Output-Only Approach for Finite Element Model Updating of AB-204 Helicopter Blade

The recent developments in the operative modal analysis made possible a new approach in the estimate of the modal parameters. In fact, they could be evaluated considering only the responses of the structure when subjected to the "natural" excitation during its operative life, output-only analysis. Therefore, this approach could reduce the costs needed for the experimental investigations, since no input measurements are required. Moreover, it takes into consideration the actual loadings and boundary conditions acting on the structure leading to a more accurate identification of the modal parameters. The experimental model so far identified could be considered as reference for a further updating of the structural model. The developed updating procedure, is based on the minimization of an error function, representing the differences between the numerical and experimental model, by means of design variables associated to the finite element model. The error function considered is built from the evaluation of the sensitivity of correlation functions of the Frequency Response Functions, FRFs, to design parameters. In this paper the effectiveness of output-only experimental analysis in both the estimate of the frequency response functions and, then, in the structural updating of the finite element model of an AB-204 helicopter blade is investigated. Specifically, a comparison between the updated finite element models obtained both from the FRFs, gained from the well established experimental modal analysis, and from the output only analysis will be performed.