Non-linear analysis of aerospace structures with weak non-linearities and coupled modes

Abstract

The modal identification of large aerospace structures like aircraft prototypes or satellites requires a great experimental effort and sophisticated test concepts in order to assure a high quality for the test results. The conventional modal identification assumes linear dynamic behaviour of the structure. However, in practice most of the investigated and tested structures exhibit some non-linear behaviour. In this article, a test concept suited for the modal identification of large aerospace structures is presented first. Then, the basics for non-linear modal identification within this concept are described. For most of the modes the non-linearity is only weak and most of the non-linear modes can be considered as uncoupled, i.e. other modes are not influenced by the non-linearity of the respective mode. However, some of the non-linear modes may be coupled with other modes. The article describes the theoretical basis for the non-linear modal identification of one single uncoupled mode and for the case of non-linear coupled modes. To illustrate the non-linear modal identification, an analytical model is investigated which features the coupling of two modes. The application of the method to measured data of a large aircraft structure demonstrates that the method can be used to identify the non-linear characteristics of aerospace structures.