Parametric Analysis Focused on Non-linear Forces in Oil-film Journal Bearings

Many investigation methods used to identify the most common faults in rotating machines do not consider the non-linear behaviour of oil-film journal bearings with an adequate care. This chapter shows the results of a parametric analysis performed to study the sensitivity of non-linear effects in the oil-film forces to changes of some parameters of the synchronous (1X) filtered orbit of the journal. This study is focused on the influence on non-linear forces caused by changes of the maximum amplitude and circularity of the journal orbit as well as by changes of the inclination angle of the major principal axis of the 1X elliptical orbit. Moreover, also the effects of the shaft rotational speed, bearing load and the average journal position have been taken into account. A procedure to perform this sensitivity analysis for different types of journal bearing is described. Then, the results obtained by the analysis of the behaviour of a two-lobe elliptical oil-film journal bearing are shown and discussed.