Advanced shaker excitation signals for aerospace testing

The need to reduce testing time without diminishing the quality of the data is an important driver for innovation in the aerospace testing industry. In this paper, the use of advanced, flexible shaker excitation signals will be investigated with the aim (1) to obtain improved Frequency Response Function (FRF) estimations and (2) to assess the non-linearities of the excited system / structure. Pseudo-random and more general multisine signals, rather than the more traditional pure or burst random signals, will be used to increase the accuracy of the FRF estimate. Moreover, special multisine data acquisition and processing methods to identify the level of non-linearity will be illustrated by means of Ground Vibration Testing data of an F-16 aircraft. The presented methods allow assessing the non-linearities at a single excitation level, which is in contrast to the more traditional method of repeating the test at multiple excitation levels and observing the FRF differences. In addition, a new perspective will be given on the post-processing of stepped sine FRFs. Stepped sine shaker excitation signals are traditionally used to highlight and study non-linear behaviour. In this paper, a curve-fitting method based on FRF data at fixed response levels is applied to identify and quantify the non-linearities of the structure. Again, the approach will be illustrated by means of F-16 aircraft data.