Experimental testing and numerical simulation of a six-story structure incorporating two-degree-of-freedom nonlinear energy sink

The nonlinear energy sink (NES) is a fully passive attachment used to rapidly dissipate a significant portion of energy induced in a linear primary structure to which it is attached. In this study, the performance of a Type III NES in reducing the response of a large primary structure when subjected to a shock-type loading is evaluated experimentally. The Type III NES is a two-degree-of-freedom device comprising two relatively lightweight masses in series coupled together and to the primary structure through essentially nonlinear (i.e., nonlinearizable) stiffness elements. The essential stiffness nonlinearity of the NES and the corresponding lack of preferential resonance frequencies enable it to resonantly interact with multiple structural modes over broad frequency and energy ranges. Hence a local NES can induce global effects in the dynamics of the structure to which it is attached. In this study, and for the first time, specially shaped polyurethane bumpers are employed for realizing these essentially nonlinear stiffness elements of the Type III NES. Measures calculated from the experiments in this study, such as the effective damping of the primary structure, indicate the ability of the NES to dissipate energy and reduce the response of the primary structure over a wide range of magnitudes of a shock loading. Good agreement between numerical predictions and experimental observations validates the identified model of the NES.