Sharif Digital Repository

Inrush Current is a form of over-current that occurs during energization of a transformer. For power transformers, the magnitude of the first peak of inrush current is initially several times the rated load current but slowly decreases until it finally reaches the normal exciting current value. This process typically takes several minutes. Time-variant axial and radial electromagnetic forces under inrush current and short-circuit current are calculated (by finite element method; FEM), and compared. An analytic method is presented for computation of inrush current in transformer. The simulation results obtained by this proposed method are compared with the measured values. A compact... 

In this study a variational framework for joint segmentation and motion estimation is provided for inspecting heart in Cine MRI sequences. In the first work, a functional including Mumford-Shah segmentation and optical flow based dense motion estimation is proposed. However, the motion estimation technique is replaced with warping estimation in the second work to reach in more regular and smooth motion field based on tracking of cardiac boundaries. Both of these functionals are then approximated by using the phase-field method to make them suitable for extracting Euler-Lagrange equations. Numerical solution to the optimization problem, when the time and image spaces are discretized by finite... 

Variation in value and initial cost of construction contracts in many cases lead to considerably increasing the finalized price. These increases are sometimes so big enough that the 25 percent of limitation which could be added to contracts couldn't make them to be finalized and exploitable, so the necessity of a new contract sometimes up to 100 percent or even up to 200 percent of initial cost for completing the same project is inevitable. Although in some specific and rare cases we couldn't avoidance from these changes, but observing the growth of these changes in public construction projects of Iran increase the requirement of special attention in order to find the main causes, prevention... 

Integrity of closed-loop systems with integral action control is characterized by using a series of successively more difficult to obtain conditions: Integral Stabilizable (IS), Integral Controllable (IC), Integral Controllable with Integrity (ICI), and Decentralized Integral Controllability (DIC). The IS condition requires that for a Linear Time-Invariant (LTI) finitedimensional (FD) plant, G(s), one finds a stabilizing decentralized controller with integral action. For G(s) to be IC, in addition to being IS, one should be able to reduce the gain of
all control loops by the same factor from a finite value to (but not including) zero without introducing instabilities. ICI requires that... 

In this thesis, the theoretical foundation, the way of implementation and the uses of Pars Morph, a Persian morphological analyzer is introduced. Pars Morph is a rule-based Persian morphological analysis system, which analyzes the internal structure of word in Persian and determines the grammatical category and function of the word parts. Pars Morph being in link with a lexicon covering about 45000 lexemes and based on morphological rules in Persian can analyze the structure of complex lexemes and their possible inflected forms and even out-of-lexicon words.
Accuracy rate of the first version of Pars Morph is about 95% which could be enhanced to 100% by applying the regulations on... 

Transportation of heavy and super heavy equipment is one of the issues that have been discussed in recent years. High cost and required expertise of Transportation for oil and gas projects has caused many organizations and Iranian companies turn to outsourcing strategy and have invested a lot of money in this field without regard to its Risks. Unfortunately, the lack of risk management in transportation projects has led to an increase in refractive index. In this thesis, have been identified the risks of heavy and super-heavy transport equipment in the oil, gas and petrochemical industries then prioritize the risks identified. Finally, each of the identified risks in Iran is investigated.... 

Liquefaction of gases is one of the applications of cryogenic science. Among the gases, Helium has the lowest boiling point, which at a pressure of 1atm is approximately 4.2K. Liquid helium can be used to cool superconductors in transportation equipment, military radars, and medical imaging equipment. For helium liquefaction, various cycles are used; these cycles have different parameters in their structure such as of input mass fraction to expanders, heat exchanger effectiveness, expander arrangement and ... which their analysis for improving the performance of the cycle is important. In this research, the aim is to study 2, 3 and 4 expander cycle with various parameters and structure. For... 

This research aims to introduce a mathematical model that is capable of producing an optimal and coordinated timetable for the entire urban rail network to minimize passengers’ travel time and the trains’ energy consumption. The proposed model focuses on different speed profiles and a skip-stop strategy while considering the stochastic nature of passengers’ arrival and departure rates. This novel approach enables it to develop a schedule that can endure unprecedented situations. To solve the model, the multi-agent deep deterministic policy gradient algorithm is implemented. This approach was first implemented in a smaller network and was validated with Genetic Algorithm. Eventually, this...