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Vibration Modeling and Analysis of a Wind Turbine Blade based on Third-Order Structural Nonliearities

Rezaei, Mohammad Mahdi | 2016

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 49243 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Behzad, Mehdi; Haddadpour, Hassan; Moradi, Hamed
  7. Abstract:
  8. Aiming to improve the extraction performance of wind energy has led to the noticeable increase of the structural dimensions in the modern wind turbines. The larger blade with more flexibility experiences large structural deformation even under nominal operational loading, so the nonlinear modeling and analysis of these structures have become as important subject of the recent wind turbine researches. In this dissertation, the geometrical exact model of the rotating wind turbine blade under the effects of the tower tip's motion, and also the operational loading comprising the aerodynamic and gravitational loadings is presented. In this way, the geometrical exact beam formulation is developed to include all specification of the real blade of wind turbine. The closed-form straightforward formulation for the structural (using various strain criterion), inertial, aerodynamic and gravitational equations are constructed. The aerodynamic formulation is obtained by re-deriving the helicopter aerodynamic model in accordance with the presented geometrical exact formulation. Moreover, the aerodynamic model is updated according to the special condition the wind turbine application including: the change in velocity parameters orders, considering the yawed inflow condition and the offset of the aerodynamic loading. Furthermore, the presented direct transformation matrices (from PDE into ODE) of inextensional beam equations, is employed in problem analysis applying the reduced order model (ROM) and finite element method (FEM). After verifying the presented ROM in comparison with the finite element commercial software of ANSYS and also the wind turbine codes of FAST, it is used in numerous static and dynamic analyses. The results reveal that ROM developed based on applying coupled modes of the blade could efficiently predict results with enough accuracy. Moreover, the significant effects of the geometrical nonlinearities are demonstrated which mainly causes the coupled behavior through edgewise-flapwise-torsional DOFs; especially for the higher values of the blade deformations. In additional nonlinear studies, the effects of the torsion induced by lateral deformation, stiffening and softening behavior of stiffness variation in static and dynamic loading, and also the change in aeroelasticity stability status are investigated. In the final stage of this dissertation, the analytical method based on perturbation approach is applied for nonlinear dynamic analysis of the rotating blade under the super-harmonic excitation due to yawed inflow condition. In this way, after obtaining and verifying the closed form expression of the solution, it is used in some additional studies to investigate the changes in the steady amplitudes and phases, stability status and bifurcation behavior of the responses for different cases of blade and operational parameters
  9. Keywords:
  10. Wind Turbine ; Aeroelasticity ; Instability ; Bifurcation ; Geometrically Nonlinear Analysis ; Instability Analysis ; Rotating Blade

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