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Compensation by fractional-order phase-lead/lag compensators
, Article IET Control Theory and Applications ; Volume 8, Issue 5 , 2014 , Pages 319-329 ; ISSN: 17518644 ; Tavakoli Kakhki, M ; Sharif University of Technology
Abstract
This study deals with a generalised version of lead/lag compensators known as fractional-order lead/lag compensators. Exact and simple formulas are found for designing this introduced type of fractional-order compensators in order to provide the required magnitude and phase at a given frequency. Also, the region in the phase-magnitude plane, which is accessible by these compensators, is analytically found. Moreover, numerical examples and experimental results are presented to show the applicability of the achievements of this study in control system design
Simultaneous compensation of the gain, phase, and phase-slope
, Article Journal of Dynamic Systems, Measurement and Control, Transactions of the ASME ; Volume 138, Issue 12 , 2016 ; 00220434 (ISSN) ; Tavazoei, M. S ; Sharif University of Technology
American Society of Mechanical Engineers (ASME)
Abstract
This paper deals with the problem of simultaneous compensation of the gain, phase, and phase-slope at an arbitrary frequency by using a fractional-order lead/lag compensator. The necessary and sufficient conditions for feasibility of the problem are derived. Also, the number of existing solutions (i.e., the number of distinct fractional-order lead/lag compensators satisfying the considered compensation requirements) is analytically found. Moreover, as a sample application, it is shown that the obtained results for the considered compensation problem are helpful in tuning fractional-order lead/lag compensators for simultaneously achieving desired phase margin, desired gain cross frequency,...
Return Predictability and Volatility, and Spillovers of Indexes Using a Multivariate Dynamic Model in Tehran Stock Exchange
,
M.Sc. Thesis
Sharif University of Technology
;
Zamani, Shiva
(Supervisor)
;
Souri, Davood
(Supervisor)
Abstract
Stock exchanges are one of the most important capital markets and let people and institutions to insvest their savings in stocks and therefore earn money. Investors are going to select a portfolio that has the maximum return and minimum risk; so, they try to forecast stock returns and volatilities. Predictability of stock return and volatility is also important for asset pricing and investigating market efficiency. Now, the question is “are stock returns and volatilities predictable using historical returns and volatilities?” In this research, return and volatility predictability of Tehran Stock Exchange indexes by using historical data are investigated. First, the outocorrelation of return...
Aeroelastic analysis of helicopter rotor blade in hover using an efficient reduced-order aerodynamic model
, Article Journal of Fluids and Structures ; Volume 25, Issue 8 , 2009 , Pages 1243-1257 ; 08899746 (ISSN) ; Salehzadeh Noubari, A ; Behbahani Nejad, M ; Haddadpour, H ; Sharif University of Technology
2009
Abstract
This paper presents a coupled flap-lag-torsion aeroelastic stability analysis and response of a hingeless helicopter blade in the hovering flight condition. The boundary element method based on the wake eigenvalues is used for the prediction of unsteady airloads of the rotor blade. The aeroelastic equations of motion of the rotor blade are derived by Galerkin's method. To obtain the aeroelastic stability and response, the governing nonlinear equations of motion are linearized about the nonlinear steady equilibrium positions using small perturbation theory. The equilibrium deflections are calculated through the iterative Newton-Raphson method. Numerical results comprising steady equilibrium...