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Analysis of Special Periodic Structures with Differential Method
, M.Sc. Thesis Sharif University of Technology ; Mehrany, Khashayar (Supervisor) ; Rashidian, Bizhan (Supervisor)
Abstract
In this thesis, the Maxwell's equations are transformed into a set of ordinary differential equations and then solved in periodic structures by using the differential method (DM). The periodic structures considered in this thesis are carved in linear anisotropic, nonlinear isotropic and nonlinear anisotropic media. Different numerical issues, e.g. stability and convergence rate, are addressed by following the conventional methods, e.g. S- and R- matrix formalism, and Fourier factorization. In addition, an algorithm is proposed for fast and efficient analysis of periodic structures with identical layers. Binary gratings and photonic crystals are examples of such structures. In this algorithm,...
Practical implementation of a new percentage-based turn-to-turn fault detection algorithm to transformer digital differential relay
, Article International Journal of Electrical Power and Energy Systems ; Volume 121 , 2020 ; Vakilian, M ; Hajipour, E ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
Turn-to-turn fault (TTF) is one of the most prominent reasons for transformer failure. This fault typically initiates by involving only a few turns and can progress to a much more severe fault in a very short time. Therefore, it is critical for the transformer protective relays to detect the TTF in the early stages of its occurrence. The conventional differential relays, in general, cannot detect a minor TTF, and thus, a supplementary protective algorithm is usually required to improve the sensitivity of differential relays against TTFs. This paper proposes a percentage-based fault-related incremental currents method for the precise detection of a low-level TTF. The proposed method employs...
Nonlinear dynamic analysis of TLP surge motion using homotopy perturbation method
, Article Ships and Offshore Structures ; Vol. 9, issue. 6 , May , 2014 , p. 569-577 ; Shoghi, R ; Sharif University of Technology
Abstract
Tension leg platforms (TLPs) are well-known structures for oil exploitation in deep water. One of the current issues in compliant structures in the sea is variation in frequency and structural response due to a nonlinear parameter in the equation of motion. Variation of frequency is important in fatigue life study of tethers. A perturbation method is used in contrast to the traditional methods. This method does not require a small parameter for finding surge motion of TLP. In this paper, homotopy perturbation method (HPM) is used to solve a highly nonlinear differential equation of surge motion. Calculated responses by HPM are compared with those obtained from both linear and nonlinear...