1 Abstract The main objective of this paper is the examination of the possibility to identify the wear percentage of the bearings that support a step rotor, applying external excitation on the rotor and analyzing its response. The rotor vibration was modeled using the equation of Rayleigh, and the two nonlinear bearing forces were computed by solving the Reynolds equation using the finite difference method. Additionally, the internal damping effect of the rotor was incorporated into the current approach and the wear is introduced using the well-known Dufrane wear model. In the present work, the system appears strongly nonlinear, due to both the fluid film forces and the wear considerations. Time histories of the response during system start-up as well as during steady state operation, with or without application of an external excitation force are analyzed simultaneously in the time and frequency domains in order to investigate the changes that the wear introduces into the system behavior. Specific system variables are judged as very sensitive to wear development and are used to identify wear extension through the bearing surface. Keywords: wear, worn bearings, wear identification, rotor bearing system, continuous system, non-linear system, external excitation. 1 Introduction The combination of a continuous rotor with worn finite fluid film bearings is developed in the current work in order to take a different approach to the study of rotor bearing system dynamics. There are three main goals in this paper: Paper 119 Applying External Excitation to a Rotor for Wear Identification of the Non-Linear Fluid-Film Bearings P.G. Nikolakopoulos, A.C. Chasalevris and C.A. Papadopoulos Department of Mechanical Engineering and Aeronautics University of Patras, Greece ©Civil-Comp Press, 2008 Proceedings of the Ninth International Conference on Computational Structures Technology, B.H.V. Topping and M. Papadrakakis, (Editors), Civil-Comp Press, Stirlingshire, Scotland