To enhance the broadband vibration attenuation capability of conventional dynamic vibration absorbers (DVAs), this study presents a grounded inerter-damper quasi-zero-stiffness DVA (GID-QZS-DVA), and conducts a comprehensive analysis on the system dynamic behaviors. A dynamic model of the system is established, and the slowly-varying amplitude harmonic balance method (SVAHBM) is employed to derive the amplitude-frequency (AF) response and stability conditions. The effects of key parameters on the saddle-node (SN) bifurcation boundary and local periodic-solution instability boundary are clarified, and the dynamic transition process of the system toward chaos is analyzed. The results demonstrate that the proposed absorber effectively suppresses the primary system resonance peak, reduces the unstable region, and mitigates the nonlinear phenomena. The parameter optimization based on the particle swarm optimization (PSO) algorithm further enhances its performance. Compared with traditional absorbers and other inerter-based counterparts, the optimized GID-QZS-DVA demonstrates a desirable vibration reduction capability under harmonic excitation, with competitive performance in resonance peak reduction and suppression bandwidth extension.
As the span of cable-stayed bridges increases, these structures become more susceptible to vibration under various complex loads. To investigate the dynamic behavior of cable-stayed bridges under vehicle loads, this study establishes a cable-stayed shallow arch model subjected to the equivalent sustained moving-force excitation, with the initial configuration of the bridge deck and cable vibration considered. First, the governing equations are derived based on Hamilton’s principle, in which the initial configuration of the shallow arch is characterized by a non-dimensional rise. Subsequently, the governing equations are reduced to ordinary differential equations (ODEs) by the Galerkin discretization, and the method of multiple time scales is used to derive the modulation equations. On this basis, the steady-state frequency-response and force-response curves are obtained. Numerical analysis indicates that the variations in the initial configuration have a significant effect on the nonlinear behavior of the system. Specifically, as the non-dimensional rise increases within the considered parameter range, the response curves exhibit more complex nonlinear characteristics, with new branches emerging alongside more stable solutions, unstable solutions, and bifurcation points.
Multi-frequency topological wave transport has been demonstrated in various acoustic and elastic metamaterial systems. However, realizing independently tunable multi-frequency acoustic channels within a single acoustic metadevice remains challenging, particularly when different topological bandgaps need to be selectively opened, closed, and routed on demand. In this work, we propose a hexagonal pendant-type acoustic metamaterial (AM) that implements an accidental-Dirac-cone-based independent tuning mechanism in an acoustic system. The designed unit cell contains two types of cylinder-frame connectors with independently adjustable rotational angles, θ1 and θ2, which provide two geometric degrees of freedom for modulating the acoustic band structure. Finite element analysis reveals that the pristine structure supports three accidental Dirac cones in low-, mid-, and high-frequency regimes. By rotating the connectors to break mirror symmetry, the degeneracies of these Dirac cones can be selectively lifted or preserved, thus leading to independently tunable acoustic bandgaps and valley topological phases. The topological characteristics are identified through modal analysis, Berry curvature distributions, and valley Chern numbers. Interfaces between domains with opposite valley Chern numbers support topologically protected interface modes in the corresponding frequency intervals. A supercell analysis confirms the existence of single-, dual-, and triple-frequency interface states with pronounced sound-pressure confinement along the interfaces. Based on these states, frequency-selective acoustic waveguides are constructed to realize directional transport, wave separation, and acoustic demultiplexing under single-, dual-, and triple-frequency excitations. The results show that acoustic waves at different frequencies can be routed along prescribed paths with high selectivity and stable transmission in the presence of typical structural defects. The present numerical study therefore provides an acoustic implementation of independently tunable accidental-Dirac-cone-based topological transport and offers a feasible route for integrated acoustic-waveguiding, filtering, and demultiplexing devices.
A surface acoustic wave (SAW) device, which is indispensable in a modern communication and sensing system, typically has a piezoelectric thin film deposited on an elastic substrate. As the operating frequency increases, the desired mode in such layered structures is increasingly accompanied by the spurious modes, which severely degrade the device performance. Although locally resonant (LR) metamaterials have shown potential for sub-wavelength wave manipulation, their coupling with layer-induced dispersion in piezoelectric layered media remains unexplored. Here, we establish an analytical model to reveal how this coupling governs the bandgap formation. By comparing the high-velocity (AlN-Si) and low-velocity (LiNbO3-Si) systems, we uncover two distinct mechanisms: the high-velocity system enables a complete bandgap; in the low-velocity system, higher-order modes traverse the resonant frequencies without the classic avoided-crossing behavior, preventing the complete bandgap formation. These findings establish quantitative design guidelines for the selective spurious mode suppression in next-generation SAW devices.
To resolve the deteriorated vibration isolation performance of existing passive quasi-zero stiffness (QZS) vibration isolators caused by time-varying loads and stiffness mismatch, this paper proposes a novel load-adaptive QZS vibration isolator (LAQVI) based on radial basis function (RBF) neural network adaptive sliding mode control (SMC). The isolator adopts a composite structure coupling linear springs and electromagnetic units, which delivers adjustable QZS characteristics based on a nonlinear stiffness compensation mechanism. This paper analyzes the influence of various key parameters on the QZS characteristics. Dynamic equation analysis clarifies the relationship between load mismatch and displacement transmissibility, and theoretical studies confirm that excitation current control effectively enhances isolation performance. In addition, a sliding mode controller based on RBF neural network adaptation is designed, leveraging the RBF neural network’s learning and adaptive capabilities for rapid load variation estimation. Simulation results show that the adaptive control of excitation current can effectively compensate for the deviation of the isolation platform and enhance vibration isolation performance. Finally, static experiments verify the QZS characteristics of the isolator, and dynamic load experiments demonstrate the controller’s adaptive adjustment ability for load changes. Vibration test results show that the LAQVI exhibits reliable load adaptability and effective low-frequency vibration isolation performance under time-varying load conditions. The proposed LAQVI provides a theoretical basis for the application of QZS vibration isolators in fields such as intelligent equipment.
