Model updating of rotors supported on journal bearings

Abstract

Heavy power-plant rotors are generally supported on journal bearings. However, hydrodynamic actions in journal bearings generate spin speed-dependent stiffness and damping forces, which induce instability beyond a spin speed limit called the stability limit speed. The presence of other rotating forces such as due to internal friction may further decrease the stability limit speed. Therefore, identification of journal bearing parameters and other rotating damping forces is important. This work extends Inverse eigen-sensitivity method to update a finite element model of a rotor-shaft system to identify journal bearing parameters and internal friction. Eccentricity ratio and coefficient of shaft material damping are updated in this process to identify bearing model and internal friction force at any speed. Updating of eccentricity ratio to identify journal bearing coefficients as proposed in this work is a novel approach that eliminates the need to update eight bearing coefficients per bearing and hence helps in effective parameterization in the model updating process.