Stability and bifurcation phenomena of Laval/Jeffcott rotors in semi-floating ring bearings

Abstract

Within this contribution, a linear-elastic Laval/Jeffcott rotor is considered, which is symmetrically supported in two identical semi-floating ring bearings. Run-up simulations and bifurcation analyses are carried out to investigate the stability and bifurcation phenomena of the rotor-bearing system. In particular, the methods of numerical continuation are applied to identify the nonlinear phenomena (jump phenomena, coexistence of solutions, etc.) and the corresponding bifurcations. The occurrence of subsynchronous oscillations is examined, which is caused by an oil whirl/whip instability due to the inner oil films. In this case, the main damping is provided by the outer oil films so that the oscillation amplitudes usually remain moderate. Besides these well-known subsynchronous oscillations with moderate amplitudes (oil whirl/whip instability due to the inner oil films), it is shown that self-excited oscillations with very high amplitudes also exist. This effect resembles Total Instability known from rotors in full-floating ring bearings. A detailed bifurcation analysis proves the coexistence of a so-called critical limit cycle with high amplitudes in the case of the perfectly balanced rotor which represents Total Instability. Finally, a variation of rotor and bearing parameters shows the influence on both the subsynchronous oscillations of tolerable amplitudes and the critical limit cycle oscillations.