Nonlinear Analysis of Stability and Rotational Accuracy of an Unbalanced Rotor Supported by Aerostatic Journal Bearings

This paper presents the nonlinear analysis of stability and dynamic rotational accuracy of an unbalanced rotor supported by aerostatic journal bearings. A finite element method is utilized with the Runge-Kutta fourth order method to solve the transient Reynolds equation and the rotor dynamics equations simultaneously for the dynamic response analysis of the rotor. The dynamic behavior of the rotor center is analyzed under different rotor masses. It is shown that the dynamic responses of the rotor strongly depend on the rotor mass. The periodic, multi-periodic or quasi-periodic motions are observed as the rotor mass changes. Under a given operating speed, the mass at which the resonance occurs is studied and its relationship with the mass of the rotor at the threshold of instability is found for the first time. The influences of supply pressure, bearing clearance, orifice diameter and eccentric distance on the rotational accuracy, the resonance and instability threshold are also investigated. The result of this study can provide guidance for designing aerostatic bearing rotor systems with required running accuracy and stability.