Extraction and Validation of Structural Models from Tests Under Operational Conditions

Experimental identification of structural dynamics models is usually based on the modal analysis approach. In the classical modal parameter estimation approach, the baseline data which are processed are Frequency Response Functions measured in laboratory conditions. However, in many applications, the real operating conditions may differ significantly from those applied during the modal test. Hence, the need arises to identify a modal model in operational conditions. This issue is even more complicated by the fact that in most cases, only response data are measurable while the actual loading conditions are unknown. Therefore, the system identification process will need to base itself on output-only data.

In this paper, the capabilities and limitations of the NexT technique and the stochastic subspace technique are evaluated for their applicability for output-only modal analysis to 3 industrial cases: the modal characterization of the rear suspension system of a family car during road tests in order to understand a booming noise problem, flight flutter analysis of a commercial aircraft and the identification of the modes of a three-span concerete bridge under ambient excitation.