Shape-optimal design of graded index sonic crystal formations using natural cubic splines

Aa, Bart van der; Forssén, Jens

doi:10.1016/j.apacoust.2013.11.002

Cited by 7 publications

(7 citation statements)

References 18 publications

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“…Readers who need to find optimum parameters for specific (geometrical) configurations are referred to, e.g., Ref. 33, where a comprehensive optimization procedure using a multiobjective genetic algorithm is explained in detail. We will start with a geometrical setup using 150 Â 3 cylindrical units, organized in square lattice, having a lattice constant a ¼ 10 cm.…”

Section: B Calculation Results Of Finite and Infinite Arraysmentioning

confidence: 99%

Scattering by an array of perforated cylinders with a porous core

Forssén

2014

The Journal of the Acoustical Society of America

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In this work multiple scattering by an array of perforated cylindrical shells with a porous core has been investigated. A semi-analytical model to predict scattering from such cylindrical units is presented in the context of the multiple scattering theory (MST), and validated against laboratory experiments. The suggested semi-analytical multiple scattering model uses an impedance expression to include the perforated shell in the scattering coefficients, which is a compact way to describe a composite scatterer in MST. Calculation results of a small array are shown to be in excellent agreement with measured data. Predictions and data show that perforated cylinders with empty cavities exhibit a strong and narrow insertion loss peak at resonance, though simultaneously suffer from amplification below resonance. By adding porous material in the core of the scatterer adverse effects below the resonance peak were suppressed. In addition, it was found that the reduction peak broadens, though at a cost of a reduced peak amplitude. Finally, it has been shown that adding porous material in a perforated shell will introduce partial absorption of the incoming field, which can be optimized by adjusting the perforation ratio of the shell.

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Section: B Calculation Results Of Finite and Infinite Arraysmentioning

confidence: 99%

Scattering by an array of perforated cylinders with a porous core

Forssén

2014

The Journal of the Acoustical Society of America

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“…A rigid boundary can be characterised by a disappearing particle velocity normal to the boundary, which is equivalent to a vanishing pressure gradient, that is satisfying the Neumann condition. An acceptable example can be the ground during outdoor sound propagation (10,11). A rigid boundary is also known as 'sound-hard' (1, p. 13) and has the plane-wave pressure reflection coefficient of +1.…”

Section: Image Condition: Rigid Interfacementioning

confidence: 99%

“…Since the inception of sonic crystals using horizontal circular cylinders as a potential tool for outdoor noise mitigation, multiple scattering works have been carried out in conjunction with the method of images due to the inevitable presence of outdoor ground (9)(10)(11). Underwater sound scattering underneath the free surface has also been analysed with similar approaches (12,13).…”

Section: Introductionmentioning

confidence: 99%

Image conditions for polar and cylindrical coordinate separation-of-variables acoustic multiple scattering models with perfectly reflecting flat boundaries

Shin

2018

The Quarterly Journal of Mechanics and Applied Mathematics

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This article addresses efficient implementation of the method of images for acoustic multiple scattering models (MSM) with perfectly reflecting flat boundaries. Time-harmonic problems are first solved in the polar coordinate system for circular scatterers; then the models are extended to the cylindrical coordinate system with (semi-)infinitely long circular cylinders. The MSM in this article is based on the method of separation of variables and Graf's addition theorem. Derivations are provided for 'image conditions' which relate the unknown coefficients of outgoing waves from image scatterers with those of real counterparts. The method of images is applied to wedgeshaped domains with apex angles of π/n rad for a positive integer n. Image conditions make the MSM numerically more efficient: the system of linear equations for unknown coefficients is formulated 2n times faster; its memory requirements are reduced by 4n 2 times for direct solvers. The proposed model is applied to a benchmark wedge in ocean environment with n = 64. Good agreement is observed between the MSM with image conditions and the boundary element method. Furthermore, half-and quarter-space measurements in an anechoic chamber are in accordance with the correct use of image conditions. Incorrect image conditions reported elsewhere for polar coordinates are also discussed.

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“…The advantage of sonic crystal acoustic barriers when compared with conventional ones, apart from the fact that it is frequency tunable, is that the action of wind is relatively small as it is an open structure [11]. Acoustic barriers based on sonic crystals are still a research topic of high interest [12][13][14][15][16], and mainly their study is based on noise transmission due to the fact that they are not continous devices. Nowadays acoustic barriers based on sonic cystals are used to reduce road traffic noise [17].…”

Section: Introductionmentioning

confidence: 99%

Subwavelength slit acoustic metamaterial barrier

Candelas¹,

Belmar²,

Gomez-Lozano³

et al. 2015

J. Phys. D: Appl. Phys.

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IOP PublishingRubio Michavila, C.; Candelas Valiente, P.; Belmar Ibáñez, F.; Gómez Lozano, V.; Uris Martínez, A. (2015). ABSTRACTReduction of noise in the transmission path is a very important environmental problem. The most usual method to reduce this noise level is the use of acoustic barriers. In this paper, an acoustic metamaterial based on sound transmission through subwavelength slits, is tailored to be used as an acoustic barrier is shown. This system consists of two rows of periodic repetition of vertical rigid pickets separated by a slit of subwavelength width, embedded in air. Here, both the experimental and the numerical analyses are presented. These analyses have facilitated the identification of the parameters that affect the insertion loss performance. The results demonstrated that the proposed barrier can be tuned to mitigate a band noise in mechanical plant for buildings where openings for air flow are required as well as industrial noise, without excessive barrier thickness.2

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Shape-optimal design of graded index sonic crystal formations using natural cubic splines

Cited by 7 publications

References 18 publications

Scattering by an array of perforated cylinders with a porous core

Scattering by an array of perforated cylinders with a porous core

Image conditions for polar and cylindrical coordinate separation-of-variables acoustic multiple scattering models with perfectly reflecting flat boundaries

Subwavelength slit acoustic metamaterial barrier

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