Alternative linear dynamic analysis method for gas foil bearing rotor systems using bearing [formula omitted]-domain impedance

Abstract

Linear dynamic analysis of bearing rotor systems is a basic content of system design. For gas foil bearings (GFBs), the force coefficients method remains the most popular method in engineering practice. However, applying the force coefficients method in the modal analysis of damped free vibrations gives inaccurate modal parameters and, more importantly, leads to missing some important modes. This paper proposes a new linear dynamic analysis method using bearing s-domain (complex frequency-domain) impedance. The bearing s-domain impedance matrix is derived for the first time to characterize the linear dynamic characteristics of GFBs. Then, the linear dynamic analysis method of the GFB rotor system using bearing impedance is presented. The standard eigenvalue problem can be established based on the state–space representation of the bearing impedance matrix. It is found that the combined complex form of force coefficients is the bearing impedance evaluated on the imaginary axis in the s-plane, and the bearing impedance can be identified using the force coefficient data. This makes the proposed method possess the main advantage of the force coefficients method. The proposed method has no inherent error because the state variables relating to gas film and foil are preserved. The error only comes from the impedance fitting process and is controllable. Numerical examples have verified the effectiveness of the proposed method. This method can serve as an alternative to the force coefficients method.