Analysis of Whirling Vibration Due to Morton Effect by Using Frequency Transfer Function Model in Journal Bearings

Abstract

In recent years, rotating machinery has been required to operate at high rotational speeds for high efficiency. However, with increase in the rotational speed, the rotating machinery may become unstable. One cause of unstable vibrations is the Morton effect that occurs in journal bearings. Thus, developing a mathematical model to predict the Morton effect is desirable to avoid the occurrence of such unstable vibrations. In this study, a model based on a frequency response that can quantitatively evaluate the Morton-effect-induced vibrations in rotating machinery supported by a journal bearing was developed. Experimental data were collected for modeling by using an experimental rig. Using the experimental data pertaining to the journal position in the journal bearing and temperature of the journal, a model for the Morton effect was established based on the frequency responses. From a control engineering viewpoint, the journal bearing was considered to be a proportional differential controller. In addition, the Morton-effect-induced vibrations were considered as a new bending mode of a rotating shaft, caused by thermal differences. Subsequently, the developed model was evaluated in the frequency domain. The characteristics of the vibrations, determined using the proposed model, exhibited good correlation with those corresponding to experimental data. The experimental data agreed well with the predicted results, and the results demonstrated the usefulness of the proposed method for predicting the Morton effect.