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Effects of shaft flexibility and gyroscopic coupling on instability threshold speeds of rotor-bearing systems
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
Vattenfall Research & Development.
2010 (English)In: 13th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery 2010 (ISROMAC-13): Honolulu, Hawaii, USA, 4 - 7 April 2010, Red Hook, NY: Curran Associates, Inc., 2010, 537-543 p.Conference paper (Refereed)
Abstract [en]

The driving speeds at which self-excited motions occur in rotor-bearing systems are commonly referred to as "instability threshold". These speeds and the magnitude of rotor (journal) trajectories are two important variables characterising the limits and states of a rotating machinery. The hydrodynamic lubrication in journal-bearing provides damping and reduces friction on rotor systems; therefore the journal amplitude should not exceed the bearing radial clearance. Linear bearing models are not able to accurately predict the journal trajectories for rotor-bearing system operating in conditions where the system does not have period one solutions, or when the journal motion is larger than 20-30% of the bearing radial clearance. Therefore the nonlinear bearing impedance descriptions method was used to model the hydrodynamic reaction forces. Two cases were analysed: 1) a rigid non-symmetric rotor and 2) a flexible non-symmetric rotor. The two models consist of a rotor supported by two identical finite-length hydrodynamic journal bearings of length to diameter ratio L/D=1, with same lubricant properties. The flexible non-symmetric rotor was modelled by the finite element method (FEM). Simulation results show that the instability threshold of the rigid non-symmetric rotor-bearing system (case1) depends on the low stability characteristics of the less loaded bearing. But when the shaft flexibility and the gyroscopic coupling effect are taken into account; the instability threshold increases for the flexible non-symmetric rotor-bearing system (case2). The gyroscopic coupling effect does not only increase the instability threshold, but the journal trajectories magnitude has also significantly increased. This is normally not a preferable condition since high vibrations will induce heat and stress in babbited bearing.

Place, publisher, year, edition, pages
Red Hook, NY: Curran Associates, Inc., 2010. 537-543 p.
Research subject
Solid Mechanics
URN: urn:nbn:se:ltu:diva-40709Local ID: ff0f2660-5921-11df-b6eb-000ea68e967bISBN: 9781617388484OAI: diva2:1014230
International Symposium on Transport Phenomena and Dynamics of Rotating Machinery : 03/04/2010 - 07/04/2010
Godkänd; 2010; 20100506 (jealun)Available from: 2016-10-03 Created: 2016-10-03Bibliographically approved

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