In this thesis, the nonlinear vibration characteristics of a rotor-bearing system supported by the fluid film journal bearing are analyzed numerically when the external sinusoidal disturbances are given to the bearing continuously. Also, the cavitation algorithm implementing the Jakobsson-Floberg-Olsson boundary condition is adopted to predict cavitation regions in the fluid film more accurately than a conventional Reynolds boundary condition. And the stability characteristics of a rotor-bearing system supported by the actively controlled fluid film journal bearing are numerically investigated. Proportional control, derivative control, integral control, proportional-derivative control and synchronous control are used for the control algorithm of the fluid film journal bearing.
When the external disturbances are applied to the bearing, the range of the full film region varies with periodic at steady state response, and it becomes smaller than its range of the static equilibrium state. The difference between the linear and the nonlinear analysis dependents upon the excitation frequency of the external disturbance, and it becomes much more remarkable as the vibration amplitude or the frequency of the external disturbance increases. It is also shown that the whirl instability of a rotor-bearing system can be suppressed effectively by actively controlled fluid film journal bearing. In the case of proportional control and derivative control, the stability threshold speed of a rotor-bearing system is increased with control gain. And the control of the coupled control gain is more effective than the control of the uncoupled control gain for the stability improvement of a rotor-bearing system.
In summary, the nonlinear vibration characteristics of a rotor-bearing system supported by the fluid film journal bearing are summarized, and the active control of the fluid film journal bearing can be adopted for the stability improvement of a rotor-bearing system.