Relative and absolute shaft vibration data have revealed that the commonly made assumption of rigidly supported bearings may be grossly inaccurate, especially for fans, generator sets, and natural gas transmission compressors. This paper provides a systematic method for modeling flexibly mounted rotating machinery utilizing 8 node isoparametric brick-type finite elements for the foundation and 4 node isoparametric “patch” type boundary elements for the soil. The rotor is modeled utilizing Euler-Bernoulli beam elements and includes disk gyroscopics and cross coupled bearing coefficients. The large number of degrees of freedom included in the model are reduced utilizing a nested superelement scheme and Guyan reduction.

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