Acoustic Simulation Research Articles

Numerical Investigation and Validation of Noise Sources of a Distributed Propulsion System

This study delves into the exploration of a distributed propulsion system consisting of three co-rotating propellers in front of a high-lift wing system, with a primary focus on understanding its acoustic characteristics. Employing high-fidelity computational fluid dynamics simulations, the flow field is simulated in climb condition. Subsequently, acoustic transport to far-field observers is conducted using the Ffowcs–Williams and Hawkings equation. Because the noise mechanisms of such a configuration are not fully understood yet, several permeable and impermeable surfaces as input for the acoustic simulation are used, aiming to separate the various noise source contributions. Results reveal that in addition to the rotor-alone noise from the propellers, noise arising from propeller–wing interaction emerges as dominant, emitting mostly at the blade passing frequency. Moreover, a boundary element method tool is applied to observe the scattering effect of propeller-generated noise by the wing. Furthermore, this study incorporates consideration of structural components in close proximity to the model, thereby achieving a more realistic acoustic field. With this knowledge, the simulation is validated with experimental data from an open wind tunnel test campaign. An overall good agreement is observed between the simulated and experimental results, substantiating the reliability of both aerodynamic and acoustic predictions.

Treatment envelope of transcranial histotripsy: challenges and strategies to maximize the treatment location profile

A 750 kHz, 360-element ultrasound array has been built for transcranial histotripsy applications. This study aims to evaluate its performance to determine whether this array is adequate for treating a wide range of brain locations through a human skull. Treatment location profiles in 2 excised human skulls were experimentally characterized based on passive cavitation mapping. Full-wave acoustic simulations were performed in 8 human skulls to analyze the ultrasound propagation at shallow targets in skulls with different properties. Results showed that histotripsy successfully generated cavitation from deep to shallow targets within 5 mm from the skull surface in the skull with high SDR and small thickness, whereas in the skull with low SDR and large thickness, the treatment envelope was limited up to 16 mm from the skull surface. Simulation results demonstrated that the treatment envelope was highly dependent on the skull acoustic properties. Pre-focal pressure hotspots were observed in both simulation and experiments when targeting near the skull. For each skull, the acoustic pressure loss increases significantly for shallow targets compared to central targets due to high attenuation, large incident angles, and pre-focal pressure hotspots. Strategies including array design optimization, pose optimization, and amplitude correction, are proposed to broaden the treatment envelope. This study identifies the capabilities and limitations of the 360-element transcranial histotripsy array and suggests strategies for designing the next-generation transcranial histotripsy array to expand the treatment location profile for a future clinical trial.

An in-air synthetic aperture sonar dataset of target scattering in environments of varying complexity

This paper describes a synthetic aperture sonar (SAS) dataset collected in-air consisting of four types of targets in four environments of different complexity. The in-air laboratory based experiments produced data with a level of fidelity and ground truth accuracy that is not easily attainable in data collected underwater. The range of complexity, high level of data fidelity, and accurate ground truth provides a rich dataset with acoustic features on multiple scales. It can be used to develop new signal-processing and image reconstruction algorithms, as well as machine learning models for object detection and classification. It may also find application in model verification and validation for acoustic simulators. The dataset consists of raw acoustic time series returns, associated environmental conditions, hardware configuration, array motion, as well as the reconstructed imagery.

Influence of variable sound-absorbing devices on room acoustical parameters of reverberation and intelligibility in medium-to-large multipurpose halls.

Multipurpose halls are designed to host various performances. However, achieving the ideal reverberation time (RT) for each of the different performance types can be challenging. This study investigates five halls of various sizes to determine the effects of sound-absorbing devices on variable RTs in multipurpose halls. The composition and sound absorption properties of the finishing materials were investigated in areas where sound-absorbing devices were not applied. Further, the changes in the room acoustic parameters of these medium-sized multipurpose halls were analyzed using computer-based acoustic simulations to find a suitable answer among the various solutions tested. By applying sound-absorbing devices (resonant-type) to 25% of the walls and ceilings of the target halls, the absorption and reflection modes displayed a variability range of more than 0.5 s in the bass-mid frequency (250-500 Hz). However, a variable range of 0.18 s was found in the high frequency (2000 Hz). To improve the low variable range in the high frequency, a partial application of a high-frequency high-performance sound absorption banner (porous-type) was used to secure a variable range of 0.35 s in the high frequency. Variable sound-absorbing devices should be considered to achieve effective RT variation for all frequencies.

Seafloor Topographic Data Processing in Near-Seafloor Acoustic Field Simulation

Near-seafloor acoustic field characteristics are essential prior knowledge for near-seafloor underwater acoustic engineering. Scholte waves are a crucial component of the near-seafloor acoustic fields. These fields, when considering Scholte waves, are susceptible to seafloor relief. However, open-source bathymetric datasets generally lack sufficient precision. Therefore, acoustic field simulations using open-source data can contain significant errors or even introduce erroneous propagation characteristics. The spectral element method (SEM) is an example of exploring the influence of an inadequate spatial-sampling rate and sea-depth precision on acoustic field simulations. In this article, appropriate methods for topographic processing are presented. The results indicate that the terrain can be corrected using cubic spline interpolation in cases of an inadequate spatial-sampling rate. Where there is insufficient sea-depth precision, this study proposes a terrain processing method. The first step involves sequentially determining the interpolation points for the rising and falling edge, depressions, bulges, and horizontal segments. Then, it adopts cubic spline interpolation. The SEM examples effectively verify this effect. Given the limited research on terrain correction in acoustic field simulations, this study introduces a low-complexity method that can effectively support exploring acoustic fields affected by seafloor terrain.

Employing deep learning model to evaluate speech information in acoustic simulations of Cochlear implants

Acoustic vocoders play a key role in simulating the speech information available to cochlear implant (CI) users. Traditionally, the intelligibility of vocoder CI simulations is assessed through speech recognition experiments with normally-hearing subjects, a process that can be time-consuming, costly, and subject to individual variability. As an alternative approach, we utilized an advanced deep learning speech recognition model to investigate the intelligibility of CI simulations. We evaluated model’s performance on vocoder-processed words and sentences with varying vocoder parameters. The number of vocoder bands, frequency range, and envelope dynamic range were adjusted to simulate sound processing settings in CI devices. Additionally, we manipulated the low-cutoff frequency and intensity quantization of vocoder envelopes to simulate psychophysical temporal and intensity resolutions in CI patients. The results were evaluated within the context of the audio analysis performed in the model. Interestingly, the deep learning model, despite not being originally designed to mimic human speech processing, exhibited a human-like response to alterations in vocoder parameters, resembling existing human subject results. This approach offers significant time and cost savings compared to testing human subjects, and eliminates learning and fatigue effects during testing. Our findings demonstrate the potential of speech recognition models in facilitating auditory research.

Optimization of speech intelligibility in street-facing rooms of adult care home based on acoustic simulation

Due to the limited availability of urban land in China, many adult care facilities have resorted to constructing roadside living spaces. However, this has led to a significant issue of traffic noise disturbance. Besides, many rooms lack of control over indoor reverberation. As a result, the communication efficiency of the residents might be greatly impacted. This study aims to investigate the impact of traffic noise level, room size, and surface sound absorption on speech transmission index (STI), based on a typical room layout and conducted using acoustic simulation. The simulation results indicated that in order to achieve the required STI over 0.79 for elderly residents, it is imperative to control the road noise interference below 40 dBA and ensure that the room reverberation time under 0.42 s. To achieve this, it is recommended that for a road with a noise emission level of 72 dBA, the distance between the roadside room and the road should not less than 10 m. Additionally, windows with Rw+Ctr over 28 dB without road sound barriers (over 20 dB with sound barriers) should be installed. Besides, the room area needs to be controlled within 20 m2 and an acoustic ceiling with NRC>0.65 should be installed.

Hydro-acoustic numerical methodology to compute noise generated by perforated plates in duct systems

The paper presents an innovative numerical methodology to determine hydro-acoustic behavior of perforated plates. One of the main objectives is to have a methodology that ensures a good prediction of radiated noise in ducts with a limited computational cost. The initial assessment is carried out considering the entire perforated plate. The acoustic source is determined by applying Lightill Analogy to the CFD results from LES for the whole perforated plate. An acoustic simulation is then performed to determine the dynamic pressure in the duct on either side of the perforated plate. An experimental set-up is built in order to obtain the noise generated by the perforated plate. It also allows to assess the validity of the established method. A good correlation is observed in terms of dynamic pressure upstream and downstream the perforated plate. An optimization of the method is then carried out to reduce the computational time by determining the acoustic source generated by a unit hole. This source is then applied in the acoustic simulation to each hole of the perforated plate. Comparison with measurements is also satisfactory for this simplified method.

Accounting for the vehicle influence on tyre noise through acoustic simulation based on equivalent monopole sources

Road traffic noise poses a risk to human health and amongst the different noise sources, tyre-road interaction plays a fundamental role. Due to the regulations introduced to limit noise levels, tyre manufacturers are committed to design acoustically optimized tyres. In this context, a numerical-experimental approach for including vehicle influence on tyre noise has been investigated. As a first step, equivalent monopole sources are identified based on the measurements of the radiated sound field of a rolling tyre in a semi-anechoic chamber. In a second step, the same sound sources are then employed for the prediction of sound propagation when tyres are mounted on a vehicle, which is included in the acoustic simulation. Finally, a validation against indoor experimental measurements is performed, yielding promising results.

Evaluating the effect of dome geometry on acoustical quality of a pavilion

Acoustic performance of structures is an emerging field of research enquiry, with limited number of studies conducted in the Indian context. To address this gap, this study examines the effect of varied dome geometry on the acoustic quality of a pavilion. In-situ measurements pertaining to energy decay curve from impulse sound were collated at a historical 'Baradari'. The square shaped pavilion considered in the study is surmounted by a shallow dome and has three doorways on each side. Virtual simulation models of the pavilion were built thereafter and validated. In this study, dome geometries that emerged between the 15th-19th century (corbelled, shallow, single-shell, bulbous, and onion) in the Indian subcontinent are examined. Acoustic simulation was conducted on treble software to assess and compare the sound quality of each dome geometry. The study found that the reverberation, RT30, for the flat dome was approximately half to that of the single-shell dome. The study established that the choice of dome geometry is crucial as it impacts the reverberation time. The study findings vary with building typology, size, and architectural features. Nevertheless, this study should be viewed as a case-specific analysis that identifies optimal dome geometry for improved pavilion acoustics.

The crossover frequency of acoustic simulation for small-scale enclosures by wave and statistic based methods

In the field of room acoustic simulation, wave-based and statistical numerical methods are pivotal for acquiring sound field characteristics. Although the Schroeder Frequency has been utilized to deduce the suitable frequency range of these methods in large enclosures, the crossover frequency warrants further investigation for the small-scale enclosures with complicated inner structures, such as car cabins. This work aims to explore the applicable frequency range of these acoustic simulation methods for a small-scale model, which means identifying the crossover frequency between wave-based Finite Element Method (FEM) and statistical Ray Tracing Method (RTM). First, the crossover frequency was analyzed by the Schroder Frequency equation and modal density estimated from the room transfer functions (RTFs) in a simplified car model, which considering the interior with and without seat occlusion. Further, the crossover frequency was validated by comparing the magnitude spectra of RTFs simulated by FEM and RTM. This work provides a foundational frequency reference for applying statistical acoustic methods in small-scale enclosures.

Enabling large-scale and high-precision fluid simulations on near-term quantum computers

Quantum computational fluid dynamics (QCFD) offers a promising alternative to classical computational fluid dynamics (CFD) by leveraging quantum algorithms for higher efficiency. This paper introduces a comprehensive QCFD method, including an iterative method “Iterative-QLS” that suppresses error in quantum linear solver, and a subspace method to scale the solution to a larger size. We implement our method on a superconducting quantum computer, demonstrating successful simulations of steady Poiseuille flow and unsteady acoustic wave propagation. The Poiseuille flow simulation achieved a relative error of less than 0.2%, and the unsteady acoustic wave simulation solved a 5043-dimensional matrix. We emphasize the utilization of the quantum–classical hybrid approach in applications of near-term quantum computers. By adapting to quantum hardware constraints and offering scalable solutions for large-scale CFD problems, our method paves the way for practical applications of near-term quantum computers in computational science.

Empirical method for predicting speech sound propagation in offices

The room acoustic parameters of ISO 3382-3 allow for an evaluation of sound propagation and speech intelligibility in open-plan offices and have increasingly been used in the planning process since their introduction in 2012. The input parameters are the speech sound pressure levels and the speech transmission indices at the workstations along a measurement path including a sound source (imaginary speaker). ISO 3382-3 is a measurement standard - a calculation method is not defined. However, it is possible to calculate the necessary input data, namely the speech sound pressure levels and the speech transmission indices, using room acoustic computer simulations. Although computing power is no longer a limiting factor today, the modeling and verification of computer models are still complex and correspondingly time and cost intensive. Hongisto and Keränen (2013, 2015) describe a model for predicting the ISO 3382-3 parameters. In this study, this prediction model was tested using measurement data from several open-plan offices in Germany. Recommendations for the application of the model are derived from preliminary investigations, and the limitations and boundaries of the method are further specified.

Optimizing a small room for critical listening with Treble

This work presents a detailed validation of new software Treble launched in 2023 that hybridizes the discontinuous Galerkin method and pressure-based geometrical acoustics methods. We investigated a small studio for voice productions both through physical measurements and treble's room acoustic simulations. By employing a dense measurement grid with a spacing of 25 cm at the ear level, a comprehensive validation of the room acoustic simulation was conducted in terms of room impulse responses, transfer functions, ISO 3382 acoustic parameters and sound pressure level distribution. Treble's simulation successfully predict the room modes, ISO 3382 acoustic parameters as well as the sound level distribution. The study demonstrates the impact of speaker positions, particularly regarding their interaction with boundary surfaces and how this can be planned with the simulation.

A pilot study: developing acoustic model for immersive environment

In the landscape of higher education in Malaysia, the adoption of immersive technologies still in its infancy, particularly within the field of building science education. This research endeavors to elevate the learning experiences of Indoor Environmental Quality (IEQ) concepts, with a specific focus on lighting and acoustics. The ongoing study seeks to revolutionize current learning methodologies by converting traditional modules into an immersive virtual environment, offering learners an interactive, and sensory-rich experience with the subject matter. To ensure the effectiveness of the acoustic immersive environment, this paper prioritizes the initial step of developing the acoustic simulation model. In an early pilot study, on-site measurements of sound pressure levels were recorded at various points within a basic classroom setting and an acoustic model will be developed subsequently. Consequently, the alignment between the developed acoustic model and real-world physical measurements establishes a solid foundation for the subsequent calibration process, during which the acoustic model will be tailored to meet VR-ready specifications delve into immersive environment model. This finding ensures a seamless transition of real-world acoustic conditions into the virtual realm, amplifying the authenticity and educational impact of the VR learning experience, thereby contributing to the advancement of immersive technologies in higher education.

Striking the right note: balancing AVAS in tomorrow's soundscapes

Soundscapes of tomorrow are defined now. Not just a mobile sonic brand signature, the AVAS is also an attention grabber and an imposed alert. The method invoked for its design must be collaborative and involve the brand, designers, marketers, stakeholders, but also drivers, residents and question its position in the soundscape. Defining the aesthetic with a shared semantic, listening, testing, in simulation, on road, with people, with sensors; any sound design should be the result of a collaborative process because it talks to people, improve the perceived quality of products, and improve the quality of life. If well made. Also AVAS sound is also regulated by international standards that are defining boundaries in the selection of the right sound. The signal emitted by the AVAS loudspeaker should follow these rules, in terms of minimum level and spectrum content at specific pedestrians' locations around the car. The simulation of the propagation of the sound from the loudspeaker to these positions in early phase of the design is important to avoid big design mistake. 3D acoustic simulations using FE acoustic software Actran and dedicated post-processing for AVAS are performed to confirm the correct location of loudspeaker and spectral content.

Adaptation and evaluation of Pyroomacoustics for auralization purposes

An open-source room simulation software that relies on geometrical acoustics - Pyroomacoustics - was used to compute Binaural Room Impulse Responses (BRIRs) of existing rooms that are modeled in the Benchmark for Room Acoustical Simulation (BRAS). Modifications were made to the software to investigate the impact of the scattering model on the acoustic parameter values. A comparison with the acoustic parameter measurements showed that the values of EDT, C80 and D50 were found to be closer when using the Vector-Mixing method in comparison with the original scattering method. Overall, the alternative method reduced by 95% the mean squared error on the acoustic parameter values. The sound source directivity was also considered in the simulations to quantify its influence on the perceived auditory scenes. A listening test was then conducted to compare binaural renderings derived from measured and simulated BRIRs. Results showed that ratings of the modified versions of the software were either not significantly different or significantly higher than those of the original version depending on the room and sound source. Including the source directivity significantly improved the perceptual ratings, which is thought to be due to the reduction of spectral and loudness differences with the measured reference.

Empirical validation and engineering model comparison of outdoor long-range 3D GPU FDTD acoustic simulations with turbulence

We build upon previous work which introduced an acoustic GPU-accelerated 3D Finite-Difference Time-Domain solver, Empapu, equipped with a dynamic moving frame and turbulence modeled as a position-dependent refractive index for long-range outdoor sound propagation simulations. This physics-based model would serve as a benchmark to assess different engineering models, e.g., ISO 9613-2, CNOSSOS-EU and sonX, in the presence of uneven terrain with different ground properties and an inhomogeneous atmosphere. The solver now integrates an improved model of turbulence reproducing the kinetic spectral energy of velocity fluctuations, derived from wind velocity fields, with an eddy (quasiwavelet) approach, relevant in long-range propagations. This study validates our model by comparing level differences in third-octave band spectra at receiver points up to 300 m to analytical methods and measurements in a mostly flat topography comprised of asphalt and grassland. Further analysis is done by comparing results in different locations in Switzerland in the presence of uneven ground and barriers. This work will provide a physics-based basis for evaluating and comparing engineering models for outdoor sound propagation in lieu of measurements.

A tool to calculate the reverberation time of rooms with uneven absorption distribution

The reverberation time in rectangular rooms with uneven distribution of absorbing elements and surfaces, for example suspended ceilings, lead to a non-diffuse sound field. This implies longer reverberation times than predicted by sabines or eyrings reverberation formula. To enable a correct prediction of the reverberation times in such rooms, the only possibility was to apply room acoustic simulations, which require high effort to model the room and to perform the simulation. In 2021, a prediction method was published by Zhou et. al. to calculate the reverberation time in such rooms much more precisely than using sabines or eyrings formula, without the need for a room acoustic simulation. This method has been transformed into an online calculation tool, named "reverberate". In this contribution the methodology will be quickly reviewed and the online tool will be presented.

Optimised implicit methods for audio rate wave-based acoustic simulation

Wave-based room acoustic computation at an audio rate (i.e., covering the complete range of audible frequencies) is computationally intensive. There is thus a great incentive to develop simulation methods that allow for "accurate" simulation at the lowest possible computational cost, taking into account requirements for massively parallel implementation. Though often formal measures of order of accuracy are employed, in this paper, we examine the optimisation of a locally-defined implicit family of schemes against wideband measures of accuracy, based on the minimisation of numerical dispersion over a specified frequency range. The resulting optimised scheme is defined over a Cartesian grid, and allows performance gains over standard schemes (such as the basic rectilinear scheme, or schemes defined over face-centered cubic grids, and other implicit designs presented in the literature). Numerical stability conditions are easily formulated, and can be built into the optimisation, alongside the computational cost of linear system solution. Simulation results and comparisons of computation times against other known methods are presented.