On the stabilizing effect of support asymmetry in rotordynamics

One of the causes of rotor instability is the damping of the rotating parts of the system. Its de-stabilizing effect can be counteracted only by introducing a suitable non rotating damping, with the instability threshold increasing with increasing ratio between non rotating and rotating damping. The aim of the present paper is showing that support anisotropy tends to increase the stability of the system, an effect here shown to take place in both cases of viscous and hysteretic damping. A heuristic explanation of the stability increase due to support anisotropy can be given considering that anisotropic supports usually cause the orbits to be elliptical, which increases energy dissipation due to rotating damping. Actually, no increase of the instability threshold was observed in a case in which the orbits remain circular in spite of the anisotropy of the supports