Stationary Study
A rotordynamics problem can be considered stationary if the following two criteria are fulfilled:
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Solid Rotor: Loads in the corotating frame do not change their magnitude and direction significantly, for example, in an inertial load due to mass eccentricity. Note that a load that appears stationary in a space-fixed frame has a very strong time dependence in the corotating frame and vice versa.
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Beam Rotor and Solid Rotor, Fixed Frame: Loads in a space-fixed frame do not change their magnitude and direction significantly, for example, gravity load. Note that a load due to mass eccentricity has a very strong time dependence.
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There is no explicit time dependence in the material model of the rotor.
In some cases, there is a variation in the load, even though the solution for each value of the load can be considered to be stationary. A typical case is that the load values are independent, and you just want to compute a number of different load cases. For example, you may want to find the stresses and magnitude of the lateral displacement of the rotor for different eccentric masses.
Note that a stationary problem is solvable only if the structure is sufficiently constrained. There must not be any possible rigid-body modes; thus, no stress-free deformation states are allowed. If the model is underconstrained, you may encounter problems like singular or ill-conditioned system matrices.