Internal Resonances of a Cracked Rotor : Major Critical Speed and Critical Speeds in Precritical Range

Internal resonances of cracked rotors are studied using rotor systems with two degrees of freedom. Phenomena at the major critical speed and other subcritical speeds in the precritical speed range are discussed theoretically and experimentally.Phenomena in a deflection (lateral) oscillation model with internal resonances and an inclination oscillation model with no internal resonance are compared. In the former model, critical speeds of a forward and a backward whirling modes coincide and, as the results, the following phenomena occur: (a) The vibration of a synchronous backward whirling mode changes from a steady-state oscillation to an unstable oscillation due to an internal resonance. (b) Superharmonic resonances of 2nd and 3rd orders of backward whirling modes and a super-subharmonic resonance of 3/2-order of a backward whirling mode occurs due to an internal resonance.