Hysteretic whirl stabilization in rotor-shaft-bearing systems on dry friction suspension

SUMMARY. The undesired whirl of rotating machines can be reduced by elastic journal box suspension systems equipped with dry friction dampers. The critical speeds can be cut off by the adhesion of the friction surfaces and the whirl amplitude can be restrained throughout the remaining sliding range by a proper choice of the suspension-to-shaft stiffness ratio and of the support-to-rotor mass ratio. The dry friction forces counteract also efficiently the well known destabilising effect of the shaft hysteresis in the supercritical range. This lecture deals firstly with the natural precession speeds, investigates the steady response to unbalance and defines the ranges of adhesive or sliding contact. Then, the stabilisation “in the small” of the hysteretic whirl by means of other external dissipative sources is studied applying the Floquet approach through a perturbation procedure, while the stability “in the large” is checked by the direct numerical solution of the motion equation.