An assumed modes method is developed to investigate the effect of multiple flexible disks on the vibrational modes of a flexible rotor system. The analysis rotor system consists of multiple disks and a flexible shaft as used for a hard disk drive spindle system. In modeling the system, the centrifugal stiffening and disk flexibility effects are taken into account in order to examine the dynamic coupling effects between the vibration modes associated with the spindle and the disk as the rotational speed is varied. To demonstrate the effectiveness of the proposed method a hard disk drive spindle system with duplicate disks commonly used in personal computers is selected as a numerical example. In this study it is shown that the disk flexibility can significantly alter certain modal frequencies and that some modes are predicted, which can not be obtained in the individual flexible disk or spindle analysis. It is also shown that the uncoupled modal frequencies of k-nodal diameter modes (k≠1) of the system can be predicted from the individual flexible disk analysis without considering the coupling.
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