Acoustic Effects Research Articles

Corrosion and wear resistance of ultrasonic vibration-assisted laser cladded Fe-based crystal/amorphous composite coatings

The ultrasonic vibration (UV) is applied during the laser cladding process of Fe88.83Si6.21B2.51Cr2.45 (wt. %) amorphous powders. The microstructure evolution and properties of the Fe-based crystal/amorphous composite coatings with and without UV were investigated in detail. The results reveal a significant decrease of 55.8% in the average grain size within the UV coating, accompanied by a 35.9% reduction in the length of columnar grains at the interface, which is primarily attributed to the acoustic streaming and cavitation effects of ultrasound. The average microhardness value of coatings rises from 659 ±33 HV0.2 to 873 ±48 HV0.2. Meanwhile, the coatings with UV exhibit outstanding wear resistance, with a 38.2% reduction in wear rate compared to normal coatings. The corrosion mechanism of the coatings is pitting corrosion and the corroded surface of the coating with UV displays a relatively smaller pitting area. The enhancement mechanism for properties by U V can be the cooperative effect of the fine-grain strengthening and the amorphous phase strengthening.

Quantifying Sound Exposure in a Pool: Comparing Hydrophones on a Grid with a Sound-Recording Tag on a California Sea Lion (Zalophus californianus)

Investigating anthropogenic acoustic disturbance and sound exposure in marine mammals requires evaluation of experimental approaches used to measure the sound levels experienced by the subjects. In previous research, exposure of California sea lions (Zalophus californianus) to eight narrow noise bands was estimated as the mean sound pressure level (SPL) measured by hydrophones placed at multiple locations and depths in a pool. We compare this method of SPL estimation with SPLs measured with a sound recording tag (“D-tag”). Measurements were taken from (1) hydrophones at locations on a grid; (2) a D-tag at the same locations; (3) a D-tag attached in its housing to a harness on a sea lion swimming freely in the pool; (4) a D-tag in its housing in one position in the pool; (5) a D-tag on the sea lion in one position in the pool; and (6) a D-tag turning in one location in the pool without its housing, in its housing, and on the sea lion while she rotated on her body axis. The SPLs recorded by the D-tag on a free-swimming sea lion were ~8 to 10 dB lower than those measured by the grid hydrophones, and the differences varied by frequency. These differences in SPL are caused by a combination of the directionality associated with the D-tag itself, the presence of the housing, acoustic effects of the sea lion’s body, and periods that the D-tag was out of the water during respirations. Measuring mean sound levels in test pools using hydrophones deployed on grids is valid; however, attaching tags to wild marine mammals may be more feasible than using hydrophone grids at sea. We summarize considerations when selecting a method to fit the design of future research.

Dynamic large-eddy simulation of hypersonic transition delay over broadband wall impedance

Three-dimensional numerical simulations of hypersonic boundary layer transition delay due to porosity representative of carbon-fibre-reinforced carbon-matrix ceramics (C/C) were carried out on a 7 $^{\circ {}}$ half-angle cone for unit Reynolds numbers $Re_m=2.43 \times 10^6$ – $6.40\times 10^6\ \text {m}^{-1}$ , at the free-stream Mach number $M_\infty =7.4$ , for both sharp and 2.5 mm nose tip radii. A broadband time-domain impedance boundary condition was used to model the acoustic effects of the porous surface on the flow field. A quasi-spectral sub-filter-scale dynamic closure was adopted to stabilize the computations upon turbulent breakdown under extreme cooling conditions, with wall-to-adiabatic temperature ratio of $T_{w}/ T_{ad} \simeq 0.08 $ , while accurately recovering the growth rates of the unstable modes present in the early transition stages. Good agreement is observed with the reference experimental data, both in terms of the predicted extent of the transition delay and the measured second-mode frequency spectrum. The latter is strongly modulated by the formation of near-wall low-temperature three-dimensional streaks. Pressure disturbances concentrate in corridors of locally thickened boundary layer, with frequencies lower than what predicted by linear theory. Here, trapped wavetrains are formed, which can persist long into the turbulent region. Finally, it is shown that the presence of a porous wall simply shifts the onset of turbulence downstream, without affecting its structure.

Non-Hermitian Skin Effect in Many-Body Thermophotonics.

The tight-binding model, foundational in depicting electronic behaviors in solid-state physics, has recently contributed to the understanding of non-Hermitian skin effects in optics, acoustics, and mechanics. However, tight-binding model is primarily built upon scalar nearest couplings, which in turn does not fit to describe the vectorial long-range interactions inherently in thermophotonics. Here, we report a strategy involving many-body radiative interactions in a two-dimensional thermophotonic lattice, and further reveal two types of orthogonal non-Hermitian skin modes in a reciprocal system. For in-plane modes, a pronounced geometry-dependent skin effect manifests at the edges, while for out-of-plane modes, skin effects induced by many-body interactions emerge at the corners instead. Our work provides a pioneering approach for understanding many-body-driven skin effect and unveils a mechanism for unexpected manipulation in thermophotonics.

Flow Separation Control and Aeroacoustic Effects of a Leading-Edge Slat over a Wind Turbine Blade

To enable wind energy to surpass fossil fuels, the power-to-cost ratio of wind turbines must be competitive. Increasing installation capacities and wind turbine sizes indicates a strong trend toward clean energy. However, larger rotor diameters, reaching up to 170 m, introduce stability and aeroelasticity concerns and aerodynamic phenomena that cause noise disturbances. These issues hinder performance enhancement and social acceptance of wind turbines. A critical aerodynamic challenge is flow separation on the blade’s suction side, leading to a loss of lift and increased drag, ultimately stalling the blade and reducing turbine performance. Various active and passive flow control techniques have been studied to address these issues, with passive techniques offering the advantage of no external energy requirement. High-lift devices, such as leading-edge slats, are promising in improving aerodynamic performance by controlling flow separation. This study explores the geometric parameters of slats and their effects on wind turbine blades’ aerodynamic and acoustic performance. Using an adequate turbulence model at Re = 106 for angles of attack from 14° to 24°, 77 slat configurations were evaluated. Symmetric slats showed superior performance at high angles of attack, while slat chord length was inversely proportional to aerodynamic improvement. A hybrid method was employed to predict noise, revealing slat-induced modifications in eddy topology and increased low- and high-frequency noise. This study’s main contribution is correlating slat-induced aerodynamic improvements with their acoustic effects. The directivity reveals a 10–15 dB reduction induced by the slat at 1 kHz, while the slat induces higher noise at higher frequencies.

Reference Speech-recognition curves for a German monosyllabic test in noise: effects of loudspeaker configuration and room acoustics

Objective Measurement of reference speech-recognition curves for a specific speech test in typical clinical testing environments and for different loudspeaker configurations. Design Speech-recognition scores were measured at four signal-to-noise ratios for five loudspeaker configurations in two anechoic rooms, and in four audiometric test rooms with low reverberation times. Study sample 240 young participants (aged 18–25 years) without hearing impairment participated in the measurements. Results Reference speech-recognition curves for speech and noise from the front (S0N0) were similar across rooms. Compared to S0N0, lower speech-recognition thresholds (SRTs) were observed for all other loudspeaker configurations in which speech and noise were spatially separated. This spatial release from masking was significantly reduced for the audiometric test rooms compared to the anechoic rooms. A binaural speech-intelligibility model was used to verify the influence of room acoustic properties and loudspeaker configuration on SRT. Conclusions Speech-recognition curves for spatially separated loudspeaker configurations depend on the room acoustic properties, even in audiometric test rooms with low reverberation times. This makes it more difficult to compare clinical measurements with reference speech-recognition curves, or even with data measured in a different test room. It is thus recommended to document the loudspeaker configuration and test room for each clinical measurement.

Acoustic features of vocalizations in typically developing and autistic infants in the first year

We describe acoustic patterns across the five most prominent vocal types in typically developing infants (TD) and compare them with patterns in infants who develop autism (ASD) or a developmental disability (DD) not related to autism. Infant-directed speech (IDS) is a potentially important influence on such vocal acoustic patterns. Both acoustic patterns and effects of IDS are important for understanding the earliest origins of communication disorders. To compare duration, pitch and loudness of infant vocalizations for three groups of infants (TD, ASD, DD) in circumstances with high or low amounts of IDS. Two five-minute segments from each of 1259 all-day recordings across the first year were coded and acoustically analyzed for three groups of infants (130 TD, 44 ASD, 21 DD). Duration, mean fundamental frequency, and root mean square amplitude were determined for >162,000 infant utterances. Cries were longest and loudest, and vowel-like sounds were shortest of the five vocal types in all groups. TD infants showed significant alterations in vocal acoustics during periods of high IDS. Strong similarities in acoustic patterns occurred across the three groups, but only the TD group showed significant acoustic effects of IDS.

A Simulation Study on the Effect of Supersonic Ultrasonic Acoustic Streaming on Solidification Dendrite Growth Behavior During Laser Cladding Based on Boundary Coupling

Laser cladding has unique technical advantages, such as precise heat input control, excellent coating properties, and local selective cladding for complex shape parts, which is a vital branch of surface engineering. During the laser cladding process, the parts are subjected to extreme thermal gradients, leading to the formation of micro-defects such as cracks, pores, and segregation. These defects compromise the serviceability of the components. Ultrasonic vibration can produce thermal, mechanical, cavitation, and acoustic flow effects in the melt pool, which can comprehensively affect the formation and evolution for the microstructure of the melt pool and reduce the microscopic defects of the cladding layer. In this paper, the coupling model of temperature and flow field for the laser cladding of 45 steel 316L was established. The transient evolution laws of temperature and flow field under ultrasonic vibration were revealed from a macroscopic point of view. Based on the phase field method, a numerical model of dendrite growth during laser cladding solidification under ultrasonic vibration was established. The mechanism of the effect of ultrasonic vibration on the solidification dendrite growth during laser cladding was revealed on a mesoscopic scale. Based on the microstructure evolution model of the paste region in the scanning direction of the cladding pool, the effects of a static flow field and acoustic flow on dendrite growth were investigated. The results show that the melt flow changes the heat and mass transfer behaviors at the solidification interface, concurrently changing the dendrites’ growth morphology. The acoustic streaming effect increases the flow velocity of the melt pool, which increases the tilt angle of the dendrites to the flow-on side and promotes the growth of secondary dendrite arms on the flow-on side. It improves the solute distribution in the melt pool and reduces elemental segregation.

Acoustic performance prediction by means of a statistical energy analysis of two adjacent workrooms used for conferences and educational proposes

AbstractThe current design of workspaces for companies is focused on minimalistic and modern styles prioritizing the aesthetic appearance with illuminated open spaces and the use of glass walls. If the acoustic performance is not considered, inappropriate Reverberation Times (RT) might lead to difficulties for hearing a speaker or teacher during courses and conferences, causing problems in the learning process. Additionally, there might be high sound transmission between adjacent work rooms. This paper presents the development and experimental validation of numerical models using Statistical Energy Analysis (SEA) to calculate the sound reduction index through a glass wall that separates two adjacent work rooms. These structures are dedicated to conferences and educational uses but cannot be properly used due to their high sound transmission and inappropriate reverberant time. The sound insulation prediction results are validated with experimental measurements carried out in the adjacent rooms under the standard ISO-140. Afterwards, a SEA model is used to provide some acoustic correction design guidelines for these types of constructions. To improve the acoustical performance in the rooms, the acoustic effects of different absorbent panels placed on the walls and ceiling were investigated, choosing a suitable material that complies with the recommended ranges of RT and with less amount of absorption area. The SEA model is then used to understand the effects of openings size between the panels that make up the glass wall on the sound insulation capacity between rooms. Finally, a SEA model is reformulated to quantify the effect of the application of double walls for sound insulation between rooms, which implies the increase of weighted sound reduction index in 9 dB with respect to measured data.

МЕЗО-ФОРТЕ ТЕРАПИЯ В НЕЙРОРЕАБИЛИТАЦИИ ДЕТЕЙ С МИОПИЕЙ — ПИЛОТНОЕ ИССЛЕДОВАНИЕ

This article presents the results of a pilot clinical and experimental study of the prospects for neurorehabilitation of children with myopia using Meso-Forte Therapy (MFT), an innovative hardware method of restorative treatment using digital music therapy programs. For the first time, data from complex psycho physiological and ophthalmological studies is published, revealing the mechanisms of corrective regulation of the psycho emotional status, the autonomic nervous system, and the tone of the accommodating muscles of the eye using the main algorithms of musical and acoustic effects.

Effect of vibration frequency on tribological characteristics of vibration-assisted micro-nano machining

Experimental findings regarding the influence of vibration frequency on the machining outcomes of vibration-assisted machining (VAM) have been inconsistent. This work aims to address this issue through both experimental and theoretical analyses. The results indicate that the circuit's frequency response is the primary source of these discrepancies. When the vibration frequency is less than half the cutoff frequency, the friction force reaches a minimum while the wear volume peaks. The solution of the heat conduction equation demonstrated that the acoustic softening effect drives the softening mechanism in nanoscale VAM. Molecular dynamics (MD) simulations further elucidate the damage mechanisms during the wear process, showing that high-frequency vibrations contribute to achieving high-precision machining.

Geophysical effects caused by the bolide fall on September 02, 2023 (Turkey)

We present the results of instrumental observations of acoustic oscillations, geomagnetic variations and variations of the atmospheric electric field during the fall and explosive destruction of the bolide in the southeast of Turkey on September 02, 2023. It is shown that the destruction of the bolide under the action of aerodynamic forces, which occurred in three stages, was accompanied by an acoustic signal of a characteristic shape and manifested in variations of the magnetic and electric fields in the near-surface layer atmosphere. The total energy of the event, estimated by the acoustic effect, was ~ 9×1012 J, which corresponds to about 2.15 kt in TNT equivalent. The maximum amplitude of geomagnetic variations caused by the explosion of the bolide ranged from 0.2 to 2.1 nT depending on the distance. At the same time, the amplitude of variations of the vertical component of the atmospheric electric field at the Mikhnevo observatory (distance ~1900 km) was ~70 V/m. The ionospheric effect of the event under consideration is demonstrated in the form of variations of the critical frequency f0F2 obtained as a result of processing ionograms of height-frequency sounding of the ionosphere at the Rome station.

Acoustic black hole effect enhanced micro-manipulator

Microparticle manipulation is a critical concern across various fields including microfabrication, flexible electronics and tissue engineering. Acoustic-activated sharp structures have been designed as simple and flexible tools to manipulate microparticles with their good compatibility, fast response, and broad tunability. However, there still lacks rational acoustic-structure design for effective energy concentration at the acoustic-activated sharp structures for microparticle manipulation. Here, we present the acoustic black hole (ABH) effect as enhancement for the acoustic micro-manipulator. It provides great reliability, simplicity and ease of use, supporting custom design of high-throughput patterning modes. Moreover, compared to commonly used configurations, such as cylindrical or conical microneedles, those microneedles with ABH profile exhibit superior acoustic energy focusing at the tip and induce stronger acoustofluidic effects. The average acoustic flow velocity induced by the ABH microneedle is 154 times greater than that of the conical one and 45 times greater than that of the cylindrical microneedle. Besides, the average acoustic radiation force (ARF) produced by the ABH microneedle against acrylic microparticles is about 319 times greater than that of the cylindrical one and 16 times greater than that of the conical one. These results indicate that ABH design significantly enhances microparticle manipulation. We demonstrate this concept with ABH effect enhanced microparticle manipulation and study the parameters influencing its performance including operating frequency, operating voltage and particle diameter. Furthermore, considering the flexibility of this system, we employ it for various patterning and high-throughput microparticle manipulation. This work paves the way for controllable microparticle manipulation, holding great potential for applications in microfabrication and biomedicine.

The effect of classroom acoustics and noise on preschool children’s listening, learning, and wellbeing: A scoping review

Preschool is an important time for children to grow in their experiences, abilities, and knowledge before entering formal school. Therefore, it is vital that the classroom acoustic environment supports children’s listening, learning, and wellbeing. The aim of this scoping review was to determine what is known from the literature about the effect of classroom acoustics and noise on preschool children’s listening, learning, and wellbeing, and what the knowledge gaps are. The scoping review followed the PRISMA-ScR guidelines. Seven papers met the criteria to be included in the review. The findings suggest that poor classroom acoustic conditions and particularly high noise levels, can have a negative effect on preschool school children’s listening and wellbeing, but may not affect word learning at the SNRs investigated. Nevertheless, it would be beneficial to install acoustic solutions and manage noise in preschool classrooms to enhance children’s listening, learning, and wellbeing. Future research avenues are discussed.

High-temperature structure, elasticity, and thermal expansion of ε-ZrH1.8

Zirconium hydride is a promising candidate material for nuclear microreactor applications as a solid-state moderator component, owing to its favorable neutronics properties and good thermal stability over other metal hydrides. In the present work, the crystal structure, thermal expansion, and elastic properties of the hydrogen-rich ε phase hydride were measured at elevated temperatures in the range 300–900 K. Samples were prepared by direct hydriding Zircaloy-4 metal – a nuclear-grade zirconium alloy. Room-temperature lattice parameters agree well with those reported from literature for unalloyed zirconium hydride and fall within an observed quadratic H-content dependence. The coefficients of thermal expansion, determined from lattice expansion and dilatometry, agree well within our work but were about 30 % lower than those reported by others for unalloyed hydrides. Density functional theory-based molecular dynamics simulations were used to compare with thermal expansion and elasticity measurements. Results showed lattice parameter temperature dependence and slope of thermal expansion align with those from measurements. Based on diffraction scans at select temperatures, ε phase remained stable in air up to at least 770 K. Likewise, dilatometry showed smooth thermal expansion up to the thermal decomposition temperature around 950 K. The precise decomposition temperature was not determined via diffraction due to sparse scanning. The complete elastic property measurements were gathered for ε-phase Ziracloy-4 hydride for the first time. Young's modulus was lower compared to the metal and δ hydride phases. High-temperature elasticity measurements were limited to <350 K due to acoustic dissipation effects.

Acoustic near field effects in distribution transformer noise measurement

This paper examines the near field effect, including the active and reactive acoustic field around a liquid-filled distribution transformer with heat-dissipating corrugated fins on the tank walls. The analysis was carried out on the basis of measurements of sound pressure and sound intensity levels along with acoustic maps including the phase correlation of acoustic waves. The acoustic field around the transformer was evaluated in the measurement planes showing normal direction radiation of up to 1,0 m distance. Discrete point measurements made with the PU (pressure - velocity) probe was used to obtain parameters such as particle velocity, active and reactive sound intensity as well as the transfer function associated with the reference microphone. The last parameter, the transfer function, allows to show the phase correlation between acoustic wave propagation, which contributes to a better understanding of acoustic near-field effects where energy circulates, creating a sound field that can have overestimated sound pressure and intensity levels.

Acoustic refurbishments in a university lecture room: effects on speaker's comfort and voice use

Poor acoustic conditions in learning spaces have a detrimental effect on the speaker´s health and constitutes a risk factor for voice disorders. Previous research indicate that an acoustic refurbishment of the learning space has the potential to increase well-being and decrease voice related health problems among teachers, but the research is scarce. In this study, we aim to investigate how different acoustic conditions affect the speakers voice use and self-perceived speaker's comfort. Voice recordings of short speech-tasks and self-evaluations of speaker's comfort were collected from fifteen participants during a three-step acoustic refurbishment of a real-life university lecture room in an experimental setting. The influence of background babble and a classroom soundfield amplification system on vocal parameters and self-perceived speaker's comfort were also investigated. Factor analysis of the speaker's comfort questionnaire revealed a two-factor solution where factor 1 represented vocal behavior and perception of room acoustics, and factor 2 represented the perception of the task in itself. Sum scores for factors 1 and 2 will be calculated and used in a mixed-effects model investigating the effect of room acoustics on self-perceived speaker's comfort.

Analysis of the physical mechanisms responsible for the Acoustic Black Hole effect

An acoustic black hole (ABH) inserted into a mechanical structure provides effective vibration damping without making the structure heavier. This property is particularly interesting in contexts where mass reduction is important. In practice, the ABH effect embedded in a beam or in a plate results from the combination of a local reduction in thickness and the addition of a thin viscoelastic damping layer. Consequently, an ABH is a weak point in the structure, which leads to the existence of local modes. An ABH can be seen as a penetrable resonant scatterer, with a high density of modes, all critically coupled. These properties intrinsically define the conditions required to obtain a true ABH effect. This definition will be presented and illustrated on examples of increasing complexity.

Metagratings for underwater acoustic wavefront manipulation

Metagratings are flat periodic assemblies of small scatterers, engineered to achieve effects such as steering, beamforming, or absorption. They have recently received attention in both electromagnetism and acoustic fields. In this work, we report the design, modeling, and experimental characterization of metagratings to steer underwater acoustic wavefronts towards anomalous directions (i.e. not classically allowed by Snell-Decartes relationships) with high efficiency (close to 100%). They are build from simple assemblies of small brass cylinders, hold by 3D-printed plastic supports, and can redirect ultrasonic wavefronts either in reflection mode (when placed in front of a reflective surface like e.g. the water / air interface) or in transmission mode. Furthermore, we demonstrate how metagratings build from an asymmetrical pattern of multiple basic elements can achieve near perfect asymmetrical transmission: a wavefront incident from side of the structure is fully transmitted, while a similar wavefront incoming from the other side is fully reflected, achieving an acoustic one-way mirror effect. This work combine theoretical analysis, finite element modeling, and experimentation in water tanks to explore and demonstrate the potential of such metagratings for various applications in underwater acoustics, like communication, noise mitigation, and stealth.

Wind tunnel testing and modelling of a rod-airfoil setup: validation and 3D acoustic imaging

This work revisits the rod-airfoil benchmark experiment from Jacob et al. (2004) with the aim of performing a detailed numerical validation in the nearfield and far field as well as to perform 3D acoustic imaging. The setup consists of a rod near the leading edge of a NACA-0012 airfoil and is placed in a semi-open wind tunnel in anechoic conditions. In addition to a far-field microphone array, the setup is equipped with two planar microphone arrays as well as wall-mounted microphones on the closed wind tunnel section and on the airfoil. The setup is modelled using a second-order finite volume method, and particular attention is devoted to including installation effects and sensor response properties in order to guarantee simulation accuracy. Validation examples are provided, including single microphone spectra as well as the acoustic field reconstructed on the test object by means of 3D acoustic imaging using the planar microphone arrays. Finally, the experimentally-validated numerical model is used as a means to gain further insight into the tested object. For instance, the model allows to separate acoustical and turbulent effects present in the sensors located within the flow section.