Unstable Vibration of a Rotating Machine Caused by a Magnetic Damping Force.

Abstract

Using the infinitesimal loop model that is moving through the nonuniform magnetic field in space, the effective expression of the magnetic damping force is derived. This method has an advantage of calculating no scalar potential and it is easy to compute the magnetic damping force by using the static magnetic field obtained by FEM, measurements and so on. By the way, a magnetic damper used in turbo-molecular pump and so on in order to reduce vibration sometimes generates unstable vibrations. In this report, it was made clear that the Jeffcot rotor with the magnetic damper generated the unstable vibration in the experiment over a critical speed, and the present method was available for investigating the cause of the unstable vibration due to asymmetric stiffness matrix. Then a good agreement between the analytical and experimental results was confirmed.