Aydin Boyaci

Nonlinear Oscillations of High-Speed Rotor Systems in Semi-Floating Ring Bearings

Semi-floating ring bearings are preferred to be incorporated in high-speed rotor systems since they usually provide a better vibration and damping behavior than full-floating ring bearings. Nevertheless, such rotor bearing systems can show whirl/whip instabilities as well which lead to subsynchronous oscillations in addition to synchronous oscillations due to unbalance. Moreover, a critical bifurcation can take place into a regime of subsynchronous oscillations with extremely high amplitudes which resembles Total Instability known from investigations of full-floating ring bearings. To illustrate the various types of subsynchronous oscillations, different rotor models are investigated under the influence of semi-floating ring bearings. First, transient run-up simulations are performed to outline the nonlinear phenomena. Then, the stability and bifurcation behavior is analyzed in detail by using the methods of numerical continuation.

Efficient Thrust Bearing Model for High-Speed Rotordynamic Applications

The dynamic behavior of rotor systems is influenced by thrust bearings. Therefore, a time-efficient model of oil-lubricated thrust bearings is introduced within this contribution. The areas of application for this bearing model are multibody simulations and more specifically high-speed rotordynamic systems. The Reynolds equation is solved at each pad of the bearing for the calculation of the fluid-film forces and moments, where the effect of misalignment of the shaft is also considered. For the solution of Reynolds equation the weak formulation is used, i.e. the Galerkin approach. This optimized bearing model results in heavily reduced simulation times especially if they are compared to the relatively large simulation times needed in co-simulations. The applied procedure can be easily implemented into commercial software and is flexible for investigating any bearing geometry and number of pads. Finally, the effect of the thrust bearing is studied in run-up simulations on an example rotor-bearing system.