Finite Element Model Updating for Very Flexible Wings

Abstract

As aircraft wings become more flexible as a result of searching for more fuel efficient and higher performance solutions, structural nonlinearities become more apparent. Geometric nonlinearities make the structure’s modal parameters a function of the deformed shape and therefore of the loading condition. Modal characterization of very flexible structures is challenging due to these nonlinearities and the very low natural frequencies (the fundamental mode is typically below 1 Hz). In traditional, stiffer structures, a single shape is sufficient to characterize the structure through ground vibration testing and finite model updating due to its linear behavior. However, with very flexible structures, different deformed shapes have different modal parameters (frequencies, damping, and mode shapes). This paper investigates the impact of large displacements on the modal parameters (frequency and mode shapes) of very flexible structures and introduces a method to update the corresponding finite element model. Results are presented to discuss the impact of deformed shapes and the development and applicability of the procedure to general very flexible wing structures.