Validating the dynamic coefficients of bearing pedestals in a multi-mode rotor—bearing system

Abstract

Over the years, methods have been developed to estimate the dynamic coefficients of bearings based on parameter identification techniques. The stage where the estimated coefficients obtained from these methods need to be validated on actual operating machines, especially those operating at hypercritical speeds, has been reached. This article extended the frequency domain parameter estimation technique normally used on bearings to extract the dynamic coefficients of the bearing pedestals in isolation. It is demonstrated here that by using only a single forcing mechanism located at an angle to the bearing pedestal, the eight possible stiffness and damping coefficients can be estimated accurately. An on-line frequency domain algorithm for estimating these coefficients was developed and tested in the laboratory for this purpose. Its ability to reduce testing time and to produce reliable coefficient estimates from structural spurious resonance is observed. Validations of the dynamic coefficients of the bearing pedestals were carried out by comparing the experimental and computer simulated responses and resonance frequencies of the arrangement of two multi-mode rotor—bearing-system's configurations. By using ANSYS Inc. finite element software as a comparison tool, the results indicated that a nine stations rotor model formulated by the stiffness coefficient method is highly accurate at predicting the rotor—bearing system's responses and resonance frequencies. The results also confirmed that rotor bearing's synchronous response is insensitive with respect to individual estimated parameters that have been determined by statistical hypothesis test to be insignificant.