Acoustic Domain Research Articles

An analytical dynamic stiffness method for efficient broadband vibro-acoustic analysis of complex built-up structures

An analytical modelling technique is presented, combining the dynamic stiffness method (DSM) with the spectral DSM (SDSM) for the broadband vibro-acoustic analysis of complex built-up structures. In particular, the structures are modelled exactly by the DSM based on particular solutions tailored for general acoustic or distributed force excitations; whereas the acoustic cavities are modelled by the SDSM where the boundary conditions are described by modified Fourier series with a rapid convergence rate. The vibro-acoustic coupling along the interfaces between the structures and the cavities is achieved by applying the normal velocity continuity condition, leading to a coupling matrix in an analytical manner. Both structural and acoustic cavity elements are assembled directly to model complex vibro-acoustic systems and no extra element discretization is required for both structural and acoustic domains. Consequently, the proposed method uses very few degrees of freedom (DoFs) but describes the broadband vibro-acoustic behaviour highly accurately. It is demonstrated that the proposed method exhibits a predominant advantage over the finite element package COMSOL in terms of accuracy and computational efficiency. This approach also has the potential to serve as the benchmark for a wide range of vibro-acoustic problems.

Design optimization of phononic-fluidic resonator systems

Phononic-fluidic resonators utilize an acoustic fluid domain as a defect inside a solid metamaterial lattice, which can be used used to precisely measure acoustic properties of liquids. The design goal is to offer ideal boundary conditions for the acoustic resonator by matching defect resonance with phononic band gap. The design space of metamaterial or phononic crystal and fluidic resonator is nearly unlimited, especially when utilizing fully three-dimensional structures. In this work, we explore numerical shape and topology optimization to focus acoustic energy into the fluid domain and maximize the quality factor of the defect resonance. This requires the use of complex multi-frequency objective functions, while taking into account practical limits such as finite size and losses in the fluid and solid domains. Results highlight notable but limited improvements of quality factor with shape optimization starting from an initial design constrained by the maximum deformation possible. On the other hand, topology optimization results offer unique and unexpected ideas, and thus a deeper dive into the design space.

Simplification of Johnson-Champoux-Allard-Lafarge model on fibrous materials

The Johnson-Champoux-Allard-Lafarge (JCAL) model, a pivotal framework in acoustics for analyzing sound absorption in fibrous materials, presents challenges in practical implementation due to its complexity. This paper introduces a refined variant of the JCAL model explicitly tailored for fibrous materials, aiming to balance accuracy and computational efficiency. The proposed model retains essential physical principles while simplifying computational intricacies, enhancing its usability for real-time applications and large-scale simulations. Through comprehensive validation against experimental data, we demonstrate the efficacy of the simplified model in accurately characterizing the sound absorption behavior of fibrous materials. This study contributes to advancing the practical applicability of the JCAL model, facilitating its broader adoption across various acoustic engineering domains. The proposed simplification approach holds promise for accelerating research and development in sound absorption materials and acoustic design methodologies within scientific and engineering communities.

Introducing the concept of acoustic personalised environmental control systems (Acoustic PECS) within the framework of IEA EBC Annex 87

The availability of systems that can locally adjust environmental parameters holds the potential to enhance building occupant satisfaction by considering individual sensitivities, expectations, and needs. To this aim, Personalised Environmental Control Systems (PECS) are being studied as solutions that can provide individually controlled environments in the immediate surroundings of an occupant, without affecting directly the entire space and other occupants' environment. The concept has been primarily developed to address individual control of the thermal environment and perceived air quality, as in chairs with heating/cooling functions and desks equipped with personalized ventilation systems. By extending the concept of PECS to the acoustic domain, a framework on Acoustic PECS is here introduced and exemplified. The study builds on ongoing research within the IEA EBC - Annex 87, dedicated to investigating the Energy and Indoor Environmental Quality Performance of Personalised Environmental Control Systems.

Robotic arm, 3D vision and geometric matching for an efficient implementation of inverse Patch Transfer Function method

The inverse patch transfer function method was developed to reconstruct the acoustic fields (velocity, pressure, intensity) at the surface of a vibrating source with a complex geometry using the concept of a virtual acoustic domain. This method can be used to manage sources with complex shapes in a non-anechoic acoustic environment, even in the presence of masking objects. However, this method is quite demanding experimentally as it requires a large number of measurement positions with good spatial positioning accuracy. This article presents a dedicated experimental platform developed to simplify and automate the entire measurement process. First, a 3D camera placed on a robotic arm constructs a point cloud characterising the source and its environment. Using a geometric matching algorithm, the CAD of the object under test is detected in the cloud of points, enabling the different coordinate systems (CAD, robot and physical part) to be matched. Secondly, the measurement points required to apply iPTF can be defined directly in the CAD and reproduced in near-real time on the test rig, regardless of the type of antenna used, providing an efficient means of applying iPTF and opening the way to many advanced applications.

Global prediction and analysis for helicopter noise footprint based on acoustic modes.

Aiming to address the significant external noise produced by helicopter rotors, an integrated process based on acoustic modes has been developed for predicting the global noise footprint. The proposed method has the advantages of global prediction, analysis, and low computational costs. The key steps involve constructing an acoustic modal database and efficient prediction of noise footprint. First, the global noise model is utilized to map the time-domain sound pressure to amplitudes and coefficients in the acoustic modal domain. Acoustic mode coefficients representing various flight states are systematically cataloged in the database. Subsequently, the coefficients are extracted based on the characteristic parameters of trajectory elements, allowing for the evaluation of noise radiation in the acoustic modal domain. To investigate the impact of descent angle and advance ratio on the noise footprint, a simulation study is conducted in the forward and approach flight with an AS350 helicopter. Results indicated that, for a region with 1800 observers, the computational time of the developed approach requires only one-fifth of the time compared to the traditional Rotorcraft Noise Model method. This remarkable reduction in computation time, along with the global predictive capability, supports the practicality of efficient noise footprint assessment in both military and civilian contexts.

Effects of Mach number on space-time characteristics of wall pressure fluctuations beneath turbulent boundary layers

Wall pressure fluctuations beneath turbulent boundary layers are a fundamental source of aerodynamic noise by exciting the wall structure, with their space-time characteristics serving as the basic ingredient for predicting the wall structural response. To this end, direct numerical simulations of fully developed compressible turbulent boundary layers at Mach numbers of 0.5, 1.2, and 2.0 are conducted to investigate wall pressure fluctuations comprehensively. The effects of Mach number on the single-point statistics of wall pressure fluctuations, such as the root mean square, skewness and flatness factors, probability density function, and frequency spectrum, are assessed to be very weak. Regarding the space-time characteristics, the convection velocity Uc determined by the space-time correlation of wall pressure fluctuations increases slightly with the Mach number, which only reflects the convective behavior of turbulent vortices. On the wavenumber–frequency spectrum, characteristic peaks of both the acoustic wave and convective vortices are identified. At Mach 0.5, the peaks of the fast (Uc+c) and slow (Uc−c) acoustic waves are unattached to others with c denoting acoustic speed, while only the peak of the fast acoustic wave is distinguishable from the convective peak at Mach 1.2 and 2.0. Due to the aerodynamic heating at supersonic conditions, the thermal effect on acoustic speed should be taken into account in determining the acoustic wavenumber. By introducing a convective Prandtl–Glauert parameter, a refined relation is proposed to provide a more accurate depiction of the acoustic domain in the wavenumber–frequency spectrum.

Interior three-dimensional acoustic modeling and modal analysis using wavelet-based finite-element approach.

This paper introduces two-dimensional (2D) and 3D acoustic modeling and modal analysis using the wavelet finite-element method (WFEM). Governed by the Helmholtz equation, the acoustic domain is parameterized and analyzed using the scaling functions of B-spline wavelets, which facilitates the construction of elements with varying numbers of nodes via multi-resolution analysis. The wavelet-based shape functions provide a semi-orthogonal basis that enables rapid searching for approximate solutions in Lebesgue spaces, thereby offering significantly reduced interpolation errors and computational burden. Numerical examples are considered using WFEM, comprising a 2D acoustic problem involving a tube for predicting acoustic pressure and eigenfrequency investigations, and 3D acoustic problems involving a cubic room and an L-shaped room for capturing acoustic characteristics. The results are compared with those of (i) standard FEM with the same mesh and (ii) analytical solutions. Importantly, WFEM demonstrates stability by being insensitive to internal mesh size variations, indicating that B-spline wavelet elements have minimal effects on the numerical results. Furthermore, B-spline wavelet elements effectively control the pollution (dispersion) error of numerical methods when imposing Neumann boundary conditions in the high-frequency range, and they reduce interpolation errors caused by polynomial interpolation in the low-frequency domain.

History and variations of Lindsay's wheel of acoustics: From a nested pie chart including words to a drawn acoustics world

In 1964, Robert Bruce Lindsay introduced “The Science of Acoustics,” a graphical representation that has become popular and is often called the Wheel of Acoustics. This communication first recalls the historical context and initial versions of this representation. Adaptations to its original design are then introduced. Some follow the idea of a wheel representation but focus on specific acoustic domains or perceptual descriptions of sound. Other adaptations propose a slightly modified arrangement of the wheel's elements while including icons to illustrate covered topics. We introduce a wheel that blends realistic and iconic representations following a primarily hand-drawn and artistic vision. This visual tool can be used for acoustics teaching and popularization to improve audience engagement and provide more in-depth and concrete examples. The Drawn Acoustics World is provided in English and French versions, and also in a text-free version that can be used to adapt to any language.

A deep learning method for reflective boundary estimation

Environment estimation is a challenging task in reverberant settings such as the underwater and indoor acoustic domains. The locations of reflective boundaries, for example, can be estimated using acoustic echoes and leveraged for subsequent, more accurate localization and mapping. Current boundary estimation methods are constrained to high signal-to-noise ratios or are customized to specific environments. Existing methods also often require a correct assignment of echoes to boundaries, which is difficult if spurious echoes are detected. To evade these limitations, a convolutional neural network (NN) method is developed for robust two-dimensional boundary estimation, given known emitter and receiver locations. A Hough transform-inspired algorithm is leveraged to transform echo times of arrival into images, which are amenable to multi-resolution regression by NNs. The same architecture is trained on transform images of different resolutions to obtain diverse NNs, deployed sequentially for increasingly refined boundary estimation. A correct echo labeling solution is not required, and the method is robust to reverberation. The proposed method is tested in simulation and for real data from a water tank, where it outperforms state-of-the-art alternatives. These results are encouraging for the future development of data-driven three-dimensional environment estimation with high practical value in underwater acoustic detection and tracking.

Influence of Immersion Time on the Frequency Domain Characteristics of Acoustic Emission Signals in Clayey Mineral Rocks.

The frequency domain characteristics of acoustic emission can reflect issues such as rock structure and stress conditions that are difficult to analyze in time domain parameters. Studying the influence of immersion time on the mechanical properties and acoustic emission frequency domain characteristics of muddy mineral rocks is of great significance for comprehensively analyzing rock changes under water-rock coupling conditions. In this study, uniaxial compression tests and acoustic emission tests were conducted on sandstones containing montmorillonite under dry, saturated, and different immersion time conditions, with a focus on analyzing the effect of immersion time on the dominant frequency of rock acoustic emission. The results indicated that immersion time had varying degrees of influence on compressive strength, the distribution characteristics of dominant acoustic emission frequencies, the frequency range of dominant frequencies, and precursor information of instability failure for sandstones. After initial saturation, the strength of the rock sample decreased from 53.52 MPa in the dry state to 49.51 MPa, and it stabilized after 30 days of immersion. Both dry and initially saturated rock samples exhibited three dominant frequency bands. After different immersion days, a dominant frequency band appeared between 95 kHz and 110 kHz. After 5 days of immersion, the dominant frequency band near 0 kHz gradually disappeared. After 60 days of immersion, the dominant frequency band between 35 kHz and 40 kHz gradually disappeared, and with increasing immersion time, the dominant frequency of the acoustic emission signals increased. During the loading process of dry rock samples, the dominant frequency of acoustic emission signals was mainly concentrated between 0 kHz and 310 kHz, while after saturation, the dominant frequencies were all below 180 kHz. The most significant feature before the rupture of dry rock samples was the frequent occurrence of high frequencies and sudden changes in dominant frequencies. Before rupture, the characteristics of precursor events for initially saturated and immersed samples for 5, 10, and 30 days were the appearance and rapid increase in sudden changes in dominant frequencies, as well as an enlargement of the frequency range of dominant frequencies. After 60 days of immersion, the precursor characteristics of rock sample rupture gradually disappeared, and sudden changes in dominant frequencies frequently occurred at various stages of sample loading, making it difficult to accurately predict the rupture of specimens based on these sudden changes.

A novel smart hybrid multimorph piezoelectric spherical shell cloak for broadband near-perfect underwater acoustic camouflage applications

Non-visual auditory camouflage plays a major role in the art of underwater deception. In this work, a hybrid active/semi-active omnidirectional cloaking shell structure composed of alternate complementary piezoelectric and smart viscoelastic (PZT/SVE) actuator layers is proposed that can effectively conceal a three dimensional underwater macroscopic object from broadband incident sound waves. The smart hybrid structure incorporates a finite sequence of fully active parallel-connected multimorph PZT constraining layers inter-stacked with semi-active SVE core layers both of which are collaboratively operative in the framework of a Particle Swarm Optimized (PSO) multiple-input multiple-output active damping control (MIMO-ADC) scheme. The elasto-acoustic modeling of the problem is conducted by coupling the spatial state space methodology based on the classical three-dimensional exact piezoelasticity theory with the wave equations for the inner and outer acoustic domains. The acoustic cloaking performance of proposed configuration is evaluated for four distinct classes of highly functional SVE interlayer materials with tunable (field-dependent) rheological properties, namely, magnetorheological elastomer (MRE), shape memory polymer (SMP), electrorheological fluid (ERF), and magnetorheological shear thickening polishing fluid (MRSTPF). Extensive numerical results reveal significant broadband reductions of the far-field backscattering amplitude in the (f∞θ=π,kexRex)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\left|{f}_{\\infty }\\left(\ heta =\\pi ,{k}_{\ ext{ex}}{R}_{\ ext{ex }}\\right)\\right|)$$\\end{document} as well as the percentage error of external cloaked field (%Err)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(\\%\ ext{Err})$$\\end{document} by incorporating a sufficient number of smart multimorph PZT/SVE material layers. Furthermore, it is concluded that comparable low frequency acoustic cloaking effects is possible without expenditure of any external energy just by employing the entirely inactive MRSTPF-based cloak as an alternative to the semiactive or fully active multimorph PZT/SVE cloaks. The outcome of proposed study can advantageously serve as the first step towards practical development and experimental implementation of future high performance smart acoustic cloaking devices with expanded broadband near-perfect omnidirectional invisibility for three dimensional objects of diverse geometries.

Two-dimensional sound pressure distribution: Visualization and calibration-free quantification via optical wave microphone CT scanning

In recent years, the optical wave microphone has emerged as an innovative technique, employing Fraunhofer diffraction of a laser beam, and shows promising applications in various acoustic domains where high electric and/or magnetic fields preclude the use of traditional microphones. This study utilized an optical wave microphone computed tomography (CT) scan and calibration-free quantification to ascertain sound pressure levels at multiple distances from the ultrasonic oscillator. The cornerstone of this study, which is different from the author’s previous studies, is the quantification of sound pressure distribution via a theoretical model that encompasses all physical parameters pertinent to the optical wave microphone’s experimental arrangement. This method has proven effective in visualizing and quantifying the two-dimensional sound pressure distribution emitted by an ultrasonic oscillator (40 kHz) without the necessity for calibration. The results demonstrate that the sound pressure distribution determined using the calibration-free optical wave microphone CT scan is in good agreement with the measurements obtained through a condenser microphone.

Deep learning-assisted structural health monitoring: acoustic emission analysis and domain adaptation with intelligent fiber optic signal processing

Structural health monitoring aims to detect damage progression in materials. This study focuses on categorizing crack stages, a critical aspect of monitoring structural integrity. By leveraging acoustic emission (AE) monitoring, cracks can be analyzed in a data-driven manner. However, applying AE analysis poses several challenges, including discrepancies between simulated AE data from models and experimental data from the field, as well as class imbalance in crack progression data, with a scarcity of late-stage data. To bridge the gap between theory and experiments, our approach employs domain adaptation to synchronize simulated and actual AE data. The model learns robust domain-invariant features through meticulous experimentation across training epochs. Quantitative analysis of the model’s performance provides key insights. F1 scores vary with feature counts, and domain adaptation outperforms by 20% on highly imbalanced datasets. This emphasizes the model’s adaptability for precise crack classification, even with underrepresented damage classes. In summary, this study advances structural health monitoring by offering a solid AE analysis approach. Core contributions include reconciling simulated and experimental data discrepancies, tackling class imbalance, optimizing feature extraction, and demonstrating robust crack stage categorization. The insights gained highlight the merits of domain adaptation and data-driven AE analysis for predicting crack progression.

Extension of optical radiation pressure force exerted on rigid sphere by non-diffracting beams to acoustical domain

Extension of optical radiation pressure force exerted on rigid sphere by non-diffracting beams to acoustical domain

Particle transport along the circular trajectory of a semi-infinite Bessel acoustic beam

We explored the propagation of semi-infinite accelerating Bessel beams along circular trajectories beyond the paraxial approximation. Until now, the complex nature of these beams has posed a challenge for the development of construction methods, resulting in primarily theoretical research within the field of acoustics. In this study, we successfully achieved experimental realization of these beams in the acoustic domain using our previously proposed acoustic Fourier transform system, which involves phase modulation through a holographic lens and Fourier transformation through a cylindrical focusing reflector. Our results demonstrate that these beams exhibit accelerated propagation along circular trajectories. Moreover, we experimentally generated and directly observed these highly curved beams during the transportation of micro-particles, where they undergo substantial bending at large angles.

On-chip quasi-light storage for long optical delays using Brillouin scattering

Efficient and extended light storage mechanisms are pivotal in photonics, particularly in optical communications, microwave photonics, and quantum networks, as they offer a direct route to circumvent electrical conversion losses and surmount bandwidth constraints. Stimulated Brillouin Scattering (SBS) is an established method to store optical information by transferring it to the acoustic domain, but current on-chip SBS efforts have limited bandwidth or storage time due to the phonon lifetime of several nanoseconds. An alternate approach known as quasi-light storage (QLS), which involves the creation of delayed replicas of optical data pulses via SBS in conjunction with a frequency comb, has been proposed to lift the storage time constraint; however, its realization has been confined to lengthy optical fibers, constraining integration with on-chip optical elements and form factors. Here, we present an experimental demonstration of QLS on a photonic chip leveraging the large SBS gain of chalcogenide glass, achieving delays of up to 500 ns for 1 ns long signal pulses, surpassing typical Brillouin storage processes' acoustic lifetime by more than an order of magnitude and waveguide transit time by two orders of magnitude. We experimentally and numerically investigate the dynamics of on-chip QLS and reveal that the interplay between the acoustic wave that stores the optical signal and subsequent optical pump pulses leads to a reshaping of the acoustic field. Our demonstrations illustrate the potential for achieving ultra-long storage times of individual pulses by several hundred pulse widths, marking a significant stride toward advancing the field of all-optical storage and delay mechanisms.

Mechanism analysis of the influence of rotor-to-rotor interactions on global rotor noise

Existing research mainly investigated the influence of rotor-to-rotor interactions on the aerodynamics performance and noise level, but did not reveal the mechanism by which loading fluctuation significantly increases the noise below the rotor. In this study, first, an acoustic modal analysis method was established by mapping the source modal domain to acoustic modal domain, to investigate the global noise generated by a twin rotor considering the rotor-to-rotor interactions. Then, it was concluded from the simulation that the rotor-to-rotor interactions have little influence on the distribution of the sound sources, while they obvious change the noise in region at high elevation angle. Next, the method proposed was verified through experiments in an anechoic chamber, and the prediction error of overall sound pressure level (OASPL) was less than 7%. Finally, acoustic modal analysis reveals that the mechanism is attributed to the high radiation efficiency of the higher-order source modal components and dominant vertical directivity pattern of new acoustic modal components. Moreover, the initial azimuth angle of the rotors has an amplitude modulation effect on those acoustic modal components. When the difference in initial azimuth angle is π/L for rotors with L blades, the new modal components generated by different rotors cancel out each other for the odd-order blade passing frequency (BPF) noises.

Identification method for inter-turn faults in transformers based on digital twin concept

A transformer inter-turn fault identification method is proposed based on the digital twin concept to tackle the challenges of high operational complexity and low accuracy associated with traditional transformer fault identification methods. Initially, the Bald Eagle Search algorithm is employed to optimize the critical parameters of the Extreme Learning Machine (ELM), determining the optimal input layer weight and hidden layer threshold of the Extreme Learning Machine. Subsequently, leveraging the digital twin concept, a digital replica of the physical transformer is established, enabling multi-physical field coupling simulation encompassing electrical, thermal, and acoustic domains to elucidate the variation patterns of various physical parameters across different operational scenarios and fault scenarios. Furthermore, key physical characteristic parameters such as sound pressure and winding hot spot temperature are carefully selected to drive a fault identification model tailored to inter-turn faults within the framework of the digital twin concept. Through a detailed investigation using 630 kV A/10 kV transformers as a case study, the results exhibit an impressive fault identification accuracy of 95.24% for the proposed method. Comparative analysis reveals notable enhancements in fault identification accuracy of 12.22%, 7.85%, and 3.73% for ELM, Support Vector Machine and Tuna Swarm Optimization—ELM models, respectively. These findings underscore the effectiveness and practicality of the transformer inter-turn fault identification method based on the digital twin concept, offering valuable insights for the real-time monitoring and diagnosis of inter-turn faults in transformers.

ShaVi-1.0: An interface enabled open source 2D acoustic full waveform inversion package

Full waveform inversion (FWI) is an approach of seismic data inversion that employs data-fitting techniques to produce a detailed image of the subsurface. The computational expense and complex mathematics involved in implementing FWI make it challenging. To address this issue, we have developed an interface enabled 2D acoustic time domain FWI package: ShaVi-1.0 (“Sha” refers to “Shabda”, a Sanskrit word meaning “sound”, and “Vi” stands for “Viparita”, representing “inversion”, the package version is labeled as 1.0). That utilizes shots parallelization on the OpenMP API to deal with computational expenses and a graphical user interface (GUI) for its easy implementation. This allows the FWI to run on standalone workstations. The base code of FWI is written in “C” language with a modular design, enabling users to modify the modules as per their requirements. The GUI, which is developed in Python, includes features such as real-time plotting and process status updates, along with message and warning boxes to ensure smooth inversion flow. We add a toolbox to the GUI’s menu bar along with the help, which users can use to generate acquisition geometry and plot source-receiver locations. The toolbar integrated into the software provides multiple other functionalities to enhance the ease of implementation. We perform testing on the benchmark models such as SEG/EAGE Overthrust and Foothill model. A comparative study is also performed to assess its efficiency relative to CSIM-KAUST and SWIT-1.0 codes. The assessment is based on two key parameters: mean absolute percentage error (MAPE and computational time. The developed GUI not only simplifies the implementation process but also enables real-time analysis of results.