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Investigation of Nonlinear Vibration and Stability Analysis of Rotor with Journal and Axial Bearings

Abbasi Gaznag, Meisam | 2021

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 54188 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Haddadpour, Hassan
  7. Abstract:
  8. Vibrational analysis of a rotor with journal and axial bearings requires modelling of forces acted on the journal of the rotor by the bearings. The aim of the present research firstly is to extract the linear dynamic coefficients of the tilting-pad thrust bearing and then to analyze nonlinear vibrations and stability of the rotor. By use of the partial derivative method along with Perturbation method the linear dynamic coefficients are calculated. Full dynamic coefficients are extracted by solving Reynolds equation and its perturbed forms using finite difference method. Dynamic equilibrium equations of pad are used to obtain reduced-order dynamic coefficients. In the following the equations of motion of four degree of freedom rigid rotor is derived. Linear dynamic coefficients of the thrust bearing along with the linear and nonlinear dynamic coefficients of the journal bearings are used in order for modelling of forces in these bearings. The Multiple Scales method is used to solve the equations of motion and analyze forced vibrations and stability of the rotor considering primary and internal resonances. Finally results of partial derivative method are validated and the effect of axial force and rotational speed on the dynamic coefficients is studied. The results reveal that the magnitude of the dynamic coefficients will increase by decrease in rotational speed and increase in axial force. The results of vibrational analysis are validated with the results of the numerical Runge-Kutta method. The results show great influence of the nonlinear effects on the amplitude and stability of vibrations in the presence of internal and primary resonances. If there was only primary resonance, response of the system would be same as the response of equivalent linear system
  9. Keywords:
  10. Nonlinear Vibration ; Primary Resonance ; Multiple Scales Method (MMS) ; Internal Resonance ; Dynamic Coefficients ; Rotor Stability

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