Acoustic Source Characterization Research Articles

Numerical simulation study of acoustic source characteristics of liquid level monitor based on infrasound waves

Abstract To investigate the sound source characteristics of infrasound waves generated during the operation of the gas explosion liquid level monitoring instrument, with a focus on the aerodynamic noise produced by the monitoring device, a mixed numerical method was used to simulate and study the impact of different nozzle diameters, gas explosion pressures, and casing pressures on the instrument’s infrasound frequency range. The results indicate that gas explosion pressure, casing pressure, and nozzle diameter primarily affect the spectral characteristics within the 10 Hz to 20 Hz range. As the gas explosion pressure and nozzle diameter increase, the sound pressure level in the internal sound field also increases, and the peak frequency shifts higher. Conversely, with an increase in casing pressure, the sound pressure level in the internal sound field decreases, and the peak frequency shifts lower. The research findings can provide a theoretical basis for the development of the instrument.

Acoustic emission noise reduction: A case of a uniaxial compression test of gypsum-like rock

In acoustic emission tests, the effective signal generated by crack initiation and propagation inside a sample is easily affected by the testing machine, earth vibration and other external noise, which increases the difficulty of data processing and analysis. To solve this problem, a gypsum sample under uniaxial compression is taken as an example to analyze and process the acoustic emission signal during the experiment. The test results show that these noises generally have the characteristics of acoustic sources far from the probe and signal types different from the effective signal. Therefore, a series of methods concerning the noise reduction of acoustic emission signals, including acoustic emission signal preprocessing, acoustic source distance denoising, and acoustic source type denoising, is proposed. Through three analyses and treatments of acoustic emission parameters, noise reduction was achieved with good results. According to the principles of these methods, some suggestions have been put forward for the position of probes in acoustic emission tests; that is, the connection of two probes should not be perpendicular to a weak plane (bedding, joints, etc.). These results could provide a theoretical reference for the postprocessing of acoustic emission signals in mechanical tests.

Acoustical Holography and Coherence-Based Noise Source Characterization of an Installed F404 Engine

Understanding the acoustic source characteristics of supersonic jets is vital to accurate noise field modeling and jet noise reduction strategies. This paper uses advanced, coherence-based partial field decomposition methods to characterize the acoustic sources in an installed, supersonic GE F404 engine. Partial field decomposition is accomplished using an equivalent source reconstruction via acoustical holography. Bandwidth is extended through the application of an array phase-unwrapping and interpolation scheme. The optimized-location virtual reference method is used. Apparent source distributions and source-related partial fields are shown as a function of frequency. Local maxima are observed in holography reconstructions at the nozzle lipline, distinct in frequency and space. The lowest-frequency local maximum may relate to noise generated by large-scale turbulence structures in the convectively subsonic region of the flow. Other local maxima are correlated primarily with Mach wave radiation originating from throughout the shear layer and into the fully mixed region downstream of the potential core tip. Source-elucidating decompositions show that the order and behavior of the decomposition lend to the local maxima being related to distinct subsources. Between the local maxima, however, there may be a combination of sources active, which is likely the cause of the spatiospectral lobes observed in other full-scale, supersonic jets.

Acoustic source characterization for chemical explosions in air

Chemical explosions in the air generate large pressure disturbances. These pressure waves propagate as non-linear shock waves near the source and transition into acoustic waves in the far-field. Since low-frequency acoustic waves propagate long distances without significant loss of energy, acoustic signals induced by explosions are often used to determine explosion energies of the events in terms of an explosion yield. In order to estimate the explosion energy accurately, the relationship between acoustic energy and explosion yield must be understood. However, explosion yields are often measured by non-linear shock waves in the near-field, and it is not clear how much acoustic energy accounts for the explosion energy. In addition, acoustic signals typically have lower-frequency contents than shock waves in the near-field, and hence frequency-dependent explosion energy should be understood to accurately infer explosion yields based on acoustic observations. In this study, we investigate the relationship between acoustic energy and explosion yield based on ground-truth explosion data. A standard acoustic source waveform will be determined by acoustic observations, and frequency-dependent energy will be explored for yield estimation. We will demonstrate that this frequency-dependent acoustic source characterization can improve the accuracy and confidence of explosion yield estimation.

Acoustic measurements of full-scale electric vertical takeoff and landing aircraft

The Advanced Air Mobility industry is progressing rapidly towards the goal of revolutionizing transportation by connecting urban and underserved communities with electric vertical takeoff and landing (eVTOL) aircraft. To achieve widespread use, eVTOL aircraft must generate acceptable noise in surrounding communities. Many eVTOL aircraft currently under development have novel configurations of rotors, propellers, and wings that may produce rotor-rotor and rotor-airframe interaction noise at certain flight conditions. Acoustic measurements of full-scale eVTOL aircraft are critical to understand the complex noise-generation mechanisms and to validate aeroacoustic models for these novel aircraft designs. In this presentation, we present acoustic measurements of Hexa, an 18-rotor, single-passenger eVTOL aircraft developed by LIFT Aircraft, Inc. We apply acoustic source characterization techniques using simultaneous acoustic measurements and vehicle telemetry data to provide a better understanding of the noise-generation mechanisms. One such analysis technique is the Vold-Kalman filter, which we apply to auralize the tonal waveforms of individual rotors. Finally, we discuss plans for upcoming acoustic measurements of a full-scale, multi-passenger eVTOL aircraft. These measurements and analyses provide the data and tools required to better understand the noise-generation mechanisms and to validate aeroacoustic models for full-scale eVTOL aircraft

Acoustic source characterization of shock-associated noise in an installed, full-scale F404 engine

Shock-associated noise in supersonic jets is an important factor in acoustic radiation, particularly in the upstream direction. A previous paper [L. T. Mathews et al., J. Acoust. Soc. Am. 154, A325 (2023)] discussed a preliminary source characterization of shock-associated noise in a full-scale, installed tactical jet engine. Acoustical holography was used to reconstruct the acoustic behavior near the jet and high-amplitude features were produced that were consistent with shock-associated noise sources. This paper presents a more detailed characterization of shock-related noise in the jet using higher-fidelity methods, such as subarray processing and bandwidth extension. The spatial and spectral characteristics of the shock cell noise sources are discussed. A virtual reference decomposition method is used to examine the source and radiative characteristics of each detected shock noise source. The results are compared with shock noise characteristics in the literature. [Work supported by ONR Grant No. N00014-21-1-2069.]

Acoustic source characterization of simulated subsonic jet noise using spherical harmonics

As subsonic jets remain one of the major contributions to aircraft noise emissions, near-field flow simulations should be included in aircraft design at an early stage using quantitatively predicted sound pressure levels and the time-domain signal properties of the noise data. In this regard, the interface from the near-field data to the far-field radiation—under consideration of acoustic reflections from objects such as fuselage and wings—remains as bottleneck. This study presents the computation of a spherical equivalent source model of jet noise with minimal complexity by means of spherical harmonic (SH) coefficients. Using spherical Hankel extrapolation of sound pressure data from virtual, concentrical microphone arrays, the results of the determination for the radius, in which all acoustic sources of a flow field are confined, indicate the source radius around the end of the potential core to be equivalent to five times the nozzle diameter. The result of the SH transform shows the dominant energy contribution to be related to nine elementary sources. The resulting equivalent source model of jet noise provides a convenient format for further use in large-scale computational fluid dynamics simulations.

On the Challenges of Acoustic Energy Mapping Using a WASN: Synchronization and Audio Capture

Acoustic energy mapping provides the functionality to obtain characteristics of acoustic sources, as: presence, localization, type and trajectory of sound sources. Several beamforming-based techniques can be used for this purpose. However, they rely on the difference of arrival times of the signal at each capture node (or microphone), so it is of major importance to have synchronized multi-channel recordings. A Wireless Acoustic Sensor Network (WASN) can be very practical to install when used for mapping the acoustic energy of a given acoustic environment. However, they are known for having low synchronization between the recordings from each node. The objective of this paper is to characterize the impact of current popular synchronization methodologies as part of the WASN to capture reliable data to be used for acoustic energy mapping. The two evaluated synchronization protocols are: Network Time Protocol (NTP) y Precision Time Protocol (PTP). Additionally, three different audio capture methodologies were proposed for the WASN to capture the acoustic signal: two of them, recording the data locally and one sending the data through a local wireless network. As a real-life evaluation scenario, a WASN was built using nodes conformed by a Raspberry Pi 4B+ with a single MEMS microphone. Experimental results demonstrate that the most reliable methodology is using the PTP synchronization protocol and audio recording locally.

Improved methods for source characterization on trains

One problem for railway noise predictions is to characterize noise from various auxiliary equipment, e.g., fans, compressors, transformers. The noise from such sources can be a dominating contribution under low-speed operation or stand still. To better handle this problem the EU-project TRANSIT investigates improved methods for acoustic source characterization. As a starting point it is assumed that an acoustic source is enclosed by a control surface. The surface is sub-divided into smaller areas and each area is assumed to act as an acoustic one-port coupled to all the other areas. The properties of each area can then be described by its volume flow and internal impedance. The resulting acoustic pressure at a receiving point, can finally be expressed as a product of the source volume flows and a matrix representing the acoustic installation effects ("source+radiation impedances"). To simplify the method one can assume uncorrelated sources and use an ISO procedure for sound power to determine the volume flows. The acoustic installation effects can be obtained using a monopole point source to measure or calculate the pressure at selected receiving positions.

Main sensitivity drivers in indoor acoustic comfort for autistic individuals

One challenge for railway noise predictions is to characterize noise from various auxiliary equipment, e.g., fans, compressors, transformers. The noise from such sources can be a dominating contribution under low speed operation or stand still. To better handle this problem the EU-project TRANSIT investigates improved methods for acoustic source characterization. As a starting point it is assumed that an acoustic source is enclosed by a control surface. The surface is sub-divided into smaller areas and each area is assumed to act as an acoustic one-port coupled to all the other areas. The properties of each area can then be described by its volume flow and internal impedance. The resulting acoustic pressure at a receiving point, can finally be expressed as a product of the source volume flows and a matrix representing the acoustic installation effects ("source+radiation impedances"). To simplify the method one can assume uncorrelated source surfaces and use an ISO procedure for sound power to determine the volume flows. The acoustic installation effects can be obtained using a monopole point source to measure or calculate the pressure at selected receiving positions. This simplified method has been validated under controlled laboratory conditions and tested on real equipment on trains.

Underwater-art: Expanding information perspectives with text templates for underwater acoustic target recognition.

Underwater acoustic target recognition is an intractable task due to the complex acoustic source characteristics and sound propagation patterns. Limited by insufficient data and narrow information perspective, recognition models based on deep learning seem far from satisfactory in practical underwater scenarios. Although underwater acoustic signals are severely influenced by distance, channel depth, or other factors, annotations of relevant information are often nonuniform, incomplete, and hard to use. In this work, the proposal is to implement underwater acoustic recognition based on templates made up of rich relevant information (UART). The templates are designed to integrate relevant information from different perspectives into descriptive natural language. UART adopts an audio-spectrogram-text trimodal contrastive learning framework, which endows UART with the ability to guide the learning of acoustic representations by descriptive natural language. These experiments reveal that UART has better recognition capability and generalization performance than traditional paradigms. Furthermore, the pretrained UART model could provide superior prior knowledge for the recognition model in the scenario without any auxiliary annotation.

Acoustic Source Characterization of Marine Propulsors

Marine propulsors represent one of the most important contributors among anthropogenic sounds radiated into water. Blade based propulsors, e.g., propellers, generate tones at the blade passing frequency and its harmonics, especially in cavitating conditions. In addition to hydrodynamic noise, pressure fluctuations cause vibrations in ship hull leading to mechanical noise. For noise prediction purposes, it is highly beneficial to characterize the noise sources as simplified, complex valued arrays having information on source positions, source strengths and phases. In this paper, procedure to characterize marine propulsors as acoustic sources with inverse method is introduced. First, the numerical model with complete hydro-acoustic sources is investigated. Second, a source model composed of sensible number and distribution of elementary (“equivalent”) compact sources is specified. Then selected responses are used as input in source characterization with inverse method. Finally, the model with equivalent sources is solved and the results are validated by comparison against the results from the complete simulation model. The introduced acoustic source characterization procedure of marine propulsors is applicable also for the responses determined experimentally, e.g., in a cavitation tunnel when the pressure transducer array is determined appropriately.

IRIS: A tunable sound sculpture based on acoustic periodic composites for musical performance

This article discusses the use of sound sculptures as tunable modulators of the transmission characteristics of acoustic sources during performance. We propose IRIS, a sculpture consisting of a periodic composite formed by an acoustic double-fishnet made up of two discs with periodic perforations and independent rotation. From the analysis of the transmitted field and binaural impulse responses, we observed a sound focusing whose spectral and spatial location varies depending on the relative angle of rotation between the disks. This effect is verified using a synthesized sustained sound and a chord progression, and finally validated perceptually in a listening test with 11 musicians.

Characterization of acoustic sources in a corrugated pipe flow with linear stochastic estimation.

The intense whistling of corrugated pipe under flow is related to a coherence between the dynamics of structures developing in the shear layer over cavities and acoustic eigenmodes of the pipe. In order to highlight the coupling between aerodynamics and acoustics, three measurement systems with complementary characteristics in terms of space and time resolutions are synchronized. The simultaneity of the measurements of velocity and acoustic pressure provided by five local probes, as two hot-wires and three microphones, with the velocity fields measured by PIV in the same flow region is used to estimate the velocity fields at frequencies compatible with the space-time characterization of the acoustic sources. The linear stochastic estimation (LSE) is performed to reconstruct these high frequency velocity fields. Two rectangular corrugated pipes with different corrugation geometry are investigated. Thanks to the LSE velocity field reconstruction, the contribution of the flow structures, both jet flapping and vortex shedding, to acoustic level is highlighted.

Acoustical holography-based sound power decomposition of a highly heated, large eddy-simulated supersonic jet

In recent years, large-eddy simulation (LES) has proved a powerful tool for modeling increasingly heated, supersonic jets and analyzing their source characteristics. This paper describes an investigation of the acoustic source characteristics from an LES of an underexpanded jet with total temperature ratio of seven. Using frequency-domain pressures and particle velocities at, and generated from, the Ffowcs Williams Hawkings surface (FWHS), holography and intensity techniques are used to perform an axial decomposition of radiated sound power from the jet, whereas a far-field arc produces a narrow, nonphysical source distribution, the intensity from the near-field array and FWHS surface yield sound power decompositions that approximate the nozzle lipline squared-pressure’s spatial distribution. For this LES, the peak sound power is radiated just upstream of the potential core tip, and over 90% of power is radiated upstream of the supersonic core tip.

Large-aperture experimental characterization of the acoustic field generated by a hovering unmanned aerial vehicle.

Unmanned aerial vehicles, specifically quadrotor drones, are increasingly commonplace in community and workplace settings and are often used for photography, cinematography, and small parcel transport. The presence of these flying robotic systems has a substantial impact on the surrounding environment. To better understand the ergonomic impacts of quadrotor drones, a quantitative description of their acoustic signature is needed. While previous efforts have presented detailed acoustic characterizations, there is a distinct lack of high spatial-fidelity investigations of the acoustic field of a quadrotor hovering under its own power. This work presents an experimental quantification of the spatial acoustic pressure distribution in the near-field of a live hovering unmanned aerial vehicle. A large-aperture scanning microphone array was constructed to measure sound pressure level at a total of 1728 points over a 2 m × 3 m × 1.5 m volume. A physics-infused machine learning model was fit to the data to better visualize and understand the experimental results. The experimental data and modeling presented in this work are intended to inform future design of experiments for quadrotor drone acoustics, provide quantitative information on the acoustic near-field signature, and demonstrate the utility of optical motion tracking coupled with a custom microphone array for characterization of live acoustic sources.

Analysis of Propagation and Distribution Characteristics of Leakage Acoustic Waves in Water Supply Pipelines.

Leakage detection methods based on the analysis of leakage acoustic signals provide an effective technical approach for detecting small leaks in water supply pipelines. From a technical perspective, the study of the propagation characteristics of acoustic waves generated by the leakage in the water supply pipeline is necessary for detecting the leak location on the basis of acoustic signals. In this study, a 3D transient leakage acoustic wave propagation equation was derived by combining the principles of fluid dynamics and Lighthill acoustic analogy theory. The propagation of the leakage-induced noise in water supply pipeline was modelled theoretically. We simulated the propagation of a leakage acoustic wave under different conditions for different target scenarios encountered in actual pipeline inspections. Specifically, we analysed the effect of different factors, such as the pipe size and acoustic source characteristics, on acoustic propagation. Finally, the simulated experiments were practically performed using a self-designed simulated water supply pipeline and self-developed spherical water supply pipeline detector to validate the simulation analysis. The results of this study provide a theoretical guidance and basis for the analysis of characteristics of leakage acoustic wave signals and the recognition of leakage conditions in water supply pipelines.

Propagation characteristics of laser-induced acoustic sources in hybrid anechoic wind tunnels

The propagation characteristics of an acoustic point source generated using laser-induced plasma (LIP) were investigated experimentally. Experiments were performed in a Kevlar-walled hybrid anechoic wind tunnel (HAWT) where the sound of the LIP was measured using a 251-element microphone array, while the flow speed in the empty test section was varied. The time instant of the LIP formation was also captured. The far field sound pressure was assessed through arrival times (source to microphones) and pressure correction levels, and these quantities were compared against a commonly used shear layer refraction model. A detailed uncertainty assessment is presented on the arrival times and pressure levels. It was found that the time domain analysis was limited by the sampling rate of the analog-to-digital converter regardless of the flow speed. The uncertainty of the pressure levels was limited by the uncertainty of the microphones at low flow speeds, while they increased with flow speed at shallow observer angles. The high-speed Schlieren imaging of the LIP was performed, which revealed that the sound of the LIP reaches the far field microphones over a shorter time duration than modeled because the wave speed was initially supersonic. The discrepancy was found to be comparable to the temporal resolution of the aeroacoustic experiments. The discrepancy between the experimental and theoretical arrival times was found to increase with flow speed, and they were nearly independent of the azimuth angles. The discrepancy between the experimental and theoretical pressure correction ratio was found to be uniform for most observer locations. With an increase in flow speed, the discrepancy became positive at large, and negative at low polar angles. The sound refraction at the Kevlar wall did not change the frequency content of the sound over the investigated range of frequencies (1–10 kHz).

Experimental Study on the Characteristics of Acoustic Emission Source of Rock under Uniaxial Compression

One of the main research problems in acoustic emission (AE) monitoring technology is to identify the source of the acoustic emission. Processing the acoustic emission signal is the only way to solve this problem, and then to achieve the purpose of identifying the material destruction mode. Using acoustic emission monitoring technology, the acoustic emission of granite under uniaxial compression was monitored and analyzed, and the coupling characteristics between the acoustic emission signal parameters of granite under different loading rates were obtained. The results show that during the process of rock shear failure, the peak intensity of the rock, the peak value of the absolute energy of acoustic emission, the cumulative amount of acoustic emission and the loading rate showed a positive correlation. The correlation diagram of the AE ringing count and the duration shows a triangular distribution, and as the rock loading rate decreases, the angle of the triangle top angle of the correlation diagram increases. The distribution relationship between the absolute energy of AE and the duration can be fitted using a unary quadratic function, and as the loading rate decreases, the opening of the fitting curve gradually increases, and the width of the correlation graph gradually decreases. The correlation graph of absolute energy and amplitude of AE is linearly distributed, and as the loading rate decreases, the slope of the fitted line of absolute energy and amplitude of AE gradually decreases, and the width of the linear channel of the correlation graph decreases. It is found that there is a good regularity between the correlation graphs of different parameters of the acoustic emission of the rock during the uniaxial compression failure process, which is an effective method to identify the characteristics of the source of the acoustic emission. Therefore, establishing the correspondence between the characteristics of the AE source and the loading conditions will promote the development of acoustic emission technology in the monitoring of the stability of the surrounding rock of underground projects.

Investigation of Wave Propagation Behavior of Partially Two-Layered Plates

Abstract In this study, the acoustic emission characteristics of a rectangular plate with a partially covered free damping viscoelastic layer excited by an acoustic source (Hsu-Nielsen) has been investigated. A partially covered plate configuration consisting of a base plate (aluminum) and free damping layer (polyethylene) is considered. An acoustic emission source generated different acoustic modes, which caused the plate to have in-plane and out-plane displacements. These plate displacements will be captured by acoustic sensors. To obtain the general form of plate displacements theoretically, Von Karman theory and a Kelvin-Voigt model were used and the equations of motion were derived using Galerkin’s method. The effects of nonlinear terms of the strain-displacement relation on wave propagation characteristics of plates were investigated. The main frequency ranges of signals and the propagation speed of acoustic modes and their attenuation are very important for source locating. These parameters depend on the acoustic source and transmitted medium. So, theoretically predicting the main frequency range of signals because of the acoustic source and propagation characteristics of different acoustic modes has an important role in an acoustic source–locating algorithm. For this purpose, acoustic emission experiments were carried out using two R15α sensors. Frequency domains of theoretical and experimental results were analyzed. A comparison of the obtained results showed good agreement between the experimental and theoretical Lamb velocities and main frequency ranges.