The study of asymmetric rotors is important because virtually all electrical machines have rotors which fall into this category and their have been a number of cracks in such rotors which have been reported in the literature. In a symmetric rotor, the diagnosis of a transverse crack from an examination of the free-free modes is relatively straightforward, but the presence of inherent asymmetry leads to a considerable complication of the situation. In this paper, a simple model is presented to represent this situation. The changes in natural frequencies, modes shapes and cross coupling of the original principal planes is examined.
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