The nonlinear dynamics of journal bearings

Abstract

The journal bearing is ubiquitous in moving mechanical systems, and is a major potential target for study in the field of lubrication theory. Despite this, theoretical understanding of its dynamic behaviour is far from complete ; in particular the essentially nonlinear interplay of rotor dynamics and fluid dynamics of the lubricant has been studied only very recently. Our own investigations have been mainly numerical, and have revealed a wide range of qualitative behaviour. They have confirmed the great importance of cavitation of the lubricant, and the sensitivity to geometrical features of the bearing. Additionally they have enabled us to identify the crucial non-dimensional parameters and their critical values. Finally they have stimulated analytical approaches (e.g. searches for Hopf bifurcations). In this paper we exploit the conceptual approach of dynamical systems theory to present many of our results in a succinct form. Our aim is to make clear not only the extent of understanding of the problem, but also the present shortcomings of theory that require further study.