Rotor–stator contact dynamics using a non-ideal drive—Theoretical and experimental aspects Said Lahriri a,c , Hans I. Weber b , Ilmar F. Santos a,n , Henning Hartmann c a Technical University of Denmark, Department of Mechanical Engineering, Nils Koppels Alle´, Bygning 403, DK-2800 Kgs. Lyngby, Denmark b Pontifı ´cia Universidade Cato ´lica, PUC-Rio de Janeiro, Department of Mechanical Engineering, Rua Marquˆ es de S ~ ao Vicente, 225-Ga ´vea-22453-900 Rio de Janeiro, Brazil c Lloyds Register ODS Strandvejen 104A 1., DK-2900 Hellerup, Denmark article info Article history: Received 6 September 2011 Received in revised form 4 April 2012 Accepted 6 May 2012 Handling Editor: L.N. Virgin Available online 8 June 2012 abstract The possible contact between rotor and stator is considered a serious malfunction that may lead to catastrophic failure. Rotor rub is seen as a secondary phenomenon caused by a primary source, i.e. sudden mass unbalance, instabilities generated by aerodynamic and hydrodynamic forces in seals and bearings among others. The contact event gives rise to normal and friction forces exerted on the rotor at impact events. The friction force plays a significant role by transferring some rotational energy of the rotor to lateral motion. A mathematical model has been developed to capture this for a conventional backup annular guide setup. It is reasonable to superpose an impact condition to the rub, where the rotor spin energy can be fully transformed into rotor lateral movements. Using a nonideal drive, i.e. an electric motor without any kind of velocity feedback control, it is even possible to stop the rotor spin under rubbing conditions. All the rotational energy will be transformed in a kind of ‘‘self-excited’’ rotor lateral vibration with repeated impacts against the housing. This paper studies the impact motion of a rotor impacting a conventional backup annular guide for the case of dry and lubricated inner surface of the guide. For the dry surface case, the experimental and numerical analysis shows that the rotational energy is fully transformed into lateral motion and the rotor spin is stopped. Based on this study this paper proposes a new unconventional backup bearing design in order to reduce the rub related severity in friction and center the rotor at impact events. The analysis shows that the rotor at impacts is forced to the center of the backup bearing and the lateral motion is mitigated. As a result of this, the rotor spin is kept constant. & 2012 Elsevier Ltd. All rights reserved. 1. Introduction The dynamics and behavior of the rotating system has been studied extensively in the past by many researchers. One of the initial studies of a high-speed rotor touching a rigid body was conducted by Szcygielski [1]. The model was based on a gyro pendulum touching a plane rigid body. The mathematical model was piecewise linear and globally strongly nonlinear. The preliminary experiments showing the trajectories of the gyro axis showed a good qualitative agreement with the analytical and experimental results. Among many, Muszynska [2] presented a comprehensive literary survey on rub- related phenomena up to 1989. Additionally, Beatty [3] introduced a mathematical model where the stiffness is given in a Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jsvi Journal of Sound and Vibration 0022-460X/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jsv.2012.05.008 n Corresponding author. Tel.: þ45 4525 6269; fax: þ45 4593 1577. E-mail address: ifs@mek.dtu.dk (I.F. Santos). Journal of Sound and Vibration 331 (2012) 4518–4536