Experimental evaluation of linear and non-linear pedestal identification

To analyse the vibration behaviour of rotating machinery such as turbogenerators, it is necessary to model not only the rotor and bearings but also the foundation. This paper evaluates experimentally pedestal parameter identification techniques which rely on measurements of the motion of the journals relative to the bearing housings, and the motions of the housings themselves. The former motions enable calculation of the transmitted forces to the housing using either journal motion amplitudes and linearised bearing coefficients (the linear approach), or using the journal orbit data directly to determine the instantaneous bearing forces (the non-linear approach). The superior identification obtained via the non-linear approach, as predicted by earlier numerical experiments, was not able to be demonstrated experimentally. Even though errors in measurement and/or modelling resulted in poor identification of pedestal masses and stiffnesses, the pedestal natural frequencies were always identified with reasonable accuracy.