The trend towards higher speeds and lighter weight rotor designs, particularly in gas turbine applications, has brought about the need to consider the flexibility of the total shaft-disk-blade system in the calculation of system frequencies and whirl modes. It has been traditional to assume that blades and disks are rigid, although recent work has been aimed at evaluating the assumption of rigid disks. These works have used Laplace transform and Liapunov methods and have been limited to simple geometries. This paper describes the development of a special shaft finite element which incorporates analytical solutions for disk dynamics and approximations of blade effects. It is shown that the addition of disk and blade dynamics does not increase the size of system matrix and that this approach can consider multiple disks. Because of the versatility of the finite element approach, complex configurations and boundary conditions can be considered.

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