Near-Field Acoustic Holography (NAH) is a sophisticated technique used for reconstructing the sound field in the vicinity of a vibrating object. However, its effectiveness is often compromised by signal contamination during measurements. This paper proposes a novel deep learning framework, termed acoustic spatial pattern (ASP) based convolutional neural network (ASP-NET), to address these challenges. Instead of solving the inverse problem with sophisticated regularization methods, ASP-NET employs a neural network-based approach to reconstruct sound fields in the presence of wave interference. The model is trained using synthetic data generated efficiently through ASPs, ensuring robust performance even in adverse conditions. For the plane wave interference even with a negative signal-to-noise ratio (SNR), the ASP-NET based NAH achieves an outstanding reconstruction accuracy with just a single layer microphone array. It is superior to other conventional NAH, such as the truncated singular value method (TSVD), by nearly three orders of relative error reduction. To alleviate the demand for extensive training data, a vibrational energy constraint-based technique is integrated into the data generation process. It significantly reduces the dataset size, which is a critical technology in the neural-network training. Numerical experiments comprehensively validate the superiority of ASP-NET, demonstrating high-precision reconstructions with single-layer microphone arrays under negative SNRs. This work presents a data-physics-driven NAH method within a defined computational framework, enabling rapid and accurate sound field reconstruction in a strong noise environment interfered by a generic plane wave model.

Two-dimensional forward-looking sonar typically relies on conventional beamforming (CBF) and matched filter (MF) for target detection due to their simplicity. However, their low resolution greatly limits the detection of small underwater targets. To enhance the performance of sonar systems, we employ deconvolution to enhance resolution and suppress sidelobes, and introduce the Fast Iterative Shrinkage-Thresholding Algorithm (FISTA) to accelerate the iterative process. Results show that the FISTA-accelerated deconvolution method achieves the best overall performance, balancing high resolution with computational efficiency. This research provides a valuable reference for the design and optimization of forward-looking sonar imaging algorithms, especially for underwater small target detection.

The accurate and efficient prediction of sound propagation in complex flow fields remains a significant challenge. This paper presents a fast direct boundary element method (BEM) for acoustic problems in moving flows based on hierarchical matrices (H-matrix). This work introduces a precise and efficient numerical framework for computing sound fields coupled with both uniform and non-uniform moving flows. It achieves this through a coupled BEM framework that first computes the potential flow field and then solves the associated sound field. The composite convected boundary integral equation applicable to moving flows is derived in detail. Then, the Adaptive Cross Approximation (ACA) within a H-matrix framework is developed to solve the dense BEM matrices efficiently. On this basis, a shared-memory parallel algorithm is constructed to further accelerate the computation. Conventional parallel algorithms often exhibit low parallel efficiency when applied to models with irregular tree structures due to load imbalance. To address this, the proposed algorithm incorporates an optimized task scheduling mechanism that ensures balanced workloads across all threads, resulting in a significant enhancement in parallel efficiency. The method’s accuracy, parallel efficiency, and convergence are rigorously validated against standard benchmarks and a representative aircraft model, demonstrating its significant potential for large-scale engineering applications.

Beamforming methods can be used to illuminate the generation mechanisms of fan noise and guide the low-noise design of turbine engines. When the microphone array and the sound sources are on opposite sides of the acoustic liner, the scattering which occurs at the liner edges is not taken into account by conventional beamforming methods, leading to inaccurate sound source localization. Since it is necessary to consider the scattering effect of an acoustically lined duct section, a beamforming method for the cylindrical duct with the acoustic liner is proposed. Moreover, the resonant mode dominates in the rigid duct, leading to the failure of the beamforming methods. It is found in this study that the acoustic liner can reduce the influence of different resonant modes on the beamforming methods across the whole frequency range. An axial particle velocity beamforming method is developed to further eliminate side lobes and locate the sound source. Simulations and experiments were undertaken to validate the effectiveness of the proposed method.

This study is motivated by the need to evaluate the jet noise experimentally in the mid-to-near field. Source inversion and sound field reconstruction offer a promising approach. The key lies in appropriately modeling the jet noise sources to ensure the invertibility, as well as the compatibility with the jet mid-to-near field. A hybrid equivalent source model and the inversion method are developed in this paper for source identification via acoustic array measurements. The model consists of two submodels corresponding to the large-scale structures and fine-scale turbulence. For the large-scale component, the wavepacket submodel is employed. An improved parameter determination algorithm, combined with an analytical criterion for determining the wavepacket equivalent radius, is proposed. For the fine-scale component, the multipole submodel and the coefficients inversion algorithm are proposed following a detailed comparison with the monopole model, which provide improved accuracy in representing the acoustic radiation in the jet mid-to-near field. The hybrid model is validated against reference measurements, and excellent agreement is achieved in both the sideline and downstream regions of the jet. This work presents a new method for efficient evaluation of the jet mid-to-near-field noise through experimental approaches.

This paper presents a fast multipole boundary element method (FMBEM) for acoustic problems in a non-uniform potential flow. Different from the BEM for acoustic problems in a quiescent medium, the non-uniform flow field has a dramatic effect on the propagation of sound. In the developed algorithm, only the Mach number of the flow field at infinity needs to be given, and both the non-uniform flow field and the sound field around the vibrating model are calculated by using the BEM. First, the FMBEM for the steady non-uniform potential flow is developed. The exponential expansions of the multipole translation and recurrence calculations of the solid harmonic functions are employed to accelerate the computation. The calculated physical quantity of the non-uniform flow can serve as the computational input for the subsequent sound field. Then, the boundary integral formulae for acoustic problems in non-uniform potential flows are derived. The convected Green's function is also derived by using the Taylor-Lorentz transformation and its inverse transformation. The formulae of fast multipole translations are derived in detail. Finally, several numerical experiments are performed to validate the accuracy and efficiency of the algorithm, demonstrating its capability for accurate and fast computation of large-scale sound fields in non-uniform flows.

This paper investigates the free vibration of coupled rectangular plate-cylindrical shell structures based on Flugge's thin shell theory using the dynamic stiffness method (DSM). The proposed approach decomposes the coupled structure into multiple subplates and open cylindrical shells and derives the dynamic stiffness matrices of each substructure through modal superposition and projection methods. By establishing the compatibility matrix of boundary displacements and forces based on the displacement continuity relations at the coupling boundaries of the substructures, a dynamic stiffness model of the coupled structure is obtained. The natural frequencies of the coupled plate - shell structure are calculated and compared with finite element analysis results, validating the effectiveness and accuracy of the proposed method. Furthermore, the effects of plate-shell coupling position and boundary conditions on the vibration characteristics of the coupled plate-shell structure are investigated.

The Fast Field Program (FFP) is a widely used computational method for calculating sound propagation through moving media in atmospheric acoustics. However, its accuracy diminishes in aeroacoustics applications compared to other numerical methods, such as the Linearized Euler equations in Frequency-domain (LEF). Particularly in scenarios involving high-velocity gradient flows, such as jets and strong shear flows, the accuracy decreasing is especially pronounced. To address these limitations, this paper introduces a Linear-velocity-profiles Fast Field Program (LFFP) method for computing the semi-analytical Green's function in two-dimensional domains with arbitrary continuous velocity parallel mean flows. By employing the layering method of linear ambient velocity within a single layer, the LFFP achieves higher precision in simulating sound fields under high gradient velocity flow conditions. Additionally, the linear velocity profiles modeling method reduces the number of computational layers required, thereby lowering computational costs compared to the traditional FFP. Validation against computational results for a two-dimensional jet flow illustrates that LFFP predicts sound fields in good agreement with LEF. Furthermore, as the velocity gradient of the shear flow becomes steeper, the discrepancy between LFFP and FFP predictions increases.

This paper presents a semi-analytical method, referred to as the linear-velocity-profile fast field program (LFFP), for predicting two-dimensional sound fields in ambient parallel mean flows. The proposed method incorporates the linear velocity layering method into the fundamental framework of fast field program (FFP) to achieve reduced computational costs and enhanced precision, particularly under high-velocity gradient conditions. The accuracy of LFFP is validated through a two-dimensional jet case by comparison with the linearized Euler equation in frequency-domain. In shear flow cases, results obtained from various combinations of Mach number difference and shear layer thickness suggest that the reason for the higher precision of LFFP, compared to traditional FFP, primarily arises from its consideration of the second velocity gradient term in the Pridmore-Brown operator within each single layer. To systematically and mathematically explain this observation, residual analysis is introduced. Furthermore, based on the residual analysis, the multi-staircase layering model is subsequently developed to improve computational efficiency and adapt to sound field calculations in environments with multiple vertically variable ambient quantities.

When a structure moves uniformly at high-speed, the structural-acoustic coupling significant alters the acoustic field distribution compared to conditions without coupling. We propose a hybrid numerical method combining the finite element method (FEM) for structural vibration and the convective boundary element method (BEM) for sound propagation in uniform flow to predict the acoustic field of a uniformly moving body. We introduce the acoustic-analogy Lorentz (a-a Lorentz) transformation to accelerate the convective BEM. To establish the structural-acoustic coupling condition, we derive a mapping method for different physical fields and spacetimes based on the time and space transformations of the a-a Lorentz transformations. A fully coupled solution scheme based on the fast multipole method (FMM) has been developed. By integrating the FEM matrix into the boundary element equation, we eliminate structural degrees of freedom and address the ill-conditioned issue of the direct coupling matrix. Additionally, the FMM efficiently handles large-scale problems. We construct a semi-analytical model to verify the proposed method's correctness and efficiency. The impact of varying Mach numbers and structural elasticity modulus on the coupling effect is analyzed indicating that coupling analysis is essential under high-speed conditions. A full-fuselage model is computed to validate the method's efficiency for large-scale problems.

Multizone sound field reproduction attempts to produce independent sound environments in a number of zones of space, providing the listener with a personalized listening experience. Many reproduction methods have been proposed to optimize the driving weights to improve reproduction performance for a given loudspeaker array configuration. Recently, various methods have explored to optimize loudspeaker placement for further improving the performance of multizone sound field reproduction. However, these methods are currently based on the pressure matching method to carry out the placement optimization study. This paper proposes a loudspeaker placement optimization method based on modal domain. An optimization model for multizone sound field reproduction is used to determine the global modal coefficients that enable the desired sound field to be accurately reproduced in the bright zone while limiting the whole sound field energy within the dark zone, where the global modal coefficients are transformed to the local modal coefficients by the harmonic translation theorem. The constrained matching pursuit method is used to select the optimal loudspeaker placement according to the obtained global modal coefficients. The driving weights of the selected loudspeakers are calculated by the pressure matching method. The simulation results and experimental results demonstrated the good potential of the proposed loudspeaker placement optimization method in multizone sound field reproduction.

Frequency-dependent dynamical systems are commonly encountered in engineering applications, such as automobiles, high-speed trains, and aircraft fuselages. The equations of motion for these systems do not follow the standard second-order form typical for regular elastic structures. The frequency-dependent characteristics complicate the frequency sweep analysis of the underlying model, and also make the application of traditional projection-based model order reduction techniques difficult or even ineffective. In this work, a data-driven approach based on the Loewner realization framework combined with tangential interpolation is applied to reduce the high computational cost of numerical simulations of structural acoustic systems with multiple terminals, incorporating representative damping treatments. The entire construction process does not require information about the system matrices of the original full-order model and knowledge of the complex material properties; only frequency samples and the associated transfer functions between a given number of inputs and outputs are needed. Afterwards, a low-dimensional reduced model in the classical second-order form without a damping term is generated. Additionally, a bi-fidelity error indicator with a masking function is developed to iteratively determine the location of error-peak frequencies used in the next step, and to further minimize the total number of sample data required for convergence. The structural dynamics with add-on viscoelastic damping, exterior acoustic scattering problems modeled by the boundary element method, interior pure acoustic as well as vibro-acoustic systems with porous sound-absorbing materials are all investigated to demonstrate the simplicity, versatility, and efficiency of the proposed approach. This provides a unified data-driven framework to ease the computational complexity of frequency sweep analysis of multiport frequency-dependent dynamical systems.

In order to analyze the high-frequency vibration response of an underwater vehicle under unit force excitation and reduce its noise, we established a model based on statistical energy analysis (SEA) and developed a method for the analysis of the transmission path, whose accuracy was verified by comparison of experimental and simulation results. Vibration and noise characteristics of the vehicle are optimized by adjusting the thickness of some key components, revealing that vibration response of the vehicle is sensitive to subtle structural adjustments in the critical frequency band. As a result, noise reduction of the vehicle can be achieved by optimizing the thickness of its substructures. Our work offers a procedure for the structural optimization of underwater vehicles, assisting their low-noise development.

Multizone sound field reproduction for synthesizing desired sound fields has various applications. The modal matching-based method can obtain global modal coefficients to accurately reproduce the desired sound field. However, the transformation of the global modal coefficients into the loudspeaker weights for reproduction is susceptible to the ill-conditioned transformation matrix that caused by loudspeaker array positions and environment conditions. This paper proposes a multizone sound field reproduction method in the modal domain to obtain the loudspeaker weights directly. An optimization model is formulated with the objective of reproducing the desired sound field within the bright zone and with constraints on acoustic energy in whole region of the dark zone. The improved Lagrange algorithm can adaptively select the Lagrange multipliers for solving the loudspeaker weights, which are the same as the solutions obtained by the CVX method regarded as a benchmark and take less computational time. For the interzone sound interference in reproduction caused by the virtual sound propagation direction of the desired sound field in bright zone and the geometry positions of the multi zones, a realizability metric coefficient is developed based on the proposed model to evaluate the reproduction efficiency. The simulation results and experimental results indicate that the proposed method outperforms the current pressure matching and mode matching methods.

Multizone sound field reproduction aims to create different acoustic environments in multiple spatial zones, allowing listeners to enjoy their individual sounds without being disturbed by sound from other zones. The conventional pressure matching method is used in practice to reproduce the desired sound field by minimizing the sound field error with a limited number of control points, whose reproduction performance decreases above the cutoff frequency. In this paper, a multizone sound field reproduction method based on a sparse equivalent source method is proposed to reproduce the sound field in the whole target region. The acoustic transfer function of each loudspeaker and the desired sound field are represented by the sparse equivalent sources. The whole target region is controlled by interpolating fine virtual control points within the region of the uncontrolled points, and the acoustic transfer functions between the virtual control points and the loudspeaker array are interpolated by the sparse equivalent sources. An optimization reproduction model with the objective of reproducing a desired sound field in the bright zone and constraining the acoustic energy in the dark zone is formulated to find the sparse loudspeaker weights. The simulation results and experimental results show that the proposed method achieves better performance than the conventional pressure matching method in free field and reverberant environments.

In many engineering applications, the solution of acoustic wave problems in the infinite domain is required over a broad frequency range with densely sampled increments. In order to achieve efficient numerical simulations via a spatial discretization, e.g. finite element method, additional artificial absorbing boundaries are necessary to truncate the computational domain into appropriate bounded sizes. One of the most commonly used non-reflecting techniques to attenuate propagating waves is known as the perfectly matched layer. However, the system matrices arising from the finite element treatment of the Helmholtz equation in the absorbing layers are frequency-dependent, implying that they must be formed and inverted at each frequency of interest. Such a procedure is rather troublesome for frequency sweeps. To address this, a surrogate of perfectly matched layers is proposed, which enables the corresponding system matrices to be independent of the frequency. Moreover, it avoids the use of a relatively large computational domain and relatively thick enclosed layers at low frequencies, thus improving the ability of perfectly matched layers across the entire frequency range. After that, an adaptive projection-based model order reduction scheme is further developed to reduce the computational complexity of exterior acoustic systems. A robust error indicator based on the relative error of two constructed reduced order models is accordingly introduced. The performance of the present solution framework is discussed and compared with other implementation strategies, in the context of multi-frequency solution of two-dimensional test models with single or multiple scatterers.

To calculate the acoustic problems of relative uniform motion between the acoustic source and the fluid, we propose a boundary element method (BEM) strategy that can calculate various forms of relative uniform motion in subsonic conditions in a unified framework and is simple to implement. The acceleration algorithm for the BEM, like the fast multipole method (FMM), in the relative motionless state between the source and the fluid can be directly used without major modifications to the program. We propose a two-step transformation method to unify the wave equations of different relative motion forms into the classical form. In the first step, we transform the wave equations for various forms of relative motion into the equation where the convective terms are present only in the source part. Then, in the second step, we propose an acoustic-analogy Lorentz (a-a Lorentz) transformation to apply Lorentz covariance further to eliminate the convection term and establish the wave equation with classical form in a-a Lorentz space. We implement the boundary integration in the transformed a-a Lorentz space and derive a transformation method to transform discretized geometry and boundary conditions in the original space to the a-a Lorentz space. The problem that the boundary conditions are difficult to apply when solving the boundary integral equation (BIE) after the time-space coordinate transformation is solved. Numerical validations for the proposed method are performed by comparing with analytical results over a wide range of relative velocities. The results show that the proposed method can efficiently compute such problems with high accuracy and concise formulation.

The whistle and squeal are two typical abnormal sounds among the radiated noise of running collaborative robots, indicating potential faults and causing discomfort through auditory perception. This study investigated whether psychoacoustic parameters for sound quality could distinguish the whistle and squeal and evaluate their discomfort. A total of 20 abnormal sound stimuli, including 6 whistles and 14 squeals, were obtained from various collaborative robots. The cepstrum characteristics and sound quality metrics (i.e., roughness, sharpness, fluctuation strength and tonality) of all stimuli were analyzed by controlling the equal loudness. Twenty-four participants rated the 'discomfort of abnormal sound in the stimuli' on an 11-point scale. The results show that the modulation frequencies of the fundamental frequency of the whistles were 2.9 Hz to 5.5 Hz, whereas the squeals had no obvious modulation characteristics. The modulation frequencies of the fundamental frequency were highly correlated (with a correlation coefficient of 0.89) to the discomfort responses for whistles, whereas tonality was significantly correlated (with a correlation coefficient of 0.82) to the discomfort responses for squeals. The linear models using single dependent variables of modulation frequency in cepstrum and tonality had determination coefficients of 0.77 and 0.66, respectively, in evaluating the discomfort of whistles and squeals.

This paper proposes an isogeometric vibro-acoustic modeling for composite panel with viscoelastic damping (VED) layer, employing a NURBS-based layer-wise (LW) plate element with the Mixed Interpolation of Tensorial Components (MITC) technique. Based on simplified LW manner, composite panel with VED layer is considered as three-layered sandwiches (VED layer, top face layer, and bottom face layer) characterized by NURBS surfaces. The assumed transverse shear strains are tied to original strain fields at pre-defined tying points, effectively alleviating shear locking. Additionally, to calculate sound transmission loss (STL), two acoustic cavities obtained through extrude operations are placed on both sides of the structure, and panel-cavity coupling is considered. Moreover, governing equations are derived from the weak formulation through the Lagrangian functional, and a discretization strategy is introduced to convert the frequency-dependent stiffness matrix into frequency-independent ones, eliminating the need for repeated matrix reconstruction. The developed model can accurately predict the natural characteristics and STL of the composite panels with VED layer. Numerical results indicate that the proposed LW plate approach based on the NURBS MITC technique exhibits favorable predictability characteristics in vibro-acoustic analysis of various types of composite sandwich panels.

A mapping relationship-based near-field acoustic holography (MRS-based NAH) is a kind of innovative NAH by exploring the mapping relationship between modes on surfaces of the boundary and hologram. Thus, reconstruction is converted to obtain the coefficients of participant modes on holograms. The MRS-based NAH supplies an analytical method to determine the number of adopted fundamental solution (FS) as well as a technique to approximate a specific degree of mode on patches by a set of locally orthogonal patterns explored for three widely used holograms, such as planar, cylindrical, and spherical holograms. The NAH framework provides a new insight to the reconstruction procedure based on the FS in spherical coordinates. Reconstruction accuracy based on two types of errors, the truncation errors due to the limited number of participant modes and the inevitable measurement errors caused by uncertainties in the experiment, are available in the NAH. An approach is developed to estimate the lower and upper bounds of the relative error. It supplies a tool to predict the error for a reconstruction under the condition that the truncation error ratio and the signal-to-noise ratio are given. The condition number of the inverse operator is investigated to measure the sensitivity of the reconstruction to the input errors.