Abstract:

The dynamic characteristics of cracked rotors and their early fault diagnosis are one of the key tasks of rotating machinery, which have been focused by many researchers. In this paper, a rotor with a transverse crack, supported on a nonlinear oil film bearing, is investigated. The bearing is considered as a long one or a short one. With consideration of the crack and the nonlinear oil film force together, the movement equation is set up and solved by the Newmark method. And their spectra are compared with the rigid support case. The results show that the oil film force affects the vibration of the cracked rotor heavily, and always reduces it. This will make it more difficult to diagnose its early faults. So when a cracked rotor is going to be studied, the conditions of bearing must be taken into account and a reasonable nonlinear dynamic model should be set up.

Key words: cracked rotor, fault diagnosis, oil film force, bearing, dynamic model