Vibration control through the robust nonlinear absorber with negative stiffness and internal resonance creation

In this study, a nonlinear absorber that works with a negative stiffness mechanism is suggested to mitigate vibration, and its effect on the reduction of vibration is investigated. The negative stiffness, which is inherently nonlinear, creates internal resonance; therefore, the vibration energy can be transmitted from low-frequency to high-frequency vibrating modes, causing vibration suppression. The nonlinear absorber is added to the primary nonlinear system, and when the main system is subjected to external resonance due to harmonic excitation, the negative stiffness parameter of absorber is so adjusted that autoparametric resonance occurs and vibration is reduced. First, the mathematical model of the system is presented and the governing differential equations of the motion are derived, and then, using the multiple scale method, the equations are solved for the case without, and with the 1:3 internal resonance. The responses and their stability are inspected, discussed, and compared. After that, the effect of negative stiffness and damping parameters on vibration amplitude reduction is investigated and the adequacy of the proposed absorber will be demonstrated by numerical analysis. Finally, the energy exchange between the primary system and the absorber will be demonstrated by plotting the responses in the state space and the displacement response Fourier spectrum.

Vibration Isolation System with Kalman Filter Estimated Acceleration Feedback: An Approach of Negative Stiffness Control

This paper presents the isolation of vibration through the acceleration feedback of the Kalman filter. In this paper, vibration isolation was analyzed both analytically and experimentally through the estimation of the Kalman filter (KF). A negative stiffness mechanism was used to reduce the level of vibration for the developed dynamic system. The technique of negative stiffness can provide stiffness of infinite level to low stiffness as well as disturbance generated by the ground vibration directly. The performance of an isolation system through a mechanism of negative stiffness was improved by the addition of acceleration feedback. Acceleration was measured using a microelectromechanical (MEMS) type accelerometer instead of traditional servo type accelerometers due to lower cost. However, the output of a microelectromechanical (MEMS) type accelerometer is usually noisy. To avoid this difficulty, an acceleration that was estimated by a Kalman filter was considered in the acceleration feedback instead of directly measured acceleration. The dynamic behaviors of the system were compared for both the Kalman-filtered acceleration and the directly measured acceleration feedback. It is observed that the former has a significant effect on the improvement of the characteristics of the vibration isolation systems than later.

An Air Spring Vibration Isolator Based on a Negative-Stiffness Structure for Vehicle Seat

This research introduces an air spring vibration isolator system (ASVIS) based on a negative-stiffness structure (NSS) to improve the vehicle seat’s vibration isolation performance at low excitation frequencies. The main feature of the ASVIS consists of two symmetric bellows-type air springs which were designed on the basis of a negative stiffness mechanism. In addition, a crisscross structure with two straight bars was also used as the supporting legs to provide the nonlinear characteristics with NSS. Moreover, instead of using a vertical mechanical spring, a sleeve-type air spring was employed to provide positive stiffness. As a result, as the weight of the driver varies, the dynamic stiffness of the ASVIS can be easily adjusted and controlled. Next, the effects of the dimension parameters on the nonlinear force and nonlinear stiffness of ASVIS were analyzed. A design process for the ASVIS is provided based on the analytical results in order to achieve high static–low dynamic stiffness. Finally, numerical simulations were performed to evaluate the effectiveness of the ASVIS. The results obtained in this paper show that the values of the seat displacement of the ASVIS with NSS were reduced by 77.16% in comparison with those obtained with the traditional air spring isolator without NSS, which indicates that the design of the ASVIS isolator with NSS allows the effective isolation of vibrations in the low-frequency region.

Evaluation of the Negative Stiffness Mechanism on the Performance of a Hinged Wave Energy Converter

This paper presents the numerical and experimental study of a new spring mechanism adapted to a cone-shaped point absorber wave energy converter (WEC). The WEC is intended to be hinged to a floating wind platform with a long arm to create a combined wind and wave harvesting concept. The main objective of the spring mechanism is to improve the platform restoring moments against the wind thrust forces, generated by the wind turbine while contributing to wave energy harvesting. However, the study is presented for the case where the WEC dynamics is investigated outside the platform and attached to a fixed frame, to validate the mathematical model of the WEC concept. Moreover, the impact on the power harvesting performance is investigated with and without negative springs in this scenario.

Design and analysis of a vibration isolation system with cam–roller–spring–rod mechanism

The vibration isolation system using a pair of oblique springs or a spring-rod mechanism as a negative stiffness mechanism exhibits a high-static low-dynamic stiffness characteristic and a nonlinear jump phenomenon when the system damping is light and the excitation amplitude is large. It is possible to remove the jump via adjusting the end trajectories of the above springs or rods. To realize this idea, the article presents a vibration isolation system with a cam–roller–spring–rod mechanism and gives the detailed numerical and experimental studies on the effects of the above mechanism on the vibration isolation performance. The comparative studies demonstrate that the vibration isolation system proposed works well and outperforms some other vibration isolation systems.

Design and evaluation of a quasi-zero-stiffness isolator using flexibly supported negative stiffness mechanism

In traditional quasi-zero-stiffness (QZS) isolation system, the negative stiffness part is usually fixed rigidly, lacking of effective amplifying mechanism. For reaching a quasi-zero state, the value of negative stiffness need to be very large to offset the positive stiffness of the structure. This paper proposes a novel isolator incorporating a flexible support to magnify negative stiffness part for effective realization of quasi-zero state. First, the concept and formulation of the innovative quasi-zero isolator are presented. Equivalent model for the flexibly supported negative stiffness part is established, followed by a parametric analysis to reveal the amplification effect. Thereafter, a design method is developed and numerical simulation is performed to verify the isolating performance. The results show that a flexible support enlarges the negative stiffness remarkably, thereby resulting in a cost-effective design. The optimized QZS isolator is capable of isolating external disturbance significantly.