Dynamics of geometrically-nonlinear beam structures, part 1: numerical modeling

The need of lightweight design in structural engineering is steadily growing due to economic and ecological reasons. This usually causes the structure to exhibit moderate to large displacements and rotations, resulting in a distributed nonlinear behavior. However, the characterization of geometrical nonlinearities is challenging and sensitive to structural boundaries and loading. It is commonly performed with numerical simulations, utilizing particularly finite element formulations. This study comprises simulations of a clamped-clamped beam with moderate to large amplitude oscillations. Four different (commercial and noncommercial) numerical approaches are considered: three finite element representations and one assumed-modes approach. A first comparison is conducted when the system is under a sine sweep excitation over one single mode. Subsequently, a modified model featuring nonlinear internal resonance is considered, to disclose differences in the modeling of the nonlinearity when coupling between modes occurs. The results show some expected features for geometrical nonlinearities in all methods, but also some important differences, especially when the modal interaction is activated.