Application of modal properties identification to multi-degree-of-freedom system using simultaneous equations of the real and imaginary parts of frequency response function

Abstract

In order to improve the noise and vibration characteristics of mechanical structures, it is well known that an identification of modal properties is important. Therefore, experimental modal analysis is widely operated for identifying modal properties represented by natural frequency, damping characteristics and mode shape from vibration test result. However, in the case that the damping characteristics is very small or large, it is difficult to identify the modal properties by the existing method. In the previous study, we proposed the identification method of natural frequency and damping characteristics for a lightly damped element. This method using simultaneous equations of the real and imaginary parts of frequency response function is the one degree of freedom method and can not be directly applied to a multi-degree-of-freedom system. In this study, we propose the identification method for a multi-degree of freedom system by using both simultaneous equations of the real and imaginary parts of frequency response function and mode separation method. First, it is explained that the theory of identification using simultaneous equations of the real and imaginary parts of frequency response function in one degree of freedom. Secondly, we investigate the identification accuracy and the analysis frequency range including the measurement error and non-targeted mode components. Finally, it is shown that identification result of modal parameters in multi-degree of freedom system using numerical analysis and its validity.

Keywords

• modal analysis
• vibraion testing
• modal properties
• identification method
• multi-degree-of-freedom