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In this paper, time-delayed feedback (TD-FB) control is introduced for a nonlinear vibration isolator (NL-VI), and the isolation effectiveness features are investigated theoretically and experimentally. In the feedback control loop, compound control with constant and variable time delays is considered. First, a stability analysis is conducted to determine the range of control parameters for stable zero equilibrium without excitation. Next, the nonlinear resonance frequency and the nonlinear vibration attenuation are studied by the method of multiple scales (MMS) to demonstrate the mechanism of TD-FB control. The results of the nonlinear vibration performances show that large variable time delays can improve the vibration suppression. Additionally, the mechanism for the time delay is not only to tune the equivalent stiffness and damping but also to induce effective isolation bandgap at high frequency. Therefore, the variable time delay is assumed as the function of frequency to meet different requirements at different frequency bands. The relevant experiment verifies the improvement of designed variable time delay on isolation performances in different frequency bands. Due to the improvement of isolation performances by compound time delay feedback control on nonlinear systems, it can be applied in the fields of ships, flexible structure in aerospace and aviation.

An adaptive vibration isolation system is proposed in this paper to combine the advantages of both linear and nonlinear isolators. Because of the proposed structural piecewise characteristics for different levels of response, the stiffness and damping properties could be designed according to the vibration performances. The adaptive stiffness and damping properties are achieved by the joined utilization of symmetrical precompression triangle-like structure (TLS) and column frame with cam. In order to design the control mechanism with optimum structural parameters, nonlinear vibration performances are analyzed by using averaging method and singularity theory. The parameter plane is divided into transition sets, and then the optimization criterions for structural design are provided according to multiple nonlinear vibration performances including frequency band for effective isolation, multisteady state band and resonance peak, etc. The experiment is carried out to verify the theoretical selection of desirable parameters and indicates the advantages and improvement of vibration isolation/suppression brought by the structural property adaptation. This study provides a novel method of achieving structural property adaptation for the improvement of isolation effectiveness, which shows the intelligent realization by passive components.

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