A dual-purpose optimal mono-stable nonlinear energy sink with a grounded electromagnetic energy harvester

Abstract

The motivation of this dissertation is to develop an optimal mono-stable nonlinear energy sink (MSNES) capable of achieving simultaneous vibration suppression (VS) and energy harvesting (EH) over a wide frequency band. Conventional nonlinear energy sinks often suffer from limited tunability for stability variation and inability of harvesting energy, motivating the development of a systematic and reconfigurable design. Accordingly, this dissertation pursues three main objectives: (1) to develop a tunable nonlinear energy sink (TNES); (2) to establish a design methodology for tuning the TNES into an optimal MSNES; and (3) to evaluate the VS and EH performance of the optimal MSNES through numerical simulations and experimental validation. For the first objective, a TNES is developed using 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 magnetically tunable nonlinear spring. As the oscillating magnets move, they pass through a pair of coils rigidly fixed to the base, forming dual electromagnetic energy harvesters (EMEHs). Because the coils are mechanically grounded and connected in series to a resistive load, the EMEHs function as a grounded electromagnetic damper while enabling large-amplitude translational motion. For the second objective, an equivalent stiffness method is employed to characterize the essentially nonlinear stiffness of a target nonlinear energy sink. A numerical optimization procedure is then developed to determine the optimal tuning parameters that allow the TNES to emulate the desired MSNES behavior. For the third objective, extensive numerical simulations are conducted to assess the transient VS and EH performance of the optimal MSNES, followed by experimental validation. The trade-off between vibration suppression and energy harvesting, as well as the effects of primary system detuning, are examined. The main contributions of this dissertation are fourfold. First, the proposed TNES architecture enables convenient reconfiguration among mono-stable, bi-stable, and tri-stable states. Second, the grounded electromagnetic energy harvester facilitates large-amplitude translational motion and efficient energy extraction. Third, a systematic design framework is established to obtain an optimal MSNES that closely emulates an ideal nonlinear energy sink. Finally, numerical and experimental results show strong agreement, confirming the effectiveness of the proposed MSNES in delivering broadband vibration suppression and energy harvesting.