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The acoustic black hole (ABH) can alter the velocity of bending waves and concentrate vibration energy with the change of thickness. However, the frequency of the ABH is primarily concentrated above the cut-off frequency and the effect on frequencies below the cut-off frequency is negligible. This paper investigates the vibration characteristics of the ABH damping oscillator (ABH-DO) structure in the frequency range below the cut-off frequency and the corresponding structural parameter influence analysis is conducted. Subsequently, the vibration property of ABH-DO in multiple array configurations are analyzed and the ability of absorbing the vibration energy is experimentally verified. Finally, orthogonal experiments are performed on ABH-DO structures in multiple array configurations. The results reveal that both single and multiple ABH-DO structures demonstrate effective vibration reduction. Among the parameters of ABH-DO, the oscillator mass has the most pronounced effect on vibration peaks. The vibration characteristics of the ABH-DO structure can be optimized by adjusting the oscillator mass. Optimal parameters are determined within a given range through orthogonal experiments. The vibration characteristics of the ABH-DO structure at the optimal factor level are enhanced to varying extents.

The underwater anechoic coating with local resonant units is an effective method to achieve low-frequency sound absorption. However, the structure obtained in this way is not satisfactory in the sound absorption effect of mid-high frequency bands. Capitalizing on the impedance gradient characteristics of functionally graded materials (FGMs) can improve the impedance matching between the structure and the medium, and enhance the dissipation of sound waves inside the structure. Based on these, we propose an underwater acoustic structure, which can improve and obtain low-frequency and broadband sound absorption performance by embedding local resonators into FGMs. To reveal the sound-absorbing mechanism and further optimize the low-frequency absorption performance of the structure, we conduct quantitative analyses on the parameters of FGMs, the materials and forms of resonators. The results indicate that by appropriately adjusting the studied parameters, different low-frequency sound-absorbing peak can be obtained and the absorption effects are also further improved.

A hybrid active sound quality control system, in which a hybrid feedforward and feedback structure is applied, can not only be used in cases where the line-spectrum noise is obtained easily with reference sensors, but it can also improve the comfortability of noise and eliminate unexpected Gaussian random noise. However, the traditional structure for a hybrid active sound quality control system, whereby a reference signal in the feedback control structure is synthesized by the output signals of the feedforward control filter, feedback control filter, and line-spectrum noise cancellation control filter, introduces couplings of the three control filters. To remove the coupling interactions of the feedforward and feedback control structures and to reduce the complexity of the control system, two modified structures with less computational complexity or a smaller increase in computation are investigated in this paper. The first one involves a simplified structure in which the reference signal in the feedback control structure is replaced by the summation of the residual error signal and the output signal of the line-spectrum noise cancellation control filter, and the second one is a modified structure which integrates the output signals of the feedback control filter and the line-spectrum noise cancellation control filter for the reference signal in the feedback control structure. Numerical simulations are carried out to show the performance of the modified structures. The results illustrate that the two modified structures have the ability to cancel Gaussian random noise and to reduce or enhance the amplitude of line-spectrum noise to promote sound quality. Moreover, a simplified structure with a new leaky filtered-x least mean square (FxLMS) algorithm is proposed to upgrade the noise reduction performance and elevate stability in the feedback control structure. The effectiveness of the proposed algorithm also is proven by the simulation results.

The finite volume method, based on the dynamic mesh method, is used to investigate the transient viscous incompressible flow around an impulsively and translationally started cylinder with strips. The strips of different shapes are installed at different locations on the surface of the cylinder. The main purpose of this paper is to investigate the influence of the locations and shapes of strips on the flow caused by boundary motion. The present solutions agree well with the experimental results reported in literature. Six placement angles of strips were selected: 0°, 20°, 60°, 90°, 120° and 150°. The development of wake shows some new phenomena with different strip locations, and the significant difference appears at α = 90°. The vortex intensity is much larger than that of other locations. On the other hand, four shapes of strips were selected: arc, triangle, rectangle and trapezoid. The rectangular strips had the greatest influence on the drag coefficient and the maximum of the drag coefficient increased from 0.4 to 2.8, compared with the smooth cylinder. The maximum of negative velocity had the most significant change when the shape of strip is arc, increasing by 34% compared with the smooth cylinder, at T = 3.

This paper presents elasticity solutions for the vibration analysis of isotropic and orthotropic open shells and plates with arbitrary boundary conditions, including spherical and cylindrical shells and rectangular plates. Vibration characteristics of the shells and plates have been obtained via a unified three-dimensional displacement-based energy formulation represented in the general shell coordinates, in which the displacement in each direction is expanded as a triplicate product of the cosine Fourier series with the addition of certain supplementary terms introduced to eliminate any possible jumps with the original displacement function and its relevant derivatives at the boundaries. All the expansion coefficients are then treated equally as independent generalized coordinates and determined by the Rayleigh-Ritz procedure. To validate the accuracy of the present method and the corresponding theoretical formulations, numerical cases have been compared against the results in the literature and those of 3D FE analysis, with excellent agreements obtained. The effects of boundary conditions, material parameters, and geometric dimensions on the frequencies are discussed as well. Finally, several 3D vibration results of isotropic and orthotropic open spherical and cylindrical shells and plates with different geometry dimensions are presented for various boundary conditions, which may be served as benchmark solutions for future researchers as well as structure designers in this field.

Inspired by the hunting strategy of spiders utilizing cobwebs, this study proposes a novel bionic cobweb structure (BCS) that facilitates the layer-by-layer nonlinear amplification of physical attributes for its embedded isolation components. By integrating a conventional quasi-zero stiffness (QZS) isolator within the BCS, a bionic QZS isolation system is achieved, exhibiting amplified negative stiffness and damping characteristics. The influences of BCS parameters on negative stiffness and damping are systematically investigated. A dynamic equation of the isolation system is formulated, incorporating the cubic trinomial stiffness and cubic quadrinomial damping terms. The displacement transmissibility is derived by the average method and verified via the Runge–Kutta method. The results manifest the effectiveness of the BCS nonlinear amplification effect on the enhancement of vibration isolation performance, accompanied by good coupling between the amplified negative stiffness and damping. Increasing the number of BCS layers, enlarging the initial angle θ i of the i-layer BCS, augmenting the pre-compression δ 20 of the negative stiffness springs, and shortening the connecting rod L s , synergistically contribute to a superior amplification of negative stiffness for better counterbalancing the substantial positive stiffness encountered in heavy-load scenarios. Furthermore, the amplified damping exhibits an anti-resonant characteristic, effectively mitigating the hardening nonlinearity without compromising high-frequency performance. The constructed bionic QZS isolation system with the BCS outperforms the initial QZS system in terms of resonance frequency, peak transmissibility, and isolation frequency band. Moreover, the proposed BCS has the prospect of emerging as a usual platform without modifying the current isolation elements. The intrinsic amplification effect and design logic can offer heuristic insights for future research.

To analyze the noise induced by moving rigid structures in low Mach number flows, acoustic governing equations based on the viscous/acoustic splitting method and the arbitrary Lagrangian–Eulerian method are rigorously derived. In order to resolve the numerical instability generated in a non-uniform mean flow, the modified viscous/acoustic method, based on the filtering method, is developed. The acoustic equations are transformed into the same form as the incompressible flow equations by introducing the acoustic co-velocity and solved based on a collocated grid finite volume method. An approach for solving acoustic equation based on the PIMPLE algorithm is presented and computed in open-source computational fluid dynamics software OpenFOAM, which brings down communication costs and speeds up computing efficiency. Furthermore, the source term decomposition is extended to study the noise generated by each source term in a motion grid. Several examples including stationary and moving meshes have been designed to prove the accuracy of this approach. Finally, the aerodynamic and acoustic properties for the flow past a transversely oscillating cylinder at Re = 200, Ma = 0.2 in lock-in and non-lock-in regions is present.

A nanofabrication method for the production of ultra-dense planar metallic nanowire arrays scalable to wafer-size is presented. The method is based on an efficient template deposition process to grow diverse metallic nanowire arrays with extreme regularity in only two steps. First, III–V semiconductor substrates are irradiated by a low-energy ion beam at an elevated temperature, forming a highly ordered nanogroove pattern by a “reverse epitaxy” process due to self-assembly of surface vacancies. Second, diverse metallic nanowire arrays (Au, Fe, Ni, Co, FeAl alloy) are fabricated on these III–V templates by deposition at a glancing incidence angle. This method allows for the fabrication of metallic nanowire arrays with periodicities down to 45 nm scaled up to wafer-size fabrication. As typical noble and magnetic metals, the Au and Fe nanowire arrays produced here exhibited large anisotropic optical and magnetic properties, respectively. The excitation of localized surface plasmon resonances (LSPRs) of the Au nanowire arrays resulted in a high electric field enhancement, which was used to detect phthalocyanine (CoPc) in surface-enhanced Raman scattering (SERS). Furthermore, the Fe nanowire arrays showed a very high in-plane magnetic anisotropy of approximately 412 mT, which may be the largest in-plane magnetic anisotropy field yet reported that is solely induced via shape anisotropy within the plane of a thin film.