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nonlinear-stability
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Nonlinear Vibrations and Stability Analysis of Rotating Cylindrical Shells Conveying Annular Fluid Medium
, Ph.D. Dissertation Sharif University of Technology ; Dehghan Firouzabadi, Rohollah (Supervisor) ; Rahmanian, Mohammad (Co-Supervisor)
Abstract
In this study, stability as well as linear and nonlinear vibrations of coaxial rotating cylindrical shells conveying annular incompressible fluid medium are investigated. To this aim the inner isotropic and elastic rotating cylindrical shell along with the rigid and stationary outer cylinder are considered. Equations of motion for the inner cylinder are determined according to the Hamilton’s principle and using the Sanders-Koiter theory assumptions. In order to generalize the boundary condition implementation, some translational and rotational springs are attached to the boundaries at the mid-plane. The final system of equations are solved by means of the extended Galerkin method – being an...
Study on the effect of jets geometry in liquid atomization based on nonlinear stability analysis
, Article ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition, GT 2018, 11 June 2018 through 15 June 2018 ; Volume 4A-2018 , 2018 ; 9780791851050 (ISBN) ; Nehzati, T ; International Gas Turbine Institute ; Sharif University of Technology
American Society of Mechanical Engineers (ASME)
2018
Abstract
In this paper, nonlinear instability of an elliptical jet is investigated by considering the impacts of orifice geometry variations using regular perturbation method. In the breakup mechanisms, created disturbances on the jet interfaces will grow owing to the nonlinear dynamics of fluid. In this study, a scrutiny of nonlinear cylindrical jet breakup is done initially. Next, Cosserat equations as a low order form of Navies-Stokes equations are solved on the nonlinear form to exert the impacts of orifice deformation on various aspect ratios. These nonlinear equations, Cosserat equations, are linearly solved in the past papers. As a result, the dispersion equation is derived to find the most...
Post-buckling analysis of geometrically imperfect nanoparticle reinforced annular sector plates under radial compression
, Article Computers and Concrete ; Volume 26, Issue 1 , 2020 , Pages 21-30 ; Forsat, M ; Mollaee, S ; Barati, M. R ; Afshari, B. M ; Hamouda, A. M. S ; Sharif University of Technology
Techno-Press
2020
Abstract
Buckling and post-buckling behaviors of geometrically imperfect annular sector plates made from nanoparticle reinforced composites have been investigated. Two types of nanoparticles are considered including graphene oxide powders (GOPs) and silicone oxide (SiO2). Nanoparticles are considered to have uniform and functionally graded distributions within the matrix and the material properties are derived using Halpin-Tsai procedure. Annular sector plate is formulated based upon thin shell theory considering geometric nonlinearity and imperfectness. After solving the governing equations via Galerkin’s technique, it is showed that the post-buckling curves of annular sector plates rely on the...
Aeroelastic modeling and dynamic analysis of a wind turbine rotor by considering geometric nonlinearities
, Article Journal of Sound and Vibration ; Volume 432 , 2018 , Pages 653-679 ; 0022460X (ISSN) ; Zohoor, H ; Haddadpour, H ; Sharif University of Technology
Academic Press
2018
Abstract
Due to the increased flexibility of modern multi-megawatt wind turbine structures, more advanced analyses are needed to investigate the effects of geometric nonlinearities originating from large blade deformations under operational loads. The main objective of this paper is to study the related dynamics and the aeroelastic effects of these nonlinearities by using a multi-flexible-body aeroelastic model of an entire three-bladed wind turbine assembly instead of a more conventional single-blade model. A geometrically-exact beam formulation is employed to model the rotating blades connected to the wind turbine tower tip via hub and nacelle components; and the revolute joint constraint is...
Stability analysis of carbon nanotubes under electric fields and compressive loading
, Article Journal of Physics D: Applied Physics ; Volume 41, Issue 20 , 2008 ; 00223727 (ISSN) ; Ozmaian, M ; Naghdabadi, R ; Sharif University of Technology
2008
Abstract
The mechanical stability of conductive, single-walled carbon nanotubes (SWCNTs) under applied electric field and compressive loading is investigated. The distribution of electric charges on the nanotube surface is determined by employing a method based on the classical electrostatic theory. For mechanical stability analysis, a hybrid atomistic-structural element is proposed, which takes into account the nonlinear features of the stability. Nonlinear stability analysis based on an iterative solution procedure is used to determine the buckling force. The coupling between electrical and mechanical models is accomplished by adding Coulomb interactions to the mechanical model. The results show...
Piecewise affine large signal modeling of PFC rectifiers
, Article 2007 IEEE International Symposium on Industrial Electronics, ISIE 2007, Caixanova - Vigo, 4 June 2007 through 7 June 2007 ; 2007 , Pages 3362-3366 ; 1424407559 (ISBN); 9781424407552 (ISBN) ; Molla Ahmadian, H ; Sharif University of Technology
2007
Abstract
A problem associated with modeling and control of the power factor correction rectifiers is that the ac variations in duty cycle, as well as in the ac input voltage and current are not small, and hence the traditional small signal analysis is not justified. Nonetheless, the low-frequency components of the converter can be modeled via the circuit averaging technique, but the resulting equivalent circuits are, in general, time varying and highly nonlinear. Nonlinear stability analysis methods are not appropriate for analysis and control design of such complicated circuits. In this paper a piecewise affine approximation is introduced for modeling of switching circuits. This approach makes the...