Abstract
The application of active magnetic bearings (AMBs) enables turbomachinery to increase power density, controllability and resilience to external disturbances. However, due to the limited load capacity of AMBs, base shock excitations may result in contact between the rotor and the touchdown bearings (TDBs), which can seriously damage the machine. This paper presents a dynamic analysis of a rotor-AMB-TDB system experiencing strong base shocks while the AMBs are operating. The contacts between the rotor and the TDBs, and the rolling-ball contacts within the TDBs are modeled based on the Hertzian contact theory. A PD controller is designed, considering saturation. The dynamic equations were solved numerically, and the results showed three different rotor motion modes after base shocks. FFT spectra, STFT spectra, Poincaré maps and bifurcation diagrams were used for the dynamic analysis. Unsuitable system parameters, including unbalance eccentricity, radial clearance, equivalent stiffness and damping ratio, may lead to complex behaviors including periodic, KT-periodic, and quasi-periodic responses as well as jump phenomena. This study reveals the mechanism of nonlinear responses, provides a method for predictions, and helps with controller designs for rotor re-levitation.
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