Acoustics

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16 pages, 2087 KiB

Open AccessArticle

Efficient Modelling of Acoustic Metamaterials for the Performance Enhancement of an Automotive Silencer

by Daniel Deery, Lara Flanagan, Gordon O’Brien, Henry J. Rice and John Kennedy

Acoustics 2022, 4(2), 329-344; https://doi.org/10.3390/acoustics4020020 - 1 Apr 2022

Cited by 12 | Viewed by 8791

Significant potential for acoustic metamaterials to provide a breakthrough in sound attenuation has been unlocked in recent times due to advancements in additive manufacturing techniques. These materials allow the targeting of specific frequencies for sound attenuation. To date, acoustic metamaterials have not been [...] Read more.

Significant potential for acoustic metamaterials to provide a breakthrough in sound attenuation has been unlocked in recent times due to advancements in additive manufacturing techniques. These materials allow the targeting of specific frequencies for sound attenuation. To date, acoustic metamaterials have not been demonstrated in a commercial automotive silencer for performance enhancement. A significant obstacle to the practical use of acoustic metamaterials is the need for low cost and efficient modelling strategies in the design phase. This study investigates the effect of acoustic metamaterials within a representative automotive silencer. The acoustic metamaterial design is achieved using a combination of analytical and finite element models, validated by experiment. The acoustic metamaterial is then compared with commonly used techniques in the silencer industry to gauge the effectiveness of the acoustic metamaterials. COMSOL simulations were used to validate the developed test rig and were compared to experimental results which were obtained using the two-load transmission loss test method. Through this testing method, the implementation of a labyrinthine metamaterial cylinder proved to be a significant improvement in transmission loss within the silencer, with an increase in transmission loss of 40 dB at 1500 Hz. The research has successfully shown that acoustic metamaterials can be used in practical settings, such as an automotive silencer, to improve the overall sound attenuating performance. The described analytical model demonstrates the potential for industrially relevant low cost design tools. Full article

(This article belongs to the Special Issue Acoustical Materials)

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16 pages, 8940 KiB

Open AccessArticle

Acoustic Attenuation of COVID-19 Face Masks: Correlation to Fibrous Material Porosity, Mask Breathability and Bacterial Filtration Efficiency

by Milena Martarelli, Luigi Montalto, Paolo Chiariotti, Serena Simoni, Paolo Castellini, Gianmarco Battista and Nicola Paone

Acoustics 2022, 4(1), 123-138; https://doi.org/10.3390/acoustics4010009 - 16 Feb 2022

Cited by 2 | Viewed by 3789

Abstract

This paper presents an experimental study on acoustic attenuation of different types of face masks in use by the general population during the COVID-19 pandemic. In particular, measurements are performed on ten samples of masks, of which four are medical masks, three are [...] Read more.

This paper presents an experimental study on acoustic attenuation of different types of face masks in use by the general population during the COVID-19 pandemic. In particular, measurements are performed on ten samples of masks, of which four are medical masks, three are respirators, and three are community masks. Breathability and Bacterial Filtration Efficiency (BFE) tests, in compliance to the standard characterization process of medical masks, are also carried out. The porosity on each layer composing the masks is measured by processing their scanning electron microscopy (SEM) images. The analysis of the results aims to establish if acoustic attenuation is correlated to any of these parameters. It emerges that porosity and breathability are strongly correlated to acoustic attenuation, while bacterial filtration efficiency is not. Full article

(This article belongs to the Special Issue Acoustical Materials)

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17 pages, 8857 KiB

Open AccessArticle

Plane and Surface Acoustic Waves Manipulation by Three-Dimensional Composite Phononic Pillars with 3D Bandgap and Defect Analysis

by Muhammad, C.W. Lim and Andrew Y. T. Leung

Acoustics 2021, 3(1), 25-41; https://doi.org/10.3390/acoustics3010004 - 8 Jan 2021

Cited by 9 | Viewed by 5261

Abstract

The current century witnessed an overwhelming research interest in phononic crystals (PnCs) and acoustic metamaterials (AMs) research owing to their fantastic properties in manipulating acoustic and elastic waves that are inconceivable from naturally occurring materials. Extensive research literature about the dynamical and mechanical [...] Read more.

The current century witnessed an overwhelming research interest in phononic crystals (PnCs) and acoustic metamaterials (AMs) research owing to their fantastic properties in manipulating acoustic and elastic waves that are inconceivable from naturally occurring materials. Extensive research literature about the dynamical and mechanical properties of acoustic metamaterials currently exists, and this maturing research field is now finding possible industrial and infrastructural applications. The present study proposes a novel 3D composite multilayered phononic pillars capable of inducing two-dimensional and three-dimensional complete bandgaps (BGs). A phononic structure that consisted of silicon and tungsten layers was subjected to both plane and surface acoustic waves in three-dimensional and two-dimensional periodic systems, respectively. By frequency response study, the wave attenuation, trapping/localization, transmission, and defect analysis was carried out for both plane and surface acoustic waves. In the bandgap, the localized defect state was studied for both plane and surface acoustic waves separately. At the defect state, the localization of both plane and surface acoustic waves was observed. By varying the defect size, the localized frequency can be made tailorable. The study is based on a numerical technique, and it is validated by comparison with a reported theoretical work. The findings may provide a new perspective and insight for the designs and applications of three-dimensional phononic crystals for surface acoustic wave and plane wave manipulation, particularly for energy harvesting, sensing, focusing and waves isolation/attenuation purposes. Full article

(This article belongs to the Special Issue Acoustical Materials)

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14 pages, 4030 KiB

Open AccessArticle

Monitoring the Nonlinear Acoustic Behavior of Fresh Cementitious Materials during the Hardening Process Using Laser Doppler Vibrometry

by Ilias K. Tragazikis, Alexia N. Koutrakou, Theodoti Z. Kordatou, Panagiota T. Dalla and Theodore E. Matikas

Acoustics 2020, 2(4), 833-846; https://doi.org/10.3390/acoustics2040047 - 30 Nov 2020

Cited by 4 | Viewed by 4285

Abstract

A challenge in the field of material science and concrete technology is to associate material properties and behavior with changes in internal microstructure. A fundamental issue for planning, implementation, and quality control of construction projects is the fundamental understanding of the hardening process [...] Read more.

A challenge in the field of material science and concrete technology is to associate material properties and behavior with changes in internal microstructure. A fundamental issue for planning, implementation, and quality control of construction projects is the fundamental understanding of the hardening process in freshly poured cement-based materials. Shortly after the mixing process, cementitious materials exhibit a substantial damping effect on ultrasonic wave propagation along with low-pulse velocity. The way a wave reflects and diffuses in the volume of a solid material can provide important information about internal heterogeneities. An important application of the wave propagation technique is the determination of layers within the material distinguished by unlike elastic properties. During the hardening process, the ultrasonic wave propagation exhibits a noticeable sensitivity at the point of phase change of the material, that is, the critical point at which the state of the suspension transforms from liquid to solid state. After that point, there is a continuous increase of pulse velocity and ultrasonic signal amplitude. The solidification point is of practical importance since at this point the load-bearing capacity of the composite material and its long-term behavior are based on the connectivity of the solid phase. This study aims to develop a nondestructive tool to monitor freshly poured cement-paste composites at early stages, during the hydration process, by means of nonlinear elastic waves. The measurement setup combined a contact ultrasonic transducer with a noncontact optical detection system, in which the principle of operation is based on the Doppler effect. This methodology enabled us to assess the amplitudes of harmonic vibrations of an acoustic wave propagating through the material with a specific fundamental frequency. This enabled the evaluation of important material properties, such as minute changes in the internal microstructure of fresh concrete during hardening, the evolution of nonlinearity parameters that relate to higher-order elastic constants of the material, as well as the ultrasonic wave velocity. Full article

(This article belongs to the Special Issue Acoustical Materials)

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17 pages, 3856 KiB

Open AccessArticle

Nonlinear Behavior of High-Intensity Ultrasound Propagation in an Ideal Fluid

by Jitendra A. Kewalramani, Zhenting Zou, Richard W. Marsh, Bruce G. Bukiet and Jay N. Meegoda

Acoustics 2020, 2(1), 147-163; https://doi.org/10.3390/acoustics2010011 - 3 Mar 2020

Cited by 7 | Viewed by 5953

Abstract

In this paper, nonlinearity associated with intense ultrasound is studied by using the one-dimensional motion of nonlinear shock wave in an ideal fluid. In nonlinear acoustics, the wave speed of different segments of a waveform is different, which causes distortion in the waveform [...] Read more.

In this paper, nonlinearity associated with intense ultrasound is studied by using the one-dimensional motion of nonlinear shock wave in an ideal fluid. In nonlinear acoustics, the wave speed of different segments of a waveform is different, which causes distortion in the waveform and can result in the formation of a shock (discontinuity). Acoustic pressure of high-intensity waves causes particles in the ideal fluid to vibrate forward and backward, and this disturbance is of relatively large magnitude due to high-intensities, which leads to nonlinearity in the waveform. In this research, this vibration of fluid due to the intense ultrasonic wave is modeled as a fluid pushed by one complete cycle of piston. In a piston cycle, as it moves forward, it causes fluid particles to compress, which may lead to the formation of a shock (discontinuity). Then as the piston retracts, a forward-moving rarefaction, a smooth fan zone of continuously changing pressure, density, and velocity is generated. When the piston stops at the end of the cycle, another shock is sent forward into the medium. The variation in wave speed over the entire waveform is calculated by solving a Riemann problem. This study examined the interaction of shocks with a rarefaction. The flow field resulting from these interactions shows that the shock waves are attenuated to a Mach wave, and the pressure distribution within the flow field shows the initial wave is dissipated. The developed theory is applied to waves generated by 20 KHz, 500 KHz, and 2 MHz transducers with 50, 150, 500, and 1500 W power levels to explore the effect of frequency and power on the generation and decay of shock waves. This work enhances the understanding of the interactions of high-intensity ultrasonic waves with fluids. Full article

(This article belongs to the Special Issue Acoustical Materials)

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16 pages, 5443 KiB

Open AccessArticle

Sound Pressure Level Analysis of a Liquid-Fueled Lean Premixed Swirl Burner with Various Quarls

by Gergely I. Novotni and Viktor Józsa

Acoustics 2020, 2(1), 131-146; https://doi.org/10.3390/acoustics2010010 - 1 Mar 2020

Cited by 1 | Viewed by 4734

Abstract

Swirl burners are widely used in numerous practical applications since they are characterized by low pollutant emission and a wide operating range. Besides reliable operation, a burner must fulfill noise emission regulations, which is often a sound pressure level in dB(A) when people [...] Read more.

Swirl burners are widely used in numerous practical applications since they are characterized by low pollutant emission and a wide operating range. Besides reliable operation, a burner must fulfill noise emission regulations, which is often a sound pressure level in dB(A) when people are affected. Therefore, the present paper evaluates the overall sound pressure level (OASPL) variation of a 15-kW liquid-fueled turbulent atmospheric swirl burner at various setups. Firstly, the combustion air flow rate was adjusted, which induced a swirl number modification due to the fixed swirl vanes. Secondly, the atomizing pressure of the plain-jet airblast atomizer was modified, which also affected the swirl number. High atomizing air jets notably increased combustion noise by intensifying the shear layer. Thirdly, a geometrical modification was performed; 0°–60° half cone angle quarls in 15° steps were installed on the lip of the baseline burner for extended flame stability. By filtering the OASPL to the V-shaped flames, a linearly decreasing trend was observed as a function of swirl number. Their derivative also has a linearly decreasing characteristic as a function of the atomizing pressure. Full article

(This article belongs to the Special Issue Acoustical Materials)

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22 pages, 2868 KiB

Open AccessArticle

Attenuation and Phase Velocity of Elastic Wave in Textured Polycrystals with Ellipsoidal Grains of Arbitrary Crystal Symmetry

by Gaofeng Sha

Acoustics 2020, 2(1), 51-72; https://doi.org/10.3390/acoustics2010005 - 11 Feb 2020

Cited by 7 | Viewed by 4265

Abstract

This study extends the second-order attenuation (SOA) model for elastic waves in texture-free inhomogeneous cubic polycrystalline materials with equiaxed grains to textured polycrystals with ellipsoidal grains of arbitrary crystal symmetry. In term of this work, one can predict both the scattering-induced attenuation and [...] Read more.

This study extends the second-order attenuation (SOA) model for elastic waves in texture-free inhomogeneous cubic polycrystalline materials with equiaxed grains to textured polycrystals with ellipsoidal grains of arbitrary crystal symmetry. In term of this work, one can predict both the scattering-induced attenuation and phase velocity from Rayleigh region (wavelength >> scatter size) to geometric region (wavelength << scatter size) for an arbitrary incident wave mode (quasi-longitudinal, quasi-transverse fast or quasi-transverse slow mode) in a textured polycrystal and examine the impact of crystallographic texture on attenuation and phase velocity dispersion in the whole frequency range. The predicted attenuation results of this work also agree well with the literature on a textured stainless steel polycrystal. Furthermore, an analytical expression for quasi-static phase velocity at an arbitrary wave propagation direction in a textured polycrystal is derived from the SOA model, which can provide an alternative homogenization method for textured polycrystals based on scattering theory. Computational results using triclinic titanium polycrystals with Gaussian orientation distribution function (ODF) are also presented to demonstrate the texture effect on attenuation and phase velocity behaviors and evaluate the applicability and limitation of an existing analytical model based on the Born approximation for textured polycrystals. Finally, quasi-static phase velocities predicted by this work for a textured polycrystalline copper with generalized spherical harmonics form ODF are compared to available velocity bounds in the literature including Hashin–Shtrikman bounds, and a reasonable agreement is found between this work and the literature. Full article

(This article belongs to the Special Issue Acoustical Materials)

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14 pages, 1084 KiB

Open AccessArticle

Estimation of Acoustic Power Output from Electrical Impedance Measurements

by Gergely Csány, Michael D. Gray and Miklós Gyöngy

Acoustics 2020, 2(1), 37-50; https://doi.org/10.3390/acoustics2010004 - 4 Feb 2020

Cited by 3 | Viewed by 7013

Abstract

A method is proposed for estimating the acoustic power output of ultrasound transducers using a two-port model with electrical impedance measurements made in three different propagation media. When evaluated for two high-intensity focused ultrasound transducers at centre frequencies between 0.50 and 3.19 MHz, [...] Read more.

A method is proposed for estimating the acoustic power output of ultrasound transducers using a two-port model with electrical impedance measurements made in three different propagation media. When evaluated for two high-intensity focused ultrasound transducers at centre frequencies between 0.50 and 3.19 MHz, the resulting power estimates exceeded acoustic estimates by 4.5–21.8%. The method was shown to be valid for drive levels producing up to 20 MPa in water and should therefore be appropriate for many HIFU (high-intensity focused ultrasound) applications, with the primary advantage of employing relatively low-cost, non-specialist materials and instrumentation. Full article

(This article belongs to the Special Issue Acoustical Materials)

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