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Accurate predictions of sound radiation are crucial for assessing sound emissions in the far field. A widely used approach is the boundary element method, which traditionally solves the Kirchhoff-Helmholtz integral equation by discretization. While the boundary integral formulation inherently satisfies the Sommerfeld radiation condition, a significant drawback of the boundary element method is its difficulty in incorporating noisy measurement data. In recent years, physics-informed machine learning approaches have demonstrated robust predictions of physical problems, even in the presence of noisy or imperfect data. To utilize these benefits while addressing acoustic predictions in unbounded domains, this study employs boundary integral neural networks for predicting acoustic radiation. These networks incorporate the residual of the boundary integral equation into the neural network’s loss function, enabling data-driven predictions of acoustic radiation from noisy boundary data. The results demonstrate that boundary integral neural networks are able to accurately predict the sound pressure field for both interior and exterior problems of a two-dimensional acoustic domain. The study also highlights that the data-driven approach outperforms the conventional boundary element method, particularly at high noise levels. Consequently, the presented method offers a promising approach for predicting sound radiation based on noisy surface vibration measurements.

Gas bubbles are the most potent naturally-occurring entities that influence the acoustic environment in liquids. Upon entrainment under breaking waves, waterfalls, or rainfall over water, each bubble undergoes small amplitude decaying pulsations with a natural frequency that varies approximately inversely with the bubble radius, giving rise to the "plink" of a dripping tap or the roar of a cataract. When they occur in their millions per cubic metre in the top few metres of the ocean, bubbles can dominate the underwater sound field. Similarly, when driven by an incident sound field, bubbles exhibit a strong pulsation resonance. Acoustic scatter by bubbles can confound sonar in the shallow waters which typify many modern maritime military operations. If they are driven by sound fields of sufficient amplitude, the bubble pulsations can become highly nonlinear. These nonlinearities might be exploited to enhance sonar, or to monitor the bubble population. Such oceanic monitoring is important, for example, because of the significant contribution made by bubbles to the greenhouse gas budget. In industry, bubble monitoring is required for sparging, electrochemical processes, the production of paints, pharamaceuticals and foodstuffs. At yet higher amplitudes of pulsation, gas compression within the collapsing bubble can generate temperatures of several thousand Kelvin whilst, in the liquid, shock waves and shear can produce erosion and bioeffects. Not only can these effects be exploited in industrial cleaning and manufacturing, and research into novel chemical processes, but we need to understand (and if possible control) their occurrence when biomedical ultrasound is passed through the body. This is because the potential of such bubble-related physical and chemical processes to damage tissue will be desireable in some circumstances (e.g. ultrasonic kidney stone therapy), and undesireable in others (e.g. foetal scanning). This paper describes this range of behaviour. Further information on these topics, including sound and video files, can be found at .

A method based on the acoustics is developed to analyze the acousto-optic tunable filter (AOTF). A design of AOTF is provided to improve the performance of AOTF based on the method. And the experiment confirms the design.

We developed a new method of earthquake-proof engineering to create an artificial seismic shadow zone using acoustic metamaterials. By designing huge empty boxes with a few side-holes corresponding to the resonance frequencies of seismic waves and burying them around the buildings that we want to protect, the velocity of the seismic wave becomes imaginary. The meta-barrier composed of many meta-boxes attenuates the seismic waves, which reduces the amplitude of the wave exponentially by dissipating the seismic energy. This is a mechanical method of converting the seismic energy into sound and heat. We estimated the sound level generated from a seismic wave. This method of area protection differs from the point protection of conventional seismic design, including the traditional cloaking method. The artificial seismic shadow zone is tested by computer simulation and compared with a normal barrier.

A principle of an acoustic Eaton lens array and its application as a removable tsunami wall is proposed theoretically. The lenses are made of expandable rubber pillars or balloons and create a stop-band by rotating the incoming tsunami wave and reduce the pressure by canceling each other. The diameter of each lens is larger than the wavelength of the tsunami near the coast, that is, order of a kilometer. The impedance matching on the border of the lenses results in a little reflection. Before a tsunami, the balloons are buried underground in shallow water near the coast in folded or rounded form. Upon sounding of the tsunami alarm, water and air are pumped into the pillars, which expand and erect the wall above the sea level within a few hours. After the tsunami, the water and air are released from the pillars, which are then buried underground for reuse. Electricity is used to power the entire process. A numerical simulation with a linear tsunami model was carried out.

We report results on the synchronization of two organ pipes positioned side by side. Special attention is put on the synchronization of the higher harmonics. As possible explanation, classical theory provides the amplitude death as explanation for the reduction to almost silence of two coupled organ pipes. With our measurements we exclude this scenario. The higher harmonics show a behavior in perfect coincidence with synchronization theory. In addition we investigate the dependence on the coupling of two pipes by varying their distance. In the context of synchronization in networks, a new synchronization effect is observed for extended systems with two distributed, slightly different delays.

The process of mesh coarsening describes the reduction and simplification of a highly detailed mesh in such a way that the original geometry is best possible preserved. The earliest coarsening algorithms were developed for real time visualizations in the upcoming field of computer graphics and later on adopted for some element topologies of the finite element method (FEM). An algorithm is presented in this article which applies the mesh decimation process to the requirements of both the FEM and the Boundary Element Method (BEM) in acoustics. The capabilities of the algorithm in order to significantly reduce the CPU times for both numerical methods are shown.

In this paper we investigate the unknown body problem in a waveguide. The Rayleigh conjecture states that every point on an illuminated body radiates sound from that point as if the point lies on its tangent sphere. This conjecture is the cornerstone of the intersecting canonical body approximation ICBA for solving the unknown body inverse problem. Therefore, the use of the ICBA requires that an analytical solution be known exterior to the sphere in the waveguide, which leads us to analytically compute the exterior solution for a sphere between two parallel plates. A least-squares matching of theoretical acoustic fields against the measured, scattered field permits a reconstruction of the unknown object.

In this paper a Control Volume Finite Element Method for harmonic acoustic problems is presented. A dispersion analysis for control volume constructed on Q1 finite elements is compared to Galerkin FEM. The spatial convergence is also given in an eigenfrequency determination process for a cavity. The application for exterior acoustic problems is also studied by dividing the whole field into inner and outer domains using a fictitious boundary. A control volume formulation is used to compute the inner field of the truncated problem, and several approaches are combined to describe the outer field behavior on the outside of the fictitious boundary. The task of coupling is easily implemented through the balance of local flux through polygonal volumes. A two-dimensional configuration with a circular interface demonstrates the validity of this approach.

In this paper, a new technique is presented for structural acoustic analysis in the case of nonconforming acoustic–solid interface meshes. We first describe a simple method for coupling nonconforming acoustic–acoustic meshes, and then show that a similar approach, together with the coupling operators from conforming analysis, can also be applied to nonconforming structural acoustics. In the case of acoustic–acoustic interfaces, the continuity of acoustic pressure is enforced with a set of linear constraint equations. For structural acoustic interfaces, the same set of linear constraints is used, in conjunction with the weak formulation and the coupling operators that are commonly used in conforming structural acoustics. The constraint equations are subsequently eliminated using a static condensation procedure. We show that our method is equally applicable to time domain, frequency domain, and coupled eigenvalue analysis for structural acoustics. Numerical examples in both the time and frequency domains are presented to verify the methods.

The variational theory of complex rays (VTCR) is a wave-based predictive numerical tool for medium-frequency problems. In order to describe the dynamic field variables within the substructures, this approach uses wave shape functions which are exact solutions of the governing differential equation. The discretized parameters are the number of substructures (h) and the number of wavebands (p) which describe the amplitude portraits. Its capability to produce an accurate solution with only a few degrees of freedom and the absence of pollution error make the VTCR a suitable numerical strategy for the analysis of vibration problems in the medium-frequency range. This approach has been developed for structural and acoustic vibration problems. In this paper, an error indicator which characterizes the accuracy of the solution is introduced and is used to define an adaptive version of the VTCR. Numerical illustrations are given.

In recent years the development of free field radiation conditions in the time domain has become a topic of intensive research. Perfectly matched layer (PML) approaches for the frequency domain are well known. In the time domain, on the other hand, they suffer in many cases from highly increased complexity and instabilities. In this paper, we introduce a PML for the conservation equations of linear acoustics. The used formulation requires three auxiliary variables in 3D and circumvents thereby convolution integrals and higher order time derivatives. Furthermore, we prove the weak stability of the proposed formulation and show their good absorption properties by means of numerical examples.

This paper proposes an extension of the variational theory of complex rays (VTCR) to three-dimensional linear acoustics, The VTCR is a Trefftz-type approach designed for mid-frequency range problems and has been previously investigated for structural dynamics and 2D acoustics. The proposed 3D formulation is based on a discretization of the amplitude portrait using spherical harmonics expansions. This choice of discretization allows to substantially reduce the numerical integration work by taking advantage of well-known analytical properties of the spherical harmonics. It also permits (like with the previous 2D Fourier version) an effective a priori selection method for the discretization parameter in each sub-region, and allows to estimate the directivity of the pressure field by means of a natural definition of rescaled amplitude portraits. The accuracy and performance of the proposed formulation are demonstrated on a set of numerical examples that include results on an actual case study from the automotive industry.

A multipole expansion approximation boundary element method (MEA BEM) based on the hierarchical matrices (H-matrices) and the multipole expansion theory was proposed previously. Though the MEA BEM can obtain higher accuracy than the adaptive cross-approximation BEM (ACA BEM), it demands more CPU time and memory than the ACA BEM does. To alleviate this problem, in this paper, two hybrid BEMs are developed taking advantage of the high efficiency and low memory consumption property of the ACA BEM and the high accuracy advantage of the MEA BEM. Numerical examples are elaborately set up to compare the accuracy, efficiency and memory consumption of the ACA BEM, MEA BEM and hybrid methods. It is indicated that the hybrid BEMs can reach the same level of accuracy as the ACA BEM and MEA BEM. The efficiency of each hybrid BEM is higher than that of the MEA BEM but lower than that of the ACA BEM. The memory consumptions of the hybrid BEMs are larger than that of the ACA BEM but less than that of the MEA BEM. The algorithm used to approximate the far-field submatrices corresponding to the cells and their nearest interactional cells determines the accuracy, efficiency and memory consumption of the hybrid BEMs. The proposed hybrid BEMs have both operation and storage logarithmic-linear complexity. They are feasible.

Spoken language identification (LID) is the identification of language present in a speech segment despite its size (duration and speed), ambiance (topic and emotion), and moderator (gender, age, demographic region). Information Technology has touched new vistas for a couple of decades mostly to simplify the day-to-day life of humans. One of the key contributions of Information Technology is the application of Artificial Intelligence to achieve better results. The advent of artificial intelligence has given rise to a new branch of Natural Language Processing (NLP) called Computational Linguistics, which generates frameworks for intelligently manipulating spoken language knowledge and has brought human–machine into a new stage. In this context, speech has arisen to be one of the imperative forms of interfaces, which is the basic mode of communication for us, and generally the most preferred one. Recognition of the spoken language is a frontend for several technologies, like multiple languages conversation systems, expressed translation software, multilingual speech recognition, spoken word extraction, speech production systems. This paper reviews and summarises the different levels of information that can be used for language identification. A broad study of acoustic, phonetic, and prosody features has been provided and various classifiers have been used for spoken language identification specifically for Indian languages. This paper has investigated various existing spoken language identification models implemented using prosodic, phonotactic, acoustic, and deep learning approaches, the datasets used, and performance measures utilized for their analysis. It also highlights the main features and challenges faced by these models. Moreover, this review analyses the efficiency of the spoken language models that can help the researchers to propose new language identification models for speech signals.

A computational procedure is developed for adaptive modeling of transient wave propagation in an unbounded acoustic layer. The adaptivity herein is concerned with controlling the error caused by imperfect modeling of unbounded domains, and the procedure aims at determining the optimal order of the absorbing boundary condition (ABC) under consideration to control the error in the solution within a predetermined tolerance. The perfectly matched layer (PML) is used as an ABC, and the size of the PML domain controls the error associated with modeling unbounded domains. As a key technique in the adaptive method, a local solution procedure is designed based on the method of bicharacteristics to extract, from the computed solution, the information flowing into the computational domain. Numerical experiments show that, under wide circumstances, the maximum pressure associated with the inflow evaluated near the truncated boundary of the PML domain can be related with the maximum error in the pressure and thus can be used as an error estimator. It is demonstrated that a simple adaptive algorithm based on this error estimator can automatically determine the PML domain size to produce solutions with controlled errors.

The benchmark problem of room acoustics, consisting on the determination of the three-dimensional (3D) sound field generated by a point source placed within a closed acoustic space is here addressed by means of the Method of Fundamental Solutions (MFS). The focus of this paper is on the behavior of a MFS numerical frequency domain approach with regards to stability, accuracy, and efficiency. Strategies of improving stability and accuracy of the method such as the use of different distributions of collocation points and virtual sources or an singular value decomposition (SVD) solver are also analyzed. It has been found that these strategies allowed increasing accuracy and attaining stability. Comparison with a classical BEM model was also performed, and has shown that the MFS can reach excellent accuracy making use of smaller-sized equation systems.

We apply the static condensation reduced basis element (scRBE) method to treat the class of parametrized complex Helmholtz partial differential equation. We construct a set of components of interoperable parametrized reference components in a Library to model a family of target models relevant to acoustic devices. The components in the Library are built upon the scRBE method by using reduced basis (RB) formulation, and are compatible to each other by a set of common interfaces, or port. We apply an offline–online computational strategy to achieve rapid and accurate prediction of any parametric systems formed from a set of components in a Library. We demonstrate that the approach can handle large scale models with many parameters and/or topology variations efficiency in several numerical examples. We show that significant computational savings can be obtained by the scRBE method.

The boundary element method (BEM), along with the finite element and finite difference methods, is commonly used to carry out numerical simulations in a wide variety of subjects in science and engineering. The BEM, rooted in classical mathematics of integral equations, started becoming a useful computational tool around 50 years ago. Many researchers have worked on computational aspects of this method during this time.

This paper presents an overview of the BEM and related methods. It has three sections. The first, relatively short section, presents the governing equations for classical applications of the BEM in potential theory, linear elasticity and acoustics. The second describes specialized applications in bodies with thin features including micro-electro-mechanical systems (MEMS). The final section addresses current research. It has three subsections that present the boundary contour, boundary node and fast multipole methods (BCM, BNM and FMM), respectively. Several numerical examples are included in the second and third sections of this paper.

The coefficient matrices of conventional boundary element method (CBEM) are dense and fully populated. Special techniques such as hierarchical matrices (H-matrices) format are required to extent its ability of handling large-scale problems. Adaptive cross approximation (ACA) algorithm is a widely adopted algorithm to obtain the H-matrices. However, the accuracy of the ACA boundary element method (ACABEM) cannot be adjusted by changing the tolerance ${𝜀}^{\prime }$ when it exceeds a certain value. In this paper, the degenerate kernel approximation idea for the low-rank matrices is developed to build a fast BEM for acoustic problems by exploring the multipole expansion of the kernel, which is referred as the multipole expansion H-matrices boundary element method (ME-H-BEM). The newly developed algorithm compresses the far-field submatrices into low rank submatrices with the expansion terms of Green’s function. The obtained H-matrices are applied in conjunction with the generalized minimal residual method (GMRES) to solve acoustic problems. Numerical examples are carefully set up to compare the accuracy, efficiency as well as memory consumption of the CBEM, ACABEM, fast multipole boundary element method (FMBEM) and ME-H-BEM. The results of a pulsating sphere indicate that the ME-H-BEM keeps both storage and operation logarithmic-linear complexity of the H-matrices format as the ACABEM does. Moreover, the ME-H-BEM can achieve better convergence and higher accuracy than the ACABEM. For the analyzed complicated large-scale model, the ME-H-BEM with appropriate number of expansion terms has an advantage in terms of efficiency as compared with the ACABEM. Compared with the FMBEM, the ME-H-BEM is easier to be implemented.