Abstract: Not only the stability of the steady state response and thebistable response but also the jumping characteratics is analysed, whensystem accelerates or decelerates through the bistable region of flexiblerotor-centralised SI1DB system. The research conclusions are:(1)Thesystem steady state responses have two unstable regions.(2)The la-rger the unbalance parameter and the smaller the bearing parameter andthe external damping ratio, the easier for system to lose stability. (3)The larger the mass ratio and the srr}aller the stiffness ratio, the lo-wer the threshold rotating speed cf instability. The instability of sys-tem steady state response determi ied in this paper is due to the sys-tem nonsynchronous response in many cases. Besides, only when theinitial rotating speed is ahead of the bistable region and system acce-lerates through bistable region, bistable jumping can occur, The smallsolution of bistable response ismorestable than the large one.

Key words: flexible rotor, squeezed film damper, steady utdte response and bistable response.