Identification of Modal Parameters of Rotating Machinery Foundations by Measuring Rotor Vibrations During Startups.

This paper illustrates an original methodology to calculate the modal parameters of the turbomachinery supporting structure by measuring the shaft and support vibrations during startups or shutdowns. The modal parameters can be evaluated by minimizing a function derived from the frequency response curve of the shaft, which can be obtained experimentally or by means of a mathematical model of the mechanical system composed of the rotor, the bearings and the foundation. Some mathematical methods used to evaluate the foundation modal parameters are illustrated, pointing out their limits of applicability. To this purpose, the results obtained by applying different algorithms to the experimental and analytical frequency response curves are illustrated.