To address the broadband torsional vibration in electromechanical coupling rotor systems, a hybrid active–passive vibration control strategy is proposed. Distributed multi-stable nonlinear energy sinks (MNESs) are incorporated as the passive component to overcome the limited vibration suppression performance of conventional single active control. The models of the motor, vector control system, and gear mesh torque are developed, and a dynamic model of the electromechanical coupling rotor system is subsequently constructed. Considering the multimodal characteristics of the motor-driven rotor system, the structure and principle of the MNESs are introduced. The hybrid control strategy that combines the active harmonic voltage injection (AHVI) with distributed MNESs is proposed for the steady-state excitation, and the corresponding dynamic model is developed in a simulation environment. For the impact excitation, the hybrid control strategy incorporating the active disturbance rejection control (ADRC) with distributed MNESs is established. Through numerical simulations, the suppression effects of the system without control, with active control, and with hybrid control are compared. The combined effect and suppression effectiveness of the hybrid control on the primary system are emphasized. Finally, the hybrid control strategy is implemented on the rotor system experimental platform, and its suppression performance is evaluated experimentally. The results indicate that implementing vibration suppression at both the electrical and mechanical levels effectively compensates for the limitations of active control in practical applications.

Three-dimensional base isolation systems (3D-BISs) have been increasingly employed owing to their excellent vertical isolation performance relative to conventional horizontal isolation systems. However, their rocking effect in structures with large aspect ratios and insufficient consideration of vertical vibrations in flexible floor slabs still need to be resolved. This study aims to address these issues by developing enhanced analytical models and an optimal design framework for 3D base-isolated structures. First, the effect of rocking on the coupled isolation mechanism of 3D-BISs is investigated via dimensionless modal analyses, and a 3D flexible model is developed and validated to capture the coupled horizontal-rocking response. The modal properties of floor slabs are then derived, enabling accurate prediction of slab vibrations through an integrated frame-slab model combined with the mode superposition method. Additionally, the effect of superstructure uplift on the seismic responses of 3D base-isolated structures is explored. It is demonstrated that the uplift mechanism of the superstructure significantly reduces seismic demands, with the vertical isolation exhibiting superior performance compared to the horizontal isolation. Building on these findings, an optimal design framework is proposed for 3D-BISs, with the objective of minimizing the peak floor accelerations of the superstructure in all directions. A detailed comparative analysis of the optimized results between rocking-restrained and rocking-free designs is presented, so as to provide informed guidance for the preliminary design of 3D base-isolated structures.

Vibrations in marine piping systems induced by internal and external excitations can lead to fatigue damage of the pipes or supporting structures and contribute to noise transmission. This study proposes a novel vibration suppression strategy for marine fluid-conveying pipeline systems by harnessing the synergistic integration of the acoustic black hole effect and phononic crystal theory. A fluid-structure interaction model based on the 14-equation pipeline formulation is established and solved using the spectral element method, enabling accurate dynamic analysis of straight and L-shaped pipeline meta structures with continuous configuration variations. Results show that periodic acoustic black hole designs create well-defined band gaps that effectively suppress bending and torsional vibrations, which is the dominant energy transmission mechanisms in pipelines. Comparative analysis indicates that L-shaped pipes promote vibration localization at elevated frequencies, resulting in improved vibration reduction performance compared to uniform-diameter counterparts. Parametric studies further identify key geometric influences on bandgap behavior, including lattice length, power-law exponent, and diameter adjustments. This study presents a novel vibration suppression technology for marine pipelines featuring complex spatial configurations, offering a promising solution for effective structural vibration control in practical engineering applications.

Fluid-conveying pipelines are critical components in various engineering systems, where abnormal vibrations induced by internal and external disturbances can lead to excessive noise, mechanical fatigue, and compromised operational safety. Conventional vibration suppression methods are often limited by inherently narrow operational bandwidths. To overcome this limitation, this study introduces a novel pipeline meta structure that integrates the acoustic black hole principle with the phononic crystal concept to achieve intrinsic, self-suppressive vibration control. Utilizing the Timoshenko beam theory, spectral element method, and Bloch theorem, we systematically analyze the dynamic characteristics of the proposed structure, including band gaps, frequency responses, and wave patterns. Furthermore, a multi-objective genetic algorithm is applied to optimize the geometric parameters of the meta structure, achieving a synergistic design that enables broadband vibration suppression in the low-frequency range without sacrificing structural lightness. Numerical results demonstrate that the optimized configuration effectively tailors vibration modes and enhances the acoustic black hole effect, leading to a significant expansion of the attenuation bandwidth and a notable reduction in vibration amplitude. This work presents a systematic design optimization methodology for ABH-based metamaterials, offering an effective solution for broadband vibration mitigation in fluid-conveying pipeline systems.

ABSTRACT Mechanical metamaterials have garnered significant attention due to their rich, counterintuitive, and programmable mechanical properties, which are enabled by their structural design. To date, most studies have focused on quasi‐static responses, primarily involving deformation modes such as tension, compression, and torsion. However, many practical scenarios involve dynamic and impact loading conditions, where loading velocity becomes a critical factor governing mechanical response. Recently, velocity‐triggered mechanical metamaterials have emerged, with certain designs exhibiting non‐Newtonian characteristics. Nevertheless, these designs remain at an early stage and are largely restricted to unidirectional loading conditions. This work proposes an inertia‐based velocity‐dependent stiffness modulation mechanism that enables distinct stiffness states under different loading velocities. Based on this mechanism, a non‐Newtonian metamaterial is designed to extend velocity‐dependent mechanical behavior from unidirectional to bidirectional loading conditions. The proposed structures are fabricated via 3D printing and experimentally characterized using a velocity‐controlled testing platform. This work provides a new design strategy for achieving multidirectional, velocity‐dependent mechanical responses in impact‐regulating metamaterials.

This work presents the competing roles of nonreciprocal advection and elastic stiffness in governing topological soliton dynamics within a one-dimensional rotator chain. The lattice model incorporates three independently tunable mechanical couplings: nearest-neighbor stiffness, fixed-span nonlocal stiffness, and a spatially uniform antisymmetric (nonreciprocal) coupling that introduces nonconservative directional forcing. A continuum reduction is performed to extract the dominant advective and elastic contributions, yielding scaling relations for propagation speed and intrinsic soliton width. Numerical experiments, benchmarked against a baseline configuration, demonstrate a continuous transition from coherent translation, through radiation-dominated propagation, to localized oscillatory trapping as the effective elastic length scale increases relative to advective strength. The antisymmetric coupling provides linear control of drift velocity, consistent with an overdamped scaling analysis. The two elastic couplings collectively determine an effective stiffness that sets the soliton width; larger widths enhance spectral overlap with linear lattice modes, promoting radiative losses. These findings establish a parameter-phase diagram that delineates regimes suitable for three operational modalities: high-fidelity directional transport, programmable radiation, and local energy trapping. This work offers a systematic framework for designing programmable wave-control devices in nonreciprocal mechanical metamaterials.

In order to mitigate the severe lateral vibrations caused by unbalanced excitation as the rotor system passes through its critical speed, a nonlinear vibration absorber directly attached to the rotor has been firstly proposed and tested in an experiment. The design of the vibration absorber involves achieving the necessary linear and nonlinear stiffness through the deformation of circumferentially arranged circular arches. A dynamic model of the rotor system, taking into account factors such as centrifugal force, the nonlinear stiffness of the absorber, and eccentric excitation, has been developed. Multiple solutions of the equilibrium position caused by the nonlinear deformation of the absorber arch are discussed, and the corresponding responses are obtained by using the Galerkin averaging incremental harmonic balance (EGA-IHB) method. Theoretical analysis has been conducted to determine an appropriate parameter range for the design of the vibration absorber. Subsequently, the vibration absorber was designed and fabricated for experimental testing. Static compression tests have confirmed the hardening nonlinear stiffness characteristics of the absorber. Experimental results have shown excellent performance in reducing vibrations in the rotor system, with a reduction in amplitude of 46.75% during steady-state operation and a reduction in peak amplitude of 44.07% during the start-up process when the rotor passes through its critical speed. Additionally, the vibration absorber has been shown to have minimal impact on the inherent characteristics of the rotor system. Overall, the proposed vibration absorber demonstrates significant potential for applications in vibration suppression in rotor systems.

Phononic crystal (PC) pipelines conveying fluid have been widely utilized in engineering structures for vibration suppression. However, their practical application remains constrained by two persistent challenges: the difficulty in achieving simultaneous low-frequency and broadband vibration attenuation, and the lack of effective strategies for directional band gap (BG) design. Inspired by metamaterial concepts, this study presents a hierarchical pipeline meta structure composed of periodically arranged lattices. Each lattice incorporates a pair of oppositely oriented sub-lattices with acoustic black hole (ABH) geometries. Through mechanical modeling based on Timoshenko beam theory and semi-analytical solutions combining the spectral element method (SEM) with the transfer matrix method (TMM), the dynamic characteristics including natural frequencies, frequency responses, and BGs are systematically investigated. The results demonstrate that the band gap (BG) width not only determines the vibration suppression frequency range but also exhibits a positive correlation with attenuation effectiveness. An increase in the flow velocity of the conveyed fluid adversely affects the stability of the pipeline meta structure. However, within the critical flow velocity range, its impact on the BGs remains negligible. Furthermore, BG characteristics are simultaneously governed by sublattice configuration and ABH geometric parameters. Specifically, asymmetric lattice designs incorporating different materials or geometric configurations facilitate broadband BG formation. The ABH parameters offer precise tunability: increasing the power-law exponent induces a low-frequency shift of the BGs, whereas enlarging the maximum outer diameter effectively broadens the BGs’ bandwidth. These findings present a promising strategy for overcoming current limitations in periodic pipeline applications.

To date, the flat bands in magic-angle bilayer metasurfaces have been observed to remain inherently parallel and non-crossing in naturally occurring 2D materials. This limitation arises from the inherent in-plane symmetry of the lattice. Here, we introduce a twinning lattice in acoustic bilayer twisted moir & eacute; metasurfaces that is mirror symmetric with respect to the twin crystal boundary. This new degree of freedom modulates the asymmetric moir & eacute; dispersive behavior and helps to achieve distinct features that are not possible in conventional symmetric twisted moir & eacute; structures. By adjusting the twin crystal angle and bilayer twisting angle, it endows remarkably different dispersion characteristics separated by the twin boundary, such as dual hyperbolic, hyperbolic-flat band combinations or dual flat bands. Crucially, this transition is governed by a nontrivial topological invariant, the number of anti-crossing points NACPS, which dictates the global phase classification. In the dual flat band regime, the intersection at the twin boundary enables low-loss acoustic propagation with tunable directionality, serving as a distinct point for wave manipulation. By providing experimental validation of dispersion crossover at the twin crystal interface, this study paves the way for the design and development of twin acoustic moir & eacute; metasurfaces.

Duffing oscillators subjected to complex-frequency excitation exhibit unique dynamic characteristics owing to the additional degree of freedom introduced by the modulation parameter, providing a new approach for tuning system stability and nonlinear resonance behavior. This work investigates a Duffing oscillator under complex-frequency excitation. The method of multiple scales is employed to derive the complex slow-flow equation for the weakly nonlinear system. The analytical solution is further validated using the Galerkin method, demonstrating full consistency between the two approaches. Based on the derived amplitude–frequency relation, the effects of the modulation parameter, damping ratio, and observation time on the steady-state response are systematically analyzed for both hardening and softening spring cases. Time-domain simulations, together with power spectral density and continuous wavelet transform analyses, are performed to characterize the transient and spectral responses. The results show that both the sign and magnitude of the modulation parameter μ significantly influence the resonance characteristics and nonlinear frequency shift. The multiple-scales solution accurately predicts both transient growth/decay and steady-state responses, as confirmed by numerical simulations. Furthermore, the power spectral density and continuous wavelet transform reveal pronounced time-dependent spectral evolution induced by complex-frequency excitation, demonstrating the nonstationary nature of the system response. This study establishes a consistent analytical and numerical framework for investigating the dynamics of Duffing oscillators under exponentially modulated excitation, providing new insights into stability regulation and nonlinear dynamic responses in systems subjected to complex-frequency excitation.

To address the problem of vehicle collisions with bridge structures, this study developed a three-stage viscoelastic energy-absorbing vibration isolator (TSVEVI). The device leverages the deformation of thin-walled viscoelastic materials to achieve variable stiffness, thereby enabling efficient energy dissipation within limited displacements, reducing the overall size of the device, and enhancing protective performance. Static and dynamic compression tests were first conducted on the TSVEVI to determine key mechanical properties, including equivalent stiffness and damping across its three stages. Subsequently, a finite element model of the vehicle-TSVEVI-bridge system was established to evaluate its impact resistance under vehicle speeds of 60 km/h, 80 km/h, and 100 km/h. The results show that the TSVEVI exhibits three distinct stages: a linear stage, a stiffness degradation stage, and a stiffness strengthening stage. Without the device, vehicle-bridge collisions produced extreme stresses of 3025.0 MPa in the vehicle and 223.3 MPa in the pier, leading to severe damage in both. In contrast, with the TSVEVI installed, the device provided excellent protective performance: pier deformations under 60 km/h, 80 km/h, and 100 km/h were 90.0 mm, 125.8 mm, and 179.1 mm, respectively, while the collision force was reduced by 55.52 %, 81.64 %, and 79.05 % compared with the unprotected pier. These reductions significantly mitigated damage to both the pier and the vehicle, improving structural and vehicular safety. Owing to its three-stage impact-resistant design and the high-damping properties of the self-developed viscoelastic material, the TSVEVI demonstrated superior crash protection.

Hyperbolic moiré materials enable exotic band hybridization, flat-band physics and magic angles1-4, but have so far been mostly restricted in two dimensions5-7. Here we introduce a nonlocal acoustic metacube architecture that lifts these intrinsic constraints and powers up a genuinely three-dimensional (3D) regime of moiré band engineering. In this 3D setting, the magic angle concept is generalized through the inequivalence of eigen-dispersion projections along three mutually orthogonal directions, enabling rich multidirectional band hybridizations that cannot occur in planar systems. As a result, the metacube stably supports multidimensional dispersion reconfiguration, flat-band formation, and asymmetric wave transport, while allowing wave propagation beyond surface confinement with pronounced out-of-plane radiation. By establishing a reconfigurable 3D nonlocal framework for moiré physics, this work defines a new regime of high-dimensional band hybridization and wave control.

Skyrmion family members, including skyrmions, merons, and skyrmioniums, have been observed in diverse physical systems, yet their coexistence and transformation within a single controllable platform remain challenging. Here, we propose and experimentally demonstrate a bilayer twisted moiré elastic system that enables the generation of multiple skyrmion family members with different topological charges. By constructing three-dimensional displacement vector fields, we establish a framework describing the evolution of topological invariants under twist-induced symmetry modulation, thereby governing controlled transitions and the stable coexistence of different skyrmion textures. In addition, manipulating the Lamb-wave phase introduces discontinuous transport of the topological textures, thereby revealing phason-like dynamics within the quasiperiodic structure. Together, these results provide a versatile route for controlling topological textures and open new possibilities for the design of integrated topological wave devices.

Most existing energy harvesters focus on nonlinear stiffness and/or nonlinear damping. Little research has been reported on exploiting nonlinear inerters for energy harvesting. By utilizing an inerter, the equivalent mass of the system can be easily tuned by adding negligible physical mass, allowing the resonant frequency to be adjusted accordingly. Based on this concept, a nonlinear inerter-based X-shaped structure is for the first time proposed to achieve ultra-low-frequency energy harvesting. The dynamic modeling is established, and power generation is predicted. The effects of the nonlinear inerter on energy harvesting performance are analyzed. Experimental tests are conducted to validate the performance of the inerter-based X-harvester. The innovations and contributions of this work lie in: (a) introducing the nonlinear inerter into the classical X-harvester, creating the novel X-inerterharvester; (b) exploiting the geometrically nonlinear inerter mechanism to extend the energy harvesting band into an ultra-low range by tuning the resonant frequency; (c) exploring the effects of the combination of nonlinear inerter, nonlinear stiffness, and/or nonlinear damping in the proposed X-inerter-harvester. These results indicate that the design and analysis of the nonlinear X-inerter-harvester could provide innovative and novel insights for designing low-frequency energy harvesting systems.

By manipulating dispersion, planar lattices can be endowed with a variety of intriguing wave propagation characteristics, which hold significant value in controlling vibration energy transfer paths, energy harvesting, noise suppression, and structural optimization design. In the realm of twisted moiré physics, dispersion modulation from elliptical to hyperbolic can be achieved through bilayer twisting; however, such designs pose certain challenges for mechanical structures. This paper proposes a two-dimensional mechanical phononic crystal model based on nonlocal dispersion engineering. By designing a spring-mass lattice structure with adjacent and nonlocal couplings, the propagation modes of mechanical waves are effectively controlled. Through flexible and straightforward design of nonlocal connection methods, structures with specific dispersion properties can be easily constructed. The paper also discusses the influence of nonlocal connection methods and stiffness parameters on dispersion. This research provides new insights for designing acoustic metasurfaces and mechanical structures with tailored wave propagation properties, offering broad application prospects, such as directional energy harvesting and intelligent vibration isolation systems.

Acoustic metamaterials have emerged as crucial approaches for sound insulation in ventilated confined spaces, but the broadband insulation performance remains restricted by the inherent limitations of local resonance mechanisms. In this paper, a nested theoretical model integrating labyrinth and ventilated panels is established, and the transfer matrix and phase changes are obtained. Results show that the combination of phase synergy effect and local resonance determines the transmission of sound waves in the metamaterial. The locations of peak frequencies and sound insulation coefficient (SIC) are closely related to phase changes. The phase synergy effect brought by the asymmetric panels significantly enhances broadband sound insulation within the range of 400-1800 Hz, finally forming an effective bandwidth exceeding 800 Hz, with an average SIC of more than 0.75. Parametric studies validate the tunability of the two insulation peaks, providing an adjustable bandwidth range of 752-1064 Hz, along with robust performance for sound waves from different incident directions. This study provides a novel, ventilation-compatible solution for noise control, highlighting the pivotal role of phase engineering in advancing new types of acoustic metamaterials.

Aero-engine pipeline systems are critical auxiliary structures that can affect engine service performance and reliability. Due to complex spatial configurations and multi-component coupling， excessive vibration and fatigue failure are easily induced under multi-source excitations and multi-physical-field interactions. Therefore， accurate and efficient dynamic models are required. Optimization design and vibration suppression should also be considered to improve the service performance of pipeline systems. In this study， the mechanical modeling methods of support components are first reviewed. Then， the principles， characteristics， applicability， and theoretical differences of semi-analytical methods， transfer matrix methods， finite element methods， spectral element methods， absolute nodal coordinate formulations， and hybrid modeling methods are summarized. The research progress in dynamic optimization design is discussed from two aspects： clamp layout optimization and pipeline routing optimization. Vibration suppression methods are further reviewed from three technical routes： support-structure-based vibration isolation， additional damping and energy dissipation， and source-side fluid pulsation attenuation. Finally， key scientific issues and future technical directions are discussed. This review is expected to provide theoretical guidance and technical support for dynamic modeling and low-vibration design of aero-engine pipeline systems.

Moiré metasurfaces generate novel optical characteristics, such as photonic polariton and topological Lifshitz transition by stacking multiple metasurfaces with periodic structures. This configuration demonstrates significant flexibility and tunability in the manipulation of optical, electrical, acoustic, and thermal properties. In this work, a bilayer twisted moiré elastic metasurface is presented, constructed using periodically arranged tilted and rhombic prism resonators in Lieb lattice configuration. By utilizing the twisting mechanism, the design enables systematic reconstruction of the moiré metasurface, which facilitates precise manipulation of elastic wave propagation, particularly achieving both the “all‐magic‐angle” and anisotropic transmission. The inherent band structure of the Lieb lattice plays a key role in reducing energy dissipation during wave transmission, thereby enhancing energy concentration. Furthermore, a novel phenomenon of unidirectional polariton‐like polarized waveguide mode is observed, where propagation is biased along specific directions. This study establishes a comprehensive theoretical framework throughderivation of the governing wave equations and systematic construction of band structures with corresponding dispersion relations. These findings significantly enhance the potential applications of moiré metasurfaces in elastic wave manipulation, particularly in critical technologies such as non‐destructive testing and energy harvesting.

Nonlinear vibrational metamaterials hold tremendous potential for vibration suppression. Recent studies have emerged on key aspects such as granular media, nonlinear stiffness, damping effects and nonlocal interaction. Discrete-continuum or hybrid granular media, including those incorporating granular-elastic continuum interfaces, present new possibilities for effective shock and vibration mitigation through Hertzian, vibro-impact, and frictional nonlinearities. Nonlinear stiffness gives rise to phenomena such as amplitude-dependent behavior, chaotic bands, higher harmonics and adaptive-broadening bandgap, which collectively enhance low-frequency, broadband and highly efficient vibration suppression. Additionally, damping effects play a critical role in improving wave attenuation and dynamic behavior, particularly when combined with inerter and collision mechanisms, thereby further enhancing broadband vibration reduction and system robustness. Furthermore, the introduction of nonlocal interactions overcomes the limitations of traditional interactions, strengthening low-frequency dispersion control and revealing distinctive phenomena such as energy return flow, which offers new avenues for vibration suppression. By reviewing these advances and presenting future perspectives on nonlinear vibration metamaterials, we aim to inspire further innovative research and offer valuable insights and guidance to address the existing challenges.