The support stiffness and connecting structure stiffness which has significant effect on rotordynamics change with different assembly conditions and operating conditions. For example, the squeeze film stiffness changes with different film force, and the elastic support stiffness changes with different temperatures. These parameters are “uncertain but bounded”, in another word, the distributions of the parameters are unknown, but the intervals of the uncertain parameters are always got easier. An interval analysis method, which solves the rotordynamics with these uncertain parameters, is presented. Based on interval mathematics and perturbation method, interval analysis method simplifies the uncertain parameters to interval vectors so that it can get the intervals within which the rotordynamics varies when less information of structure is known. The interval analysis method is efficient under the condition that probability approach cannot work because of small samples and spare statistics characteristics. The formulation of natural frequencies of rotor using interval perturbation analysis method is formulated. A numerical example of comparison between interval perturbation method analysis and monotonic method is given. The rotordynamic analysis of a turbofan rotor is performed with this method, and the test data validates the numerical results.

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