Identification of bearing dynamic coefficients by unbalance response measurements in rotor bearing systems

Abstract

The accurate prediction of the responses of a dynamic system is the primary concern in the area of structural dynamic analysis. The success of the dynamic analysis therefore relies completely on the adequacy of the model and the accuracy of the parameters involved in the model. In the dynamic analysis of rotor bearing systems, baring parameters in the dynamic model are the major sources which not only give rise to the difficulty in response computation due to the complicated dynamic properties such as spin speed dependency but also make the discrepancy between measurements and predictions due to the inaccurate information. The primary objective of this work is to develop a dynamic analysis scheme which handles the spin speed dependent bearing properties and to develop an analytical and experimental identification scheme which ensures the accurate estimation of bearing dynamic coefficients. The spin speed dependency mostly due to the bearing properties and the gyroscopic effects in rotor bearing systems has prohibited the direct use of the standard modal analysis to calculate the forced response of the system because of the inefficiency in calculation of the modal responses at every spin speed considered. In this work, an efficient harmonic response analysis scheme is developed to easily take into account the spin speed dependency in the model by introducing a generalized modal anaolysis based upon the lambda matrix, the spin speed dependency of bearing parameters being assumed to be well represented by polynomial functions of spin speed. The proposed scheme requires far less computational efforts compared with the conventional methods due to the features such that it deals with closed form solution in response calculations and that the influence coefficients and the critical speeds for an asynchronous excitation are readily identified. So far many experimental identification schemes for bearing parameters have been developed but their implementations to actual ...