The defect of wear in journal bearings appears usually after long-time operation of rotating systems and the main symptom is the decrease in the bearing load carrying capacity. Wear in aligned or misaligned pattern can result in higher eccentricities of whirling and changes the properties of stiffness and damping of the fluid film. In this work the operation of worn journal bearings is investigated by incorporating a radial active magnetic bearing (AMB) on the same shaft which acts as a collocated sensor/actuator unit. This combination offers a possibility to identify and observe the characteristic symptoms that the wear provokes under external excitation and without disturbance from the nominal operation conditions of the system. Under specific electromagnetic excitation the harmonic components that are introduced due to wear are detected. A simple rotor mounted in two worn journal bearings is used and the response at steady operational speed and at transient electromagnetic external excitation with linearly varying frequency (chirp) is analyzed in the time and frequency domains. The occurrence of additional sub- and super-harmonic components is observed when the external frequency lies in the region of the first natural frequency of the operating system. The time-frequency analysis discloses the onset of additional frequency components, especially in the sub-harmonic domain. This offers a distinct detection of wear if wear depth becomes higher than 20% of the radial clearance. An experimental test rig is outlined for future studies in order to benchmark the observations from the present numerical calculations.

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