systems can have constraints on output, input, and states. These constraints make it difficult to design a controller. In this project, controller design methods for fractional-order systems with output constraints are investigated. A controller is designed for a strict feedback nonlinear system with unknown dynamics subject to asymmetric and variable output constraints, unknown direction of the controller, and unmeasurable states. To design the controller, the direct and backstepping technique is used and the Lyapunov barrier function is applied for the first... 

In the study of heat transfer in micro-channels, free and force convections are two limit cases and these two methods of heat transfer are combined together generally, so to achieve the most accurate informations about the flow field they should be considered in combination. In the first part of the thesis the fully developed slip flow mixed convection in vertical micro-ducts of arbitrary shapes is investigated.Uniform axial heat flux and uniform peripheral wall temperature (H1) is considered. The method considered is analytical-numerical in which the governing equations and three of the boundary conditions are exactly satisfied but the remaining slip boundary condition on the duct wall... 

Engineering, Procurement and Construction (EPC) contracts commonly used in the construction of oil and gas production facilities in Iran. These projects are subjected to many uncertainties. Because in these projects contractor is responsible for most of the activities related to the Engineering, Construction and Procurement, EPC contractors often assume most of project risks. Therefore, project risk management is very essential for achieving project goals. Several studies have focused on the identification and analysis of EPC project risks. However, they fail to identify appropriate risk management strategies. The objective of this study is to identify fair and efficient risk allocation and... 

Lean premixed flames bring both benefits and challenges to combustion systems. While they have low emission levels and high efficiencies, they are also very susceptible to combustion instabilities. Low swirl burners have been shown to be very capable in stabilizing lean premixed flames.
In this thesis, behavior of low swirl flames under conditions of variable equivalence ratio (0.6 – 0.8), mean flow velocity (3.5 – 5.5 m/s), and excitation frequency is investigated. In static stability diagram of the flame, a region is observed in which stability mode of the flame is dependent on the path that takes the flame to its operating point (hysteresis region). Increasing the recess distance of... 

Because of deregulation and economic issues, power systems operate closer to their stability limits than before. So, security assessment of power system has gained a lot of attention in power system studies. Transient stability and its real time assessment is a great concern in power system security. Among all different methods for transient stability assessment, Automatic Learning methods are used the most in real time assessment problems. These methods can provide fast assessment of transient stability, sensitivity analysis and means of control of the transient stability phenomena. In this paper Adaboost algorithm is used as a brand new method in transient stability assessment of a medium... 

The use of unbonded post-tensioned precast concrete walls with horizontal joints as the primary lateral load resisting system in seismic zones has been considered in several previous studies. These walls are constructed by post-tensioning precast wall panels across horizontal joints using post-tensioning steel which is not bonded to the concrete. The behavior of the unbounded post-tensioned precast structural wall under lateral loads strongly depends on base panel geometry and concrete confinement properties. In this research an analytical parametric investigation on base panel design parameters is conducted using DRAIN-2DX software. Fiber beam-column elements are used to represent the... 

Despite major environmental and economic benefits of cold recycled asphalt mixtures, many agencies have not yet made widespread use of this technology due to its so-called poor field performance and lack of accurate information on mechanical properties of cold recycled mixtures. Fiber is one the additives that is sometimes used to enhance asphalt mixture properties. Using fibers to improve the performance of cold recycled asphalt mixture has been studied by a few researchers with somehow contradictory results. In this research, the effects of adding four synthetic fibers (Polypropylene, A-glass, Para-Aramid, and Polyester) and two waste fibers (Waste Polyester and Waste Nylon) with different... 

In this project, different types of optical frequency selector devices are compared with each other and the factors limiting their behavior (losses, throughput, quality factor, etc.) are precisely analyzed. Change this behavior in near-field and far-field scales as well as the behavior of these devices in nano-dimensions are analyzed. Also, the main theoretical and technological limitations of different types of optical filters in far-field and near-field regimes are compared. In the following, the scaling behavior of different filter families in passing to nanometric dimensions is investigated and finally the limitations of the possibility of making the selected sample are analyzed. For... 

Domain shift is an inevitable issue when histopathological images are analyzed in a standard laboratory. This is due to the variations in tissue handling, manual procedures for sample preparation, and differences in scanners. This can result in reduced performance of machine learning algorithms trained on images from one laboratory when applied to another. In this framework, the goal of utilizing domain generalization techniques in machine learning is to develop models that perform well in different domains. This research examines various methods of dealing with the domain shift challenges within the context of detecting mitotic cells, and proposes algorithms to improve domain generalization... 

If nuclear radiation is not weakened and absorbed, it can cause serious damage to human devices or the environment. Dual-purpose dry casks are one of the sources of nuclear radiation production as a place to keep the spent fuel assemblies. One of the ways to protect against them is to use shield. One of the most common of them is composite shield. The composite used in this study has a polymer matrix. The matrix of the used polymer is epoxy resin. In this study, two separate composites have been made to attenuate neutron and gamma radiation. In this thesis, first, by using the MCNPX code, the necessary simulations for the design and construction of composite shields have been carried out.... 

Improvement of numerical solutions and application of them is very important section of engineering researches. So, there are several numerical methods and procedures for solution of equations or problems. All of them have advantages and disadvantages for selection best method. The efficiency of a method is a function of Limitation parameter like time, software and hardware. One of the recent numerical methods for engineering problems is Direct Discrete Method (DDM). This method prepares modern theory for balance equations; also this method combines some advantages of the other numerical methods like finite element and finite difference. DDM uses a double set of mesh structures namely primal... 

The issue of spending companies' resources on marketing measures, due to the lack of a proper mechanism to explain the impact and role of these measures has always been one of the most challenging problems for many stakeholders of companies, especially managers. In this study, we have tried to explain the relationship between marketing costs and credit policies with the financial performance of companies by examining the information published by companies listed on the Tehran Stock Exchange. In this study, the required information was collected from the sources of valid tools and then, using statistical methods, regression models that express the relationship between variables were... 

In recent years, advances have been made in the field of miniaturization of the devices (in order to increase their efficiency, lessen the materials needed for the constructions and experiments, reduce costs and energy usage) resulting in the dramatic increase of surface to volume ratio in these devices. This progress has led to the dominance of surface forces which can be used to control very important interface phenomena having a special application such as electrokinetic. Using today’s manufacturing technology; it is possible to construct micro-nanochannels made from different materials such as silicon, glass, quartz, polydimethylsiloxane (PDMS), polymethyl methacrylate (PMMA) whose... 

PET systems are a kind of functional nuclear medicine instruments. In this systems a radionuclide is injected to body and output gamma rays is detected. PET can recognise cancer 10 times earlier than other imaging systems such as CT scan also the treatment plan can followed by PET. In the last two decades, the use of small-animal models in the field of biomedical research for studying disease have accelerated and dedicated small animal PET systems have started playing their role as strong imaging modalities in investigating cellular and molecular processes in live animals. Animal and human PETs have similar technology just human PET is bigger, so at this project, animal PET is designed for... 

The present work has been planned to elaborately investigate the key parameters which affect the formation of shrinkage porosities during centrifugal casting of ductile cast iron pipes. The porosity defects can be mostly found in the Hot Mould centrifugal casting products and adversely affect the final mechanical properties of ductile iron pipes namely Ultimate Tensile Strength and Elongation.
In the first point of view, the created defects were detected through microstructural observations and the corresponding responsible mechanisms were also discussed. The results showed that the inner porosity is produced because solidification occurs from both the inner and outer surfaces... 

Load following operations on PWRs that Adjusted based on demand of network electricity, in fact is not easy, because of the complex conditions of the reactor heart.One of the reasons for the complexity when changing the reactor power level is the production of Xe in the heart and its associated oscillations, which also cause oscillations in the power distribution.Many studies have been performed on the control of xe oscillations based on solving complex mathematical problems and neutron diffusion equations. But what is the research method of choice is the simple and practical TRIAX method. In this method by Convergence control of elliptic trajectory related to three axial offset (Axial...