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In acoustic temperature measurement, precise determination of sound propagation characteristics is critical for calculating sound propagation velocity. This study investigated the sound wave propagation path in loose coal by assessing the impact of average porosity and temperature on coal particles. Utilizing principles from acoustic temperature measurement and wave equation theory, we propose an equivalent path model for sound wave propagation in quasi-porous media of loose coal. We designed an experimental system and conducted acoustic propagation path tests on loose coal samples with three particle sizes: 0.6–1.5 cm, 1–3 cm and 3–5 cm. Through rigorous analysis, we identified key factors that influence the acoustic propagation path, such as particle size, temperature, and burial depth, which affect the average porosity of the quasi-porous medium. The measured sound velocities for coal samples of 0.6–1.5 cm, 1–3 cm, and 3–5 cm loose coal samples were 238.16 m/s, 252.11 m/s, and 277.36 m/s, respectively. We introduced the equivalent path conversion factor λ for sound wave propagation in loose coal, demonstrating its decrease with larger coal particle sizes. The research validated the accuracy of our equivalent path model, showing a minimal difference between measured and calibrated sound velocities (±4.47 m/s; 4.68% error rate). Our results have theoretical significance for acoustic temperature measurement in the field of loose coal body temperature assessment, offering valuable insights and methods for the advancement of acoustic coal temperature detection technology.

This work presents the application and validation of a novel auralization approach for the evaluation of wind turbine noise annoyance under diverse conditions. The approach is based on the decomposition of each turbine blade into elementary short-segment sources, whose acoustic radiation in the far field is obtained by coupling Amiet’s emission model with the Harmonoise engineering model for outdoor sound propagation. The transfer functions between the elementary source positions and receivers are obtained. Then, the average and instantaneous sound pressure levels are calculated over one blade rotation. The realism of the audio signals is evaluated through listening tests with audio signals of the real and simulated environments. The predicted noise spectra from five wind turbines capture well the measured trends and the absolute levels. Finally, we present a study of the weather effects on noise emissions and propagation by using the numerical model developed.

Noise from traffic, industry and neighborhood is a prominent feature in urban environments. In these environments, sound reaches receiver points through reflections and diffractions. Real-time auralization of outdoor scenarios is a common goal for presenting sound characteristics in a realistic and intuitive fashion. Challenges in this attempt can be identified on many levels, however the most prominent part is sound propagation simulation. Geometrical acoustics has become the de-facto standard for the prediction of acoustic propagation in a virtual scenario. A considerable difficulty is the determination of the diffracted sound field component, because it is a wave effect that must be be explicitly integrated into the search algorithm of valid propagation paths. A deterministic solution to this problem is implemented that establishes propagation paths with an arbitrary constellation of far-field interactions at geometrical boundaries, i.e. reflecting surfaces and diffracting edges in large distance to each other. The result is an open-source code algorithm for propagation paths that follows the wave front normal and assembles metadata required for further acoustic modelling, such as incoming and outgoing angles, reflection material and geometrical details for the construction of the diffracting wedge. Calculation times are outlined and a proof of concept is presented that describes the employment of the propagation algorithm as well as the determination of an acoustic transfer function based on the input of the intermediate path representation. Future research will focus on prioritization of path contributions according to physical and psychoacoustical culling schemes.

The problem of sound propagation in a cylindrical duct with a uniform flow is considered with nonlinear impedance boundary conditions resulting from the dependence of the impedance of acoustic liners on the sound pressure level. An iterative procedure for solving this problem has been constructed, in which sound propagation is described by an asymptotic solution to the problem of the propagation of sound modes in a cylindrical duct with a uniform flow with a smoothly non-uniform impedance of the walls in the axial direction, and the nonlinear mode of operation of the liners is based on a semiempirical model of a two-layer acoustic liners. It is shown that the constructed iterative algorithm converges within the limits of applicability of the asymptotic solution and diverges beyond them. It is shown that, for the parameters with which the calculations were carried out, the nonlinear effect of the liners operation leads to an increase in sound attenuation compared to a linear solution of a similar problem, and this effect is when sound propagates along rather than against the flow.

—A review of modern methods of modeling acoustic fields based on their representation as a superposition of normal modes is presented. Most of the described methods are based on an approach to calculating mode amplitudes by solving parabolic equations of various types, both narrow-angle and wide-angle. We also consider two-dimensional methods for calculating acoustic fields, to which the above-mentioned three-dimensional approaches are reduced in the absence of dependence of the field and medium parameters on one of the horizontal coordinates. The computation of both time-harmonic acoustic fields and pulsed sound signals is discussed. A number of numerical examples are considered in which such calculations are performed taking into account three-dimensional sound propagation effects. For the first time within the framework of this approach, the calculation of particle accelerations at the pulse signal reception points, as well as the calculation of the energy density flux of the vector field were performed.

Traditional sound-absorbing materials, which are intended to address the issue of low-frequency noise control in automobile air-conditioning duct mufflers, have limited noise reduction effects in small spaces. Because of their straightforward structure and excellent controllability, acoustic metamaterials—particularly Helmholtz resonators—have emerged as a research hotspot in low-frequency noise reduction. However, existing technologies have issues such as restricted structural scale, narrow absorption frequency bands, and conflicts with ventilation requirements. To address these, this paper proposes a new type of Helmholtz perforated and tortuous-characteristic duct muffler for the unit cell of acoustic metamaterials. Through the innovative structural design combining a perforated panel with a multi-channel tortuous cavity, the length of the channel is changed in a limited space, thereby extending the sound wave propagation path and enhancing the dissipation of sound wave energy. Meanwhile, for the muffler, acoustic theoretical modeling, finite element simulation, and parametric optimization methods are adopted to systematically analyze the influence of its key structural parameters on the sound transmission loss (STL) of the muffler. Compared with the traditional folded-channel metamaterial, the two differ in resonance frequency by 38 Hz, in transmission loss by 1.157 dB, and in effective bandwidth by 1 Hz. This research provides theoretical support and design basis for solving the problem of low-frequency noise control in ventilation ducts, improves low-frequency broadband sound absorption performance, and promotes the engineering application of high-efficiency noise reduction devices.

Variations in the underwater sound speed significantly influence sound propagation in the ocean, thereby impacting both underwater navigation systems and a substantial portion of marine organisms reliant on sound. This study utilizes cruise data from the Beibu Gulf during the summer and winter of 2023–2024 to explore the seasonal variations in temperature and salinity affecting the sound speed distribution and characteristics of sound propagation. Results indicate significant differences in the sound speed on either side of the 30-m isobath in the Beibu Gulf, with pronounced changes corresponding to seasonal temperature and salinity variations. In summer, the sound speed in the Beibu Gulf exhibits a north-high–south-low pattern. In areas shallower than 30 m, the sonocline is predominantly positive or absent, whereas, in deeper areas, it is mainly negative. During winter, there is a south-high–north-low pattern in sound speed across the Beibu Gulf, with pronounced sound speed extremes in areas shallower than 30 m. Sound propagation simulations based on the Beibu Gulf sound-speed field reveal that sounds at the 100-Hz frequency propagate significantly farther and cover larger areas in depths less than 30 m compared to deeper areas. In summer, this phenomenon is more pronounced than in winter due to the presence of positive sonoclines. The results have significant implications for target detection, underwater acoustic communication, and the protection of aquatic animals that rely on underwater sound for survival in the Beibu Gulf.

The leakage of subsea oil and gas pipelines can have adverse impacts on production progress and the ecological environment. Investigating the sound source and near-field sound propagation of pipeline leaks is essential for understanding the acoustic characteristics of and variations in these leaks. Such understanding is significant for the accurate detection and location of small leaks in pipelines. In this study, we designed an experimental system to study the characteristics of leakage sound signals. We introduced the formation mechanism of leakage sound sources and reviewed corresponding theoretical research. The leakage sound signal’s characteristic frequency range was determined to be between 1 kHz and 2 kHz. We examined the effects of pipeline pressure, leakage aperture, and detection distance on the acoustic signal characteristics. The results show that as internal pipe pressure increases, the leakage sound signal intensity first increases and then decreases. As the leakage aperture increases, the intensity of the leakage sound signal increases. Within a short distance, the intensity remains consistent regardless of detection distance. The results of this experimental study can guide the acoustic internal detection of pipelines. This study has practical significance in the timely detection of small leaks in pipelines and preventing leakage accidents from occurring.

—In experiments on a stationary acoustic track under a solid ice cover, estimates of possible sound signal propagation time variations at distances of ∼4 km with a period of more than 100 s were obtained. The experiments were carried out on Lake Baikal in the spring period, when the vertical profile of the sound speed has two sections characteristic of freshwater areas: an upper layer with a near constant sound speed and a lower layer with linear growth of sound speed. Under these conditions, the variations of the propagation time did not exceed ~10 –4 s. Numerical modeling showed that the variations of propagation times due to the variability of the medium are minimal for the case when the sound source and receiver are located in the upper layer. It is demonstrated that in this case it is acceptable to take the sound speed in the upper quasi-homogeneous layer as the effective value of the sound speed, which determines the propagation time. The obtained results allowed us to formulate recommendations on under-ice acoustic positioning of autonomous underwater vehicles.

This work presents a numerical study on atmospheric sound propagation over rough water surfaces with the aim of improving predictions of sound propagation over long distances. A method for generating pseudorandom sea profiles consistent with sea wave spectra is presented. The proposed method is suited for capturing the logarithmic nature of the energy distribution of the waves. Sea profiles representing fully developed seas for sea states 2, 3, 4, and 5 are generated from the Elfouhaily et al. (ECKV) sea wave spectra. Excess attenuation caused by refraction and surface roughness is predicted with a parabolic equation (PE) solver. A novel method for estimating equivalent effective impedance based on PE predictions at different sea states is presented. Parametric expressions using acoustic frequency and significant wave height are developed for effective surface impedances. In this work, sea surface roughness is on a scale comparable with the acoustic wavelength. Under this condition, the acoustic scattering is primarily incoherent. This work shows the limitations of using an equivalent surface impedance in such incoherent scattering cases.