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The stable and unstable vibrational characteristics of rigid shafts symmetrically supported on short journal bearings are obtained directly from Reynolds equation and conveniently represented in terms of two important parameters.

This paper describes work in which the feasibility of controlling the synchronous and non-synchronous vibrational behaviour of a flexible rotor was investigated using squeeze-film isolators in series with the supporting journal bearings.

The non-linear dynamics of a multimodal exible rotor running in an unsupported squeeze-lm damper (SF D ) bearing are investigated analytically and experimentally. The main aim is to assess the ability to predict and explain the non-linear performance using an integrated analytical technique and a standard model for the SF D . A fast harmonic balance method that uses receptance functions is used to determine periodic solutions. A modal-based approach is used for the analysis of the stability and bifurcation of these solutions, as well as the analysis of aperiodic motion. N onsynchronous motion with combination frequencies and subharmonic motions are correctly predicted. It is also shown that such an SF D introduces subcritical superharmonic resonance when it is apparently inactive. It is concluded that, despite the economy in design, the bene ts of using an unsupported SF D in a exible rotor-rigid bearing housing system are dubious. NOTATION a …s † X J , a …s † Y J , a …s † X B , a …s † Y B displacement cosine coef cients (m) A x , A y x , y half peak-to-peak displacements (m) b …s † X J , b …s † Y J , b …s † X B , b …s † Y B displacement sine coef cients (m) c radial clearance (m)

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