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Vibration and Stability Analysis of a Rotor with Nonlinear Bearings

Hojjati, Mohammad | 2021

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 54280 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Haddadpour, Hassan; Mohammad Navazi, Hossein
  7. Abstract:
  8. In the present study, the nonlinear vibrations of the rotor on the nonlinear bearing have been studied by the multiple scale method. To achieve this goal, Jeffcott models, two degrees of freedom and rotating Euler-Bernoulli beam have been used as rotors and insulators and nonlinear tilting-bearing bearings have been used as supports.To better understand the importance of the supports in the analysis of rotating systems, the rotor joints with isolates with high static stiffness and low dynamic stiffness have been considered and the dynamic behavior of the system has been studied using the multiple scale method. The results of this study showed that this type of nonlinear isolator has a good efficiency to reduce the vibrations of the rotors. To better understand the role of bearings and since bearings play an important role in the dynamic behavior of the system, a nonlinear model based on dynamic coefficients has been proposed to simulate the dynamic behavior of a tiling-bearing bearing.The methods of partial derivatives, perturbations and finite difference are used simultaneously to solve Reynolds equations and linear and nonlinear reduced order coefficients are extracted and presented. The effect of parameters such as bearing-to-diameter ratio, number of pads and how the pads are placed has been investigated and the results are shown graphically. In this study, to ensure the accuracy of the results, dynamic coefficients have been compared with other reliable sources in this field.The linear and nonlinear dynamic coefficients of the bearing have been used to analyze the dynamic behavior of the rotor-bearing system. For this purpose, first, assuming it is rigid, the rotor is modeled by a two-dimensional discrete model, and its main resonance and stability are studied using the second-order multiple-scale method. In the last step, assuming the flexibility of the rotor, the Bernoulli rotary Euler beam model is used and the primary, secondary and combined intensification of the rotor are investigated and the effects of parameters such as excitation frequency and excitation force on the amplitude of vibrations are studied.Using the results of these studies, it was shown that the nonlinear coefficients of the bearing can cause phenomena such as jumping, softening or stiffening in the system. Due to these phenomena, the system at frequencies close to the linear frequency may have more than one stable answer
  9. Keywords:
  10. Rotor ; Multiple Scales Method (MMS) ; Primary Resonance ; Nonlinear Vibration ; Combined Resonance ; Secondary Resonance ; Tilted Bearings

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