Test and theory of electrodynamic bearings coupled to active magnetic dampers
Electrodynamic bearings exploit repulsive forces due to eddy currents to produce positive stiffness by passive means. Such a feature would make this type of bearing a viable alternative to active and permanent magnet bearings. Although electrodynamic bearings do not violate Earnshaw’s theorem, the open issue remains the stabilization system that is needed to make the rotating body stable, due to the low rotational speeds. Stabilizing solutions proposed in the literature are partially effective and not totally convincing. This limits real industrial applications. The present paper proposes a combination of electrodynamic and active magnetic bearings. At low speed the active part behaves as a conventional active magnetic bearing, while at high speed it provides damping. The readiness of the proposed solution is demonstrated by experimental results obtained using a dedicate test rig.
Fully Passively Levitated Self-Bearing Machine Implemented Within a Reaction Wheel
Self-bearing machines offer a highly integrated solution to achieve the rotor drive and magnetic levitation within a single structure. Although the trend is toward a diminution in the number of actively stabilized degrees of freedom to reduce the requirement for sensors, power electronics, and controllers, no self-bearing machine relying solely on passive phenomena has been successfully tested so far due to the restrictions highlighted by Earnshaw's theorem. Recent researches have demonstrated, through electromechanical models and in-depth experimental investigations, that electrodynamic thrust self-bearing machines (EDTSBMs) can gather, within a combined winding, both the rotor axial passive suspension and motor functions. Nonetheless, the test rigs implementing them still comprised external means to ensure the rotor radial and tilt support. In this context, this article takes the study of EDTSBMs to the final step by combining them with two permanent magnet centering bearings, yielding the first fully passively levitated self-bearing machines. A reaction wheel demonstrator based on the latter is designed and sized according to an optimal approach. Thorough experimental analyses dealing with the axial forces that support the rotor and its resulting axial position as well as the drive torque are carried out, notably proving that stable fully passive levitation can be achieved. Finally, the motor and suspension currents as well as the corresponding losses are investigated.
A Gas-Operated Bearing Damper for Turbomachinery—Theoretical Predictions Versus Experimental Measurements: Part II—Experimental Results and Comparison With Theory
This is the second of two papers described results of a research project directed at developing a gas-operated vibration damper for high-temperature turbomachinery applications. This paper presents the experimental measurements made on a gas damper hardware and compares them with the theoretical predictions given in Part 1. It is found that the isentropic theoretical model predicts the damper characteristics quite well. A maximum damping of 2,310 N-s/m (13.2 lb-s/in.) was measured at a natural frequency of 118 Hz using the present design and the results suggest that significantly higher damping levels are possible with design modifications.