Modeling Of Acoustic Field Research Articles

Clustering of passive tracers in a random acoustic velocity field

We consider the effects of passive tracer clustering (e.g., the magnetic field energy in stellar atmospheres) in a random acoustic velocity field. A method for numerical modeling of a two-dimensional random acoustic field is proposed. The field is described by a correlation tensor defined by traveling isotropic waves, taking into account dissipation. Two metrics for measuring the clustering effects are used: concentration and density. Using numerical modeling, we show that the tracer concentration is almost always clustered. The situation with the density is different; as the dissipation tends to zero, the time to reach the clustered states increases significantly. In addition, due to the tracer transport out of the density clustering regions, only a part of the tracer is clustered. For the presented analyses, we considered ensembles of Lagrangian particles and introduced and applied the statistical topography methodology.

Моделювання акустичного поля на основі дисперсії звуку при відбитті трасуючих хвиль на відкритих майданчиках

A method of numerical modeling of acoustic fields in open areas with the possibility of parallelization of calculations is proposed. This method is part of a developed software solution that allows you to perform physical field modeling in various subject areas, being scalable in the sense of using an arbitrary set of parallel calculators. The use of existing modeling systems is associated with great difficulties in solving complex problems with a high degree of detail of the simulated object. Greater accuracy implies a high degree of discretization, a greater number of elementary model calculations performed. Parallel and distributed computing systems have a much better ratio of accuracy-approximation and time and cost costs compared to single-processor systems. Modern general purpose modeling systems use a simplified ray model of sound propagation, which neglects diffractional and interference effects, which are often critical in industrial acoustics. The article proposed a method based on the approximation of the principle of superposition of sound fields. It is accurate, while the linearity of the equations of acoustics is relevant. The basis is the Rayleigh integral and the approximation of reflective surfaces by flat point radiators. A parallel form of such a method is presented, as well as an analysis of its properties, both in sequential and parallel forms.

A meshfree approach for vibro-acoustic analysis of combined composite laminated shells with variable thickness

The vibro-acoustic responses of combined composite laminated shell structures with variable thickness immersed in acoustic medium is investigated by using a meshfree method in this paper. The theoretical model of structural field is established by employing the energy principle in conjunction with the first-order shear deformation theory (FSDT) and the theoretical model of acoustic field are established by using Kirchhoff-Helmholtz integral equation. The displacement components of shell segments and the sound pressure variables of acoustic medium are described by using the meshfree Tchebychev point interpolation (TPIM) shape function and Double Fourier series in meridional and circumferential directions. The non-uniqueness problem of Kirchhoff-Helmholtz integral equation is overcome by adopting CHIEF method. The validation of the presented theoretical model is proved by comparing the results calculated by the proposed model with those results of existing literature and FEM/BEM. Based on the established theoretical model, vibro-acoustic responses of combined composite laminated shell structures with variable thickness immersed in acoustic medium are performed by analyzing the influences of thickness parameter, external load and boundary condition on the sound pressure level (SPL) and sound power level (SWL) of combined composite laminated shell structures. The above investigations can provide the theoretical thesis and technique guidance of preliminary design of combined composite laminated shell immersed in various acoustic medium.

Random matrix theory for description of sound scattering on background internal waves in a shallow sea

The problem of propagation of low-frequency sound in a shallow waveguide with random hydrological inhomogeneity caused by background internal waves is considered. A new approach to statistical modeling of acoustic fields, based on the application of the random matrix theory and previously successfully used for deep-water acoustic waveguides, is used to the case of shallow-water waveguides. In this approach, sound scattering on random inhomogeneity is described using an ensemble of random propagator matrices which describe the transformation of the acoustic field in the space of normal waveguide modes. A study of the effect of sound “escaping” from a waveguide was carried out. The term “escaping” here means energy transfer to modes with stronger attenuation due to scattering on internal waves. A model of an underwater sound channel with an axis at a depth of about 45 meters is considered. It is shown that the first few modes propagating inside the water column are very little subject to losses due to the “escaping”. The strongest impact of the leakage scattering is experienced by the middle group of modes capable of reaching the sea surface. It is revealed as significant increasing of losses as compared to a horizontally homogeneous waveguide. On the other hand, the existence of linear mode combinations for which loss enhancement is practically absent has been revealed. These linear combinations correspond to the eigenfunctions of an inhomogeneous waveguide. Statistical analysis of propagator eigenfunctions indicates on qualitative differences of mechanisms of scattering for frequencies of 100 and 500 Hz.

Learning-based acoustic displacement field modeling and micro-particle control

Acoustic manipulation has emerged as a promising microtarget control method with potential applications in microchip assembly, noncontact control of chemical materials, and cell control. However, the precision of acoustic micro-/nano-manipulation is constrained by the ambiguity of the acoustic displacement field. The nonlinear properties of displacement fields cannot be appropriately simulated using conventional mathematical fitting techniques. In this study, considering the complexity of particle motion on a thin plate driven by acoustic waves, the original displacement dataset was collected based on an experimental platform and was then trained using a neural network to model the displacement of unknown points on the plate. The corresponding cost functions were designed based on a manipulation task and particle number to determine the frequency sequence and achieve motion control of micro/nano targets by selecting the driving frequency with the lowest cost during the controlling process. Based on the above predictions and control effects, the acoustic manipulation platform constructed in this study could be used to manipulate the linear motion of a single particle and control multiple particle encounters as well as to manipulate the complex trajectory “NK”. This work opens up an accessible path for an acoustic displacement field and enables achievable microtarget motion control.

Three-dimensional acoustic vector field model using Gaussian beam tracing.

A three-dimensional acoustic vector field model was developed using Gaussian beam tracing. The field at any location is computed by coherently summing all contributing beams, where the beam equation of particle velocity depends only on beam width and eikonal. A deep-sea long-range sound propagation experiment in the South China Sea was analyzed using vector hydrophone measurements of particle velocity and sound pressure. The results were compared with the model predictions, indicating that beam tracing is effective in predicting sound pressure and acoustic vector fields in deep water.

Numerical Investigation of Background Noise in a Circulating Water Tunnel

The presence of excessive background noise in hydrodynamic noise experiments conducted in circulating water tunnels can significantly impact the accuracy and reliability of experimental test results. To address this issue, it is crucial to evaluate and optimize the background noise during the design stage. In this research, acoustic field model and fluid–solid coupling numerical calculation model of circulating water tunnels are established. Utilizing the finite element method, we analyze the flow noise and flow-excited noise resulting from wall pressure pulses in the circulating water tunnel. Furthermore, we conduct a noise contribution analysis and explore strategies for structural vibration noise control. The results demonstrate that both flow noise and flow-excited noise decrease with increasing frequency, with flow-excited noise being the primary component of the tunnel’s background noise. The presence of resonant peaks significantly contributes to the elevated flow-excited noise levels. Moreover, enhancing structural stiffness and damping proves less effective in suppressing low-frequency peaks. Additionally, employing sound measurement pods suspended from the side of the test section for noise measurement exhibits a high error rate at low frequencies. This research provides insights into optimizing background noise in water tunnels, thereby informing future enhancements in tunnel design.

Study on the effect of seafloor sound speed dispersion on sound propagation

As one of the boundaries of ocean waveguide, the acoustic properties of seafloor sediments have been a hot research problem in ocean acoustic propagation and acoustic field modeling. The existing research has shown that the sound velocity in seafloor sediment is frequency dependent. In order to solve the problem that the sedimentary sound speed dispersing often be ignored in actual applications, this article uses the parabolic Newton to iterate to solve the dispersion equation to obtain the characteristic value of the normal mode. And the impact of frequency dispersion of sediment sound speed through simulation are studied. The results show that the sound wave in the time domain will appear more obvious broadening phenomenon, and the propagation loss will be reduced after considering the sound velocity dispersion of the sediment. Also, with the increase of frequency, the more obvious the effect of sound velocity dispersion on the sound propagation in the frequency range of sound velocity dispersion.

Vibration and critical pressure analyses of functionally graded combined shells submerged in water with external hydrostatic pressure

This paper describes a unified nondestructive semi-analytical formulation for the critical pressure of underwater functionally graded combined shells subjected to external hydrostatic pressure. The structural model of combined shells is constructed from the first-order shear deformation theory, Voigt mixing law, and virtual spring technology. The admissible displacement functions are uniformly expressed with Legendre polynomials along the generatrix direction and Fourier series along the circumferential direction. The Kirchhoff-Helmholtz boundary integral equation is discretized by using the Legendre-Gauss spectral boundary element method, and the external acoustic field model is derived by expanding the Green's function, sound pressure, and displacement of combined shells with one-dimensional Fourier transformation. The linear elastic material theory is applied to deduce the work done by the hydrostatic pressure. The key technology to predict the critical pressure is to create an accurate equivalent model of the hydrostatic pressure. Through solving the final coupled governing equation, the critical pressure is obtained from the linear relationship between the hydrostatic pressure and the square of natural frequency. The convergence and correctness are verified by comparison with the results from published papers and numerical methods. The effects of different hydrostatic pressures, power-law exponents, geometric parameters, and boundary conditions on the critical pressure are investigated in several examples. Computed results can provide security guidance for the nondestructive prediction of underwater functionally graded combined shells at the beginning of engineering application design.

2D frequency-domain finite-difference acoustic wave modeling using optimized perfectly matched layers

Seismic forward modeling is fundamental in sensitivity analysis and full-waveform inversions. In finite-difference acoustic wavefield simulation, the absorption boundary, especially the perfectly matched layer (PML), is widely used, but the setting of PML parameters is empirical. An optimized complex frequency-shift PML (CFS-PML) for the modeling of acoustic fields has been developed. It refines the selection of parameters for improving the artificial attenuation. The improved CFS-PML boundary condition is applied to a 2D frequency-domain acoustic wave simulation using an optimal 17-point finite-difference scheme. Numerical results are compared with a conventional nine-point scheme in terms of computational time and physical memory consumption. These tests indicate that our CFS-PML absorption boundary can effectively improve numerical accuracy without increasing the computational burden remarkably.

An Ocean Acoustic Modeling Based on the Physical Parameters Clustering of the Arctic Ice Floes: Applied to the Study of Acoustic Field Response as Ice Floes Thickness Varies

AbstractThe varies of ice floe thickness (IFH) is a very influential research content in the Earth system academic research, it is closely related to the distribution of underwater acoustic fields. However, the discontinuous physical parameters of ice floes make it difficult to clear this relationship with conventional acoustic propagation models or measured data. Unlike the conventional acoustic models that treat ice floes as one or more physical simplified acoustic reflection layers, this study employs machine learning and FEM (finite element method) modeling to incorporate ice floes' physical parameters into the acoustic field model. The physical parameters of ice floes associated with acoustic field modeling are screened by using the principal component analysis method. On this basis, these ice floes were spatially divided into three highly differentiated and interpretable typical ice clusters using the K‐Means method. We treated ice as a multi‐layer elastic medium, and then the FEM acoustic model was built under the fluid‐structure coupling condition. Measured data (UNDER‐ICE) and MIT acoustic models (OASES) were used to validate our FEM results. We demonstrated that the modeling improves the distribution characteristics of surface channel arrival amplitude under ice floes cover. From the perspective of the model application, the acoustic field response as IFH varies is closely related to the category and region of ice floes.

Research on passive localization method of shallow water acoustic source with single hydrophone based on hierarchical grid histogram filtering

An acoustic field model in the form of a probability density function is established to solve the problem of environmental instability in shallow water. A Bayesian underwater acoustic localization model with the state vector of the acoustic source as a posteriori probability is generated for the purpose of trading time for space in an iterative form and realizing localization of a moving source with a single hydrophone. A hierarchical grid histogram filtering algorithm is proposed, which solves the integral problem in the process of Bayesian filtering and improves the efficiency of the histogram filtering algorithm greatly. The SWellEx-96 experimental results show that in the range of 200 m * 10 km, the relative error of depth positioning is controlled at 12%, the relative error of distance positioning is controlled at 7%, and the efficiency of the algorithm is improved by N1/2 times where N is the number of grids of the histogram filter. The method proposed in this paper is suitable for concealed and low energy consumption platforms in shallow water.

Far field acoustic radiation and vibration analysis of combined shells submerged at finite depth from free surface

A completely submerged underwater vehicle is modeled as a conical-cylindrical-spherical combined shell, the vibro-acoustic response near free surface of which is rarely analyzed in existing studies. In this paper, a Ritz-Legendre spectral method is proposed to analyze the vibro-acoustic response of combined shells under different submerged depths from the free surface. A theoretical structural model is established based on the Love shell theory, virtual spring technology and coordination relationship between displacements and rotation angle of adjacent subshells. The half-space external acoustic field model with the free surface is formulated by the Legendre spectral method, image method and Kirchhoff–Helmholtz boundary integral equation. The unified displacement admissible function of each subshell is expanded as Legendre orthogonal polynomial along generatrix direction and Fourier series along circumferential direction. The free surface treated as an ideal infinite acoustic soft boundary is substituted into acoustic wave equation and the half-space Green's function is obtained. The key technology to construct final coupled governing equation is how to expand the half-space Green's function with two-dimensional Fourier transform. Computed results are compared with those of the references and finite element method. The convergence, applicability, and correctness of the present method are verified. Influence of the free surface on the vibration and far-field acoustic radiation of combined shells under different submerged depths is analyzed, providing engineering significance for predicting external acoustic radiation of complicated combined shells with free surface.

Hybrid assessment of acoustic radiation damping combining in-situ mobility measurements and the boundary element method

A hybrid experimental-numerical approach is proposed for assessing acoustic radiation damping – a major energy dissipating mechanism in lightweight structures. The vibrational behavior is characterized by distributed mobility measurements using laser Doppler vibrometry allowing to realistically capture the mechanical behavior of the structure under test. The experimentally obtained matrix of mobilities are coupled to a boundary element model to evaluate the radiated sound power numerically. Thereby, acoustic measurements and associated low frequency limitations are avoided, which results in two salient features of the proposed hybrid approach: modeling of diffuse incident acoustic fields and consideration of acoustic short-circuiting induced by slits and gaps. These features contribute to an accurate and excitation-dependent estimation of acoustic radiation damping in the low frequency range. The proposed hybrid approach is applied to flat and C-shaped aluminum sandwich panels mounted onto a tub-shaped foundation. The results are compared to those obtained by a previously reported numerical method.

Structure-Acoustic Coupling Analysis of Vibration and Underwater Acoustic Radiation of a Ring-Stiffened Conical Shell

The underwater acoustic radiation of the submarine power cabin has recently become a hot topic in the industry and also in the academia. In this article, the vibration and underwater acoustic radiation of a ring-stiffened conical shell with bases are investigated numerically by means of the combination of the finite element method and boundary element method. The acoustic radiation field is obtained by the traditional acoustic field model and ISO acoustic field model, respectively. A series of numerical examples are given, and the results are compared. Besides, the sound pressure at different positions with frequency is further studied. It is shown that the sound radiated by the structure mainly propagates to the side directions of the shell and propagates relatively less to the front side and the rear side.

Characteristics of Low-Frequency Acoustic Wave Propagation in Ice-Covered Shallow Water Environment

Mastering the sound propagation law of low-frequency signals in the Arctic is a major frontier basic research demand to improve the level of detection, communication, and navigation technology. It is of practical significance for long-distance sound propagation and underwater target detection in the Arctic Ocean. Therefore, how to establish an effective model to study the characteristics of the acoustic field in the Arctic area has always been a hot topic in polar acoustic research. Aimed at solving this problem, a mathematical polar acoustic field model with an elastic seafloor is developed based on a range-dependent elastic parabolic equation theory. Moreover, this method is applied to study the characteristics of polar sound propagation for the first attempt. The validity and effectiveness of the method and model are verified by the elastic normal mode method. Simultaneously, the propagation characteristics of low-frequency signals are studied in a polar sound field from three aspects, which are seafloor parameters, sea depth, and ice thickness. The results show that the elastic parabolic equation method can be well utilized to the Arctic low-frequency acoustic field. The analysis of the influence factors of the polar sound field reveals the laws of sound transmission loss of low-frequency signals, which is of great significance to provide information prediction for underwater submarine target detection and target recognition.

Variable Aperture Method of Ultrasonic Annular Array for the Detection of Addictive Manufacturing Titanium Alloy

The ultrasonic annular array transducer usually has a stronger focusing acoustic field than the linear array and matrix transducer with the same number of array elements, and is more suitable for the detection of large thickness and high attenuation components. However, due to the special arrangement of array elements, the focusing beam cannot be deflected and has a large near field, which limits its application in practical detection. The element parameters of annular array transducer are often designed and analyzed according to the 2-D acoustic field model of a linear array transducer. Therefore, the 3-D acoustic field distribution model of the annular array transducer is established, and the influence of the element parameters on its spatial acoustic field focusing characteristics is analyzed. The design criteria of the array element division mode and element size are proposed, which can avoid the generation of high-energy side lobe and grating lobe, and have good axial acoustic field. Then, the influence of excitation aperture on the energy and size of focal spot at different depths is discussed. The dynamic focusing method with variable aperture of annular array is established, and the C-scan detection experiment is carried out on the addictive manufacturing titanium alloy specimen. The detection results show that the variable aperture method has better central amplitude consistency and imaging accuracy for different depth defects, and has better near surface detection ability than the fixed aperture method.

3D matching positioning method for landslide using infrasound signal received by triangular pyramid vector array, based on ray theory

Several hours before landslides occur, part of the rock and soil body begin to burst, rub, and fracture, generating infrasound signals propagate outward. 3D advanced positioning of the landslide has remained unsolved, which is important for disaster prevention. Using the infrasound signal send from location of the landslide, this work aimed at proposing an advanced 3D matching positioning method, based on ray theory. We first proved vectority of the instantaneous sound pressure field from the perspective of air dynamics, and used ray theory to deduce a point’s instantaneous sound pressure in the air as the sum of all characteristic sound ray vectors. Based on this, the 3D vector acoustic field model was established through simulation. We also found that the triangular pyramid array has vertical and horizontal sampling capabilities, which can collect the vector signals due to the directional anisotropy between the elements. Consequently, the 4-element triangular pyramid vector array was designed to be placed in the acoustic field to receive infrasound signals. Since the infrasound signal is issued before the landslide, we then proposed the 3D matching positioning method: by calculating the cost function of the measurement signal of the triangular pyramid vector array and the copy signals calculated by the propagation model in the predetermined space, point by point, the maximum value was predicted as the infrasound source position, also as the predicted location of landslide. We performed simulations in complex mountainous terrain and applied the method to localization of infrasound sources before the occurrence of the landslide. As a result, by searching and matching in massive space points, we obtained the accurate infrasound source coordinates. This study shows the application prospects of this method for predicting geohazards position several hours in advance.

Modeling of acoustic fields during gas flow around bodies

The article describes the modeling of the acoustic field based on the analysis of pressure fluctuations. For this a model based on the laws of mass, energy and momentum is implemented in a two-dimensional setting. For the calculations, the HLLC scheme for solving the Rieman problem and the WENO scheme for reconstructing the gas-dynamic parameters on the faces between the cells are used. To simulate the acoustic field, a time-averaged characteristic was chosen - the overall sound pressure level (OASPL). The paper considers the acoustic field obtained when a gas flows around a single square body, a cascade of square bodies, a step and a cavity, an interpretation of the ongoing processes is given. The result of the study is the visualization and description of the phenomena that arise when a gas flow around bodies, as well as the study of the effect of removing the observation point on acoustic effects within the simulated area.

Direction Finding with a Vector–Scalar Receiver in the Field of Anisotropic Interference

A mathematical model of an anisotropic acoustic field is constructed based on the multidimensional Poisson process. The relationship between the probabilistic characteristics of the process and the angular density of the acoustic field is established. It is shown that variances and cross-correlation functions of pressure pulsations and oscillatory velocity components depend only on the constant component and coefficients of the first and second harmonics of expansion of the angular density in a Fourier series. The relationship between the anisotropy parameters of the noise field significant for direction finding and the experimentally measured values is found. The relationship between the direction finding results and the anisotropy parameters of the interference field for several algorithms is demonstrated.