Sound Propagation Path Research Articles

Sound Speed Inversion Based on Multi-Source Ocean Remote Sensing Observations and Machine Learning

Ocean sound speed is important for underwater acoustic applications, such as communications, navigation and localization, where the assumption of uniformly distributed sound speed profiles (SSPs) is generally used and greatly degrades the performance of underwater acoustic systems. The acquisition of SSPs is necessary for the corrections of the sound ray propagation paths. However, the inversion of SSPs is challenging due to the intricate relations of interrelated physical ocean elements and suffers from the high costs of calculations and hardware deployments. This paper proposes a novel sound speed inversion method based on multi-source ocean remote sensing observations and machine learning, which adapts to large-scale sea regions. Firstly, the datasets of SSPs are generated utilizing the Argo thermohaline profiles and the empirical formulas of the sound speed. Then, the SSPs are analyzed utilizing the empirical orthogonal functions (EOFs) to reduce the dimensions of the feature space as well as the computational load. Considering the nonlinear regression relations of SSPs and the observed datasets, a general framework for sound speed inversion is formulated, which combines the designed machine learning models with the reduced-dimensional feature representations, multi-source ocean remote sensing observations and water temperature data. After being well trained, the proposed machine learning models realize the accurate inversion of the targeted ocean region by inputting the real-time ocean environmental data. The experiments verify the advantages of the proposed method in terms of the accuracy and effectiveness compared with conventional methods.

A convenient approach to manufacturing lightweight and high-sound-insulation plywood using furfuryl alcohol/multilayer graphene oxide as a shielding layer

ABSTRACT With the requirement of green construction, the building envelope system urgently needs lightweight material with high sound insulation performance. In this study, a kind of plywood with furfuryl alcohol/multilayer graphene oxide (FA/MLGO) layer was prepared by lamination. The four-microphone impedance tube method measured the sound insulation to evaluate optimal process parameters. At the same time, the acoustic impedance, damping performance, interface microstructure, and chemical components were characterized to discuss the sound insulation mechanism of FA/MLGO as a shielding layer. It showed that the weighted transmission loss of plywood with different FA/MLGO layers was enhanced, and acoustic impedance increased while the acoustic radiation damping coefficient decreased. In addition, considering economic costs, the optimal preparation process was three layers with 0.5 wt.% MLGO concentration and 50 wt.% FA concentration, followed by curing for three h. The surface properties, micromorphology, and chemical composition results indicated that FA/MLGO layer formed more complex sound propagation paths in the plywood, thereby increasing the loss of sound energy inside. Thus, the sound insulation of the plywood was improved.

2D acoustofluidic distributions in micro-chambers modulated by Sierpiński-type structural plates

In this study, a series of Sierpiński-type structural plates have been artificially introduced to generate diversified acoustofluidic distributions in the originally-static microfluidic chambers, which are stimulated under the oscillation of incident acoustic waves at different input frequency points. The complicated interactions between quasi/pseudo-Sierpiński-carpet shaped structural plates and incident ultrasonic waves, including acoustic reflection and diffraction, can initiate sophisticated spatio-temporal discrepancies along the sound propagation path and induce heterogeneous acoustic streaming vortices. In comparison with the existing construction strategies of microfluidic lab-on-a-chip devices, the introduction of fractalized elements like quasi/pseudo-Sierpiński-carpet shaped structural components can provide remarkable insights and expand application scenarios of unconventional acoustofluidic approaches, which is conducive to driving ultrasonic micro/nano manipulation technology from monotonousness to diversification. The preliminary research demonstrates the feasibility of considering Sierpiński-type structural features as tunable ingredients to customize acoustofluidic apparatuses for the exploration of topographical manipulation of micro/nano-scale particles and orientational operation of biological specimens.

Simultaneous reconstruction of 3D non-uniform temperature and velocity fields in a furnace using a bidirectional acoustic path separation tracking method

Acoustic measurement techniques applied to furnace measurements are based on the coupling of multiple fields, such as sound, temperature, and flow. To better measure high-temperature fluids within furnaces using acoustic technology, this study establishes a physical model that separates the bidirectional propagation path of sound. Additionally, a novel nonlinear acoustic ray-tracing method is proposed that allows the simultaneous measurement of temperature and flow. The combustion process of high-temperature swirling flow in a furnace is simulated, the effective path of sound propagation is tracked, and the existence of a sound shadow zone in the low-temperature jet region of the burner is discovered. After reasonably arranging sensor positions, three-dimensional nonuniform temperature and complex flow fields are simultaneously reconstructed by combining ray tracing and nonlinear acoustic tomography. The feasibility of the method is analyzed via the error analysis of the computational fluid dynamics simulation data and the reconstructed data. The proposed method provides a solution for improving the existing acoustic measurement techniques in furnaces.

An Implementation of Inverse Cosine Hardware for Sound Rendering Applications.

Sound rendering is the process of determining the sound propagation path from an audio source to a listener and generating 3D sound based on it. This task demands complex calculations, including trigonometric functions. This paper presents hardware-based inverse cosine function calculations using the table method and linear approximation. This approach maintains a high accuracy while limiting hardware size for suitability in sound rendering applications. Consequently, our proposed hardware-based inverse cosine calculation method is a valuable tool for achieving high efficiency and accuracy in 3D sound rendering.

Steady-state sound propagation through hot exhaust jets in cooler cross-flow: A computational study

An analysis has been carried out to investigate the sound radiation through a heated jet in cooler cross-flow, which is representative of many industrial exhaust systems, using a hybrid steady-state computational fluid dynamics and computational acoustic model. The mean flow and temperature fields are modelled using steady-state computational fluid dynamics, with the turbulence modelled using Reynolds Averaged Navier-Stokes equations. The corresponding mean flow and temperature fields are used in the computational sound propagation model using linearised acoustic wave equation with mean flow based on a scalar flow potential. The results obtained from the computational simulations show that the flow significantly changes the sound propagation path and that the sound levels downstream of the duct outlet are higher than expected from using an acoustic monopole radiation pattern. The dominant mechanism affecting the propagation of sound is the refraction arising from the plume's temperature and velocity gradients. The sound propagation is highly dependent on the proximity from the duct outlet, normalised wavenumber, temperature and the jet to cross-flow mean velocity ratio. This computational study builds upon previous experimental work to analyse the fluid-acoustic interaction for heated jets in cooler cross-flow to understand the complex radiation pattern that leads to higher-than-expected sound levels downstream of the duct outlet.

Experimental investigation of composite metamaterial for underwater sound absorption

We propose an underwater metamaterial combining aluminum foam and polyurea. Three samples with different aluminum foam scatterers were prepared and tested for sound absorption coefficient in the water-filled impedance and anechoic tank. The results show that the large and small conical scatterers significantly improve the sound absorption of the polyurea. This improvement in sound absorption comes from the change in the sound propagation path and waveform transformation. The design of the proposed underwater metamaterial and relevant experimental results presented in this paper have potential guiding values in developing underwater sound-absorbing functional materials.

Applicability of the structure-borne sound source characterisation Two-Stage method as well as the parameters derived in sound pressure level predictions in lightweight constructions

When predicting structure-borne sound-induced sound pressure levels, in addition to describing the sound propagation path through the building structure as exactly as possible, it is necessary to characterise the vibration behaviour of the structure-borne sound sources. The investigations described here were carried out to extend the applicability of the structure-borne sound source characterisation two-stage method described in EN 15657 and to describe its uncertainties. Furthermore, the suitability of the structure-borne sound parameters determined with TSM in the sound pressure level prediction according to EN 12354–5 was tested and statements on the achievable accuracy were derived. For both methods - characterisation of structure-borne noise sources and prediction of structure-borne noise-induced sound pressure levels - data on prediction accuracy are only available to a very limited extent but are essential for a reliable prediction model.Firstly, different sources of structure-borne sound were characterised using the two-stage method on different reception plates. In the process, structure-borne sound sources with defined acting moments were also investigated to analyse their influence on characterisability. Using the characterised vibration parameters of the structure-borne sound sources, the power introduced into different reception plates was then calculated and compared with measurements to establish the achievable accuracy of the characterisation method.Subsequently, the investigated structure-borne sound sources were installed in a lightweight test stand and the resulting sound pressure levels were measured in an adjacent receiving room. These were compared with the sound pressure levels predicted according to EN 12354–5 to obtain reliable statements on the achievable accuracy when using source quantities determined using TSM in the normatively described prediction procedure for structure-borne sound-induced sound pressure levels. A mean deviation between predicted and measured sound pressure levels of approx. 7 dB could be determined across all investigated sources.

Study on air gun wavelet characteristics under different source and towed-streamer sinking depths in the Bohai sea

It is important to optimize air gun source design when exploring resources in the Bohai Sea. To date, the majority of related research has focused on the optimal design of array combinations, while research on sources and towed-streamer sinking depths is very limited. In this work, air gun wavelet numerical models were established based on nonideal gas conditions. Then, the wavelet morphologies and spectral characteristics of a single air gun were studied according to the sound wave propagation path under shallow sea conditions. A method for evaluating source performance using wavelets considering the towed-streamer ghost wave was proposed. Finally, 64 simulation experiments considering source and towed-streamer sinking depths were carried out, focusing on analyzing the wavelet and its spectral characteristics under different working conditions. The simulation results verify the reliability of the proposed method and show that this work has important guiding significance for the optimal design and quality evaluation of air gun sources in the Bohai Sea.

A multi-channel hear-through filter design approach and its applications

Sound characteristics change when propagating through materials and structures, such as vehicle cabins or space partitions. These structures usually block the sound propagation path and cause significant distortion to the sound heard by the other side of the structures while, in many applications, clear speech communication is needed. Especially during the Pandemic of Covid-19, it has become common to have space partitions at face-to-face service locations, for example, places providing food or banking services, for the prevention of virus spread. However, the degraded conversation sound quality caused by these partitions can negatively affects the service quality. A multi-channel active hear-through system is developed in the current work to provide a solution to provide more realistic sound environments for conversation through partitions which can preserve both the spectrum and the spatial distribution of the original sound field. This would also be useful for the improvement of augmented reality experiences and sound transmission quality in divided spaces. Compared with a direct inverse filter design, the coupling effect across channels and the superposition effect of original and reproduced sound are considered in the proposed method.

Acoustic Limescale Layer and Temperature Measurement in Ultrasonic Flow Meters

Guided acoustic waves are commonly used in domestic water meters to measure the flow rate. The accuracy of this measurement method is affected by factors such as variations in temperature and limescale deposition inside of the pipe. In this work, a new approach using signals from different sound propagation paths is used to determine these quantities and allow for subsequent compensation. This method evaluates the different propagation times of guided Lamb waves in flow measurement applications. A finite element method-based model is used to identify the calibration curves for the device under test. The simulated dependencies on temperature and layer thickness are validated by experimental data. Finally, a test on simulated data with varying temperatures and limescale depositions proves that this method can be used to separate both effects. Based on these values, a flow measurement correction scheme can be derived that provides an improved resolution of guided acoustic wave-based flow meters.

Monitoring Tidal Currents and Macroturbulence in a High-Flow Tidal Channel Using a Kilometer-Scale Acoustic Travel-Time Instrument

A challenge in exploiting tidal energy resources is to determine the most suitable sites for development, and as the industry grows, to monitor the progressive impacts of tidal farms on the flow field and sediment transport regimes. A feasibility experiment was carried out with the fluvial acoustic tomography (FAT) system to assess the combined effects of irregular bathymetry, horizontal and vertical sound-speed gradients, and macroturbulence on the quality of FAT-estimated velocities. The experiment involved reciprocal transmissions at 30-s intervals for four days with two 7-kHz broadband transceivers. To determine the origin and potential interpretive value of the frequent multiple arrivals in the unstratified, highly-turbulent flow conditions, we performed a series of simulations with the Bellhop3D model. We demonstrate that the multiple arrivals mainly arise from out-of-plane sound propagation paths resulting from the effects of the local bathymetry. The maximum mean difference between FAT-estimated currents and the coincident moving-vessel acoustic Doppler current profiler (ADCP) transects is found to be less than 10%. Comparisons are also made between velocity spectra during the full flood and the ebb determined using the FAT velocities and the vertically-averaged velocities from a bottom-mounted ADCP deployed in a later experiment. The spectra exhibit similar shapes in the frequency and wave number overlap regions, indicating that FAT is able to detect macroturbulence. Good agreement is also obtained between the sound-speed estimates based on the travel time and those from <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> temperature and salinity data. Overall, the results demonstrate the potential of shallow acoustic tomography for monitoring environmental conditions in high-flow tidal channels.

On Sound Scattering and Acoustic Properties of the Upper Layer of the Sea with Bubble Clouds

The presence of bubbles near the sea surface under certain conditions leads to abnormal sound scattering and a significant change in the acoustic properties of the upper layer of the sea. The article presents some results of sound scattering studies under various sea conditions, up to stormy conditions, when extensive bubble clouds arise. By the method of unsteady acoustic spectroscopy, data on the size distribution of bubbles at various depths have been obtained, which can be described by a power function with exponential decay at small bubble sizes of the order of 10 microns. Estimates of the gas content in bubble clouds and their influence on the acoustic characteristics of the upper layer of the sea have been carried out. It is shown that at sufficiently high concentrations, sharp increases in absorption and dispersion of the sound velocity are observed. Modeling of sound propagation in the presence of a quasi-homogeneous bubble layer shows that it leads both to a change in the laws of the average decay of the sound field along the sound propagation path and to a change in the shallow spatial structure of the field.

The attenuation mechanism and regular of the acoustic wave on propagation path in farmland soil

Understanding the propagation process of acoustic waves in the soil is very important for designing high-performance acoustic wave detection devices. In this study, the discrete element method was used to simulate the propagation process of acoustic waves in the soil. A single factor experiment was carried out with soil compression ratio, excitation frequency, and excitation amplitude as factors. The influence of various factors on the time and frequency domain were analyzed from the perspective of the received signal and the force signal on the particle. The results showed that: with the increase of soil compression ratio, the speed of the acoustic wave, the amplitude of the received signal's first wave and the dominant frequency increased; with the increase of excitation frequency, the amplitude of the received signal's first wave decreased, and the dominant frequency and speed of acoustic wave remained unchanged; with the increase of excitation amplitude, the received signal amplitude increased, and the dominant frequency and speed of acoustic wave remained unchanged. According to the force signal of the particles on the sound wave propagation path, as the soil compression ratio increased, the dominant frequency of the acoustic wave increased, and the amplitude attenuation coefficient increased; as the excitation frequency increased, the dominant frequency and amplitude attenuation coefficient of the acoustic wave first increased and then decreased; as the excitation amplitude increased, the dominant frequency of the acoustic wave remained unchanged, and the amplitude attenuation coefficient increased. The occurrences of these phenomena were related to the natural frequency of the soil and the sound wave attenuation mechanism. During the propagation process, the dominant frequency of the sound wave would continue to attenuate and eventually reached the natural frequency, resulting in the same dominant frequency of the received signal under different excitation frequencies. Under different parameters, the decay speed of the sound wave amplitude was different, and the initial signal amplitude was different, which led to the various first wave amplitude of the received signal. The conclusion could be drawn through the simulation experiment: the DEM method could well characterize the acoustic wave propagation process in the soil and analyze the acoustic wave propagation law in the soil. Thus, it provides theoretical support and reference for the research and instrument manufacture of the acoustic wave detection of soil characteristics.

Study on sound absorption model of porous asphalt concrete based on three-dimensional morphology of air voids

In this paper, the authors are mainly committed to studying the influence of 3D morphology of air voids based on sound absorption performance of porous asphalt (PA) concrete. CT scanning technology was used to get the digital cross-sectional images of PA concrete samples, and image processing technology was used to identify air voids in all the digital cross-sectional images. Based on overlapping principle, sequential splitting theory was developed for searching and reconstructing the three-dimensional (3D) morphology of all the sound propagation paths in PA concrete samples. In order to reveal the sound absorption mechanism, a kind of equivalent hypothetical model consisting of tubes and cavities was proposed to predict the sound absorption coefficient of PA concrete. In the process, a decomposition method was developed to decompose sound propagation paths into tubes and cavities; Equations for calculating sound absorption coefficient were derived based on electric-acoustic analogy. The main conclusions: (1) Two-dimensional (2D) gamma dodging algorithm can greatly improve the accuracy of image segmentation; (2) There are 142.8e4, 156.6e4, 1168.2e4, and 2478.6e4 interconnected sound propagation paths that were found according to the sequential splitting theory in the Sample-I – Sample-IV, respectively; (3)The minimum sound propagation path length is generally more than twice the thickness of PA concrete samples, and maximum length even reaches more than 10 times the thickness; (4) With the increase of void content in PA concrete, the sound-absorbing frequency band will become wider, absorption peak will move to higher frequency, and the peak value of sound absorption coefficient will become larger; (5) There is a small difference between the test values and predicted values of sound absorption coefficient, except Sample-I, indicating that hypothetical PA concrete models can well explain the sound absorption mechanism of PA concrete; (6)For Sample-II to Sample-IV, the mean value of predicted sound absorption coefficient reaches 82.22%, 85.71% and 91.92% of test results respectively.

Acoustic coding metamaterial based on non-uniform Mie resonators

Acoustic coding metamaterials have important applications in simplifying design procedure and providing a flexible approach to realize complicated functions. Here, we design a 1-bit coding metamaterial for flexibly manipulating the sound propagation path. The capability of subwavelength acoustic propagation control on coding metamaterial is attributed to the dipole-like characteristic of the Mie resonator. The Mie resonator with a subwavelength scale is constructed with a non-uniform structure, which can generate Mie resonance with dipole-like characteristic. Two kinds of coding elements are introduced by horizontally or vertically reversing the Mie resonator in each element. To verify the performance of the designed coding metamaterials, three specific metamaterial patterns are fabricated to give different trajectories of sound propagation. Our finding may open an avenue for designing acoustic metamaterials and is expected to design intelligent acoustic devices with exciting reconfigurable and programmable applications.

Azimuthal deviation for outdoor sound propagation in a moving medium with a crosswind

Current codes for ray tracing in a moving atmosphere involve solutions of a set of differential equations. In this presentation, ray tracing is suggested, which is based on a closed-form expression for the sound propagation path in a stratified moving atmosphere. This approach can complement existing ray tracing codes, perform with improved computational efficiency, and serve as a benchmark solution. The closed-form expression for the sound propagation path enables other analytical formulations in geometrical acoustics such as the prediction of the azimuthal deviation as driven by the crosswind. This result also allows estimation of the crosswind provided that the azimuthal deviation between the true and apparent source location is measured. The result is validated by numerical simulations of sound propagation in the atmospheric surface layer with different meteorological regimes.

Modeling methods for dispersive sound speed profiles of the Martian atmosphere and their effects on sound propagation paths

At present, Mars acoustic detection is gradually becoming an important new tool for the knowledge and exploration of Mars. To explore the sources of Mars sound, it is necessary to study the sound speed and the sound attenuation in the thin and low-temperature Martian atmosphere, and to model the sound propagation in the stratified atmosphere. Based on the extremely low pressure of Mars and the large variation of gas composition with altitude, we proposed a simulation method based on the Navier-Stokes (NS) equation and the mixed-gas model to calculate the vertical profiles of sound speed and attenuation in the Martian atmosphere at 0~250 km altitude in this paper. By comparing sound-speed profiles at different frequencies, there is notably sound dispersion in the Martian atmosphere, especially at high altitudes and in the high frequency range. It is also verified through sound speed measurement experiments verify that significant sound dispersion does exist in low-pressure carbon dioxide, illustrating the need to consider sound dispersion in the modelling of Martian sound speed profiles. The scope of application of the NS equation in modelling the sound speed of the Martian atmosphere is also discussed, as the NS equation may fail in a too rarefied gas. Next, the non-dispersive ideal-gas sound speed profiles and the dispersive NS sound speed at different frequencies (0.01 Hz, 0.1 Hz, 1 Hz) were applied to simulate the sound propagation paths in the multilayered Martian atmosphere. And both cases of the Martian ground-based and high-altitude sources were compared respectively. It is found that the dispersive sound speed has a significant effect on the sound propagation path on Mars. The main impact is that the first fold back height and the first return distance of the sound ray to the surface are shortened, which directly changes the area and location of the acoustic quiet zone. The effect of dispersion on the sound propagation path becomes more notable with both the increasing frequency and the elevation of the acoustic source, confirming that consideration of dispersion has a significant effect on the calculation of the sound propagation path.

Methods of modelling dispersive sound speed profiles of Martian atmosphere and their effects on sound propagation paths

At present, Mars acoustic detection is gradually becoming an important new tool for understanding and exploring Mars. To explore the sources of Mars sound, it is necessary to study the sound speed and the sound attenuation in the thin and low-temperature Martian atmosphere, and to model the sound propagation in the stratified atmosphere. According to the extremely low pressure of Mars and the large variation of gas composition with altitude, we propose a simulation method based on the Navier-Stokes (NS) equation and the mixed-gas model to calculate the vertical profiles of sound speed and attenuation in the Martian atmosphere at 0–250 km altitude in this work. A comparison among sound-speed profiles at different frequencies shows that there is a notable sound dispersion in the Martian atmosphere, especially at high altitudes and in the high frequency range. It is also verified through sound speed measurement experiments that significant sound dispersion does exist in low-pressure carbon dioxide, implying the need to consider sound dispersion in the modelling of Martian sound speed profiles. The scope of application of the NS equation in modelling the sound speed of the Martian atmosphere is also discussed, as the NS equation may fail in a too rarefied gas. Next, the non-dispersive ideal-gas sound speed profiles and the dispersive NS sound speed at different frequencies (0.01, 0.1, 1 Hz) are used to simulate the sound propagation paths in the multilayered Martian atmosphere. And both cases of the Martian ground-based and high-altitude sources are compared with each other. It is found that the dispersive sound speed has a significant effect on the sound propagation path on Mars. The main influence is that the first fold back height and the first return distance of the sound ray to the surface are both shortened, which directly changes the area and location of the acoustic quiet zone. The effect of dispersion on the sound propagation path becomes more notable with both the frequency and the elevation of the acoustic source increasing, confirming that consideration of dispersion has a significant effect on the calculation of the sound propagation path.

Ray tracing in a stratified moving atmosphere: Azimuthal deviation in sound propagation.

Ray tracing based on a closed-form expression for the sound propagation path in a stratified moving medium such as a stratified atmosphere is suggested. The approach involves a one-dimensional (1D) integration over the vertical coordinate and can complement existing ray tracing codes based on a set of differential equations. It can also be used as a benchmark solution, because 1D integration is usually computationally simpler than these codes. Using this approach, a closed-form expression for the azimuthal deviation between the true and apparent source location is obtained. The result enables estimation of the azimuthal deviation given a crosswind or remote sensing of the crosswind provided the azimuthal deviation is measured. Based on these formulations, sound propagation in the atmospheric surface layer characterized by the friction velocity and surface heat flux is studied.