Flexural Vibrations of Rotating Electromagnetic Shields

Much interest currently exists in the design and construction of superconducting electrical machines for power generation. All machines of this type include, as part of their rotating member, one or more cylindrical shells. These shells are influenced by elastic, inertial, and electromagnetic forces. Electrical tests on an experimental superconducting alternator at M.I.T. produced unexpected vibrations in one such shell, the electromagnetic shield. The flexural vibrations were in the form of traveling waves, of differing wave speeds, and produced a significant deterioration in shield performance. A simple theoretical analysis of the effects of rotation on the vibrations of long cylinders is presented. These effects are verified over a significant speed range by two experiments as well as data from tests on the experimental alternator. Results are related to the design of electromagnetic shields for superconducting alternators.