Non-Linear Experimental Modal Analysis and Application to Satellite Test Data

Kurzfassung

The DYNAMITED project realised by a European space industry and university team associated around EADS ASTRIUM and funded by the European Space Agency (ESA) aimed to assess and improve dynamic test data. In the field of post test activities, the detection, characterisation, identification and prediction of the non-linear behaviour of space structures during tests is of prime importance. The paper therefore starts with a short overview of such methods. Present evaluation methods for spacecraft vibration tests are based on the assump-tion of linear structural behaviour. The resonance shifts and frequency response (FRF) peak variations observed in the case of non-linear structural behaviour are generally not reflected in practice by non-linear evaluation procedures. In order to avoid overloading of the struc-ture during the qualification test on a shaking table the dynamic response is generally con-trolled at specified levels and locations by input notching. This approach generates an effectively quasi linear structural behaviour at the different input levels which enables the utilization of classical linear modal extraction tools to be applied separately at each level. However, the measured dynamic responses (transmissibilities) reveal peak shifts and ampli-tude changes depending on the input level of the base excitation. In the paper an approach is presented where three different input levels are used with the response levels controlled to be constant within a narrow frequency band around the dominant resonances. The premises of a technique will be described and how its aim of predicting the responses to not measured input levels is achieved by applying interpolation and extrapolation techniques to the modal data extracted by conventional modal analysis from the transmissibilities measured at three differ-ent input levels. Results are presented from an application of the technique to the vibration test data measured during a typical qualification test campaign of a satellite structure.