A basic problem inherent with the operation of supercritical shafting is the application of appropriate external damping, which is generally necessary to suppress nonsynchronous instabilities and limit the synchronous response of even a well-balanced shaft. Typically, coulomb or squeeze film-type dampers are used, in which case the damping properties tend to change with temperature, and the necessary contact results in additional torque loading and wear. An alternative damping method currently under investigation is the application of a noncontact electromagnetic damper that dissipates energy through induced eddy-currents generated in a small disk mounted to, and rotating with the shaft (Frederick, 1990). Research is underway on the design and development of a damper of this type that could eventually lend itself to active control applications. The objectives of this investigation are the initial design of a magnetic circuit, an appropriate d-c power supply, and the characterization of preliminary performance experiments on a composite shaft. Damper operation was evaluated during rotating shaft tests and compared to prior tests which involved the use of a permanent magnet eddy-current damper. This Note concerns some interesting results obtained from these preliminary tests. The damper worked well at low speeds, but some high-speed stability problems were encountered. Potential solutions to these problems as well as areas of future research are discussed.

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