Analysis of the sensitivity to non-linear effects in the oil-film forces of journal bearings

Often, the presence of unexpected super-synchronous harmonic components in the vibrations of rotating machines is considered a reliable symptom of serious faults like: shaft cracks, rotor-to-stator rubs and severe misalignments. However, the not unusual occurrence of malfunctions that cause high synchronous vibration levels can generate non-linear forces in oil-film journal bearings, which, in turn, give rise to unexpected super-synchronous vibrations of the shaft. The knowledge of the sensitivity to non-linear phenomena in oil-film journal bearings can give significant information that allows the identification of false faults to be avoided. This paper shows the results provided by a model-based method focused on the investigation of the influence of the synchronous vibration level on the generation of non-linear effects in the behaviour of oil-film journal bearings and super-synchronous vibrations in rotating machines