A methodology for identification of dynamic parameters in assembled aircraft structures

Abstract

Finite Element Models (FEM) are widely used in order to study and predict the dynamic properties of structures. Comparing dynamic experimental data and analytical results, respectively, of the real and modelled structure, shows that the prediction of the dynamic response can be obtained with much more accuracy in the case of a single component than in the case of assemblies. Generally speaking, as the number of components in the assembly increases the calculation quality declines because the connection mechanisms among components are not represented sufficiently. Specifically for aircrafts, it is quite common that Frequency Response Functions (FRF) obtained via Ground Vibration Test (GVT) show a certain degree of discrepancy from the FRF calculated with the FEM, particularly across the sections where joining is discontinued. When this happens it is necessary to tune up the values of the dynamic parameters of the joints, to allow the numerical FRF to match the results of the experimental FRF. From a modelling and computational point of view, these types of joints can be seen as localized sources of stiffness and damping and can be modelled as lumped spring/damper elements. In this paper this is done by formulating an optimization problem. The approach has been applied to a FEM that mimics the rear fuselage of a commercial aircraft and the numerical results shows that the procedure is very efficient and promising.