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approximated-equations
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Comparison of Approximate Methods for Analysis of Arch Dams with Finite Element Methods
, M.Sc. Thesis Sharif University of Technology ; Ghaemian, Mohsen (Supervisor)
Abstract
Dams are huge structures in which safety is a very important issue because a failure will result in loss of lives and finance. Several approximate equations for the approximate analysis of arch dams already exist. These equations are usually obtained by considering the behavior of the dam as a shell. Approximate methods are much faster in comparison to the exact methods and give young design engineers who do not have the experience of designing inside view of displacements, stresses and strains. The aim of this project is to compare the results of approximate analysis of arch dams with the results of finite element models and clarify the points of dams in which approximate analysis methods...
Extending protection selectivity in low voltage DC microgrids using compensation gain and artificial line inductance
, Article Electric Power Systems Research ; Volume 188 , 2020 ; Vahidi, B ; Razani, R ; Nafisi, H ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
Vulnerability of power electronic converters in DC microgrids in case of fault occurrence in DC cables necessitates using a fast fault detection and isolation scheme. In this paper, a modified, fast and selective protection scheme has been presented, which provides the required tripping of low voltage DC (LVDC) microgrids. This protection scheme has been developed based on the natural characteristics of the fault current, in which the first and second derivatives of the fault current have been employed to define thresholds for discriminating between faulted and non-faulted situations. To enhance fault detection capability of the protection scheme, definition of thresholds have been improved...
Stagnation-point flow of upper-convected maxwell fluids
, Article International Journal of Non-Linear Mechanics ; Volume 41, Issue 10 , 2006 , Pages 1242-1247 ; 00207462 (ISSN) ; Hajibeygi, H ; Taghavi, M ; Sharif University of Technology
2006
Abstract
Two-dimensional stagnation-point flow of viscoelastic fluids is studied theoretically assuming that the fluid obeys the upper-convected Maxwell (UCM) model. Boundary-layer theory is used to simplify the equations of motion which are further reduced to a single non-linear third-order ODE using the concept of stream function coupled with the technique of the similarity solution. The equation so obtained was solved using Chebyshev pseudo-spectral collocation-point method. Based on the results obtained in the present work, it is concluded that the well-established but controversial prediction that in stagnation-point flows of viscoelastic fluids the velocity inside the boundary layer may exceed...
Performance evaluation of k out of n detector
, Article 14th European Signal Processing Conference, EUSIPCO 2006, Florence, 4 September 2006 through 8 September 2006 ; 2006 ; 22195491 (ISSN) ; Greco, M. S ; Nayebi, M. M ; Sharif University of Technology
2006
Abstract
In this paper the problem of k out of n detection, between sequence of M random bits is addressed. The main application of the result is in a radar system, when we want to detect a target (with unknown time of arrival (TOA)), using binary integration. Another application is in ESM systems, when the system wants to detect the existence of a swept jammer or a gated noise jammer. But as any other mathematical problem, it may have some other applications. In this paper some simple equations for P fa and P d calculation of a detector which detects the existence of sequence of n ones between M random bits, is derived. These equations are then used to find the optimal detector structure in some...