Rotary-impact nonlinear energy sink for shock mitigation: analytical and numerical investigations

The reliability of the hysteretic nonlinear energy sink in shock mitigation is investigated herein. The hysteretic nonlinear energy sink is a passive vibration control device which is coupled to a primary linear oscillator. Apart from its small mass and a nonlinear elastic spring of the Duffing oscillator, it also comprises a purely hysteretic and a linear elastic spring of potentially negative stiffness. The Bouc–Wen model is used to describe the force produced by both the purely hysteretic and linear elastic springs. The hysteretic nonlinear energy sink protects the primary system through the energy pumping mechanism which transfers energy from the primary system and dissipates it in the hysteretic nonlinear energy sink. Three nonlinear equations of motion describe the resulting two-degree-of-freedom system response. The parameters of the system to be considered as uncertain are the natural frequency of the primary system and the hysteretic nonlinear energy sink linear elastic spring, which follow a normal distribution. A reliability analysis is then performed to evaluate the robustness of the coupled system in the presence of uncertainty. Specifically, the reliability index is calculated based on first passage probabilities of distinct dissipation energy level crossings using the Monte Carlo method. Several examples are examined considering various levels of initial input energy, and useful conclusions are drawn concerning the influence of uncertainty in the system robustness.

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Nonlinear Energy Sinks With Nontraditional Kinds of Nonlinear Restoring Forces

Journal of Vibration and Acoustics ◽

10.1115/1.4035479 ◽

2017 ◽

Vol 139 (2) ◽

Cited By ~ 19

Author(s):

Mohammad A. AL-Shudeifat

Keyword(s):

Energy Transfer ◽

Nonlinear Energy Sink ◽

Nonlinear Coupling ◽

Closed Loops ◽

Strong Resonance ◽

Shock Mitigation ◽

Restoring Forces ◽

Initial Shock ◽

Energy Sink ◽

Nonlinear Energy

The nonlinear energy sink (NES) is usually coupled with a linear oscillator (LO) to rapidly transfer and immediately dissipate a significant portion of the initial shock energy induced into the LO. This passive energy transfer and dissipation are usually achieved through strong resonance captures between the NES and the LO responses. Here, a nontraditional set of nonlinear coupling restoring forces is numerically investigated to introduce enhanced versions of the NESs. In this new set of nonlinear coupling restoring forces, one has a varying nonlinear stiffness that includes both of hardening and softening stiffness components during the oscillation, which appear in closed-loops under the effect of the damping. The obtained results by the numerical simulation have shown that employing this kind of the nonlinear restoring forces for passive targeted energy transfer (TET) is promising for shock mitigation.

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Numerical Investigation of Rotating Nonlinear Energy Sink for Shock Mitigation

Volume 8: 22nd Reliability, Stress Analysis, and Failure Prevention Conference; 25th Conference on Mechanical Vibration and Noise ◽

10.1115/detc2013-13177 ◽

2013 ◽

Author(s):

Mohammad A. Al-Shudeifat ◽

Lawrence A. Bergman ◽

Alexander F. Vakakis

Keyword(s):

Energy Transfer ◽

Linear Structure ◽

Nonlinear Energy Sink ◽

Initial Energy ◽

Shock Mitigation ◽

Nonlinear Targeted Energy Transfer ◽

Primary Test ◽

Energy Sink ◽

Two Degree Of Freedom ◽

Nonlinear Energy

Passive nonlinear targeted energy transfer (TET) is addressed here by investigating a lightweight rotating nonlinear energy sink (NES). The rotating sink mass has an essentially nonlinear inertial coupling with the two degree-of-freedom linear system (the primary test structure). The proposed rotating NES is numerically investigated where it is found to passively absorb and rapidly dissipate a considerable portion of the initial energy induced by impulse to the linear structure. The parameters of the rotating NES are optimized for the best performance in the vicinity of intermediate and high loads. The fundamental mechanism for significant energy transfer to the NES is its rotational mode; the oscillatory mode of the NES dissipates far less energy. The frequency-energy dependences are investigated through the frequency-energy plot (FEP). Early and strong resonance capture at the lowest modal frequency is observed between the rotator and the structure, at which a significant portion of the induced energy is transferred and dissipated by the rotator. The performance of this device is found to be comparable to existing, stiffness-based NES designs. However, this device is less complicated and more compact.

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Asymmetric Magnet-Based Nonlinear Energy Sink

Journal of Computational and Nonlinear Dynamics ◽

10.1115/1.4027462 ◽

2014 ◽

Vol 10 (1) ◽

Cited By ~ 27

Author(s):

Mohammad A. AL-Shudeifat

Keyword(s):

Permanent Magnets ◽

Nonlinear Energy Sink ◽

Weakly Nonlinear ◽

Strongly Nonlinear ◽

Shock Mitigation ◽

Energy Inputs ◽

Energy Sink ◽

Dynamic Structures ◽

Nonlinear Energy ◽

Weakly Linear

The nonlinear energy sink (NES) is a light-weighted device used for shock mitigation in dynamic structures through its passive targeted energy transfer (TET) mechanism. Here, a new design for the NES is introduced based on using an asymmetric NES force. This force is strongly nonlinear in one side of the NES equilibrium position, whereas it is either weakly nonlinear or weakly linear in the other side. This is achieved by introducing the asymmetric magnet-based NES in which the asymmetric nonlinear magnetic repulsive force is generated by two pairs of aligned permanent magnets. Consequently, this proposed design is found to provide a considerable enhancement in the shock mitigation performance compared with the symmetric stiffness-based NESs for broadband energy inputs.

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Experimental Investigation of a Rotational Nonlinear Energy Sink for Shock Mitigation

Volume 6: 10th International Conference on Multibody Systems, Nonlinear Dynamics, and Control ◽

10.1115/detc2014-35375 ◽

2014 ◽

Cited By ~ 1

Author(s):

Nicholas E. Wierschem ◽

Mohammad A. AL-Shudeifat ◽

Billie F. Spencer ◽

Alexander F. Vakakis ◽

Lawrence A. Bergman

Keyword(s):

Ground Motion ◽

Primary Structure ◽

Nonlinear Energy Sink ◽

Small Scale ◽

Rotational Mode ◽

Story Structure ◽

Energy Dependency ◽

Shock Mitigation ◽

Energy Sink ◽

Nonlinear Energy

Rotational nonlinear energy sinks (NESs) have been proposed to mitigate the response of underlying primary structures subjected to shock loading. This type of NES, which is composed of a passive mass that is free to rotate, has the potential to be easier to realize and more compact than other types of NESs. Like other types of NESs, these devices engage in targeted energy transfer, which allows for the broadband transfer of energy from the primary structure to the NES where it can be rapidly dissipated. Additionally, these devices can couple the dynamics of the primary structure and facilitate the transfer of energy from lower modes to higher modes, where it can be dissipated at a faster rate. This paper experimentally investigates the performance of this type of NES by using the results from tests of a rotational NES attached to a small-scale two-story structure. For these experiments, a shock load is provided to the primary structure using a shake-table-produced impulse-like ground motion. Additionally, by varying the amplitude of the input ground motion, the energy dependency of the performance of these devices can be investigated. The results of these experiments show that this type of NES can attenuate the response of a structure by responding in a highly effective rotational mode.

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