Vibro-impact Nonlinear Energy Sink Research Articles

Numerical and experimental investigation of a highly effective single-sided vibro-impact non-linear energy sink for shock mitigation

In this paper a highly asymmetric, lightweight, vibro-impact non-linear energy sink (NES) leading to very efficient passive non-linear targeted energy transfer (TET) is investigated. To this end, a two degree-of-freedom linear system (the primary structure) is coupled to a single-sided vibro-impact (VI) attachment with highly asymmetric impact non-linearity (the VI NES). The proposed NES passively absorbs and rapidly dissipates a considerable amount of the impulse energy induced into the linear structure, leading to very effective shock mitigation compared to a double-sided (symmetric) VI NES. We find that appropriate selection of the weak linear stiffness that couples the non-linear VI attachment to the linear structure plays a significant role in the proposed design. Moreover, in contrast to the double-sided VI NES which has optimal performance for a narrow range of input energies, the proposed single-sided asymmetric VI NES maintains a high level of performance over a broad range of high input energies. Hence, the proposed design is especially suitable for severe shock mitigation in infrastructure. To quantify the enhanced shock mitigation performance of the asymmetric VI NES we employ measures of effective damping and stiffness developed in previous works to demonstrate that the primary structure with attached NES possesses drastically increased effective damping and stiffness compared to its nominal properties when no NES is attached. A series of experimental results fully validates the theoretical predictions.

Analytic treatment of a system with a vibro-impact nonlinear energy sink

This Communication reports on an approximate analytic procedure for analysis of transient damped response in a system comprising a primary linear oscillator and vibro-impact nonlinear energy sink (NES). Multiple-scale expansion reduces the problem in the first approximation to low-dimensional vibro-impact system with forcing and damping; the latter problem yields to direct analytic approach. The results computed by this way fairly correlate with direct numeric simulations. The analysis takes advantage of small ratio of the NES and the primary masses, but does not require the restitution coefficient to be close to unity. The proposed approach paves the way for efficient design of systems with vibro-impact NESs.

Application of broadband nonlinear targeted energy transfers for seismic mitigation of a shear frame: Computational results

In this work we show that it is possible to successfully apply the concept of nonlinear targeted energy transfer (TET) to seismic protection of structures; moreover, this passive strategy of seismic vibration control is found to be feasible and robust. We consider a three-story shear-frame structure, modeled as a three-degree-of-freedom system, subjected to four historic earthquakes as seismic excitation. Seismic mitigation is achieved by applying single or multiple nonlinear energy sinks (NESs) to the test structure. We study the performance and efficiency of the NESs through a set of evaluation criteria. First we consider a single vibro-impact NES (VI NES) applied to the top floor of the structure. In order to assess the robustness of the VI NES, the NES parameters are optimized for a specific seismic excitation (Kobe), and then tested against the three other earthquake records to demonstrate effectiveness of the NES for these cases as well. To further improve the effectiveness of the seismic mitigation, we then consider a system of two NESs—an NES with smooth nonlinearity at the top floor of the test structure and a VI NES at the bottom floor. We show that it is indeed possible to drastically reduce the structural seismic response (e.g., displacements, drifts, and accelerations) using this configuration.

Periodic orbits, damped transitions and targeted energy transfers in oscillators with vibro-impact attachments

We study complex damped and undamped dynamics and targeted energy transfers (TETs) in systems of coupled oscillators, consisting of single-degree-of-freedom primary linear oscillators (LOs) with vibro-impact attachments, acting, in essence, as vibro-impact nonlinear energy sinks (VI NESs). First, the complicated dynamics of such VI systems is demonstrated by computing the VI periodic orbits of underlying Hamiltonian systems and depicting them in appropriate frequency–energy plots (FEPs). Then, VI damped transitions and distinct ways of passive TETs from the linear oscillators to the VI attachments for various parameter ranges and initial conditions are investigated. As in the case of smooth stiffness nonlinearity [Y. Lee, G. Kerschen, A. Vakakis, P. Panagopoulos, L. Bergman, D.M. McFarland, Complicated dynamics of a linear oscillator with a light, essentially nonlinear attachment, Physica D 204 (1–2) (2005) 41–69], both fundamental and subharmonic TET can be realized in the VI systems under consideration. It is found that the most efficient mechanism for VI TET is through the excitation of highly energetic VI impulsive orbits (IOs), i.e., of periodic or quasiperiodic orbits corresponding to zero initial conditions except for the initial velocities of the linear oscillators. In contrast to NESs with smooth essential nonlinearities considered in previous works, VI NESs are capable of passively absorbing and locally dissipating significant portions of the energies of the primary systems to which they are attached, at fast time scale. This renders such devices suitable for applications, like seismic mitigation, where dissipation of vibration energy in the early, highly energetic regime of the motion is a critical requirement.

Application of broadband nonlinear targeted energy transfers for seismic mitigation of a shear frame: Experimental results

In an earlier work we showed computationally that it is possible to successfully employ nonlinear targeted energy transfers (TETs) for seismic mitigation. Moreover, we demonstrated that this passive strategy of seismic vibration control was feasible and robust. In this work, we report experimental validation of these results by performing a series of experimental tests with a three-story shear-frame structure under seismic excitation in the form of two different historic earthquakes. As in the computational part of this work, the experimental seismic mitigation design consists of either a single nonlinear energy sink or a combination of two nonlinear energy sinks (NESs) attached at floors of the test structure. We study the performance and efficiency of the NES(s) through a set of certain evaluation criteria. With a single vibro-impact NES (VI NES) applied to the top floor of the test structure, we find significant reduction of the response levels. To further improve the effectiveness of the seismic mitigation design, we consider a combination of two NESs—an NES with smooth stiffness nonlinearity at the top floor and a VI NES at the bottom floor of the test structure—and show dramatic reduction of the structural seismic response. Robustness of the proposed designs is addressed.