Modal Identification of Aerospace Structures

Kurzfassung

The modal identification is a common and necessary procedure performed on large aerospace structures. Aeronautical structures like prototype of new large aircraft have to be investigated within a ground vibration test (GVT) in order to validate the analytical Finite Element Model and to enable reliable flutter predictions for flight tests. Spacecraft structures like large satellites are investigated by so called modal survey tests. Here, the main purpose is also to validate the analytical model. With the validated model the severe dynamic loads which emerge during launch can be predicted. The dynamics of aeronautical structures and spacecraft are characterized by their modal parameters like natural frequencies, mode shapes, modal damping and generalized masses. These modal parameters can be obtained using two different philosophies resp. methods: Modes, which are important within the scope of the certification process can be identified using the phase resonance method. On the other hand, not all modes have to be known with the same precision and to the same extent, e.g. including linearity checks. Here, phase separation techniques, which are nowadays standard in the modal analysis of large aerospace structures, can save time compared with the phase resonance method. In this lecture the theory of modal identification methods is presented. After that we focuses on the performance of vibration tests. The test equipment is described in detail. In the last chapter of the lecture, examples from vibration tests which were recently performed on aerospace structures are shown.