Robustness Analysis of Asymmetric Nonlinear Energy Sink via Nonlinear Normal Modes

Nonlinear energy sink (NES) absorbers excel compared to traditional tuned mass dampers (TMD) due to their superior efficiency over a wider range of frequencies. However, despite the advantages of NES over TMDs, their susceptibility to variations in system energy poses a challenge, particularly in applications where the main structure is subjected to random excitations. A modified NES, referred to as Asymmetric NES, significantly enhances NES robustness, expanding its potential uses. This study investigates the factors contributing to the superior robustness of asymmetric nonlinear energy sink (ANES) in comparison to the performance of traditional cubic NES. Through an analysis utilizing nonlinear normal modes (NNM) and frequency energy plots (FEP), this research shows that the improved effectiveness of asymmetric NESs is due to the intricate interaction between their NNM and the primary structure's kinetic energy FEP, leading to more robust targeted energy transfer (TET). In this work, the NNMs of tuned ANES and NES with similar mass are plotted alongside the kinetic energy FEP of a three-story shear building subjected to various earthquake ground accelerograms. The findings obtained here reveal that the NNM of the ANES absorber intersects more effectively with the system's energy FEP inducing a more effective modal energy redistribution, explaining the superior robustness of the ANES against variations in the input spectrum power.