A new nonlinear dynamic analysis method of rotor system supported by oil-film journal bearings

This paper studies the nonlinear dynamic analysis of a flexible rotor supported by externally pressurized porous gas journal bearings. A time-dependent mathematical model for externally pressurized porous gas journal bearings is presented. The finite difference method and the Successive Over Relation (S.O.R.) method are employed to solve the modified Reynolds’ equation. The system state trajectory, Poincare´ maps, power spectra, and bifurcation diagrams are used to analyze the dynamic behavior of the rotor and journal center in the horizontal and vertical directions under different operating conditions. The analysis reveals a complex dynamic behavior comprising periodic and quasi-periodic response of the rotor and journal center. This paper shows how the dynamic behavior of this type of system varies with changes in rotor mass and bearing number. The results of this study contribute to a further understanding of the nonlinear dynamics of gas-lubricated, externally pressurized, porous rotor-bearing systems.

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Nonlinear Dynamic Analysis of a Rotor System With Aerodynamic Journal Bearings

Volume 5: Turbo Expo 2007 ◽

10.1115/gt2007-27748 ◽

2007 ◽

Author(s):

T. N. Shiau ◽

W. C. Hsu ◽

B. W. Deng

Keyword(s):

Nonlinear Dynamic ◽

Nonlinear Dynamic Analysis ◽

Journal Bearings ◽

Rotor System ◽

Least Square ◽

Filter Method ◽

System Response ◽

Recursive Least Square ◽

Bearing Force ◽

Rotor Mass

This paper investigates nonlinear dynamic characteristics of a rotor system with aerodynamic journal bearings. The Finite Difference Method (FDM) is employed to solve the Reynolds equation, which is used to determine the nonlinear compressible gas force of the aerodynamic bearing. By applying the gas bearing force to system equations of motion, the system response can be determined by the numerical integration method. Results show that the aerodynamic bearing will provide higher loading capacity to support the rotor when the eccentricity ratio is increased. The aerodynamic bearing force increases when the rotor is speeding up or the squeeze frequency is raised. The rotor trajectory presents aperiodic behavior, and it becomes significant as the rotor mass increases. When the squeeze frequency decreases or the rotor mass increases, the radius of the rotor trajectory will increase. Recursive Least Square Method and Kalman Filter Method are used to identify the aerodynamic bearing parameters from the system response. The parameters include the damping and stiffness coefficients of the aerodynamic bearing. According to the results of identification, both identified parameters by these two methods are in good accordance. The results show that the aerodynamic bearing force can be precisely identified and the system response can be quickly solved by the identified system with less computer time. But the identified system lost its accuracy as the rotor speed or the squeeze frequency increase because these will enhance the nonlinearity of the aerodynamic bearing force.

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