Geometrical Acoustics Research Articles

Benchmarking of finite-difference time-domain method and fast multipole boundary element method for room acoustics

Compared to geometrical acoustics, wave-based methods which solve the wave equation either in the time domain or in the frequency domain are known for their high accuracy. However, their systematic use as professional room acoustic simulation tools is less popular due to the modelling effort and computational time requirements, especially in the case of complex scenarios. This paper aims at providing guidelines for the use of two wave-based methods in complex room acoustics simulations, namely the finite-difference time-domain (FDTD) method and the fast multipole boundary element method (FMBEM). Numerical experiments are conducted to address the convergence issues of the two solvers, more specifically, the selection of the convergence tolerance of the iterative solver in FMBEM and the temporal sampling frequency in FDTD. To evaluate the capability of the solvers in simulating complex scenarios, five cases with increasing complexity of material input data are presented. The results show that both solvers give close predictions for various room acoustics parameters. In addition, an uncertainty sensitivity study is performed in a case where experimental data is available. Large deviations between measured and simulated reverberation time reveal that typical material data-sets poorly represent the behaviour of real materials in a room acoustics context. Lastly, the efficiency of the two solvers is discussed. With parallelization implemented, both solvers can simulate sizeable room acoustic problems with good accuracy within a reasonable time.

Research on Energy Harvesting of Piezoelectric Vibration Using 2D ABH Structure

The acoustic black hole (ABH) effect can achieve energy concentration by changing the structural characteristics and reducing the propagation velocity of curved waves. This way of energy gathering provides a new idea for the harvesting of vibration energy. In this study, an energy collection structure with 2D ABH characteristics is proposed and studied, which can effectively provide energy harvesting efficiency. According to the theory of geometric acoustics, the size of the piezoelectric patch is designed to be smaller than the half wavelength of the bending wave at the centre of ABH, so as to avoid the situation of positive and negative charge cancellation caused by multiple bending waves on a single piezoelectric patch, and improve the energy utilization rate. The electromechanical coupling model of 2D ABH structure and piezoelectric energy collection circuit was established to study the energy harvesting performance of the plate with 2D ABH structure under transient and steady state conditions. The results show that the 2D ABH structure can effectively increase the frequency width range of vibration energy harvesting and improve energy harvesting efficiency

Numerical Geometric Acoustics: An Eikonal-Based Approach for Modeling Sound Propagation in 3d Environments

Numerical Geometric Acoustics: An Eikonal-Based Approach for Modeling Sound Propagation in 3d Environments

Numerical Simulation of Diffracted U-Shaped Sonic Boom Waveform

U-shaped sonic booms associated with the dive maneuver of a supersonic vehicle are numerically simulated in this paper. Usual prediction tools for ordinary sonic booms are not suitable for such a waveform because of the breakdown of geometrical acoustics near the caustic. In this paper, nonlinear Tricomi equation approach is used near the caustic to take diffraction into account, whereas augmented Burgers equation analysis is applied away from the caustic where geometrical acoustics is applicable. The U-shaped waveforms predicted by this method are in good agreement with measured data. The effects of atmospheric turbulence are also considered by replacing one-dimensional analysis using augmented Burgers equation with multidimensional wave propagation analysis near the ground surface. Results with the atmospheric turbulence effects show better agreement with measured U-shaped waveform than ones without such effects. It is also found that the amplitude of the tail shock wave, which is much larger than the front shock wave, is more sensitive than the front shock to atmospheric turbulence.

A generalized computational approach to predict high-frequency acoustic pressure response of cavity structures for structural health monitoring of wind turbine blades

This paper details the development of a generalized computational approach that enables prediction of cavity-internal sound pressure distribution due to flow-generated noise at high frequencies. The outcomes of this research is of particular interest for development of an acoustics-based structural health monitoring system for wind turbine blades. The methodology builds from existing reduced-order aeroacoustic modeling techniques and ray tracing based geometrical acoustics and is demonstrated on the model NREL 5 MW wind turbine blade as a case study. The computational predictions demonstrated that damage could be successfully detected in the first half of the blade cavity near the root and that the change in frequency content may be indicative of the type of damage that has occurred. This study provides a foundation to analyze specific blades and likely damage cases for determining key factors of system design such as number and placement of sensors as well as for hardware selection.

On the performance investigation of distinct algorithms for room acoustics simulation

The purpose of this research is to investigate the accuracy provided by different algorithms for room acoustics simulation. Three software packages are used to simulate the monaural room impulse responses of a medium-sized concert hall. All algorithms deal with geometrical acoustics but with distinct implementations. The simulated room is one of those adopted as a benchmark for the first round robin on room acoustical simulation and auralization, the last international inter-comparison, for which the geometrical and acoustic data were carefully measured. The main novelty is the inclusion of the software RAIOS, which participated in the round robin but did not finish the simulations in time to be included in the publication. Four acoustical parameters, namely the reverberation time, the early decay time, the clarity factor for music, and the definition for speech, are computed for ten source-receiver pairs at octave band frequencies from 125 Hz to 8 kHz. The results obtained by the three software are then compared with the measured data for all source-receiver positions and frequency bands. The relative mean errors to the just noticeable difference (JND) are also computed. The main findings are that there are deviations relative to the measured results for all software, with some of the parameters being better evaluated than others are. Preliminary insights into the advantages and limitations of the software packages with respect to the monaural impulse response are also given.

3D sound spatialization with game engines: the virtual acoustics performance of a game engine and a middleware for interactive audio design

This study analyses one of the most popular game engines and an audio middleware to reproduce sound according to sound propagation physics. The analysis focuses on the transmission path between the sound source and the receiver. Even if there are several ready-to-use real-time auralization platforms and software, game engines' use with this aim is a recent study area for acousticians. However, audio design needs with game engines and the limits of their basic releases require additional tools (plugins and middleware) to improve both the quality and realism of sound in virtual environments. The paper discusses the use of Unreal Engine 4 and Wwise's 3D audio production methods in a set of different test environments. It assesses their performance in regard to a commercial geometrical acoustics software. The results show that the investigated version of the game engine and its sound assets are insufficient to simulate real-world cases and that significant improvements can be achieved with use of the middleware.

Prediction and analysis of 220kV substation based on geometric acoustic simulation

With the continuous improvement of people's living standards, the city has gradually formed a residential community with high residential density. In order to meet the power demand of the community, each new community basically needs to establish a supporting indoor substation according to the power load of the residents. Considering the residents' electricity habits, the electricity room of the supporting substation in the residential area works 24 hours a day, resulting in frequent noise nuisance incidents. Therefore, the detailed analysis of the indoor noise distribution and the radiated noise from the envelope surface of the substation has a positive significance for the reasonable control of substation noise. In this paper, the method of combining indoor and outdoor simulation is used to predict the 220 kV indoor substation noise. The indoor noise is simulated by Odeon software, and the outdoor noise is simulated by Cadna / a software, the two kinds of software are also based on the virtual sound source and sound ray tracking method of geometric acoustics. Firstly, the noise spectrum of each wall is calculated by Odeon software, and then the noise spectrum is interpolated and attenuated according to the sound insulation spectrum of the composite wall. The calculated spectrum is used as the plane source intensity for noise prediction in Cadna / a software, and finally the noise value of sensitive points at the boundary of substation can be predicted.

Progress and applications of acoustic black holes

<p indent=0mm>The problem of vibration and noise has always been one of the difficulties in the development of society. Therefore, the innovation of vibration and noise reduction methods has never stopped. In recent years, the introduction of acoustic black holes to manipulate flexural waves has become a hot topic in the field of vibration and noise. In this review, the acoustic black hole is defined as a kind of structure which can converge the flexural wave by changing the geometric parameters or material properties. In the absolute ideal case, the flexural wave velocity gradually decreases to zero in the acoustic black hole region. Acoustic black hole structures, as a new kind of flexural wave manipulation technique, can effectively reduce the propagation speed of flexural waves in the structure, thus reducing the reflection at the end of the boundary and forming a region with high energy density. Therefore, it has a broad application prospect in vibration reduction, noise reduction, fluctuation control and energy recovery. Different from the composite structure of vibration reduction and noise reduction in the past, the acoustic black hole has some certain advantages in practical application because of its simple structure, material and preparation process. Up to now, a great deal of theoretical modeling and experimental research has been carried out on the structural form of acoustic black holes, and some certain research results have been obtained. This review first introduces the origin, basic definition and principle of acoustic black holes, then introduces the theoretical calculation and experimental research methods, including frequency domain methods (semi-analytical method, Gauss expansion method, geometric acoustics method, transfer matrix method, finite element method, unit decomposition finite element method, spectral element method, and finite difference method) and wave-number domain method. Additionally, the laser ultrasonic scanning technology is emphasized in the experimental research. Next, the four main functions of acoustic black holes are classified and described, which are vibration reduction, noise reduction, fluctuation control and energy recovery, and the research status and existing problems of each application direction are summarized. The application of acoustic black holes in vibration reduction and noise reduction is becoming more and more comprehensive, and its applications in wave regulation and energy recovery are emerging in recent years. As a new research direction, the basic theory and practical application of acoustic black holes still need to be widely studied further. The breakthrough points include: (1) The acoustic vibration coupling mechanism of acoustic black holes and the matching with functional materials need to be further clarified; (2) the nonlinear wave behavior in acoustic black holes needs to be further improved; (3) according to different engineering scenarios, the bearing integrated design method of acoustic black hole composite structures is developed; (4) theoretical modeling and application development of imperfect acoustic black hole structures. The development of acoustic black holes is also a supplement and broadening to the related research of vibration and noise reduction. From the perspective of social development needs, the related research of acoustic black holes has potential applications in the independent research and development of functional structures and materials.

Filter and correction for a hybrid sound field analysis of geometrical and wave-based acoustics

Filter and correction for a hybrid sound field analysis of geometrical and wave-based acoustics

ABOUT HEAD WAVES AND UNDER-SURFACE LONGITUDINAL WAVES, RADIATED BY THE NORMAL PROBE WHICH IS TAKING PLACE ON A FREE FLAT SURFACE OF THE ELASTIC ENVIRONMENT

On the basis of integrated representations Fourier–Bessel a component of displacement of elastic waves, radiating by the normal converter which is taking place on a free flat surface of the elastic environment, receives analytical estimations of displacement a under-surface longitudinal and head (it is surface-longitudinal) waves. Components of displacement a under-surface longitudinal wave are the sum a component in approximation of geometrical acoustics (GA), the diffraction amendments to this approximation and the amendments which are taking into account influence of feature when the parameter of integrated representation is equal to wave number of a longitudinal wave. Components of displacement of a head wave are defined as the sum appropriate diffraction amendments for a component of displacement of a volumetric longitudinal wave in approximation GA and a component of displacement of a lateral wave. The maximum of amplitude of displacement a under-surface longitudinal wave in angular area of a direction of distribution near to a free surface of environment is caused by one of local maxima of the directivity characteristic of the normal probe. Thus dependence of change of amplitude of this wave of distance wave from the centre of the probe practically corresponds to similar dependence for displacement of a volumetric longitudinal wave in GA approximation. Quantitative estimations of maxima of amplitude of displacement under-surface longitudinal and head waves concerning the greatest amplitude, radiated by the normal probe of a volumetric longitudinal wave.

The use of (bi-)normal modal expansions for modeling sound propagation in the atmosphere

One method for solving the equations of sound propagation in the atmosphere is to expand the propagating acoustic pressure with respect to the eigenfunctions (or modes) of the vertical part of the equations in the frequency domain. In the approximation that the atmosphere is vertically stratified, using an expansion in vertical modes is an implementation of seperation of variables. In the simplest case, the propagation is described by a wave equation with the sound speed depending on altitude. Finding the vertical modes requires that one solve the eigenvalue problem for the resulting vertical operator. When attenuation is included, this operator is not self-adjoint, increasing the complexity of the problem and leading to modes which are not orthogonal, but rather bi-orthogonal: that is, orthogonal to the corresponding modes of the adjoint operator. The use of and methods for obtaining modal expansions for sound propagation in the atmosphere will be discussed, ranging from low frequency audible sound propagating in the nocturnal boundary layer to infrasound propagating in the global atmosphere. If the number of modes required is small, the modes provide a compelling physical picture complimentary to that provided by geometrical acoustics.

Experiences with industrial application of wave-based architectural acoustics simulations

Current state-of-the-art tools for simulation of acoustics in the built environment largely utilize geometrical acoustics technology, such as ray-tracing. Wave-based methods are known to be much more accurate than thatof geometrical acoustics methods with the accurate inclusion of wave-effects such as resonant behavior, diffraction, focusing, and interference, but the computational burden has been the roadblock preventing the practical commercial application. However, recent advancements in both numerical methodology and cloud computing are now enabling the industry to explore the benefits of this technology. In this talk, we will present the findings from multiple case-studies of practical application of a cloud-based wave-based acoustics simulation tool. The case-studies include several real-world industrial projects, but a study of the scenes provided in “GRAS—Ground truth for room acoustical simulation” is also presented. The results are compared to traditional modelling approaches and measurement where available. It is found that there are significant accuracy improvements to be gained from shifting towards the use of wave-based acoustical simulation tools, and with the lower levels of uncertainty, it is assessed that the new methods can enable more efficient and robust design processes in building design.

Development of analytical models for calculating the characteristics of intense acoustic waves propagating in a stratified atmosphere

The time profiles and characteristics of sonic boom waves during propagation in a density-stratified atmosphere are calculated. It is shown that this stratification leads to a significant change in wave parameters: the wave amplitude, the characteristic distances at which the wave transformation is manifested, the width of the shock front. It is shown that the effective role of viscosity decreases when the shock wave propagates down to the earth's surface. So the width of the shock front decreases. Two methods are being developed for analytical calculation. The first one, the nonlinear geometric acoustics approximation, allows obtaining the Burgers equation with a variable viscosity to describe the wave field along the ray. Some exact solutions and asymptotic solution for low viscosity are obtained. This method is not applicable in focusing regions. The second method is based on the application of a modular nonlinearity model. Replacing the quadratic nonlinearity with a modular one allows obtaining a system of linear equations, the solution of which is possible. The difficulty lies in the correct construction of the discontinuity in the profile and subsequent stitching of solutions for different polarities. [This study was supported by the Russian Foundation for Basic Research (Project No. 20-02-00493-a).]

An Archaeoacoustics Analysis of Cistercian Architecture: The Case of the Beaulieu Abbey

The Cistercian order is of acoustic interest because previous research has hypothesized that Cistercian architectural structures were designed for longer reverberation times in order to reinforce Gregorian chants. The presented study focused on an archaeoacacoustics analysis of the Cistercian Beaulieu Abbey (Hampshire, England, UK), using Geometrical Acoustics (GA) to recreate and investigate the acoustical properties of the original structure. To construct an acoustic model of the Abbey, the building’s dimensions and layout were retrieved from published archaeology research and comparison with equivalent structures. Absorption and scattering coefficients were assigned to emulate the original room surface materials’ acoustics properties. CATT-Acoustics was then used to perform the acoustics analysis of the simplified building structure. Shorter reverberation time (RTs) was generally observed at higher frequencies for all the simulated scenarios. Low speech intelligibility index (STI) and speech clarity (C50) values were observed across Abbey’s nave section. Despite limitations given by the impossibility to calibrate the model according to in situ measurements conducted in the original structure, the simulated acoustics performance suggested how the Abbey could have been designed to promote sacral music and chants, rather than preserve high speech intelligibility.

ИНЖЕНЕРНЫЕ ФОРМУЛЫ ДЛЯ ОЦЕНКИ ВЛИЯНИЯ ЕСТЕСТВЕННОЙ КОНВЕКЦИИ У ПОВЕРХНОСТИ ТВС ВВЭР-1000 НА РЕЗУЛЬТАТЫ ИЗМЕРЕНИЯ ЕЕ РАЗМЕРОВ УЛЬТРАЗВУКОВЫМ МЕТОДОМ В БАССЕЙНЕ ВЫДЕРЖКИ АЭС

Engineering formulas are presented for calculating the value of methodological error in measuring the distances from the ultrasonic sensor to the surface of the irradiated fuel assembly of WWER-1000 caused by decay heat from the fuel assembly. The methodical error arises due to the water temperature gradient along ultrasonic wave path. This is due to the presence of natural convection at the surface of the fuel assembly discharged from the reactor into cooling pool at nuclear power plant. The paper presents a methodology for calculating the methodical error. It is assumed that the water temperature between the sensor and the surface of the fuel assembly is determined by convective heat transfer between the fuel assembly and the water in cooling pool at nuclear power plant. The surface of VVER-1000 fuel assemblies is modeled by a flat vertical plate with a uniform surface heat flux. The propagation of an ultrasonic wave in a medium between the surface of a fuel assembly and an ultrasonic sensor is described in the approximation of geometric acoustics. The results of numerical calculations according to the presented method are executed in the form of nomograms. Engineering formulas for calculating the value of methodological error are obtained by processing an array of calculated data. The obtained formulas are used in the development of measuring systems for monitoring the deformation of fuel assemblies of WWER-1000 in cooling pond of nuclear power plant.

A Trial Acoustic Improvement in a Lecture Hall with MPP Sound Absorbers and FDTD Acoustic Simulations

Sound absorbing micro-perforated panels (MPPs) are being increasingly used because of their high quality in terms of hygiene, sustainability and durability. The present work investigates the feasibility and the performance of MPPs when used as an acoustic treatment in lecture rooms. With this purpose, three different micro-perforated steel specimens were first designed following existing predictive models and then physically manufactured through 3D additive metal printing. The specimens’ acoustic behavior was analyzed with experimental measurements in single-layer and double-layer configurations. Then, the investigation was focused on the application of double-layer MPPs to the ceiling of an existing university lecture hall to enhance speech intelligibility. Numerical simulations were carried out using a full-spectrum wave-based method: a finite-difference time-domain (FDTD) code was chosen to better handle time-dependent signals as the verbal communication. The present work proposes a workflow to explore the suitability of a specific material to speech requirements. The measured specific impedance complex values allowed to derive the input data referred to MPPs in FDTD simulations. The outcomes of the process show the influence of the acoustic treatment in terms of reverberation time (T30) and sound clarity (C50). A systematic comparison with a standard geometrical acoustic (GA) technique is reported as well.

Relation between Direction-of-Arrival distribution of reflected sounds in late reverberation and room characteristics: Geometrical acoustics investigation

It has been reported that Direction-of-Arrival (DoA) distribution of reflected sounds is not isotropic in late reverberation. However, it is not clear how room characteristics contribute to the anisotropic DoA distribution. In this paper, the relation between DoA distribution in late reverberation and room characteristics is analyzed by using geometrical acoustic simulation and plane wave decomposition. The computational results showed that the DoA distribution in late reverberation is biased depending on the arrangement of absorptive surfaces and the shape of the room while the source position does not have prominent effects.

The image edge model

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

Sonic Boom: From the Physics of Nonlinear Waves to Acoustic Ecology (a Review)

A history of the topic is presented. First, information is given about the development of supersonic aviation. Then, the history of studying the phenomenon of sonic boom generated by flying bullets and projectiles is briefly described. The results of the renowned aeroacoustic scientists K. Doppler and E. Mach are presented, as well as little-known historical facts found in old foreign sources. The need for correct use of the term “sonic boom” is pointed out, which is not limited to aviation acoustics problems, but is inherent to many natural and technogenic phenomena. A 100-year priority of the acoustic effect over its weaker optical counterpart, Vavilov–Cherenkov radiation, is mentioned. Problems related to calculating the generation of perturbations in the interaction of transonic and supersonic flows with real bodies are described: the need to take into account the details of the shape of the aerodynamic profile, peculiarities in the behavior of the boundary layer, the formation of shock waves, generation of flow turbulence, and the kinetics (relaxation and dissociation) of atmospheric gases. The phenomenon of wave resonance, responsible for the formation of the boom when breaking the sound barrier, is discussed. Nonlinear processes in N-wave formation in the propagation of complexly shaped signal are described. The influence of the main effects distorting the N-shaped profile is explained: diffraction, focusing, and multiple relaxation phenomena broadening the shock front. The theory of N-waves in an inhomogeneous medium is discussed. Examples of ray patterns in a standard atmosphere and in the region behind the turbulent boundary layer are constructed. Calculation methods based on nonlinear geometric acoustics and nonlinear quasioptics approximations are presented. Problems related to the consequences of sonic booms and their harmful effects on the environment, structures, and living organisms are indicated. An extensive bibliography and a list of fundamental reviews in the domestic and foreign literature are presented.