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Stability analysis and dynamic behaviour of a flexible asymmetric rotor supported by active magnetic bearings

Attia Hili M., Bouaziz S., Haddar M.

Journal of Theoretical and Applied Mechanics

2017

Vol. 55 nr 3

751--763

The objective of this work is to show the influence of dynamic characteristics of Active Magnetic Bearings (AMBs) on the stability and dynamic response of an asymmetric and unbalanced rotor. Indeed, AMBs have been successfully applied in several industrial machinery facilities. Their main advantages are the contactless working principle, frictionless suspension and operation in very high speeds. Firstly, the AMBs dynamic support parameters have been obtained through electromagnetic theory. Then, a generalized system equations of motion have been derived using the finite element method. The motion of a rotor the shaft cross-section of which is asymmetric is generally governed by ordinary differential equations with periodic coefficients. Floquet’s theory is used to investigate the stability of this system of equations. Finally, numerical simulation results are presented and discussed.

Processing Transient Response of a Flexible Rotor-Bearing System with Unbalanced Disk

Attia Hili M., Bouaziz S., Maatar M., Fakhfakh T., Haddar M.

Machine Dynamics Research

2010

Vol. 34, No. 1

23-37

Turbomachinery rotors are frequently supported on several oil lubricating bearings and so are statically indeterminate. In such cases, the bearings reaction forces and hence their stiffness and damping properties affect the relative location of the bearing centres, thereby significantly the vibration behaviour of the rotor bearing system. In this paper, the dynamic behaviour of symmetrical rotor bearing system with unbalanced disk is analyzed based on a continuum model. The finite difference method is employed with the successive over relaxation technique to solve the Reynolds equation. The finite element method with an iteration scheme is adopted in the analysis of the system state trajectories. Bearing's stiffness and damping are considered. The motions of journal and disk have been simulated with Newmark method. Linear transient simulation, with time integration procedure, and unbalanced responses are investigated. The present results provide a deeper understanding to predict undesirable behaviour of the rotor and bearings centres can be avoided.