Sound Propagation Effects Research Articles

An explicit granular-mechanics approach to marine sediment acoustics.

Here, we theoretically and computationally study the frequency dependence of phase speed and attenuation for marine sediments from the perspective of granular mechanics. We leverage recent theoretical insights from the granular physics community as well as discrete-element method simulations, where the granular material is treated as a packing of discrete objects that interact via pairwise forces. These pairwise forces include both repulsive contact forces as well as dissipative terms, which may include losses from the fluid as well as losses from inelasticity at grain-grain contacts. We show that the structure of disordered granular packings leads to anomalous scaling laws for frequency-dependent phase speed and attenuation that do not follow from a continuum treatment. Our results demonstrate that granular packing structure, which is not explicitly considered in existing models, may play a crucial role in a complete theory of sediment acoustics. While this simple approach does not explicitly treat sound propagation or inertial effects in the interstitial fluid, it provides a starting point for future models that include these and other more complex features.

Interpolation of scheduled simulation results for real-time auralization of moving sources

A central part of auralization is the consideration of realistic sound propagation effects. This can be achieved using computationally efficient physics-based simulations based on the principle geometrical acoustics. When considering complex effects, e.g. curved propagation due to atmospheric refraction, those simulations can be computationally demanding. This can become the bottleneck for real-time auralizations, as the run-time exceeds the duration of one audio block even for large block sizes. A solution is to schedule the simulations into a separate thread. However, this leads to an irregular update rate which is lower than the rate of the audio blocks. Consequently, the output signal can contain audible artifacts. This especially holds when considering the Doppler effect for dynamic scenarios with fast moving sources, like aircraft. This paper introduces a method for interpolating, and thereby upsampling, the results of scheduled simulations in an auralization context in order to avoid such artifacts. The method is applied to an aircraft flyover auralization considering curved sound propagation in an inhomogeneous, moving atmosphere. Using this method, it is possible to auralize such scenarios in real time.

Modern Methods of Sound Propagation Modeling Based on the Expansion of Acoustic Fields over Normal Modes

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.

Brillouin Interaction between Two Optical Modes Selectively Excited in Weakly Guiding Multimode Optical Fibers.

A multimode optical fiber supports excitation and propagation of a pure single optical mode, i.e., the field pattern that satisfies the boundary conditions and does not change along the fiber. When two counterpropagating pure optical modes are excited, they could interact through the stimulated Brillouin scattering (SBS) process. Here, we present a simple theoretical formalism describing SBS interaction between two individual optical modes selectively excited in an acoustically isotropic multimode optical fiber. Employing a weakly guiding step-index fiber approach, we have built an analytical expression for the spatial distribution of the sound field amplitude in the fiber core and explored the features of SBS gain spectra, describing the interaction between modes of different orders. In this way, we give a clear insight into the sound propagation effects accompanying SBS in multimode optical fibers, and demonstrate their specific contributions to the SBS gain spectrum.

Developing a modelling approach for sound propagation through turbulent boundary layer and applying to train pantograph

Sound propagation through turbulent boundary layer (TBL) is of great significance in transports where a TBL is attached to their external surfaces, for instance, air planes and high speed trains. Precise predictions of sound propagation through TBLs to their external surfaces can be extremely useful for their corresponding interior noise control. It is well known that a TBL is classified as an inhomogeneous flow medium and existing approaches are not capable to well predict its influence on sound propagation. Insight of sound propagation through TBLs is required but relevant research on this topic is limited in the literature. In this work, a modelling approach is developed to predict the influence of TBLs on sound propagation. In the proposed approach, the ray tracing method is employed to predict the evolution of sound waves when they are passing through a TBL, with which the equivalent phase speed of sound can be obtained and used to calculate the the Doppler factor so that the traditional methods can be extended to predict sound distribution in inhomogeneous flow media. The validation of this modelling approach is performed by using two cases. The first case is to predict the convective effect of sound propagation in a uniform mean flow and the predicted results are compared with analytical solutions. The second case is sound propagation through a TBL and the predictions obtained from this proposed approach are compared with numerical simulations obtained from the finite element (FE) method. In both cases, the convective effect obtained from this proposed approach is close to the analytical solution or the FE prediction. After that, the proposed approach is used to predict the sound propagation from a high speed train pantograph to the external surfaces of the train with considering the influence of the TBL. The corresponding results are verified by using FE simulations. This work shows that the proposed approach is effective and efficient, and also, it enhances the understanding of sound propagation in inhomogeneous flow media.

Real gas effects in sound wave propagation through two-phase systems

We study sound wave propagation through a two-phase system of gas with dispersed liquid droplets. The key element of the study is a combination of real gas effects, entering the model via a suitable equation of state, with steady and unsteady contributions to the drag force and heat transfer. This feature makes the model applicable for arbitrary pressures and temperatures. In the cases of low and high wave frequencies, ω, analytical solution is derived. At low ω, the model yields a generalization of the homogenous flow approximation to real gases. At high ω, the speed of sound tends to its value in the real gas in the absence of droplets while the attenuation coefficient diverges as ω. The model predicts the phenomenon of resonant attenuation demonstrated by the maximum of the growth rate of attenuation coefficient when ω is close to the eigen frequency of particle relaxation. In the absence of droplets (single-phase limit) for the gas satisfying the van der Waals equation of state, the model yields the corresponding states principle for the speed of sound: The ratio of the actual speed of sound to its ideal-gas value is the universal function of reduced density and temperature. This ratio demonstrates a nonmonotonous behavior of the speed of sound as a function of density reflecting the competition between the repulsive and attractive terms in the intermolecular interaction potential.

The influence of sea ice on the detection of bowhead whale calls

Bowhead whales (Balaena mysticetus) face threats from diminishing sea ice and increasing anthropogenic activities in the Arctic. Passive acoustic monitoring is the most effective means for monitoring their distribution and population trends, based on the detection of their calls. Passive acoustic monitoring, however, is influenced by the sound propagation environment and ambient noise levels, which impact call detection probability. Modeling and simulations were used to estimate detection probability for bowhead whale frequency-modulated calls in the 80–180 Hz frequency band with and without sea ice cover and under various noise conditions. Sound transmission loss for bowhead calls is substantially greater during ice-covered conditions than during open-water conditions, making call detection ~ 3 times more likely in open-water. Estimates of daily acoustic detection probability were used to compensate acoustic detections for sound propagation and noise effects in two recording datasets in the northeast Chukchi Sea, on the outer shelf and continental slope, collected between 2012 and 2013. The compensated acoustic density suggests a decrease in whale presence with the retreat of sea ice at these recording sites. These results highlight the importance of accounting for effects of the environment on ambient noise and acoustic propagation when interpreting results of passive acoustic monitoring.

Accuracy and robustness of sparse reconstruction techniques for azimuthal mode analysis of in-duct sound fields

Sparse reconstruction techniques enable the detection of the dominant azimuthal mode content in ducts with a limited number of sensors. This is of great importance in various fields of application, such as fan noise analyses. The analysis of weaker azimuthal modes has hardly been considered or looked at, although they can contribute considerably to the total sound field and can provide important information on sound propagation effects. To address this shortcoming, the Enhanced Orthogonal Matching Pursuit (EOMP) algorithm presented in this paper was developed. It is based on the established Compressed Sensing Orthogonal Matching Pursuit (OMP) algorithm, which is used to reliably detect the dominant azimuthal modes. In an extension step, the weaker modes are determined by applying a Least Squares Fit or a Discrete Fourier Transform to the deconvolved measurement vector. The capabilities and limitations of the different versions of the EOMP algorithm are tested on experimental data of multiple rotor-coherent sound field components generated by a fan stage. Furthermore, the EOMP algorithm is explored in detail for typical practical application scenarios using Monte-Carlo simulations. In both cases, the performance is compared with an alternative method, the Basis Pursuit Denoising (BPDN) algorithm. Within the Monte-Carlo framework, extensive parameter variations for the signal-to-noise ratio, mode sparsity (number of dominant modes) and mode field sparsity-level (magnitude ratio of dominant modes to weak modes), are performed over a wide frequency range. These Monte-Carlo simulations allow the comprehensive evaluation of the accuracy of the algorithms under investigation. Sensor ring designs and the considered analysis mode ranges can have a large impact on the overall reconstruction accuracy. Therefore, both aspects are also addressed in the presented study to provide helpful insights for future applications of the azimuthal mode analysis. Additionally, the EOMP algorithm is further improved by a regularised Least Squares Fit for the enhanced step and is shown to provide the best accuracy and robustness among the investigated algorithms.

Towards a process description of acoustic uncertainty in the upper ocean

The upper ocean is a region that hosts the worlds largest biomass, is the boundary layer mediating the exchange of momentum, energy, heat, gasses, etc. between the air and sea, and it is a region of critical Naval tactical importance. Acoustic modalities are important tools for sensing this region as evidenced by the ground-breaking results of bio-acousticans monitoring whales, fish, zooplankton, and other marine organisms. But while the significance of upper ocean acoustics has been long appreciated, the understanding of key ocean acoustic processes is lacking. Here, we define upper ocean as the region of the water column where the impacts of winter mixing are evident, usually two to three times the depth of the maximum mixed layer. The classical view of the thermohaline structure posits a combination of mostly one-dimensional mixing processes, slow mesoscale stirring and advection, and subsequent subduction towards the main thermocline. However, a number of recent studies points to an important role played by three-dimensional, small-scale, rapidly evolving, submesoscale fronts and their potential interaction with internal waves. A few observational highlights will be reviewed with an emphasis on sound-speed and spice distributions, and implications for deterministic and stochastic sound propagation effects will be discussed.

Uncertainty Quantification for Aircraft Noise Emission Simulation: Methods and Limitations

Implementing measures for the reduction of aircraft noise impact, such as optimization of flight paths and aircraft, requires sophisticated simulation capabilities. These tools have to incorporate simulation of aircraft noise generation at the source (i.e., emission) and account for prevailing sound propagation effects to ultimately predict noise levels as received on the ground. Obviously, understanding the associated uncertainties is crucial when aiming at a reliable and meaningful assessment. It also becomes essential when comparing different technologies, mixing experimental and numerical data, or using simulation methods of different fidelity (e.g., semi-empirical and first-order methods). This research focuses on quantifying uncertainties in the first step in aircraft noise simulation (i.e., the prediction of the emission situation). The quantified uncertainties reflect imperfections of models for different aircraft noise sources and variability of model input parameters at different operating conditions. A general framework is presented, which also accounts for limited knowledge of the underlying data distributions, and quantitative comparisons of different uncertainty methods are provided. In particular, the first-order second-moment analysis is compared to higher-order polynomial chaos methods, and the advantages and disadvantages of the different methods are discussed.

Urban Sound Auralization and Visualization Framework—Case Study at IHTApark

In the context of acoustic urban planning, the use of noise mappings is a worldwide well-established practice. Therefore, the noise levels in an urban environment are calculated based on models of the sound sources, models of the physical sound propagation effects and the position of the receivers in the area of interest. However, the noise mapping method is limited to sound levels in frequency bands due to missing temporal and spectral information of the sound signals. This, in turn, leads to missing information about the qualitative sound properties, as they can be evaluated in psychoacoustic parameters. Beyond the scope of the classical noise mapping, auralization and physically-based simulation of sound fields can be applied to urban scenarios in the context of urban soundscape analysis. By supporting the auralization technology with a visual counterpart of the urban space, a plausible virtual representation of a real environment can be achieved. The presented framework combines the possibilities of the open-source auralization tool Virtual Acoustics with 3D visualization. In order to enable studies with natural human response or for public communication of urban design projects, those virtual scenes can be either reproduced with immersive technologies—such head-mounted displays (HMD)—or using online video platforms and traditional playback devices. The paper presents an overview of what physical principles can already be simulated, which technological considerations need to be taken into account, and how to set up such environment for auralization and visualization of urban scenes. We present the framework by the case study of IHTApark.

Three Dimensional Volume Coverage in Multistatic Sonar Sensor Networks

Recent changes in the design of enemy threats such as submarines and the technological achievements in sensor development have paved the way for multistatic sonar applications, which increase security and situational awareness in underwater tactical operations. Previously, coverage in multistatic sonar sensor networks (MSSN) was studied using Cassini ovals and the traditional sonar detection model in two dimensions without any discussion of the practicability and feasibility in terms of conditions related to the underwater acoustic propagation environment. In this study, a practical three-dimensional MSSN channel model is proposed. The proposed model covers a spectral variation of absorption loss, ambient noise, sound speed profile, and shadow zones. The realistic effects of sound propagation and environmental conditions are modeled and evaluated using Lybin, which is a well-known sonar performance prediction tool. Using the practical MSSN channel model, the number of source-receiver pairs required to cover a three-dimensional MSSN volume is calculated. The impacts of frequency, source-to-receiver distance, and source level are investigated. The results are compared to the Cassini oval and traditional sonar detection models via an error expression derived according to our verified practical model. The results reveal that the inclusion of ambient conditions and sound propagation characteristics in the channel model leads to huge error levels of 4700000% in the Cassini oval model and 170000% in the traditional sonar detection model, depending on frequency. Thus, the applicability of these models in realistic MSSN deployment scenarios is limited.

Finite-amplitude sound propagation effects in volume backscattering measurements for fish abundance estimation

Scientific advice for governmental management of marine resources relies on acoustical observation methods. Quantification and identification of fish and plankton species are often achieved using multi-frequency acoustic data. Accurate measurements of backscattering cross-sections and volume backscattering coefficients are essential. Systematic errors from finite-amplitude sound propagation are demonstrated in experimental survey measurements on Atlantic mackerel using 120 kHz and 200 kHz echosounders and high power settings. Finite-amplitude signal distortion causes excess transmission loss that is not accounted for in fisheries acoustics today, other than by fixed limits on the maximum transmitted power. The demonstrated errors are of a magnitude that can seriously bias abundance estimation and species identification. It is shown how the finite-amplitude effects can be modelled and predicted quantitatively, within a framework of electroacoustic power budget equations. A method is provided to calculate related errors in echosounder calibration and oceanic measurement of acoustic volume backscattering. When accounting for finite-amplitude effects in echosounder signal processing, higher transmit powers can be used when needed to improve signal-to-noise ratio or extend measurement range. The results indicate that historical survey data can be adjusted for such errors using numerical simulations. The echosounder characteristics relevant to finite-amplitude effects can be determined by laboratory measurements.

Sound Propagation Modelling for Manned and Unmanned Aircraft Noise Assessment and Mitigation: A Review

This paper addresses one of the recognized barriers to the unrestricted adoption of Unmanned Aircraft (UA) in mainstream urban use—noise—and reviews existing approaches for estimating and mitigating this problem. The aircraft noise problem is discussed upfront in general terms by introducing the sound emission, propagation, and psychoacoustic effects. The propagation of sound in the atmosphere, which is the focus of this paper, is then analysed in detail to isolate the environmental and operational factors that predominantly influence the perceived noise on the ground, especially looking at large-scale low-altitude UA operations, such as in the envisioned Urban Air Mobility (UAM) concepts. The physics of sound propagation are presented, considering all attenuation effects and the anomalies due to Doppler and atmospheric effects, such as wind, thermal inversion, and turbulence. The analysis allows to highlight the limitations of current mainstream aircraft noise modelling and certification approaches and, in particular, their inadequacy in addressing the noise of UA and, more generally, UAM vehicles. This finding is important considering that, although reducing noise at the source has remained a priority for manufacturers to enable the scaling up of UAM and drone delivery operations in the near future, the impact of poorly considered propagation and psychoacoustic effects on the actual perceived noise on the ground is equally important for the same objective. For instance, optimizing the flight paths as a function of local weather conditions can significantly contribute to minimizing the impact of noise on communities, thus paving the way for the introduction of full-scale UAM operations. A more reliable and accurate modelling of noise ground signatures for both manned and unmanned low-flying aircraft will aid in identifying the real-time data stream requirements from distributed sensors on the ground. New developments in surrogate sound propagation models, more pervasive real-time sensor data, and suitable computing resources are expected to both yield more reliable and effective estimates of noise reaching the ground listeners and support a dynamic planning of flight paths.

Model-based localization of deep-diving cetaceans using towed line array acoustic data.

Passive acoustic monitoring using a towed line array of hydrophones is a standard method for localizing cetaceans during line-transect cetacean abundance surveys. Perpendicular distances estimated between localized whales and the trackline are essential for abundance estimation using acoustic data. Uncertainties in the acoustic data from hydrophone movement, sound propagation effects, errors in the time of arrival differences, and whale depth are not accounted for by most two-dimensional localization methods. Consequently, location and distance estimates for deep-diving cetaceans may be biased, creating uncertainty in abundance estimates. Here, a model-based localization approach is applied to towed line array acoustic data that incorporates sound propagation effects, accounts for sources of error, and localizes in three dimensions. The whale's true distance, ship trajectory, and whale movement greatly affected localization results in simulations. The localization method was applied to real acoustic data from two separate sperm whales, resulting in three-dimensional distance and depth estimates with position bounds for each whale. By incorporating sources of error, this three-dimensional model-based approach provides a method to address and integrate the inherent uncertainties in towed array acoustic data for more robust localization.

A Pore-Scale Model for Dispersion and Mass Transfer during Acoustically Assisted Miscible Displacements in Porous Media

Enhancing flow and transport in porous media by acoustic stimulation has been investigated for the past several decades. Most studies focused on the effect of sound propagation in immiscible displa...

МОДЕЛЬ ОБЧИСЛЕННЯ РІВНІВ ЗВУКУ ШУМУ ВІД КОМПРЕСОРНИХ СТАНЦІЙ ДЛЯ ОБГРУНТУВАННЯ ГРАНИЦЬ САНІТАРНО-ЗАХИСНОЇ ЗОНИ

This article is devoted to the study of sound levels for noise from a gas turbine plant and technological equipment of a compressor station in everyday operation, in order to assess the sustainability of the conditions of sanitary protection zones around the compressor station and in order to protect the population living near the compressor station. The main purpose of the study is to assess the compliance of the sizes of sanitary protection zones in terms of noise load on environment. The main source of noise at compressor gas-pumping stations is determined by the noise regime at the industrial site, in addition to auxiliary equipment; include gas-pumping devices, systems of technological gas discharge from the blower circuits, fuel and starting gas of gas-pumping devices. The dependence of the noise conditions at the production site and in the environment on the sound power level of gas-pumping apparatuses, the installed power of gas-turbine plants, the sound power of the turbocompressor, service life of gas-pumping apparatuses, the number of simultaneously operating gas-pumping apparatuses, the characteristics of production premises, the design of the gas-pumping apparatuses, the state of means of noise absorption of gas-pumping apparatuses. In gas turbine installations of compressor stations, intense noise occurs in the air intake and exhaust systems, in the cooling system fan, in the turbomachine housing and in the generator. To calculate the sound levels at a separate point, depending on the distance to the noise source, a model was used taking into account the effects of sound wave propagation in atmospheric air and the characteristics of the noise source, such as: directivity and spectral characteristics of radiation, the height of the source above the surface; distance from the source to the point of determining the sound level; absorption of sound in atmospheric air, depends on the frequency and parameters of the state of the atmosphere; the effect of the influence of the earth; weather effects and others. The methodology of the standard and the international method CONCAW were used based on the results of calculating sound levels at the border of the sanitary protection zone at the compressor station. The calculation results, for standard atmospheric conditions, according to the international CONCAW method indicate that at a distance of 700 m from the sound source, the sound propagation will be 50.0 dBA, which coincides with the calculation results using the standard method and also exceeds the night noise standard by 5 dBA for conditions in the residential area. Development even when only one gas compressor is in operation, which proves the relevance of studying the environmental risks of compressor stations. KEY WORDS: NOISE, ENVIRONMENTAL RISKS, NOISE SOURCE, COMPRESSOR STATIONS, GAS PUMPING UNIT, GAS PUMPING APPARATUS, SOUND.

Interactive real-time auralization of airborne sound insulation in buildings

Sound insulation auralization can be used as valuable tool to study the perceptual aspects of sound transmission in built environments for assessment of noise effects on people. It may help to further develop guidelines for building constructions. One advanced goal of real-time sound insulation auralization is to appropriately reproduce the condition of noise effects on the human perception and cognitive performance in dynamic and interactive situations. These effects depend on the kind of noise signal (i.e. speech, music, traffic noise, etc.) and on the context. This paper introduces a sound insulation auralization model. The sound insulation filters are constructed for virtual buildings with respect to complex sound propagation effects for indoor and outdoor sound sources. The approach considers the source room sound field with direct and diffuse components along with source directivity and position. The transfer functions are subdivided into patches from the source room to the receiver room, which also covers composite building elements, thus providing more detail to the actual building situations. Furthermore, the receiving room acoustics includes the reverberation of the room based on its mean free path, absorption and binaural transfer functions between its radiating walls elements and the listener. This more exact approach of sound insulation model agrees reasonably well with the ISO standard (i.e. diffuse field theory) under standard settings. It is also shown that the sound field significantly influences the transmitted energies via building elements depending on the directivity and position of the source. The proposed method is validated as a general scheme and includes more details for real-time auralization in specific situations especially in the cases where the simplified diffuse sound field approach fails. It is capable to be used in interactive Virtual Reality (VR) systems, which opens new opportunities for psychoacoustics research in noise effects on human.

90 Years of Galbrun’s Equation: An Unusual Formulation for Aeroacoustics and Hydroacoustics in Terms of the Lagrangian Displacement

The field of aeroacoustics has gained much attention since the well-known acoustic analogies were first published in the 1950s. In parallel, the continuous growth of computational resources has enabled researchers and engineers to investigate phenomena involving flow-induced noise or sound propagation effects related to arbitrary velocity fields. To describe the latter mentioned physical processes, Galbrun utilized a mixed Eulerian–Lagrangian framework to describe perturbations of the underlying fluid dynamics. While less known compared to the more common linearized Euler equations, Galbrun’s equation provides an original framework. Since its publication in 1931, a number of scholars have further developed the approach first proposed by Galbrun. This paper provides a review of the existing literature dedicated to the use of Galbrun’s equation by highlighting possible advantages of the underlying theory as well as difficulties when utilizing numerical methods for solving problems in time or frequency domain. Furthermore, this work intents to serve as a companion for researchers interested in the field of aeroacoustics and hydroacoustics associated with Galbrun’s equation.

FiniteAmplitude Power Budget Equations for Acoustic Fish Abundance Estimation

Finiteamplitude (nonlinear) sound propagation effects in seawater may cause measurement errors in fish and zooplankton abundance estimation and species identification for accessible echo sounder transmit electrical power levels and operating frequencies of about 100 kHz and higher. A sufficiently validated framework to quantify, control, and compensate for such errors in these applications is not available. The conventional power budget equations in fisheries acoustics are valid for smallamplitude signals only. The study aims to fill this “gap”. The conventional theory is generalized to account for finiteamplitude incident sound propagation, arbitrary electrical termination, and the range of electrical and acoustical echo sounder parameters. Equations for use in calibration and oceanic surveying are derived in terms of the backscattering cross section,, and the volume backscattering coefficient,. The “finiteamplitude terms” in these expressions can—for relevant transmit electrical power levels of relevant echo sounders—be measured in controlled tank experiments. Alternatively, they can be calculated using numerical models. The resulting equations enable estimation of finiteamplitude measurement errors in these applications; development of recommended upper limits for echo sounder power levels; controlled reduction of finiteamplitude errors in calibration and surveying; and development of correction factors for survey data already subjected to such measurement errors.