Vibration reduction of a rotating machinery by magnetic damper with rotating circular magnet (nonoccurrence of an unstable vibration caused by magnetic damping force)

The magnetic damping force is generated by not only a rotating-conductor- type magnetic damper composed of a rotating conductor and a fixed magnet but also a rotating-magnet-type magnetic damper composed of a rotating magnet and a fixed conductor. In the previous report, it was demonstrated analytically and experimentally that a rotating conductor-type magnetic damper for a rotating machine caused unstable vibrations at a rotating speed over the critical speed. In this report, the authors show that the rotation of the axisymmetric magnet on its axisymmetric axis affects the magnetic damping force very slightly by a simple experiment, and that a rotating-magnet-type magnetic damper for a rotating machine can be modeled by considering the whirling of the magnet only. As the resit, the rotating-magnct type magnetic damper never generates unstable vibrations analytically. The analytical results agree well with the experimental ones.