A dual-purpose optimal mono-stable nonlinear energy sink: Design, optimization, and evaluation

In this article, a tunable nonlinear energy sink (TNES) is developed for simultaneous vibration suppression (VS) and energy harvesting (EH) over a wide frequency band. The TNES consists of an S-shaped pinned-pinned beam carrying a pair of oscillating magnets at its midpoint. These magnets interact with four tuning magnets mounted on the primary structure to form a tunable magnetic spring. As the oscillating magnets move, they pass through a pair of coils rigidly fixed to the base, functioning as dual electromagnetic energy harvesters (EMEHs). Because the coils are fixed to the base rather than attached to the primary mass, and are connected in series to a resistive load, the EMEHs serve as a grounded electromagnetic damper. By adjusting the spatial positions of the tuning magnets, the TNES can be configured to exhibit mono-stable, bi-stable, or tri-stable behavior. A systematic methodology is proposed to tune the TNES into an optimal mono-stable nonlinear energy sink (MSNES) that closely emulates an ideal NES. A multi-objective optimization is conducted to investigate the trade-off between VS and EH with regard to initial displacement and load resistance. The results reveal that with a set of appropriately selected variables, the optimal MSNES is able to simultaneously achieve a performance index of 62.37% in VS and 32.37% in EH. The transient VS and EH performance of the optimal MSNES is examined through numerical simulation and experimental validation. The results show strong agreement, confirming the effectiveness of the proposed MSNES in delivering broadband vibration mitigation and energy harvesting.