Novel Eddy Current Damping Mechanism for Passive Magnetic Bearings

Abstract

It is often advantageous to add lateral damping in rotating systems to suppress excessive vibration in both the transverse and torsional directions. Magnetic dampers are advantageous to other damping mechanisms because they provide damping independent of temperature, and are non-contact in nature, which allows for maintenance and lubrication free operation. These damping mechanisms function through the eddy currents that are formed in a conductive material when it is subjected to a time changing magnetic flux. The currents circulate inside the conductor in such a way that a new magnetic field is generated with a polarity that varies with the change in the applied magnetic flux. The interaction between the applied magnetic field and the field due to the eddy currents causes the generation of a force that opposes the change in flux. However, due to the internal resistance of the conductor the eddy currents will dissipate into heat, causing a removal of energy from the system. This dissipation of energy allows a magnet and conductor to form a damper that may be used to suppress the vibration of a structure. However, when used in a rotating system this additional damping often comes at the cost of a drag force which reduces the system efficiency. The present study will develop a novel eddy current mechanism in which the rotational drag is negligible. The damper will be theoretically modeled and the damping energy will be determined, while finite element analysis will be used to predict the force exerted on the shaft as it vibrates. Experiments will be performed to validate both the theoretical and finite element model and demonstrate the high damping levels available when using this system.

An Overview on Electrodynamic Bearings

“…One of the major challenges in PMB is low damping, hence a new type of eddy current damper [21] was developed to decrease the amount of vibration. Here two concentric ring magnets were placed around the rotating shaft.…”

“…The theoretical model of the magnetic field developed by Cheah and Sodano [21] was validated by FEA. 2D FEA was accomplished using Ansys by employing the plane53 element.…”

“…Stable levitation was achieved only when threshold speed was overcome. Using experiments [21], the damping coefficient and stiffness of the damper determined by the theoretical model and FE analysis were validated. The electromagnetic shaker was utilized to supply excitation energy to the rotor during modal testing.…”

Evaluation of eddy current damper for vibration control of a frame structure

“…Eddy current damping was also introduced to reduce rotational motion [5][6][7]. The induced electric field intensity relies on geometric boundary conditions.…”

On the nonlinear electromagnetic coupling between a coil and an oscillating magnet

“…Some of the more recent applications of induction have been related to friction reduction through such means as magnetic bearings [7,8]. Furthermore, the dissipative nature of induction has led to developments in such areas as magnetic brakes [9][10][11] and structural vibration suppression [12][13][14][15][16], effectively replacing friction as a means of energy dissipation.…”