A quantitative approach to target mode selection for component-level modal survey

Modal survey at component level is often used in the aerospace industry to complement the system-level modal survey test, especially when a more accurate and complete modal characterization of a component that contributes significantly to the system-level structural response is desired. The relationship between the component modes and the significant system-level modes is often ignored in component modal survey test planning. This paper presents a quantitative approach for selecting the target modes for a component-level modal survey. The proposed method provides quantitative measures for identifying the significant component modes that are active in the system-level target modes and that contribute substantially to system-level dynamics. The proposed quantitative measures for target mode selection are particularly important for modal survey tests with free-free boundaries where the more traditional approaches used for target mode selection in fixed boundary modal survey test can not be employed. A combination of system-level effective mass; component and system-level kinetic and strain energy; and modal tracking between the system-level and component-level modes are utilized in the proposed method. Also discussed is the application of the proposed method to target mode selection for an International Space Station truss segment component.