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helicopter-rotors
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Improvement of dynamic response prediction of helicopters
, Article Aircraft Engineering and Aerospace Technology ; Volume 79, Issue 6 , 2007 , Pages 579-592 ; 00022667 (ISSN) ; Saghafi, F ; Sharif University of Technology
2007
Abstract
Purpose – This paper aims to focus on mathematical model development issues, necessary for a better prediction of dynamic responses of articulated rotor helicopters. Design/methodology/approach – The methodology is laid out based on model development for an articulated main rotor, using the theories of aeroelastisity, finite element and state-space represented indicial-based unsteady aerodynamics. The model is represented by a set of nonlinear partial differential equations for the main rotor within a state-space representation for all other parts of helicopter dynamics. The coupled rotor and fuselage formulation enforces the use of numerical solution techniques for trim and linearization...
Preconditioning Methods to Accelerate and Improve Solution of Compressible Flow around Rotor
, Ph.D. Dissertation Sharif University of Technology ; Hejranfar, Kazem (Supervisor)
Abstract
In the present study, the numerical simulation of the compressible inviscid flow around helicopter rotor is performed using the solution of the preconditioned Euler equations. Three preconditioners proposed by Eriksson, Choi and Merkel, and Turkel are implemented in two- and three-dimensional upwind Euler flow solvers on unstructured meshes. The mathematical formulations of these preconditioning schemes for different sets of primitive variables are drawn and their eigenvalues and eigenvectors are compared with each others. For this aim, these preconditioning schemes are expressed in a unified formulation. A cell-centered finite volume Roe's upwind method is used for the discretization of the...
A novel method to detect rotor blades echo
, Article IEEE National Radar Conference - Proceedings, 10 May 2010 through 14 May 2010, Washington DC ; 2010 , Pages 1331-1334 ; 10975659 (ISSN) ; 9781424458127 (ISBN) ; Nayebi, M. M ; Sharif University of Technology
2010
Abstract
In this paper, the effect of the main rotor of an armed helicopter on radar return signal and its modulation condition are considered. After analyzing references and experimental data, this paper proposes a new method based on inherent modulation in main rotor echo. This method is able to enhance the probability of detection. The simulation is performed for both simulated and practical echo signal. Simulation results confirm that our proposed scheme is effective. Moreover, a new domain for distinguishing and measuring the rotation feature of a rotary target is proposed. This paper is based on practical experiments (rotation domain)
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...