Two transient modal simulation models are presented based on the Jeffcott-Green flexible-rotor formulation. One of the models is based on the conventional “non-spinning” formulation, while the second employs a rotor fixed formulation. Numerical results are presented for these two basic models for the SSME (Space Shuttle Main Engine) turbopumps. The results presented demonstrate that either of the basic formulations is a computationally efficient simulation approach for a flexible rotor, which is to be modeled by a large number of rigid bodies. They also demonstrate that the models can readily account for an arbitrary number of bearings having nonlinear or speed-dependent characteristics, and for the motion of the bearing support structure. The results presented demonstrate that the rotor-fixed formulation generally requires less computer time than does the conventional formulation. Moreover, the modal cordinate solutions in the rotor-fixed formulation provide a significantly clearer picture of potential flexible-rotor-instability problems.

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