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When a vibrating structure is located in a half-space bounded by a reflecting surface, the measured sound pressures are polluted by the reflection, so that they cannot show the actual sound radiation from the structure. The half-space spherical wave function expansion-based near-field acoustical holography approach is proposed to reconstruct the direct radiation from the sound source using the polluted sound pressures, which has been validated by numerical simulations. This paper deals with the experimental validation of this approach applied in an underwater halfspace bounded by a water-air interface. The sound pressures measured in the half-space are used as the input data. The reconstructed sound pressures obtained are compared with benchmarks measured in a free space. The results indicate that the influences of the water-air interface reflection on the measured sound pressures can be greatly reduced in the entire frequency range investigated. The normalized relative reconstruction error introduced by the parameters of the hydrophone array and the water tank in the experiment is analyzed. The results of the experimental validation show that the proposed approach is promising for accurately measuring sound signals radiated from manned or unmanned vehicles or equipment underwater near a water-air interface. [ABSTRACT FROM AUTHOR]

Straight through perforated tube silencers are widely used in intake and exhaust noise control, and their acoustic behaviors are influenced by the gas flow and high amplitude sound remarkably. To investigate the acoustic attenuation performance of straight through perforated tube silencers in the presence of flow and high amplitude sound, an approach based on the three-dimensional (3D) time-domain computational fluid dynamics (CFD) simulation is employed and validated by comparing predictions and measurements. Transmission loss of the straight through perforated tube silencer under pure tone and multi-tone sound excitations is predicted. Results show that, under the pure tone sound excitations, the acoustic attenuations are affected remarkably by the high amplitude sound, and the nonlinear effects turn to weaken as flow velocity increases. With the sound pressure level (SPL) decreasing along the axis of the silencer, the acoustic nonlinearity in the orifice weakens gradually. The shedding vortices are restricted to the region near perforations because of the transport of flow. When the multi-tone sound excitation is enforced on the inlet, transmission loss of the silencer is different from the pure tone excitation at the same SPL of every compositional frequency. [ABSTRACT FROM AUTHOR]

Introduction: Construction and operation of high-speed trains in railway stations can induce substantial vibrations, resulting in impermissible structure-borne noise (SBN), occasionally causing disruptions for passengers and staff. This issue poses serious challenges in the advancement of novel multi-story high-speed railway stations in large cities. Until now, limited methods have been introduced to predict and evaluate SBN for guiding station design and construction. Besides, the computational speed and accuracy of these methods often fall short of expectations. Objectives: In response to this need, a simulation method for SBN based on Auto CAD, Altair HyperMesh, and MSC Actran software was proposed. Methods: Firstly, numerical models were established for the elevated waiting hall and underground entrance hall of Beijing Fengtai Railway Station. Secondly, field measurements were conducted to validate the reliability of the simulation method by comparing the measured and simulated results. Subsequently, numerical analysis under different conditions was performed to study the transmission characteristics of SBN. Finally, the SBN in the elevated waiting hall and the underground entrance hall were evaluated accordingly. Results: The frequency of the simulated SBN at the elevated waiting hall prominent ranges from 20 to 40 Hz and 125 to 200 Hz, while frequencies at the underground entrance hall exhibit a significant band between 80 and 125 Hz. The peak A-weighted overall SPL under various conditions for the elevated waiting hall is 69.33 dB, while for the underground entrance hall is 71.63 dB. Conclusion: SBN in the elevated waiting hall primarily originates from the elevated track floor, which is different from the underground entrance hall where it stems from the ground track floor. The A-weighted overall sound pressure level (SPL) in the elevated waiting hall satisfies the SBN comfort criteria, whereas the A-weighted overall SPL in the underground entrance hall falls short of the chosen specification. This study enhances the prediction method and understanding of the transmission characteristics of SBN. Consequently, it provides valuable insights for constructing multi-story railway stations with improved comfort in the future. [ABSTRACT FROM AUTHOR]

Purpose: The goal of this work is to propose a local Active Noise Control system for an aircraft seat's headrest. This system should be able to extend the quiet zone beyond the physical microphones that can be placed behind the passenger's head due to space constraints. Furthermore, the control algorithm should perform efficiently when non-linear phenomena exist during the sound propagation. Methods: A functional link neural network and a computationally efficient Multiple Input Multiple Output approach are used for the system's implementation. The quiet zone is extended by linearly estimating the acoustic pressure in front of the headrest surface. The main novelty of this paper is the combination of these methods in an attempt to improve acoustic pressure attenuation performance, while keeping computational complexity low. Results: The proposed control algorithm has been evaluated through numerical simulations, including Finite Element Method and experimental tests at an aircraft cabin mock-up. The results show that for a real-world acoustic disturbance, a 10 dB reduction in sound pressure level was achieved 10 cm away from the headrest surface. In addition, the attenuation of some harmonics can reach 20 dB and in most cases is bigger than the linear FxLMS algorithm. Conclusions: To summarize, it has been demonstrated that a multichannel functional link neural network using a simple virtual sensing technique can efficiently attenuate synthesized and real world acoustic disturbances captured in a tilt-rotor aircraft's cabin. Finally, it can create an adequate quiet zone for gentle head movement while maintaining its stability. [ABSTRACT FROM AUTHOR]

Organisms, such as fishes and invertebrates and including their larval stages, listen to underwater soundscapes to detect information about nearby habitats. Such soundscapes may be influenced by habitat degradation or enhancement, which can lead to acoustically mediated feedback loops affecting the overall ecosystem.Despite the importance of underwater sounds on ecological functioning, there have been limited studies documenting soundscapes of intertidal ecosystems and few, if any, of living shoreline soundscapes. Living shorelines would especially benefit from acoustically mediated effects for objectives like encouraging fish and invertebrate settlement.This case study used a Before‐After‐Control‐Impact design to sample soundscapes and nekton (i.e., fishes and mobile macroinvertebrates) at a living shoreline construction and a nearby hardened shoreline in Cedar Key, FL (USA). Diel soundscape patterns and acoustic attenuation at the two sites were also described a year following the living shoreline construction.In the acoustic sampling, the high frequency bands of both shorelines were dominated by invertebrate sounds that were influenced by season, site and time of day, while the low frequency band of the living shoreline was often dominated by a loud anthropogenic sound. About a year after the living shoreline installation—despite similar measured acoustic attenuation at both sites—the living shoreline featured louder sound pressure levels compared to the hardened shoreline, which may be particularly beneficial for promoting foundational species and other organism settlement.These results demonstrate that Gulf of Mexico intertidal habitats may have soundscape differences even within close proximity and that living shorelines may enhance acoustic characteristics in ways beneficial to continued shoreline development. This represents an important step in better understanding the relationships between habitat structures, nekton communities, and their associated soundscapes as well as the application of passive acoustic monitoring to improve coastal management and conservation. [ABSTRACT FROM AUTHOR]

This research examines the application of periodic materials in wall–slab structures to mitigate impact noise and vibration propagation, a prevalent issue in multifamily housing. Traditional methods, such as floating floors, have proven insufficient in addressing low-frequency impact noises and in facilitating the identification of noise origins, leading to increased resident annoyance. Periodic materials, known for their effectiveness in controlling plane waves in civil engineering, were applied to the intermediate slab of a wall–slab experimental setup. The research involved assessing the attenuation of noise and vibration over distance before and after the application of periodic materials by measuring indoor sound pressure levels and the natural vibration amplitude of the structure's members upon impact. The results showed that periodic materials not only facilitated distance attenuation but also significantly diminished noise and vibration throughout the structure, without the side effects of vibration amplification seen in prior civil engineering applications. This indicates a practical advancement in using these materials, offering a novel approach to sound insulation and enabling more precise impact source localization. Ultimately, this study contributes to improving urban living by suggesting a method to enhance acoustic comfort in multifamily housing, underlining the importance of further exploration in architectural applications of periodic materials. [ABSTRACT FROM AUTHOR]

Automotive fans, small wind turbines, and manned and unmanned aerial vehicles (MAVs/UAVs) are just a few examples in which noise generated by the flow's interaction with aerodynamic surfaces is a major concern. The current work shows the potential of a new airfoil shape to minimize noise generation, maintaining a high lift-to-drag ratio in a prescribed Reynolds regime. This investigation uses a multifidelity approach: a low-fidelity semiempirical model is exploited to evaluate the sound pressure level (SPL). Fast evaluation of a low-cost function enables the computation of a large range of possible profiles, and accuracy is added to the low-fidelity response surface with high-fidelity CFD data. The constraint of maintaining a predefined range of the lift coefficient and lift-to-drag ratio ensures the possibility of using this profile in usual design procedures. [ABSTRACT FROM AUTHOR]

Bottlenose dolphins (Tursiops truncatus) rely on frequency- and amplitude-modulated whistles to communicate, and noise exposure can inhibit the success of acoustic communication through masking or causing behavioral changes in the animal. At the US Navy Marine Mammal Program (MMP) in San Diego, CA, dolphins are housed in netted enclosures in the San Diego Bay and exposed to noise from vessels, unmanned underwater vehicles, and other remote sensing devices. The acoustic behavior of 20 dolphins was monitored and whistle rates during noise events were quantified. Whistle rates during the onset of the event (i.e., the first 5 min) did not significantly differ from the pre-onset (5 min immediately preceding). Whistle rates were also not significantly different for the entire duration of the event compared to a matched control period. The noise's frequency range (i.e., control, mid-frequency (0–20 kHz) or high-frequency (21–80 kHz)), signal-to-noise ratio, and sound pressure level were not significantly related to the dolphins' whistle rate. Considering this is a location of frequent and moderate noise output, these results lend support to established guidelines on anthropogenic noise exposure for cetaceans, suggesting that moderate noise exposure levels may not impact communication efforts in bottlenose dolphins. [ABSTRACT FROM AUTHOR]

Determining reliable noise emission values for machinery is key to successfully implement the Sell and Buy Quiet concept. ISO 11202 is a basic noise emission standard to determine the emission sound pressure level of machines outside of special acoustic test rooms (in situ measurements) and enables machinery manufacturers to determine the noise emission data of their products within their own premises. However, a recent amendment to this standard was made on the basis of an unsatisfactory amount of experimental data. Therefore, this paper systematically examines the validity and accuracy of the amended part of the method. It answers the question, whether the amendment represents an improvement of the existing method. Measurements on a model machine with two configurations allow for an extensive investigation of the effects of the amendment. To that end, the emission sound pressure levels at eight positions near the machine are determined in three different acoustic environments. One finds that the amendment leads to an overestimation of the local environmental correction for the L p A , which, in turn, could lead to an underestimation of the determined emission sound pressure level. [ABSTRACT FROM AUTHOR]

Aiming at raising the efficiency of multidisciplinary optimization of UAV rotor aerodynamics and aeroacoustics, this paper established a low-order method of rotor aerodynamics and noise prediction based on lifting line theory (LLT) and FWH acoustic analogy theory. The maximum errors between the low-order method and the high-fidelity CFD results are 1.53% and 3.3 dB for the thrust and overall sound pressure level (OASPL) respectively, demonstrating the ability of design optimization by the low-order LLT method. Combined with the proper orthogonal decomposition (POD) dimension reduction technique to reduce the variable space, a multidisciplinary optimization of rotor aerodynamics and noise was implemented. The rotor thrust and OASPL were taken as the optimization objectives, and the chord length, thickness, and blade twist angle at different spanwise positions were taken as the design variables. The results show that the proposed optimization strategy effectively reduces the design space, the convergence process is greatly accelerated by coupling the low-order LLT-FWH prediction method, and the whole optimization process is only about 0.094% of the computational resource of the method based on unsteady CFD and conventional optimization method. Compared with the original rotor, the thrust at the design condition is increased by 1.66%, and the OASPL is maximally reduced by 3.10 dB. After optimization, the aerodynamic load fluctuation in the middle of the rotor blade (40%–80% spanwise) is significantly reduced, and the high vorticity area in the wake is reduced from the middle to the blade tip (45%–100% spanwise). [ABSTRACT FROM AUTHOR]

Turbulent mixing noise is a vital component of jet noise, and its rapid, accurate prediction has always been persistently pursued. Recent advancement in machine learning has been applied to jet noise prediction. However, these applications are pure curve fitting and lack physical constraints. In this study, a physics-merged deep neural network (PMNN)-based prediction method was developed for turbulent mixing jet noise by merging the physics of the jet noise. This deep neural network (DNN)-based method employed recent advancements in jet turbulent mixing noise containing large- and fine-scale turbulence structures. Two simple rational functions for large- and fine-scale turbulent noise similarity spectra were proposed to replace the original complex similarity spectra functions and incorporated into the DNN-based prediction method. For comparison, we present two data-driven DNN-based prediction methods (DDNN). The first DDNN method used the sound pressure level (SPL) as the output of neural networks, directly establishing the nonlinear relationship between the input features and SPL. In the second DDNN method, the dominant modes of the jet noise spectra extracted using the proper orthogonal decomposition method were merged with DNN. These DNN-based methods were then trained using a set of experimental data over a wide range of jet operating conditions. Their performance was evaluated and compared. It was evident that all these DNN-based methods were capable of predicting turbulent mixing noise reasonably well. In contrast to the DDNN methods, the PMNN method could provide insights into the jet turbulent mixing noise components. It demonstrates that the turbulent mixing jet noise spectra at the mid polar angle is generated by the large-scale noise component at low-frequency range and by the fine-scale noise component at high-frequency range. [ABSTRACT FROM AUTHOR]

The three-dimensional turbulent mean flow and acoustic field of a supersonic jet impinging on a solid plate is studied computationally using the general purpose CFD code Ansys Fluent. A pressure-based coupled solver formulation with the second order weighted central-upwind spatial discretization is applied to compute transient solutions. Cold and hot jet thermal conditions are considered. Mean flow characteristics are investigated by a steady-state modeling approach. Acoustic radiation of impingement tones is simulated using a transient time-domain formulation. The effects of turbulence in steady-state are modeled by the SST k-ω turbulence model. The Wall-Modeled Large-Eddy Simulation (WMLES) model is applied to compute transient solutions. The near-wall mesh on the impingement plate is fine enough to resolve the viscosity-affected near-wall region all the way to the laminar sublayer. Nozzle-to-plate distance is parameterized in the model for automatic re-generation of the mesh and results. Steady-state predictions of hover lift loss and mean jet velocity distributions are compared with experimental data, and favorable agreement is reported. The transient solution reproduces the mechanism of impingement tone generation by the interaction of large scale vortical structures with the impingement plate. The acoustic near-field is directly resolved by Computational Aeroacoustics (CAA) to accurately propagate impingement tone waves to near-field microphone locations. Calculated impingement tone frequencies and sound pressure levels agree with experimental values. [ABSTRACT FROM AUTHOR]

The impact-echo method (IE) is a non-destructive testing method commonly used in civil engineering. We propose a completely new approach for air-coupled actuation based on supersonic jet flow. The impinging jet sound generates continuously high sound pressures with a broad frequency bandwidth. This novel concept of utilising aeroacoustic sound for air-coupled IE was evaluated on two concrete specimens and validated using a classical IE device with physical contact. The results show a high agreement with the expected frequencies. Delaminations are correctly detected in depth and size. This proves the high reliability of air-coupled IE based on supersonic jet flow. [ABSTRACT FROM AUTHOR]

This article presents techniques used to observe the shear behaviour of modified Z-shaped concrete specimens, experimental results, and a method proposed to classify the shear cracking pattern of a concrete bridge based on acoustic emission (AE). Z-shaped specimens under shear were designed with steel plate reinforcement. A finite element (FE) model for this specimen was developed to validate the concrete crack propagation. AE parameters, including the peak amplitude, counts, cumulative energy, average frequency (AF) and rise angle (RA), were found to successfully correlate with the observed cracking process in the specimens. A cluster analysis based on the K-means algorithm was proposed to automatically classify the AE signal into tensile and shear clusters. An existing bridge underwent reinforcement and then testing under two test scenarios. AE signals were detected at the web of the bridge under heavy truck loads or full random traffic flows. Using the proposed crack classification showed that the signals from the bridge belonged to shear crack clusters characterized by lower AE energy. Thus, this work developed an AE method to classify cracks in concrete shear tests and extended the method to classify the shear cracks in a bridge to provide an early warning of future failure. [ABSTRACT FROM AUTHOR]

The expansion chamber serves as the primary silencing structure within the exhaust pipeline. However, it can also act as a sound-emitting structure when subjected to airflow. This article presents a hybrid method for numerically simulating and analyzing the unsteady flow and aerodynamic noise in an expansion chamber under the influence of airflow. A fluid simulation model is established, utilizing the Large Eddy Simulation (LES) method to calculate the unsteady flow within the expansion chamber. The simulation results effectively capture the development and changes of the unsteady flow and vorticity inside the cavity, exhibiting a high level of consistency with experimental observations. To calculate the aerodynamic noise sources within the cavity, the flow field results are integrated using the method of integral interpolation and inserted into the acoustic grid. The acoustic analogy method is then employed to determine the aerodynamic noise sources. An acoustic simulation model is established, and the flow noise source is imported into the sound field grid to calculate the sound pressure at the far-field response point. The calculated sound pressure levels and resonance frequencies show good agreement with the experimental results. To address the issue of airflow regeneration noise within the cavity, perforated tubes are selected as a means of noise suppression. An experimental platformfor airflow regeneration noise is constructed, and experimental samples are processed to analyze and verify the noise suppression effect of perforated tube expansion cavities under different airflow velocities. The research findings indicate that the perforated tube expansion cavity can effectively suppress low-frequency aerodynamic noise within the cavity by impeding the formation of strong shear layers. Moreover, the semi-perforated tube expansion cavity demonstrates the most effective suppression of aerodynamic noise. [ABSTRACT FROM AUTHOR]

The deformation of a fluid interface by the acoustic radiation pressure has been used for surface tension measurements or to design exotic structures such as acoustic diodes. However, few studies focus on the characterization of the spatial characteristics of deformation induced by transient excitation, making research requiring precise spatial control of deformation challenging. This paper investigates experimentally and numerically the effects of transient excitation on deformation generated by an acoustic radiation pressure at the water–air interface. A numerical model using the finite-element method and based on theoretical background for permanent excitation is generalized to transient excitation. An experimental setup is developed to evaluate the maximum height of interface deformation for different durations and amplitudes of ultrasonic excitation using two complementary methods: the first using a camera and an edge detection algorithm and the other using a multichromatic confocal displacement sensor. Numerical and experimental results for a non-steady-state excitation show a quadratic evolution of the height of deformation as a function of incident pressure and also a linear increase as a function of the excitation duration. The evaluation of the deformation height induced by acoustic radiation pressure at a water–air interface for a transient excitation paves the way to applications requiring noncontact space-time interface modulation, such as subwavelength phenomena. [ABSTRACT FROM AUTHOR]

There are few reports on the near-field acoustic signals corresponding to lightning return strokes. One rocket-triggered lightning flash, which contains 13 return strokes, initial continuous current (ICC) processes, and abundant M-components, was observed in the summer of 2018 and reported in this study. The complete near-field acoustic pressure signals initiated by the flash were recorded and analyzed. It is found that the near-field acoustic pressure signals from each return stroke are composed of the first arrived N-shape shock waveform and the subsequent low-frequency oscillating waveforms. The characteristic of the acoustic waveforms has been parametrically defined and quantitatively analyzed, with a comprehensively acoustic-electrical correlation investigation. The acoustic pressure signals from intensive ICC processes and M-component pulses with different discharge intensities are also discussed. It is found that the too-close time interval between M-component and previous current pulses would affect the generation and measurement of the acoustic pressure waveforms from the M-component, even though the discharge amplitude is competitive and the wavefront is fast. The same phenomenon has also been observed in the acoustic signals from a return stroke with a too close interval from the previous pulse. The acoustic source localization with great accuracy for lightning channel reconstruction was realized based on the measured acoustic signals. The reconstructed channel structure agrees with that of the synchronously captured optical image. The study of the characteristics of acoustic signals from lightning discharge contributes to the recognition of thunder signals, source localization for channel reconstruction, and understanding of the lightning discharge process. [ABSTRACT FROM AUTHOR]

The study carried out the zoning of the city of Shelekhov, based on the assessment of acoustic pollution of the territory. Field observations were made and the number of vehicles moving along intracity roads and the federal highway R-258 “Baikal” was calculated. With the help of sound level meters, instrumental measurements were made in the daytime and at night, and maps of the sound pressure level of the road network were built. The calculation of statistical characteristics was carried out and the daily course of the distribution of the noise level on the main and secondary roads was constructed. The analysis of the obtained results and their comparison with the established sanitary standards for their excess was carried out. Evidence has been identified to support the implementation of strategies aimed at reducing acoustic pollution and, as a result, creating favorable conditions for the population to live.

Wind power plants are increasingly being installed across the world to combat energy deficits and climate change. One of the policy constraints for installing wind turbine plants is acoustic emissions from blades during operation. In this work, a concise review of the quasi-empirical methods important for predicting noise from rotating wind turbine blades is presented. For wind turbines, self-noise mechanisms from blades and random turbulent inflow noise sources influenced by atmospheric turbulence are two major classes which contribute to overall noise signature. It has been found that these sources exhibit narrowband and broadband frequency characteristics. Trailing edge noise from the blade is an important source at mid-band to high frequencies in overall noise spectra while at infrasonic and low frequencies, inflow and impulsive noise sources are dominant which produce high annoyance and harmful effects on inhabitants. Previous research findings related to self-noise mechanisms are discussed thoroughly to provide an insight of aerodynamically produced noise generation.

In this study, gearbox radiated noise was successfully reduced through housing shape optimization. First, dynamic and structural–acoustic coupled analysis models of an agricultural UTV gearbox were developed. Then, the test equipment was configured to match that of the simulation model, and a test was conducted. The analysis and test results showed errors within 0.1 dB for vibration and 0.2 dB(A) for noise, indicating that the models were reliable. The housing design was then optimized using topology optimization based on the developed structural–acoustic coupling analysis model. The sound pressure level around the housing was used as an objective function for topology optimization. The optimal distribution of materials for the housing was also derived to reduce the radiated noise. Lastly, the housing rib was designed based on the optimization result, and an improvement in the radiated noise by approximately 2.43 dB(A) was confirmed in the operation area. [ABSTRACT FROM AUTHOR]

Introduction: Several studies have reported a significant correlation between noise-induced hearing loss and cognitive decline. However, comprehensive analyses of this relationship are rare. This study aimed to assess the influence of hearing impairment on cognitive functions by analyzing organ samples in the a erent auditory pathway of deafened mice using mRNA sequencing. Methods: We prepared 10 female 12-week-old C57BL/6N mice as the experimental and control groups in equal numbers. Mice in the experimental group were deafened with 120 dB sound pressure level (SPL) wideband noise for 2 h. Cochlea, auditory cortex, and hippocampus were obtained from all mice. After constructing cDNA libraries for the extracted RNA from the samples, we performed next-generation sequencing. Subsequently, we analyzed the results using gene ontologies (GOs) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway databases for di erentially expressed genes (DEGs) of each organ. Results: Our results revealed 102, 89, and 176 DEGs for cochlea, auditory cortex, and hippocampus, respectively. We identified 294, 203, and 211 GOs; 10, 7, and 17 KEGG pathways in the cochlea, auditory cortex, and hippocampus, respectively. In the long term (12 weeks) from noise-induced hearing loss, GOs and KEGG pathways related to apoptosis or inflammation persistedmore actively in the order of hippocampus, auditory cortex, and cochlea. Discussion: This implies that the neurodegenerative e ects of noise exposure persist more longer time in the central regions. [ABSTRACT FROM AUTHOR]

The acoustic response of a five-bladed rotor to an axisymmetric turbulent boundary layer at the tail end of a body of revolution (BOR) is investigated numerically to elucidate the physical sources of acoustics, particularly the role of coherent structures in sound generation. The BOR is at a length-based Reynolds number of 1.9 × 106 and free-stream Mach number of 0.059. Two rotor advance ratios, 1.44 and 1.13, are considered. The turbulent boundary layer on the nose and midsection of the BOR is computed using wall-modelled large-eddy simulation, whereas that in the acoustically important tail-cone section is wall-resolved. The radiated acoustic field is calculated using the Ffowcs Williams-Hawkings equation. The computed flow statistics and sound pressure spectra agree well with the experimental measurements at Virginia Tech. In addition to broadband turbulence-ingestion noise, spectral humps near multiples of the blade-passing frequency and accompanying valleys are captured. They are shown to be caused by correlated blade unsteady-loading dipole sources and their constructive and destructive interference as a result of successive blades cutting through the same coherent structures. The latter undergo rapid growth in the decelerating tail-cone boundary layer before their interaction with the rotor. The acoustic radiation is dominated by the outer region of the blade owing to a combination of larger blade chord-length, inflow turbulence intensity and blade speed. The numerical results also correctly predict the effect of the rotor advance ratio on the acoustic field. A mixed free-stream/convection Mach-number scaling successfully collapses the sound pressure spectra at the two advance ratios. [ABSTRACT FROM AUTHOR]

High‐quality acousto‐holographic patterns and images, integral to applications like 3D displays, acoustophoresis, and midair haptics, require precise distribution of ultrasound waves to achieve. Essential tools for this task are spatial sound modulators (SSMs), which control constituent elements to enable dynamic distribution of sound pressure. However, current ultrasonic SSMs face limitations due to high costs and the intricate actuation of numerous small, closely spaced units. This study introduces "segmented SSMs," novel devices that combine traditional acoustic metasurface pixel units into custom‐shaped segmented elements. These segmented SSMs reduce actuation costs and complexity while retaining pressure distribution quality. This approach includes a custom phase agglomeration algorithm (PAA), that offers a hierarchy of potential segmentation solutions for user selection. An SSM fabrication method is detailed using off‐the‐shelf 3D printers and bespoke control electronics, completing an end‐to‐end methodology from conception to realization. This approach is validated with two prototype SSM devices that focus sound waves and levitate polystyrene beads using dynamic segmented elements. Further enhancements to the technique are explored through hybrid SSM devices with both static and dynamic elements. The pipeline facilitates efficient SSM construction across diverse applications and invites the inception of future devices with varying sizes, uses, and actuation mechanisms. [ABSTRACT FROM AUTHOR]

Simple Summary: Urban noise imposes significant challenges for the acoustic communication of birds that are able to survive inside cities. Birds sing most intensely during two periods of the day called dawn and dusk choruses, and although various responses to the urbanization of dawn songs have been reported, very little attention was paid to the dusk chorus. Our objective is to evaluate in urban and non-urban populations of the Chiguanco Thrush (Turdus chiguanco), a very common bird in the city of La Paz (Bolivia) if there are differences between the songs of both choruses, and if these variations are altered by urbanization. Our results show that the loudness, frequency range and number of songs per individual are greater in the dawn chorus and that urban individuals must increase the frequency and loudness of their songs in both choruses to cope with urban noise. Urban Chiguanco Thrushes even produce less than half as many songs per individual compared to non-urban individuals, probably due to the high cost of increasing loudness and frequency. If wild birds are forced to modify their songs so much within the city, this should alert us to the possible negative effects of urban noise on human health. Urbanization is one of the more important phenomena affecting biodiversity in the Anthropocene. Some organisms can cope with urban challenges, and changes in birds' acoustic communication have been widely studied. Although changes in the timing of the daily organization of acoustic communication have been previously reported, there is a significant gap regarding possible variations in song structure between dawn and dusk choruses. Considering that urbanization imposes different soundscapes for dawn and dusk choruses, we postulate two hypotheses: (i) there are variations in song parameters between dawn and dusk choruses, and (ii) such parameters within the city will vary in response to urban noise. We studied urban and extra-urban populations of Chiguanco Thrush in La Paz, Bolivia, measuring in dawn and dusk choruses: song length; song sound pressure level; minimum, maximum, range and dominant frequency; and the number of songs per individual. The results support our two hypotheses: there were more songs, and songs were louder and had larger band widths at dawn than at dusk in urban and extra-urban populations. Urban Chiguanco Thrushes sing less, the frequency of the entire song rises, and the amplitude increases as compared with extra-urban Chiguanco Thrushes. Understanding variations between dawn and dusk choruses could allow for a better interpretation of how some bird species cope with urban challenges. [ABSTRACT FROM AUTHOR]

The goal of this paper is to fabricate innovative diaphragm headphones using graphene oxide paper (GOP) and GOP/epoxy nanocomposites (GOPC). Initially, graphene oxide suspension is fabricated, and the vacuum filtration method is adopted to make GOP. Then, vacuum bag molding is used to fabricate GOPC from GOP. Hot pressing and associated molds are adopted to fabricate line-indented (GOPC-L) or curve-indented patterns (GOPC-C) on the GOPC. The performances of one kind of GOP and three kinds of GOPC diaphragm headphones are analyzed based on their sound pressure level (SPL) curves achieved by the Soundcheck measurement system. There are four important processing parameters that will influence the performance of the diaphragm, including material type GOP versus GOPC, indented pattern type, sonication time on suspension, and graphene weight fraction in suspension. Compliances of various diaphragms are measured by the Klippel LPM laser measurement system. The results indicate that effects of sonication time and graphene weight fraction on SPL of GOP and GOPC headphones are in reverse, and this is associated with their difference on compliance (modulus), mass, damping ratio, and microstructure uniformity. Either GOPC-L or GOPC-C seems to improve the microstructure of the GOPC, and leads to better SPL performance. The correlation between the previous four factors and SPLs of four kinds of diaphragm headphones is proposed by using scanning electron microscope (SEM) to examine the microstructure of these diaphragms. [ABSTRACT FROM AUTHOR]

This study proposes an uncertainty quantification method based on deep neural networks and Catmull–Clark subdivision surfaces for vibroacoustic problems. The deep neural networks are utilized as a surrogate model to efficiently generate samples for stochastic analysis. The training data are obtained from numerical simulation by coupling the isogeometric finite element method and the isogeometric boundary element method. In the simulation, the geometric models are constructed with Catmull–Clark subdivision surfaces, and meantime, the physical fields are discretized with the same spline functions as used in geometric modelling. Multiple deep neural networks are trained to predict the sound pressure response for various parameters with different numbers and dimensions in vibroacoustic problems. Numerical examples are provided to demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The construction of marine ranches can enrich and conserve the fishery resources and improve themarine ecosystem, which helps realize the sustainable utilization of these resources. Sebastes schlegelii is a major breeding and releasing fish species in the marine ranches of North China. Its behavioral characteristics can be understood better by researching its vocalization, whichwill provide data support for constructing acoustic taming marine rancheswith S. schlegelii as the target fish species. However, there are few studies focusing on its sounds and behaviors. Therefore, based on the passive acousticmonitoring technology, the audios of underwater noises made by S. schlegelii were extracted using an AQH hydrophone. The high-definition internet protocol camera was used to monitor the behavior change of S. schlegelii. Then, by collating and replaying the collected audios and videos, the feeding behavior and biological noises of S. schlegeliiwerematchedtoanalyze their relationship. Results are as follows: (1) The noise of chewing settling granular baits (F5.0 mm) has a main frequency band and sound pressure level of 2000~4500 Hz and 96.53 ± 0.65 dB, respectively; in this feeding process, the main frequency band and sound pressure level of the swimming noise are 25~400 Hz and 95.63 ± 0.38 dB, respectively; the values are 500~700 Hz and 97.34 ± 4.91 dB, respectively, for the noise of flapping the waterwith the tail. (2) The sound signals emitted by S. schlegelii aremostly presented as single pulses during normal habitation or ingestion of baits on the surface of the water tank. However, S. schlegelii will attack and fight against each other when scrambling for baits, during which these signals are presented as continuous pulses. To sum up, the vocalization of S. schlegelii is closely related to feeding activities, and the sounds produced under different behaviors have specific biological significance. [ABSTRACT FROM AUTHOR]

Chuprov's interference invariant (II) well describes the properties of a sound field in shallow water. However, the question of how applicable Chuprov's II concept is to deep water, where the patterns of sound field decay with distance are more complex has been insufficiently studied. Therefore, the authors studied the II properties in the near and far fields of acoustic illumination, as well as in the shadow zone. A new definition of the invariant was proposed and studied, and its characteristics were compared with Chuprov's II as a function of distance, reception and emission depths, and summer or winter propagation conditions. The new invariant is called the phase-energy invariant (PEI), since orthogonal components of the phase gradient are used to describe the spatial sound energy distribution. The stability of the new invariant, its independence on different influencing factors, and its natural change with distance from zero to one are shown. It has been established that in winter conditions, at almost all distances, the PEI is equal to unity, and the II does not have stable values and varies jumpwise over a very wide range. In summer conditions, in the shadow zone, with increasing distance, the PEI increases, just like the II, from close to zero to one. In the near and far fields of acoustic illumination, the PEI is approximately equal to unity, and the II in these zones, both in summer and winter, is characterized by unlimited oscillations, caused by division by a value close to zero. It is shown that the definition of PEI is valid both in single-mode waveguides and in free unbounded space with a dispersive medium. [ABSTRACT FROM AUTHOR]

The theoretical study of sound field formation in an acoustic interference array presented in this article is motivated by an analysis of the physical principle of operation of a highly directional interference microphone. One of the objectives of the study is to determine the sound pressure acting on the microphone membrane inside the array. The sound field inside the interference array is analyzed using a matrix method, similar to the reverberation matrix method. The solution is formally represented as a Schwarzschild series. The result calculated by this method agrees well with the experimental data. [ABSTRACT FROM AUTHOR]

The inverse problem of acoustic sounding of a three-dimensional nonstationary medium is considered, based on the Cauchy problem for the wave equation with a sound speed coefficient depending on the spatial coordinates and time. The data in the inverse problem are measurements of time-dependent acoustic pressure in some spatial domain. Using these data, it is necessary to determine the positions of local acoustic inhomogeneities (spatial sound speed distributions), which change over time. A special idealized sounding model is used, in which, in particular, it is assumed that the spatial sound speed distribution changes little in the interval between source time pulses. With such a model, the inverse problem is reduced to solving three-dimensional Fredholm linear integral equations for each sounding time interval. Using these solutions, the spatial sound speed distributions are calculated in each sounding time interval. When a special (plane-layer) geometric scheme for the location of the observation and sounding domains is included in the sounding scheme, the inverse problem can be reduced to solving systems of one-dimensional linear Fredholm integral equations, which are solved by well-known methods for regularizing ill-posed problems. This makes it possible to solve the three-dimensional inverse problem of determining the nonstationary sound speed distribution in the sounded medium on a personal computer of average performance for fairly detailed spatial grids in a few minutes. The efficiency of the corresponding algorithm for solving a three-dimensional nonstationary inverse sounding problem in the case of moving local acoustic inhomogeneities is illustrated by solving a number of model problems. [ABSTRACT FROM AUTHOR]

Aiming at the consensus problem of slow convergence for the active noise control (ANC) model based on standard FxLMS algorithm that leads to performance degradation, this paper takes the error signal and its variation as the inputs of fuzzy logic control, and proposes an improved FxLMS algorithm by fuzzy control mechanism with two-input-two-output TSK fuzzy rules (TSK-FxLMS); In addition, the four-channel ANC models based on standard FxLMS and TSK-FxLMS are constructed using the noise signals from four measuring points inside an electric bus under uniform and variable speed conditions, respectively. Ultimately, the offline simulation and acoustic parameter calculation results indicate that the A-weighted sound pressure level (ASPL) and loudness of the two FxLMS models within the low and middle frequencies are significantly reduced, whereas the TSK-FxLMS model has faster convergence rate, higher average reduction percentage of ASPL and loudness, which proves that the established four-channel TSK-FxLMS model has a better sound quality improvement effect than the standard FxLMS. [ABSTRACT FROM AUTHOR]

The acoustic holography method was used to characterize a therapeutic focused fully populated 256-element ultrasonic transducer array. Elements of the array with the shape of equal area polygons are densely arranged in an irregular pattern on a spherically concave surface with a radius of curvature of 150 mm and a diameter of 200 mm. The array has a central frequency of 1.2 MHz and is designed to operate in water. The performance of individual array elements was studied based on the holographically reconstructed normal velocity distribution over the array surface. It was shown that with the same electrical signals applied to the elements, their acoustic responses had a phase deviation relative to the nominal values, which can be caused either by the asphericity of the array surface, or by the introduction of additional phase delays by the electrical matching network. To compensate for the detected parasitic phase shifts of the elements and restore the effective sphericity of the radiating surface, the Verasonics V-1 control system was used. The hologram measured after making the correction, as well as the shape of the focal region and acoustic pressure magnitude at the focus, separately measured by a hydrophone, showed that the proposed method reconstructed the nominal operating parameters of the array with high accuracy. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The diffusion stability of a single cavitation bubble in a spherical liquid cell surrounded by an infinite elastic solid is considered. The time-periodic pressure in the solid far away from the liquid cell is used as an external driving, which initiates bubble oscillations along with the gas diffusion process in the bubble-in-cell system. The work is based on the engineering approximation according to which the bubble growth/reduction is considered on average, assuming that during the period of the external driving the mass of gas in the bubble does not noticeably change. This theory predicts the existence of stably oscillating bubbles in confined liquid undergoing an external driving force. Three possible diffusion regimes are revealed: 1) total bubble dissolution, 2) partial bubble dissolution, and 3) partial bubble growth, where the last two regimes provide the diffusion stability in the bubble-in-cell system. The parametric study of the influence of the gas concentration dissolved in the liquid on the resulting stable bubble size is conducted. The obtained results are compared with the results for the case of the stable bubble oscillations in the pressure sound field in a bulk (infinite) liquid. The theoretical findings of the present study can be used for improvement of the modern applications of ultrasound technology. [ABSTRACT FROM AUTHOR]

One of the beach protection techniques is using natural methods based on the coastal ecosystem. Studies show the reducing effect of forest covers on wave destruction intensity in different areas. However, it is not yet well understood how various densities of terrestrial coastal forest (TCF) affect the wave attenuation and reduce their strength. Studying the impact of various forest parameters, such as density, distance, and arrangement type on the wave force attenuation, this research measures the wave forces directly. TCF model was installed in a knife edge flume, which equipped with a load cell and an acoustic Doppler velocimeter. The experiments were performed in two staggered and parallel arrangements consisting of different densities from 12 to 273 stems per unit area. Based on obtained results, TCF had significant effects on the wave force absorption. An increase in the number of trees (density) increased TCF resistance force and the absorbed wave force. In its best, the TCF could absorb the wave force 3.76 times more than the no-TCF case. It could reduce the wave height by up to 81% at the highest density and maximum wave height. The absorbed wave force and drag coefficient rose as the number of rows of trees opposing the flow decreased and the intervals between trees were shortened. Increasing tree density from 12 to 273 stems per unit area increased the drag coefficient by the average of 61.82% for parallel and staggered arrangements, which means an average increase of 9.7% for each TCF row. [ABSTRACT FROM AUTHOR]

The configuration of rotors significantly impacts the aerodynamic efficiency and noise emission of multicopters. To date, there are no general guidelines regarding how many blades a rotor should use for optimal aerodynamic performance and minimum noise emission. From the perspectives of aerodynamics and acoustics during the hovering condition, two key parameters, i.e., figure of merit (FM) and overall sound pressure level (OASPL), are evaluated to determine the optimal blade number (BN). The number of blades chosen in this study is BN = 2–6, which is largely observed in commercial multicopters. A genetic algorithm was developed to optimize blade design for each BN-rotor configuration. The individuals are evaluated by steady computational fluid dynamics (CFD) simulations and acoustic analogy for optimizations, and the detailed analyses of optimal ones are further explored by unsteady CFD simulations. The planform of the baseline blade is maintained, and the radial distribution of twist angles is the parameter for optimization. While generating the same thrust, the value of FM keeps increasing as the number of blades increases from 2 to 4, after which the FM value reaches a plateau. The value of OASPL keeps decreasing as the number of blades increases. The reason for the FM and OASPL value trends vs blade number is explained with the numerical simulation results, and a general design rule is suggested at the end. [ABSTRACT FROM AUTHOR]

Encapsulated microbubbles serve as suitable drug carriers in medicine. This paper proposes corrections for the resonance frequency of lipid-coated bubbles under various acoustic pressure levels and the critical pressure for bubble rupture based on the Marmottant model. The suggestion to induce the rupture of lipid-coated bubbles using acoustic waves leans toward utilizing pulse waves rather than continuous waves. Corresponding experiments validate the accuracy of these corrections and the rationale behind the suggestion, aligning closely with theoretical predictions. This study offers a more precise predictive framework for the behavior of lipid-coated bubbles under acoustic waves. [ABSTRACT FROM AUTHOR]

Flame stabilizers employing pylons within scramjet engines are becoming more prominent for enhancing fuel penetration and mixing. Studies have highlighted the enhanced mixing efficiency achieved by positioning a pylon ahead of the cavity. Nonetheless, the potential of a pylon positioned downstream of the cavity has not been thoroughly examined. To bridge this gap, the present study explores the effects of fuel injection when a pylon is positioned downstream of the cavity, as well as investigates injection upstream of the cavity. Numerical simulation is employed, utilizing a hybrid Reynolds-averaged Navier–Stokes/large eddy simulation simulation with an improved delayed detached eddy simulation turbulence model. To gain a deeper understanding of the mixing dynamics, additional investigation using dynamic mode decomposition has been performed. The upstream injection with a pylon downstream of the cavity has an improved mixing performance in comparison to the cases without it. The pylon placed downstream also assists in increasing the penetration height. The placement of the pylon leads to an increase in the total pressure loss. The low-frequency vortices are observed within the cavity due to back pressure caused by the pylon. Large-scale and higher-frequency vortices are observed downstream of the pylon. It is found in the modal analysis that the low-frequency vortices within the cavity and high-frequency modes downstream of the pylon enhance the mixing. The acoustic loading is observed to be higher when the pylon is placed downstream of the cavity. [ABSTRACT FROM AUTHOR]