Modal truncation in substructure testing (1st report, Coupling analysis of simple Beams)

Abstract

As a testing method for large structures, such as aerospace structures, substructure testing was considered. The main subject of this investigation is modal truncation. As the characteristics of substructures are represented by the lower vibration modes, an error due to truncated higher modes is inherent. In order to evaluate the truncation error, numerical analyses were performed on the flexural vibration of simple beams. Modal parameters of the beam were calculated based on the beam theory. Then two or three beams were coupled analytically using these parameters. The relations between the frequency error and the number of component modes were examined under various conditions. The results of the analyses indicate that the process of modal truncation depends highly on the types of system mode shapes. When substructures are tested on free end boundary conditions, a great number of component modes are required, and testing must cover very high frequencies.