Swept-Sine Excitation During Modal Identification of Large Aerospace Structures

Kurzfassung

The European aircraft industry is constantly calling for a reduction in the testing times of prototypes without diminishing the accuracy of the data. Substantial changes in the testing strategy of ground vibration tests (GVT) have therefore been recently introduced. This improved test strategy is mainly based on the combination of the very reliable but time-consuming phase resonance method with the application of phase separation techniques on data stemming from slow swept-sine excitation. The initial results lead to a time reduction of about 30%. However, testing experience has shown that reliable modal data from swept-sine tests depend on a proper data processing. Moreover, the test performance initiated the idea to complete the test sequences by investigating the swept-sine results with respect to non-linear structural dynamics behaviour. This report reviews the strategy of modal analysis based on swept-sine excitation. The theoretical background of swept-sine testing is expounded with particular emphasis on the transition through structural resonances. The effect of different standard procedures of data processing is investigated and recommendations on the proper estimation of frequency response functions are given. A procedure for the detection of structural non-linear behaviour is proposed that yields the functions of the modal parameters dependency on the vibration amplitude. All proposed methods are applied to numerical examples in order to investigate their capabilities. Tinally, their practical use is demonstrated on test data taken from different tests on large aerospace structures. This enables the optimization of swept-sine application for future GVTs.