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بررسی ارتعاشات غیرخطی پوسته‌های مخروطی در حضور جریان سیال داخلی و خارجی
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بررسی ارتعاشات غیرخطی پوسته‌های مخروطی در حضور جریان سیال داخلی و خارجی

رحمانیان، محمد Rahmanian, Mohammad

Nonlinear Vibrations of Conical Shells with Concurrent Internal and External Flows

Rahmanian, Mohammad | 2016

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 49125 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Dehghani Firouz Abadi, Ruhollah
  7. Abstract:
  8. In the current study, nonlinear vibration and stability of conical shells with both separate and concurrent internal and external flows are studied. External and internal flows are in the supersonic and subsonic regimes, respectively. The Krumhar’s aerodynamic piston theory is utilized to model the external loading on the structure as well as the compressible potential flow model to capture the internal fluid dynamics. The so-called compressible fluid model is obtained via simplification of the Navier-Stockes equations after applying the inviscid and irrotational assumptions. The nonlinear structural equations of motion are derived using the Hamiltonian dynamics approach and utilizing the Flugge theory assumptions. Shear deformation effects are included to provide a feasible model for short and thick shells. In order to solve the structural equations of motion, a Ritz-based (Energy-based) approach is followed (this approach is also denoted as the extended Galerkin method) and the free vibration characteristics are obtained for all possible combinations of the classical boundary conditions. The proposed algorithm is so flexible in modeling all classical and elastic boundary conditions and also rapid convergent. The convective fluid equation governing the internal fluid flow is solved by the finite element method and verified by several commercial and academic packages. Moreover, the structural motions and fluid loadings are interrelated via the so-called impermeability condition present at the interface and the Bernoulli relation. Verifications of the free vibration results of the coupled-field problem (with internal fluid) are conducted. The efficiency of solution is then enhanced by developing a robust reduced order model (ROM) based on the static condensation technique. This ROM minimizes the number of required degrees of freedom and consequently the computational costs, especially in nonlinear analysis. Both stationary and flowing internal air/liquid containments are considered and the corresponding dynamical and stability behaviors are investigated. Stability margins for both conical and cylindrical shells with internal flows are also provided for the first time in literature for 8 sets of structural and 4 sets of fluid boundary conditions by a single unified solution procedure. A comprehensive study is then conducted over the linear stability of conical shells with external supersonic flows at three sets of structural boundary conditions. Effect of static prestress loading on the dynamics of different shells is also investigated. The present research is culminated by the nonlinear results for 3 cases which are namely, nonlinear shells with internal flows, nonlinear shells with external flows and nonlinear shells with concurrent internal and external fluid loadings. Nonlinear post-flutter analysis are provided for clamped-free conical and cylindrical shells in the form of time history plots, phase plots, FFT-PSD plots and Poincare maps and a variety of periodic, quasi-periodic and chaotic motions are detected
  9. Keywords:
  10. Compressibility ; Chaotic Behavior ; Conical Shell ; Nonlinear Vibration ; Fluid-Structure Interaction ; Fluid Flow

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