Journal of Sound and Vibration最新文献

The resonance behaviors of defects, specifically local defect resonance (LDR), are useful for defect detection in structures. However, there is a lack of intuitive elucidation regarding the underlying mechanisms governing defect resonance. This study aims to analyze the LDR of a horizontal crack in a plate activated by Lamb waves using the modal decomposition method (MDM). The MDM involves an approximate decomposition of the wavefield into finite constituent Lamb wave modes, including propagating, non-propagating, and inhomogeneous modes. The amplitude of each mode is determined according to the continuous boundary conditions of displacement and stress between the damaged zone and the intact zone. Analytical results reveal specific frequencies at which the damaged zone exhibits significantly stronger vibrations than the intact zone, indicating the emergence of LDR. The corresponding wavefields exhibit various resonance patterns, encompassing both in-plane LDR and out-of-plane LDR types. In contrast to finite element simulations and experimental observations, the MDM unveils the dominant constituents of resonance patterns: out-of-plane LDR results from the combination of reflected and transmitted A0 and A1 modes within the damaged zone, while in-plane LDR is formed by the superposition of reflected and transmitted A0, A1, and S0 modes.

Damping properties in elastic metamaterials are essential for enhancing vibration suppression within frequency ranges known as bandgaps. However, fabricating metamaterials with high-damping materials through additive manufacturing presents challenges, limiting the design freedom of metamaterials. This study proposes locally resonant metamaterials damped by particles, embedded using powder bed fusion of metals with a laser beam. Particles that remain unfused in the powder bed fusion process are retained as particle dampers, adding damping through friction and collisions between particles. Unlike traditional viscoelastic damping materials, metal particles offer advantages in terms of thermal durability. To investigate the damping effect on wave propagation within the metamaterials, we identified the frequency- and acceleration-dependent damping properties of the particle dampers through vibration testing. These properties were then used to define analytical models for the interaction between the metamaterials and the transition of damping via dispersion analysis. The dispersion analysis indicates that wave attenuation occurs over wider frequency ranges. Additionally, the vibration suppression capability of the proposed metamaterials was experimentally demonstrated through vibration testing of fabricated specimens, resulting in the suppression of vibration responses in the out-of-band gaps frequencies by more than 10 dB. The findings of this study enable the fabrication of elastic metamaterials with damping properties via additive manufacturing, offering a method to suppress vibrations across a wide range of frequencies.

An acoustic capsule is designed utilizing equivalent anisotropy of density and of sound speed. The designed capsule can carry any object with dimensions smaller than those of its inner cavity. The capsule achieves internal shielding of the sound field, thus ensuring that the capsule and its contents experience the same acoustic radiation force (ARF), regardless of any changes in the contents. An acoustic capsule design method is proposed and its feasibility is verified using a combination of theoretical analysis and finite element simulations. Additionally, optimization strategies to enhance the ARF and enable selection of appropriate material parameters are discussed, and these strategies pave the way toward practical applications of the ARF in life sciences and other fields.

Hybrid resonance structures, characterized by parallel arrangements, play a crucial role in expanding the bandwidth of sound absorption. It involves the assembly of a set of resonators with different resonance frequencies to form broadband sound absorption a peak-dip band structure. While the mechanism behind peak formation is well elucidated, the genesis of dips remains shrouded. In this study, we utilize two coupled resonators to demonstrate that dips arise from anti-resonance, induced by the mutual coupling of resonator impedances with neighboring resonance frequencies. Further investigations uncover that the origin of mutual coupling can be attributed to the velocity dipole response of coupled resonator, resulting in the generation of evanescent waves and the effect of excessive acoustic resistance. Contrary to intuition, we introduce local acoustic resistance by shunt electromechanical diaphragm (SEMD) to mitigate this excessive acoustic resistance of the coupled resonators, exhibiting a promising reduction in overall acoustic resistance at the anti-resonance frequency. Subsequent exploration reveals that this 'acoustic resistance reducing acoustic resistance' approach significantly enhances sound absorption at the dip frequency, particularly under random incidence conditions. Our research encompasses analytical, numerical, and experimental studies, which are in concordance with each other.

The flow-induced noise has become an important noise source in marine sonar self-noise, which can adversely affect the normal operation of sonar. The marine sonar cabin is simplified as a cavity-plate-exterior space coupled system whose flow-induced vibro-acoustic characteristics are investigated in this paper. An isogeometric vibro-acoustic formulation is proposed in which the cavity with an irregular geometry is precisely described by adjusting the control points and corresponding weights. The flow-induced vibro-acoustic response is obtained by transferring the turbulent pressure data from computational fluid dynamics into the isogeometric vibro-acoustic model. Imposing turbulent pressure into the isogeometric control points is proposed to achieve this objective using a node-based interpolation method. The vibro-acoustic modeling is validated and compared with previous experimental results. These comparisons demonstrate that the developed formulation accurately predicts the vibro-acoustic characteristics of the fluid-excited coupled system. The influences of flow speed, acoustic medium, and cavity shape on flow-excited vibration and sound radiation are discussed. Results show a decrease in radiated acoustic power and radiation efficiency in the exterior space, and a shift in the plate-exterior space coupling modal frequency to lower frequencies when the cavity changes from convex to concave.

Structural health monitoring (SHM) involves continuously surveilling the performance of structures to identify progressive damage or deterioration that might evolve over time. Recently, machine learning (ML) algorithms have been successfully employed in various SHM applications, including damage detection. However, supervised ML algorithms often require labelled data for multiple possible damage states of the structure for successful damage identification. Although it may be feasible to gather such data for low-value structures, obtaining damage data for expensive structures such as aircraft could be highly challenging. Herein, this data insufficiency is addressed by combining Finite Element (FE) models with domain adaptation, specifically transfer component analysis (TCA) and joint domain adaptation (JDA). The proposed methodology is showcased in two case studies, a Brake–Reuß beam, where damage scenarios correspond to different torque settings on a lap joint and a wingbox laboratory structure where damage is introduced as saw-cuts. Supervised learning algorithms in the form of Artificial Neural Networks (ANNs) and K-Nearest Neighbours (KNNs) are trained based on FE data after domain adaptation is applied and are then tested with the experimental data. It is shown that even though the performance of classifiers in distinct scenarios of dual, three, four and five-class cases is sensitive to choices in the training stage, the use of TCA or JDA allows for the use of FE data for training and significantly reduces the need for expensive experimental damage data to be used for training. These results can pave the way for a broader use of ML algorithms in SHM of critical and/or expensive structures.

Passive isolation of low-frequency vibrations poses a significant challenge due to the requirement of possessing a low stiffness. Herein, a compliant curved beam support (CCBS) for near-zero frequency vibration isolation is proposed and systematically investigated. The CCBS exploits nonlinear negative stiffness provided by an arc-shaped beam support to modulate nonlinear positive stiffness of a spiral-shaped beam support. This nonlinear configuration gives rise to an interesting phenomenon, that is, the stiffness modulation of the CCBS for quasi-zero stiffness (QZS) can be flexibly fulfilled by performing a translation transformation on negative stiffness instead of reshaping it. A thorough static analysis is implemented to reveal this stiffness modulation mechanism. The dynamic governing equation is derived and solved analytically and numerically to calculate the displacement transmissibility, and the effects of excitation amplitude, damping, and applied load are dissected. Finally, various excitation tests are conducted to experimentally evaluate vibration isolation performance. The results demonstrate that the CCBS exhibits a remarkably low resonance frequency of 0.5 Hz and achieves near-zero isolation starting at 0.8 Hz, showcasing excellent performance in isolating low-frequency vibrations. The proposed CCBS provides a novel paradigm for achieving flexible low stiffness modulation in compact QZS isolators, making it highly deserving of promotion.

Extreme value analysis is a central aspect of random vibration applications. Most studies focus on a univariate process. System reliability necessitates the extreme value across multiple correlated processes, but analytical methods are scarce and confined to low-dimensional problems. Recently, the authors proposed an analytical method for the extreme analysis of multivariate Gaussian processes. The exact upcrossing rate is derived for the maximum process representing the instantaneous maxima over all processes, and the extreme value distribution is obtained from the Poisson approximation. Nevertheless, for applications involving the wave-passage effect that is commonplace in random vibration, the upcrossings manifest in clumps, rendering the Poisson approximation conservative. The clumping from wave-passage is a complex novel phenomenon, differing from the clumping in narrowband processes. This paper extends the prior work by developing an analytical method for predicting the clump size, thereby providing an accurate prediction of the multivariate extreme value while accounting for the wave-passage effect. The method is powerful as it is fast and amenable to high-dimensional problems. Two examples include the propagation of ocean waves and a multi-span bridge subjected to propagating ground motions. The proposed method is shown to accurately predict the clumping factor and the probability of failure, compared to numerical simulations. In contrast, the Poisson approximation using the exact upcrossing rate noticeably overestimates the failure probability.

The Doppler effect caused by the rotation of turbine fans brings significant challenges to the identification of fan noise sources inside the nacelle. Current methods of rotating source localization inside the cylindrical duct are executed with tough requirements for the microphone array mounted on the duct wall, which includes a fair enough number of microphones and equal-space distribution of each microphone in the azimuthal direction. A methodology based on nonuniform measurements and duct spin modes superposition (NMDMS) is proposed to identify rotating sources with high spatial resolution and few side lobes even near cut-on frequencies, which requires much fewer microphones and no uniform distribution of each microphone in the circumference. The sparsity in the azimuthal domain of the duct field generated by multiple rotating sources is verified theoretically, after which the azimuthal mode in each duct cross-section is reconstructed by the inhomogeneous measurements through the orthogonal matching pursuit (OMP) method. Followed by the identification of mode amplitude in the rotation frame, the sound pressure distribution as well as the axial acoustic velocity distribution on the source plane is reconstructed through duct modes summation. Numerical simulations and experiments are implemented to validate the method. Localization results indicate that rotating sources identification using the proposed method could not only save more than half the microphones without requirements of equal-space distribution but obtain good accuracy of localization and remarkably fewer side lobes.