HOPF-BIFURCATION IN ROTORS SUPPORTED IN GAS-BEARINGS

In this paper we describe a problem of control of the Hopf bifurcation . We illustrate the problem by three examples of a rotor system suppor ted in two gas bearings. The bearing bushes are connected to the casin g by means of additional air rings. In the case when parameters of the air ring are improperly chosen, at a sufficiently high rotational vel ocity the rotor undergoes the Hopf bifurcation and the bearing may be damaged by the growing amplitude of self-excited vibrations. We may av oid this danger by a proper selection of stiffness and damping coeffic ients of the air ring or, in the worst case, by a temporary change of the stiffness or damping coefficients of the air ring. Our method then guarantees a safe passage through the unstable zone between the Hopf and reversed Hopf bifurcation points. (C) 1997 Elsevier Science Ltd.