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Total 167 records

    A fluid-structure interaction model for stability analysis of shells conveying fluid

    , Article Journal of Fluids and Structures ; Volume 26, Issue 5 , July , 2010 , Pages 747-763 ; 08899746 (ISSN) Firouz Abadi, R. D ; Noorian, M. A ; Haddadpour, H ; Sharif University of Technology
    2010
    Abstract
    In this paper, a fluid-structure interaction model for stability analysis of shells conveying fluid is developed. This model is developed for shells of arbitrary geometry and structure and is based on incompressible potential flow. The boundary element method is applied to model the potential flow. The fluid dynamics model is derived by using an inflow/outflow model along with the impermeability condition at the fluid-shell interface. This model is applied to obtain the flow modes and eigenvalues, which are used for the modal representation of the flow field in the shell. Based on the mode shapes and natural frequencies of the shell obtained from an FEM model, the modal analysis technique is... 

    Optimal design of two-dimensional porosity distribution in shear deformable functionally graded porous beams for stability analysis

    , Article Thin-Walled Structures ; Volume 120 , 2017 , Pages 81-90 ; 02638231 (ISSN) Jamshidi, M ; Arghavani, J ; Sharif University of Technology
    Abstract
    In the present study, considering two-dimensional porosity distribution through a functionally graded porous (FGP) beam, its optimal distributions are obtained. A multi-objective optimization problem is defined to maximize critical buckling load and minimize mass of the beam, simultaneously. To this end, Timoshenko beam theory is employed and equilibrium equations for two-dimensional functionally graded porous (2D-FGP) beam are derived. For the solution, we present generalized differential quadrature method (GDQM) and consider two symmetric boundary conditions (Clamped-Clamped and Hinged-Hinged). Solving generalized eigenvalue problem, critical buckling load for 2D-FGP beam is then obtained.... 

    Estimation and stability over AWGN channel in the presence of fading, noisy feedback channel and different sample rates

    , Article Systems and Control Letters ; Volume 123 , 2019 , Pages 75-84 ; 01676911 (ISSN) Sanjaroon, V ; Farhadi, A ; Khalaj, B. H ; Seyed Motahari, A ; Sharif University of Technology
    Elsevier B.V  2019
    Abstract
    This paper is concerned with estimation and stability of control systems over communication links subject to limited capacity, power constraint, fading, noisy feedback, and different transmission rate rather than system sampling rate. A key issue addressed in this paper is that in the presence of noisy feedback associated with channel, which models transmission of finite number of bits over such links as is the case in most practical scenarios, the well-known eigenvalues rate condition is still a tight bound for stability. Based on an information theoretic analysis, necessary conditions are derived for stability of discrete-time linear control systems via the distant controller in the mean... 

    An analytic methodology to determine generators redispatch for proactive damping of critical electromechanical oscillations

    , Article International Journal of Electrical Power and Energy Systems ; Volume 123 , 2020 Setareh, M ; Parniani, M ; Aminifar, F ; Sharif University of Technology
    Elsevier Ltd  2020
    Abstract
    This paper presents a model-based method for applying online proactive generators redispatch to improve damping of the critical electromechanical oscillations of power system. The proposed method comprises two stages: 1) monitoring modal characteristics of oscillatory modes in ambient condition, and 2) applying generators redispatch based on sensitivities of the critical mode to the generators active power changes using a new analytic method. An online identification method such as error feedback lattice recursive least square adaptive filter is applied for online estimation of the oscillatory modes. Then, whenever the damping ratio of an identified mode is less than a preset threshold, its... 

    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) Shahverdi, H ; 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... 

    Nonlinear aeroelastic response of slender wings based on Wagner function

    , Article Thin-Walled Structures ; Volume 46, Issue 11 , 2008 , Pages 1192-1203 ; 02638231 (ISSN) Shams, Sh ; Sadr Lahidjani, M. H ; Haddadpour, H ; Sharif University of Technology
    2008
    Abstract
    This paper presents a method for nonlinear aeroelastic analysis of Human Powered Aircraft (HPA) wings. In this type of aircraft there is a long, highly flexible wing. Wing flexibility, coupled with long wing span can lead to large deflections during normal flight operation; therefore, a wing in vertical and torsional motion using the second-order form of nonlinear general flexible Euler-Bernoulli beam equations is used for structural modeling. Unsteady linear aerodynamic theory based on Wagner function is used for determination of aerodynamic loading on the wing. Combining these two types of formulations yields the nonlinear integro-differentials aeroelastic equations. Using the Galerkin's... 

    Towards obtaining more information from gas chromatography-mass spectrometric data of essential oils: An overview of mean field independent component analysis

    , Article Journal of Chromatography A ; Volume 1217, Issue 29 , 2010 , Pages 4850-4861 ; 00219673 (ISSN) Jalali Heravi, M ; Parastar, H ; Sereshti, H ; Sharif University of Technology
    2010
    Abstract
    Mean field independent component analysis (MF-ICA) along with other chemometric techniques was proposed for obtaining more information from multi-component gas chromatographic-mass spectrometric (GC-MS) signals of essential oils (mandarin and lemon as examples). Using these techniques, some fundamental problems during the GC-MS analysis of essential oils such as varying baseline, presence of different types of noise and co-elution have been solved. The parameters affecting MF-ICA algorithm were screened using a 25 factorial design. The optimum conditions for MF-ICA algorithm were followed by deconvolution of complex GC-MS peak clusters. The number of independent components (ICs) (chemical...