A novel method for calculating the dynamic force coefficients of Gas Foil Bearings and its application in the rotordynamic analysis

Bearing force coefficients are a fundamental and convenient concept in the dynamic analysis of a bearing-rotor system. However, for a rotor system supported by gas foil bearings (GFBs), recent studies have shown that the onset speed of instability (OSI) predicted using the force coefficients model is inconsistent with that obtained using nonlinear time-domain analysis. To solve this problem, this study proposed a novel method for calculating the dynamic force coefficients of GFBs. The correctness and effectiveness of the proposed method were confirmed by examining the calculation of the bearing force coefficients, the stability prediction and the calculation of unbalance responses. For a classical symmetric GFB-rotor system, application of the proposed calculation method demonstrated that the OSI predicted by the force coefficients model can be in complete agreement with the OSI predicted by the fully coupled model for all compliance levels. This indicates that the force coefficient method has the potential to make accurate prediction for the stability characteristics of GFB-rotor systems. Furthermore, the proposed method is derived based on the general dynamic equation for linear structures; hence it is able to adopt a complex foil structure model. The one-dimensional finite element foil model that considers detachments of the top foil from the bump foil was used to show the ability of the proposed method to use a complex foil structure model.