651 A low frequency vibration of an overhang rotor on water lubricated bearings

If we use water-lubricated bearings for an overhang turbo machine to obtain high efficiency, it is important to assure vibration reliability, because the damping of the bearing placed far side of overhung part becomes very small. To figure out the vibration characteristics of rotors of this type, we conducted vibration tests of a motor mounted rotor. We observed jump phenomenon of vibration amplitude and sub-harmonic vibration on these tests. We considered these phenomena are caused by the gap around magnets of motor, and conducted numerical simulations to verify the assumption. The calculated results agreed well with measured results.