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.
Model Based Design of a Rotor Supported by Radial Electrodynamic Bearings
The paper presents the design phases of a test rig to test the feasibility of passive full electrodynamic radial suspension of high speed rotors. A reference case from an automotive application is used to establish the design specifications in order to keep the characteristics close to those of an industrial application. The design is carried out in a model based approach where all the properties are analysed taking into account the coupling between the subsystems by means of finite element models and state space models. Some experimental results are used to validate the design approach, confirming the validity of the models and assumptions.
Cavitation and Air Entrainment Effects on the Response of Squeeze Film Supported Rotors
This paper analyzes the effects of air entrainment and cavitation on the synchronous response of squeeze film supported rigid rotors. The fluid film force coefficients are obtained from experimental measurements corresponding to a wide spectrum of operating conditions. These conditions include regimes in which air entrainment effects are dominant. Other conditions where vapor cavitation and fluid inertial effects are dominant are included for comparison. The effects of air entrainment are shown to produce a nonlinear response representative of a softening spring effect not previously known to exist in squeeze film dampers.