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To effectively isolate low-frequency vibrations, we present a rigid–flexible coupling quasi-zero-stiffness (QZS) vibration isolator with high-static-low-dynamic stiffness (HSLDS) characteristics. Specifically, the QZS isolator is realized by the development of a compliant constant-force mechanism, formed by parallelly combining a diamond-shape mechanism and a nonlinear bi-stable beam in parallel. To evaluate performance of the QZS isolator, we derived an analytical force–displacement model and dynamic model based on pseudo-rigid body method and Lagrange's equations. Then, finite element analysis was performed in Workbench to verify theoretical analysis and identify the optimal design parameters. Furthermore, the dynamic responses of the QZS isolator are established with the harmonic balance method. Finally, the relationships among displacement transmissibility and factors including damping, BSB, payload mass, and material property are discussed. The results have shown that our QZS isolator design can effectively isolate vibrations in low frequency. [ABSTRACT FROM AUTHOR]

Purpose: The design of a new meta-structure with quasi-zero stiffness (QZS) characteristics based on human body structure not only expands the diversity of quasi-zero stiffness structures but also demonstrates excellent performance in the field of low-frequency vibration damping. Methods: Firstly, a quasi-zero stiffness unit structure combining a horizontal cosine beam and vertical cosine beam is designed based on the human body structure, and multiple unit structures are combined into one meta-structure; secondly, according to the material-structural properties of the unit, a functional relationship is established for the positive stiffness structure using the segmental function method, which is combined with the functional relationship of the negative stiffness structure to obtain the theoretical model of the unit structure and then derives the mechanics of the whole meta-structure behavior of the whole meta-structure. Then, the unit structure model and the meta-structure model are designed and simulated, the static properties of the meta-structure are investigated, and photosensitive resin is chosen as the material in the simulation process. Finally, the transmittance comparison between the meta-structure and the linear vibration isolation structure with different damping coefficients is analyzed by theory, and the vibration isolation performance of the meta-structure is simulated. Results: The static simulation analysis of the meta-structure verifies the theoretical solution of the meta-structure very well. According to the theoretical formulation, different parameters can be input to obtain the quasi-zero stiffness properties of the structure. The quasi-zero stiffness properties of the structure are independent of the inherent material properties. Due to the nonlinear nature of the quasi-zero stiffness unit structure, it not only has a lower peak transmittance, but also a lower resonant frequency and a wider isolation range compared with the linear vibration isolator. Conclusions: The designed quasi-zero stiffness meta-structure is suitable for low-frequency vibration isolation of precision instruments, which can be realized by different materials, and more complex meta-structures can be designed on this basis in the future, which has great potential for application in engineering practice. [ABSTRACT FROM AUTHOR]

Purpose: To suppress the low-frequency vibration of dynamic systems such as underwater vehicles, this research proposes a novel geometrically nonlinear vibration isolator using hybrid nonlinear inertial and negative stiffness element. Methods: A spring and an inerter are integrated together into a 4-rod linkage structure to form geometric nonlinearity. The performance of isolator under force or base-motion excitation is analysed. The performance of the proposed isolator in a flexible base structure simulating vibration isolation in ships is also considered. The transmissibilities and vibrational energy transfer are used to evaluate the effectiveness of isolation. Results: The results demonstrate better performance in low-frequency vibration isolation comparing to conventional linear isolator. The combined use of spring and inerter in the linkage mechanism can create a frequency band of ultra-low transmissibility and energy flow at low frequencies. Conclusion: Structural parameters of the proposed hybrid nonlinear element can be designed to alter the dynamic characteristic of the nonlinear isolator to attenuate low-frequency vibration transmission. The proposed nonlinear isolator demonstrates a strong potential for application in naval architecture. [ABSTRACT FROM AUTHOR]

Quasi-zero stiffness (QZS) isolators have attracted extensive attention due to their high-static–low-dynamic stiffness. The effectiveness of the traditional QZS (T-QZS) isolators to attenuate low-frequency vibration has been extensively studied. The T-QZS isolator, however, cannot usually provide satisfactory vibration mitigation performance under ultra-low frequency excitation. To tackle this challenge, we propose a semi-active QZS isolator featuring magnetorheological elastomer (SAQZS-MRE isolator). The prominent merit of the proposed design is that the applied MRE material can provide varying stiffness and damping to the proposed SAQZS-MRE isolator, making the isolator suitable for vibration isolation under wide-band low-frequency range. The dynamic viscoelasticity properties of the MRE are experimentally characterized, to formulate the dynamic modeling of the SAQZS-MRE isolator. The open-loop vibration isolation characteristics of the SAQZS-MRE isolator are assessed using the harmonic balance method (HBM). Subsequently, two semi-active control strategies including skyhook and fast convergence switch (FCS) are effectively utilized in the proposed SAQZS-MRE isolator to evaluate their closed-loop performance. The results demonstrate that the SAQZS-MRE isolator with FCS control can eliminate the resonance peak and reduce the initial isolation frequency. In the higher frequency range, it can also improve the vibration isolation performance compared with the SAQZS-MRE isolator with passive control. [ABSTRACT FROM AUTHOR]