Predicting the flow-induced interior noise of curved thick plate-cavity systems presents theoretical and computational challenges. Classical thin-shell models may become insufficient when the thickness-to-radius ratio is no longer negligible, and evaluating the vibro-acoustic response under stochastic turbulent boundary layer (TBL) excitation requires computing oscillatory quadruple spatial integrals, leading to high computational burdens. To address these issues, this study establishes a three-dimensional vibro-acoustic framework based on 3D elasticity theory and the Rayleigh-Ritz method, utilizing Chebyshev polynomials and artificial boundary springs to accommodate general elastic restraints. A comparison with a Donnell shell formulation is also included to examine the influence of finite-thickness modeling. To overcome the computational bottleneck associated with the TBL excitation, an effective computation strategy is proposed. By separating the modal shape correlation function and truncating the integration region, this method reduces the computational costs while preserving the resolution of convective hydrodynamic loads. Parameter analyses reveal that boundary stiffness governs a fundamental transition in the dominant boundary motion from sliding to bending. Furthermore, 3D stress analysis shows that increased plate thickness enhances the intrinsic wavenumber filtering effect, resulting in stronger through-thickness attenuation of the convective turbulent loads compared with transmitted acoustic plane waves.
Computationally efficient simulation of time-varying underwater acoustic channels is challenging because dense snapshot ray tracing is computationally expensive, particularly in range-dependent environments where eigenray families can change discontinuously. We propose a ray-history interpolation method with path-family consistency to address this challenge. The method first computes eigenrays at sparse time snapshots and clusters them using a history descriptor. Within each cluster, delay, amplitude, and phase are interpolated to reconstruct intermediate impulse responses and synthesize received signals at intermediate times. In simulations with moving sources and receivers, the proposed method achieves correlation coefficients above 0.95 relative to dense snapshot references, while reducing total computation time by approximately 70%. These results indicate that the proposed method provides a practical approach for time-varying channel modeling under realistic computational constraints.
Features of Rayleigh scattering from a spherical object located near a planar rigid boundary at distances smaller than the wavelength are revealed. The expansion in terms of the wave parameter reduces a scattering problem to a sequence of potential problems. The need to describe the effects associated with the normal to the boundary components of vibrational velocity of the particle and the radiation pressure force necessitates taking into account the corrections to the results obtained earlier in the lowest order of expansion. The generalized optical theorem is used to find the imaginary correction to the scattering amplitude that takes into account the effects of the bounding surface.
Accurate characterization of acoustic radiation from submerged structures is crucial for underwater noise assessment and vibro-acoustic analysis. In practical engineering, acoustic measurements are often confined to limited near-field regions and contaminated by noise, rendering sound field reconstruction an ill-posed inverse problem. The conventional Equivalent Source Method (ESM), employing Tikhonov regularization, typically yields over-smoothed solutions prone to spurious artifacts. In contrast, compressive sensing approaches using [Formula: see text]-norm regularization often suffer from amplitude bias in source strength estimation. To address these limitations, this study proposes a physically consistent reconstruction framework for underwater structural acoustic radiation. The non-convex Generalized Minimax-Concave (GMC) penalty is utilized to promote sparsity while mitigating the amplitude bias inherent in convex regularization. To overcome the inherent non-sparsity of submerged elastic structures in the spatial domain, acoustic radiation modes are employed. This transformation maps the dense source distribution into a sparse modal domain, inducing the requisite sparsity. The resulting optimization problem is solved within the framework of the Alternating Direction Method of Multipliers (ADMM). Numerical investigations on a complex cone-cylinder-sphere assembly demonstrate that the proposed method yields superior reconstruction accuracy and robustness compared to conventional techniques. The method suppresses spatial aliasing artifacts, especially in sparse measurement scenarios. Furthermore, a sparsity analysis is conducted to validate the effectiveness of the proposed sparse representation strategy.
Reference sound speed is a critical parameter for direction-of-arrival (DOA) estimation of underwater acoustic source. The horizontal-line-array (HLA) exhibits deterministic systematic error of DOA estimation when reference sound speed deviates from phase velocity at receiver. However, the existence of similar regularity in multidimensional array requires further research. Firstly, this work employs ray theory and normal-mode theory to derive phase forms of received signals in horizontally invariant or horizontally varying waveguides, clarifying intrinsic relationship between reference sound speed and estimated azimuth and elevation angle of stereo-array (SA). Then simplified models of horizontal-plane-array (HPA) and vertical-plane-array (VPA) are further investigated. Moreover, the beam bending caused by angles coupling is analyzed to design optimal array shape. Finally, through simulations and experiments on DOA estimation, the following conclusions can be concluded. For azimuth, SA can achieve unbiased estimation when reference sound speed is close to sound speed at receiver; When reference sound speed satisfies the constraint condition, HPA can achieve unbiased estimation; When reference sound speed is equal to sound speed at receiver, VPA can achieve unbiased estimation. For elevation angle, the above three arrays can achieve unbiased estimation only when reference sound speed is equal to sound speed at receiver.
Underwater acoustics, governing the propagation and scattering of sound in the complex ocean environment characterized by multipath propagation, varied sound speed profile, and high ambient noise, is fundamental to acoustic applications like source localization, active sonar, and ocean acoustic tomography. Direction of Arrival (DOA) estimation is critical in this context, as it provides the direction location of acoustic sources using hydrophone arrays. Atomic norm minimization (ANM) theory has found its way into DOA estimation, alongside well-known compressive sensingbased and subspace-based methods, which enables gridless approaches to DOA estimation. This paper provides an overview of recent work on ANM-based DOA estimation. These new methods are motivated by techniques in atomic norm and the Vandermonde decomposition. Most of them have been proposed for locating the acoustic sources in challenging scenarios that require computational efficiency, high robustness performance, super-resolution capability, and even integration with deep learning techniques. These approaches provide important support for the further development of array signal processing in underwater acoustics.
This paper presents a passive dual-hydrophone method for estimating target motion parameters, including the closest point of approach range and source speed. The proposed approach exploits broadband time-frequency striation patterns that embed target motion information, whose structure is governed by the waveguide-invariant parameter beta. Time-frequency striation information extracted from two horizontally separated hydrophones is incorporated into a joint nonlinear least-squares framework. This framework reduces the unbounded ambiguity inherent in single-hydrophone striation-based estimation to a finite set of geometrically ambiguous solutions. We further show that four geometrically distinct solutions persist within this reduced solution set and present an in-depth analysis of the associated residual ambiguity. The proposed method is validated using both numerical simulations and experimental data obtained from a surface ship radiating broadband noise in approximately 100m deep shallow water, recorded by two bottom-moored hydrophones with a separation of 5.6km.
Duct acoustic mode identification is easily biased by faulty microphones, whose abnormal channel deviations degrade the performance of traditional discrete Fourier transform and compressive-sensing methods. To address this issue, this paper proposes a row-sparse Bayesian integrated detection (RBID) method for simultaneous faulty-microphone localization and duct mode identification. In the proposed framework, abnormal channel deviations and mode coefficients are jointly modeled under a multi-snapshot row-sparse hierarchical prior, and their posterior estimates are inferred within a Bayesian framework. Faulty microphones are then automatically localized from the estimated abnormal deviations, after which a second-stage Bayesian compressive-sensing identification is performed using the remaining healthy channels. Numerical simulations show that, when the proportion of faulty microphones does not exceed 10%, the proposed method achieves fault-detection accuracies above 90% and dominant-mode amplitude errors below 1 dB. Experiments on a 1.5-stage axial compressor further show that, after excluding the detected faulty channels, the dominant-mode amplitude error is around 0.5 dB. The proposed method is effective for duct mode identification under a relatively small proportion of persistent or quasi-persistent faulty microphones, while reducing the need for case-by-case tuning of regularization coefficients.
The adiabatic normal mode (ANM) method efficiently handles weakly range-dependent underwater acoustic propagation. While the WKB approximation underpins solving for ANM modal coefficients, existing work primarily focuses on the first-order solution; the potential of higher-order WKB approximations remains unexplored. To address this gap, this paper systematically derives second- and third-order WKB solutions for ANM. Key steps include: (1) Expanding modal coefficients exponentially to formulate a standard WKB equation; (2) Applying the dominant balance principle to establish coupled equations satisfied by WKB coefficients at each order; (3) Solving coupled equations to obtain the higher-order solutions. Six representative shallow-water test cases were designed to evaluate these theories. Results demonstrate that source frequency critically governs the applicability: (1) At 200 Hz, higher-order solutions yield superior accuracy. The third- and second-order solutions reduce computational errors by 69.35% and 35.48%, respectively, compared to the first-order. (2) Below 200 Hz, accuracy diminishes with increasing order due to wavelength reduction violating the slowly-varying medium assumption, causing compensation terms to diverge. This work bridges the gap in applying higher-order WKB methods to underwater acoustics and provides crucial guidance for selecting the optimal WKB order.
The simultaneous operation of multiple acoustic-homing underwater vehicles (UVs) can expand engagement coverage, but concurrent transmissions may also cause cross-UV acoustic interference. This study develops an interference-aware acoustic simulation framework for evaluating simultaneous multiple-launch UVs operation under simplified but operationally relevant conditions. The framework combines time-varying relative geometry generation with active target-echo modeling, passive cross-UV interference modeling, and matched-filter-based suppression within a unified detection process. On this basis, a frequency-separation design criterion is examined using the matched-filter mismatch margin, FL. Within the present simulation setting, near-independent detection performance is empirically maintained when FL is at least 80dB. The framework is then used to compare single and multiple UVs operation in shallow- and deep-sea environments under representative countermeasure scenarios. The results should be interpreted as comparative trends within the assumed modeling conditions rather than as predictive field-performance metrics. Under these assumptions, multiple-launch UVs operation provides larger benefits when sufficient acoustic independence and spatial diversity are secured, whereas insufficient spectral separation or limited spatial diversity reduces the cooperative advantage. These results illustrate the usefulness of the proposed framework for analyzing both performance gains and degradation mechanisms in simultaneous multiple-launch UVs operation.
Frequency-dependent acoustic attenuation plays a central role in shaping photoacoustic wave propagation in biological media. However, its interaction with interfacial reflections and wave interference in multilayered media remains insufficiently understood. This study investigates the physical effects of frequency-dependent acoustic attenuation on photoacoustic wave propagation in multilayered human skin using a Fourier-domain semi-analytical approach. The formulation extends a previously developed lossless model by incorporating attenuation and its associated dispersion while preserving explicit interface-resolved wave interactions. Analytical expressions for the frequency-domain pressure field are obtained in each layer, and time-domain responses are reconstructed via inverse Fourier transformation. The results show that, in multilayered media, attenuation not only reduces signal amplitude but also alters the relative contributions of reflected and transmitted waves through preferential suppression of high-frequency components. This leads to systematic modification of interference patterns and corresponding changes in waveform structure and temporal broadening. Dispersion introduces additional phase variation but has a comparatively minor influence on the overall waveform under the conditions considered. These results provide a unified framework for interpreting attenuation effects in layered media, highlighting the dominant role of attenuation in shaping photoacoustic signals while retaining physically consistent wave propagation.
Vibro-acoustic coupling systems between closed acoustic cavities with complex geometric shapes and elastic structures are commonly encountered in engineering applications. In the mid-frequency range, their dynamic characteristics are quite complex, and accurate deterministic analysis poses significant challenges. In this study, an improved wavelet finite element method is developed for complex cavity-plate coupling systems, aiming to maintain high precision for complex acoustic geometries while broadening the applicable frequency range and improving computational efficiency. The proposed method adopts the interval B-spline wavelet scaling functions as basis functions to formulate the discrete governing equations of the coupled acoustic-plate system, while enforcing physically consistent fluid-structure coupling conditions. The performance of this method is evaluated using a numerical validation example consisting of a semi-ellipsoidal acoustic cavity coupled with a fixed circular plate. Under different excitations, the results obtained using this method are systematically compared with reference finite element solutions. The results show good agreement within the studied frequency range, including regions with relatively high modal density. Furthermore, the relative error analysis indicates that the improved method significantly outperforms the traditional finite element method in terms of the accuracy per degree of freedom. These results demonstrate that the proposed method provides an effective and reliable alternative tool for deterministic mid-frequency vibro-acoustic analysis of coupled systems with complex geometric acoustic cavities.
In the deep water environment, estimating the motion parameters of underwater acoustic targets holds significant military and civil value. Aiming at underwater acoustic targets moving at a constant speed in a straight line in deep water, this paper proposes a parameter estimation method based on the time-frequency interference structure of two hydrophones. The radiated signals from the target received by the hydrophones form interference fringes in the time-frequency domain due to the multi-path interference effect. By analyzing the full-plane warping transformation in the time-frequency domain, parameters such as the velocity, the nearest distance, and sound source depth of the constant-speed linear-motion target can be estimated. The method is validated through numerical simulations and channel tank experiments. In the scaled channel tank experiment, the estimation errors of velocity, the nearest distance, and sound source depth are 2.0%, 4.9%, and 4.4% respectively under a signal-to-noise ratio (SNR) of - 3 dB. Compared with traditional methods, the proposed method demonstrates distinct advantages in processing low-SNR signals.
In recent years, the emerging technology of Distributed Acoustic Sensing (DAS), measuring the strain in an optic fiber (OF) caused by acoustic waves, has been used in land and water for monitoring and imaging of moving vehicles (trains, ships), stationary installations (pipelines), physical phenomena (earthquakes), marine mammals, oil fields, etc. DAS systems have an advantage over traditional measuring systems since they can provide a densely sampled array along the OF and exploit the features of wide-band signals, particularly at very low frequencies. In this study, the Tampnet DAS dataset released from "The Global DAS Month of February 2023" is used on the purpose of studying its efficiency for the retrieval of critical parameters of the marine environment. The dataset is not entirely continuous in time but contains patches of continuous data. A patch of two-hour continuous strain data is analyzed. The data are dominated by periodic shoaling waves and their interaction with the seabed, which generates primary and secondary microseims (PMs and SMs). The PMs and SMs are observed and separated by frequency-wavenumber decomposition, which demonstrates the excellent low-frequency performance of the DAS system. The opposing wind-wave trains mix nonlinearly and produce Scholte waves at near-acoustic speeds. Passive seismic interferometry (PSI) is performed on the two-hour strain data to obtain the Greens' function which contains dispersive Scholte wave. The shear-wave speeds of the upper sediments are estimated by a non-linear geoacoustic inversion algorithm using the dispersion property of the Scholte wave.
Predicting the frequency spectrum from sources on non-circular trajectories is challenging because closed-form representations are scarce. This study derives Mathieu-function-based solutions for harmonic sources moving on elliptical paths. First, the two-dimensional sound field of line sources traveling along an ellipse is analyzed for a single revolution and for periodic motion over infinitely many revolutions. The resulting frequency spectrum is expressed in terms of Mathieu functions. As the eccentricity of the ellipse decreases and the orbit approaches circularity, the solution converges to that of the corresponding circular orbit. The discrete line spectrum of the periodic case coincides with the continuous spectrum obtained for a single revolution. In the second part, a monopole moving along an elliptical helix is investigated. The three-dimensional spectral sound field generated by the source is represented by a series expansion in Mathieu functions. The series solution shows good agreement with that derived from the integral formulation of the Cartesian Convolution Integral over a range of source frequencies and angular velocities. As the cross section of the elliptical helix approaches a circular shape, the computed sound field converges to the known solution for the circular helix. The results enable sound-field prediction for imperfect rotating sources and propellers.
Helmholtz resonators represent one of the most utilized acoustic objects whose popularity was re-gained with the rise of metameterials. Despite the long history of investigations, the description still can be regarded as incomplete, and one of the gaps lies in the area of acousto-mechanical coupling. We contribute to solving the problem by providing a wide-range parametric analysis of Helmholtz resonators prepared as cylinders with longitudinal slits (parallel to the cylinder axis). Resonance frequencies of such resonators are evaluated depending on geometric parameters of the cylinders (slit width and wall thickness) as well as mechanical characteristics of the material making the resonators. In particular, we reveal an interplay between acoustic resonances and vibrational resonances of the walls, which may be qualitatively different depending on the parameters and materials. Given the absence of reliable analytical models (except for idealised limiting cases), we deem our results useful for any practical implementation of such resonators, especially for the design of acoustic metastructures.
For effectively suppressing low-frequency vibration and noise and broaden the elastic wave bandgap, a coated truncated cone structure metamaterial for low-frequency broadband characteristics is designed based on the local resonance mechanism. The bandgap width is derived by combining the mass-spring equivalent model and the equivalent dynamic mass method. The band structure of the acoustic metamaterial is calculated by the Finite Element Method (FEM) to investigate the formation mechanisms of the band gaps and to systematically study the influence of the resonant unit's geometric and material parameters on the bandgap characteristics. The vibration transfer function and sound transmission loss are also calculated. Finally, laser scanning vibration tests and acoustic impedance tube sound insulation experiments are employed to verify the theoretical and simulation results, and good agreements are obtained. The main results are: (1) The coated truncated cone structure metamaterial exhibits a low-frequency broadband bandgap ranging from 210Hz to 336Hz, with a bandwidth of 126Hz. (2) With the decrease of lattice constant, the increase of density of scatterer and the increase of filling factor, the bandgap lower frequency shifts to low frequency and the bandwidth increases. (3) Within the bandgap range, the metamaterial plate achieves a maximum vibration transmission loss of 58dB and an improvement of up to 19.3dB in sound insulation performance. The findings of this research provide valuable guidance for the design of metamaterials tailored for low-frequency vibration and noise control, underscoring its potential for practical engineering applications.
Green's function extrapolation provides an efficient framework for predicting acoustic fields at adjacent locations from a reference observation. Conventional formulations of this approach have been developed primarily under the assumption that the waveguide invariant beta equals unity, which is valid for range-independent waveguides with flat bathymetry. This study demonstrates the applicability of Green's function extrapolation in more general ocean waveguides where beta deviates from unity due to either bathymetry-induced range dependence or sound-speed-induced effects. The extrapolation is formulated as a two-step procedure consisting of a geometric time delay followed by a Doppler-like resampling operation, with the latter governing the dilation or compression of the arrival-time structure. Numerical simulations show that accurate extrapolation cannot be achieved by considering the time delay alone; instead, proper scaling of the arrival structure must be incorporated through the appropriate value of beta. Results are presented for range-independent shallow-water waveguides with flat bathymetry, range-dependent waveguides with linearly sloping and bow-shaped bathymetry, and a deep-water Arctic waveguide characterized by an n(2)-linear sound speed profile (SSP). While the assumption beta approximate to 1 fails in environments where beta not equal 1, close agreement is recovered when the appropriate value of beta is employed. These findings establish the central role of beta in Green's function extrapolation and extend its applicability to a broad class of realistic ocean waveguides.
Diffraction and attenuation of nonlinear acoustic waves propagating through multi-layered media are important in a wide range of applications. While many existing models address nonlinear wave propagation on a layer-by-layer basis, they often fail to adequately capture diffraction effects. To address this challenge, first, this study generalizes the current layer-wise model (limited to three layers) for n-layered media. Subsequently, three hypotheses were proposed to understand nonlinear wave propagation through layered media: (a) the presence of a single Fresnel zone for second harmonic in layered media, (b) diffraction and (c) attenuation characteristics of second harmonic wave in the 2(nd) and subsequent layers. Based on these hypotheses, a unified model was developed, which accounts for both diffraction and attenuation effects. These models were examined using four cases that were designed specifically to test the hypotheses. Case I: beta = 0 for layer 1, beta not equal 0 for layer 2 to determine if second harmonic in 2(nd) layer will propagate in such a way that its source was at the start of second or first layer. Case II: beta not equal 0 for layer 1, beta = 0 for layer 2 to check if accumulated second harmonic from 1st layer propagating as a linear wave in 2(nd) layer will diffract with fundamental or second harmonic frequency. In Case III: the effect of only attenuation and no diffraction using plane wave solution. Finally in Case IV: fluid-solid two-layer case are explored. The analytical results were validated using numerical simulations, which showed that the unified model has good agreement with numerical results for all the cases compared to the layer-wise model.
Explosions in fluids generate sound pulses with shocks. In this article, we analyze the effect of the initial waveform on the nonlinear propagation of the sound pulses. We focus on peak pressure, pulse duration, waveform, and sound exposure integrated over the waveform. We use an analytical method based on weak-shock theory and the equal-area rule. For an N wave and an exponential wave, the analytical solutions for peak pressure and pulse duration agree with solutions reported in the literature. For a Friedlander wave, we present a solution that illustrates how analytical solutions for other, more complex, waveforms can be derived. We also describe an efficient numerical method for nonlinear propagation of sound pulses with shocks. Numerical results are in good agreement with analytical results. We use the numerical method to calculate the effect of dissipation. The analytical and numerical solutions are developed for plane, cylindrical, and spherical sound pulses. For sound pulses generated by explosions in water and in air, we compare analytical and numerical results with experimental data and empirical relations from the literature.
