Excitation methods and modal parameter identification in complex modal testing of rotating machinery

Abstract

Complex modal testing experiments are performed with a flexible rotor bearing system by using an electromagnetic exciter developed in the laboratory. Various excitation methods for the complex modal testing are tested with the rotor to investigate the practical advantages and disadvantages as well as the requirements for realization of each method. The excitation methods, based on the input/output relationships for complex signals, aim at the assessment of two-sided frequency response functions (FRFs) and coherence functions between complex inputs and outputs which are essential to the complex modal testing. The complex modal testing theory for general anisotropic rotors is also developed in a rigorous way along with the complex curve fitting method adequate to the complex modal testing. Laboratory experiments show that the complex curve fitting and modal parameter identification scheme developed is effective identifying the first and second flexural modes of the test rotor.