Analytical and Experimental Investigation of a Magnetic radial Passive Damper

Passive radial magnetic bearings are well suited for magnetic bearing systems both for one active-axis type and for hybrid solutions in which a passive radial magnetic bearing works together with a conventional rolling element bearing for stability. In both cases^ and particularly in the first one, the damping of the system is a critical factor to achieve the required performance, as the very low stiffness and damping characterizing the radial passive suspension can cause severe dynamic problems. The possible existence of instability regions within the supercritical working range must be avoided by adding adequate damping elements. An eddy-current passive radial damper with a simple geometrical configuration is studied firstly using analytical techniques of different complexity. The distribution of the magnetic flux density in the conductor is obtained through FEM numerical modeling. The.results obtained through the combined analytical and numerical technique are found in very good agreement with those obtained through experimental testing. The passive radial damper here studied can have applications beyond the field of passive radial magnetic bearing as it allows to raise the threshold of instability of a rotor of any type with the addition of a simple and basically low-cost device. If the magnetic field is supplied by an electromagnet instead of a permanent magnet, the possibility of supplying a damping which is both controllable and well predictable is an attractive feature added to its simplicity and low cost.