Complex model testing and parameter dentification of rotor-bearing systems

Abstract

As the modern rotating machines have a tendency of being operated at higher speed and designed to be lighter, the knowledge of the dynamic behavior becomes more and more important because of increasing requirement in accuracy and reliability. Modal testing of such rotating machines has provided a major contribution to our efforts to understand and to control many vibration phenomena encountered in practice. However, the rotation inherent in such systems is known to create a number of theoretical and practical barriers against the application of classical modal testing methods in their usual form. The primary objective of this work is to develop a genuine modal parameter identification scheme for rotating machinery and the various excitation / curve fitting techniques. A few attempts have been made to develop modal testing methods for rotating machinery with consideration of the system``s non-self-adjointness. However they completely ignore the directivity of backward and forward modes and thus the heavy overlapping of those modes is inevitable in the frequency domain. Recently, a complex modal testing theory, based on the complex input/ output relations, has been developed for modal parameter identification of rotating machinery. In this work, the complex modal testing theory is re-formulated, in a rigorous way, for general anisotropic rotors as well as isotropic rotors. The complex modal testing features that it gives not only the directivity of backward and forward modes but also completely separates those modes in the frequency domain so that the effective modal parameter identification is possible. As the complex inputs and outputs are introduced, the conventional definitions of spectral quantities such as spectral density functions and coherence functions (COHs) are also extended to account for complex quantities. The complex modal testing method is different from the classical modal testing method in measurements, excitaion techniques and, in particular, ...