 Parent Institution: Department of Mechanical Engineering, Indian Institute of Technology, Guwahati 781039, India (rtiwari@iitg.ernet.in). Journal of Sound and < ibration (2002) 254(5), 967}986 doi:10.1006/jsvi.2001.4140, available online at http://www.idealibrary.com on IDENTIFICATION OF SPEED-DEPENDENT BEARING PARAMETERS R. TIWARI, A. W. LEES AND M. I. FRISWELL Department of Mechanical Engineering, ;niversity of = ales Swansea, Swansea SA28PP, ;.K. E-mails: r.tiwari@swansea.ac.uk, a.w.lees@swansea.ac.uk, m.i.friswell@swansea.ac.uk (Received 30 July 2001, and in ,nal form 22 October 2001) Bearing dynamic characteristics have been a major unknown in the modelling and analysis of large turbo-generators. An identi"cation algorithm for bearing dynamic characterization by using unbalance response measurements is developed for multi-degree-of-freedom (m.d.o.f.) #exible rotor-bearing systems. The algorithm identi"es the bearing dynamic parameters, consisting of four e!ective sti!ness and four damping coe$cients for each bearing, utilizing frequency domain synchronous unbalance response measurements from the accelerometers attached to the bearing housings in the horizontal and vertical directions, for a minimum two di!erent unbalance con"gurations. The procedure of identifying bearing dynamic coe$cients by using the proposed algorithm is presented and demonstrated through a numerical example. Adding noise to the simulated signal checks the robustness of the algorithm against measurement noise. Combinations of regularization and the generalized singular value decomposition (SVD) are used to tackle an ill-posed problem due to the nearly circular orbit of the rotor at the bearings, as a special case for nearly isotropic bearings. It is demonstrated that by measuring noisy bearing responses with the direction of rotation of the rotor both in the clockwise and anticlockwise directions, the bearing estimation problem for circular orbit becomes well-conditioned. The regularization algorithm is tested for an experimental rotor-bearing rig. The response reproduction capabilities are excellent even in the presence of measurement noise.  2002 Elsevier Science Ltd. All rights reserved. 1. INTRODUCTION In modern power plants, because of ever-increasing demand for high power and high speed with uninterrupted and reliable operation, the accurate prediction of the dynamic behaviour of such machinery has become increasingly important. The most crucial part of such large turbo-generators is the machine elements that allow relative motion between the rotating and the stationary machine elements, i.e., the bearings. Historically, the theoretical estimates of the dynamic bearing characteristics have always been a source of error in the prediction of dynamic behaviour of rotor-bearing systems. Consequently, accurate parameter identi"cation is required to reduce the discrepancy between the measurements and the predictions. In particular, physically meaningful experimental identi"cation of bearing dynamic coe$cients is necessary because of the di$culty in accurate system modelling and analysis [1]. Obtaining reliable estimates of the bearing static load in actual test conditions is quite di$cult and this leads to inaccuracies in the well-established theoretical bearing models. 0022-460X/02/$35.00  2002 Elsevier Science Ltd. All rights reserved.