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This paper presents a unique human body inspired passive vibration isolation system with a special coupled nonlinear inertia design. This human body inspired anti-vibration structure with nonlinear inertia consists of a compact X-shaped structure with a horizontally-installed spring system to simulate the functions of legs and muscles, and a compact rotational unit to mimic the arms swinging (or upper body movement) and/or muscle extension-flexion motion during human walking. It is particularly focused on the beneficial nonlinear effect incurred by the rotational unit, including a nonlinear equivalent mass and a very special nonlinear inertia incurred conservative force. It is shown that, the nonlinear properties (in equivalent stiffness, damping and mass simultaneously) can obviously improve the vibration isolation at low frequencies and/or in a broadband frequency range, and increase the stability of the mass center of the overall isolation system during vibration, irrespective of the loading and excitation conditions. The muscle function and swinging arms of human body are for the first time employed with an innovative and simple mechanical design for vibration control and successfully validated by experimental prototypes for their excellent beneficial nonlinear features. This paper presents a unique simple passive and adjustable anti-vibration solution of great potential in extensive engineering applications.

To truly reflect the influence on structural seismic response control using viscoelastic dampers with strong nonlinear properties and reduce the cost and difficulty of experimental research, a new user-programmable hybrid simulation platform is developed. The core implementation details of this platform, including the core architecture, software system, and testing setup, are described. To better realize accuracy and stability of the hybrid simulation experiment, methods for solving the equivalent force equilibrium equation for hybrid simulation experiments on viscoelastically damped structures are proposed. Then, the mechanical properties of the experimental substructure (viscoelastic damper) are tested under different temperatures, amplitudes and frequencies, and the mathematical model parameters of the experimental substructure are identified. A seismic response comparison of viscoelastically damped structures obtained by the hybrid simulation experiment and the time history analysis verifies the robustness and reliability of the hybrid simulation platform to test nonlinear systems. Lastly, a series of hybrid simulation experiments for viscoelastically damped structures under different temperatures, seismic intensities and seismic waves are implemented using this hybrid simulation platform for the first time. The experimental results reveal the influence on structural seismic response control by viscoelastic damper under different temperatures, seismic intensities and seismic waves.

A unique bio-inspired multi-joint leg-like or limb-like vibration isolation structure is studied by mimicking the skeleton and joint structures of animal legs, and its advantage in passive vibration isolation is systematically investigated. This bio-inspired structure uses several small quadrilateral structures composed by short adjustable rods and a transverse spring to simulate the multi-articulation of animal legs and adopts long rods to simulate the skeleton. The equivalent static stiffness property, loading capacity and dynamic vibration isolation performance of the structure are systematically studied. It is shown that the nonlinear stiffness characteristics of the structure can lead to very excellent vibration isolation capability in the low-frequency band. Different from many existing quasi-zero-stiffness (QZS) isolators in the literature, this novel anti-vibration structure can demonstrate superior high static but low dynamic stiffness (HSLDS) property and thus excellent vibration isolation performance, subject to large vibration amplitude. Through adjusting proper structural parameters including the rod-length, assembly angle, spring stiffness and layer number according to the influence of the structural parameters on the nonlinear stiffness property, the new structure can have the optimal vibration isolation performance without sacrificing its loading capacity to meet actual requirements. Especially, the length of long rods which is used to simulate the skeleton can be adjusted to obtain better vibration isolation performance than adjusting other parameters, followed by the adjustment of the parameters of small quadrilateral structures. The analysis of the influence of structural parameters on the vibration isolation performance shows that the symmetry between different layers has an important role in maintaining the characteristic of the HSLDS. The comparison with other existing vibration isolation structures of the QZS property also indicates that, the new vibration isolation structure can have a better vibration isolation performance with relatively a smaller size of the overall structure. Experiments are successfully conducted and validated the beneficial nonlinear properties of the structure. This novelbio-inspired anti-vibration structure would have great advantages in practical engineering applications.

A comparative study is conducted on a class of typical X-shaped structures to explore critical design parameters in passive vibration isolation. Several benchmark X-shaped structures are therefore studied, considering the effects of several critical structural parameters on potential vibration isolation performance in different cases. Theoretical calculations, finite element simulations and experimental results show that this class of X-shaped structures in vibration isolation is critically affected by the ratio between the horizontal displacement in the installed spring and the vertical displacement of the structure, which is further nonlinearly dependent on the values of other structure parameters. This critical design parameter can act as a convenient optimization objective for selecting structural parameters in various practical applications. The results of this study thus present a new understanding of the nonlinear dynamics of the X-shaped structures which can facilitate the design or parametric selection of these structures in practices.

This paper deals with the synchronization problem of chaotic neural networks with both interval time-varying and distributed time-varying delays. By introducing an improved Lyapunov–Krasovskii functional and employing definition on a convex set, a delay-dependent feedback controller is derived to achieve exponential synchronization with the help of a drive-response concept and a linear matrix inequality method. The addressed time-delays are interval ones and the limitation on the derivative of a time-varying delay being less than 1 is released. Moreover, the activation functions are assumed to be of more general descriptions, which generalizes and improves those existent methods. Finally, three numerical examples are given to show the effectiveness of the synchronization scheme.

In this paper, the global exponential stability is investigated for a class of Cohen–Grossberg neural networks with time-varying and continuously distributed delays. By using an appropriate Lyapunov–Krasovskii functional and equivalent descriptor form, the sufficient conditions are obtained to guarantee the exponential stability of the addressed system. These conditions are expressed in terms of LMIs and can be checked by resorting to the Matlab LMI toolbox. In addition, the activation functions are of more general descriptions and the derivative of a time-varying delay can take any value, which generalize and further improve those earlier methods. Numerical examples are given to show the reduced conservatism of obtained methods.

Magnetorheological (MR) damper is a prominent semi-active control device for earthquake responses mitigation of structures. The most important topic for the intelligent MR structures is choosing the control current of MR dampers quickly and accurately. The typical control strategy is on–off control strategy, i.e. bi-state control strategy, while inherent time-delay and coarse control precision lie in this strategy. This paper proposes neuro-fuzzy control strategy, in which the neural-network technique is adopted to solve time-delay problem and the fuzzy controller is used to determine the control current of MR dampers quickly and accurately. Through comparison between the bi-state control and the neuro-fuzzy control strategies and a numerical example about a three-story reinforced concrete structure, it can be concluded that the control strategy is very important for semi-active control, the neuro-fuzzy control strategy can determine currents of MR dampers quickly and accurately, and the control effect of the neuro-fuzzy control strategy is better than that of the bi-state control strategy.