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Sound attenuation in ducts using locally resonant periodic aluminum patches
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.ORCID iD: 0000-0002-6069-4636
2016 (English)In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 139, no 6, 3276-3286 p.Article in journal (Refereed) Published
Abstract [en]

In recent years, the control of low frequency noise has received a lot of attention for several applications. Traditional passive noise control techniques using Helmholtz resonators have size limitations in the low frequency range because of the long wavelength. Promising noise reductions, with flush mounted aluminum patches with no size problems can be obtained using local resonance phenomenon implemented in acoustic metamaterial techniques. The objective of this work is to introduce locally resonant thin aluminum patches flush mounted to a duct walls aiming at creating frequency stop bands in a specific frequency range. Green's function is used within the framework of interface response theory to predict the amount of attenuation of the local resonant patches. The two-port theory and finite elements are also used to predict the acoustic performance of these patches. No flow measurements were conducted and show good agreement with the models. The effect of varying the damping and the masses of the patches are used to expand the stop bandwidth and the effect of both Bragg scattering and the locally resonant mechanisms was demonstrated using mathematical models. The effect of the arrays of patches on the effective dynamic density and bulk modulus has also been investigated.

Place, publisher, year, edition, pages
Acoustical Society of America (ASA), 2016. Vol. 139, no 6, 3276-3286 p.
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-192861DOI: 10.1121/1.4948990ISI: 000379164900042Scopus ID: 2-s2.0-84977109960OAI: oai:DiVA.org:kth-192861DiVA: diva2:972571
Funder
EU, FP7, Seventh Framework Programme, 289352
Note

QC 20160929

Available from: 2016-09-21 Created: 2016-09-21 Last updated: 2017-11-21Bibliographically approved
In thesis
1. Innovative noise control in ducts
Open this publication in new window or tab >>Innovative noise control in ducts
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The objective of this doctoral thesis is to study three different innovative noise control techniques in ducts namely: acoustic metamaterials, porous absorbers and microperforates. There has been a lot of research done on all these three topics in the context of duct acoustics. This research will assess the potential of the acoustic metamaterial technique and compare to the use of conventional methods using microperforated plates and/or porous materials. 

The objective of the metamaterials part is to develop a physical approach to model and synthesize bulk moduli and densities to feasibly control the wave propagation pattern, creating quiet zones in the targeted fluid domain. This is achieved using an array of locally resonant metallic patches. In addition to this, a novel thin slow sound material is also proposed in the acoustic metamaterial part of this thesis. This slow sound material is a quasi-labyrinthine structure flush mounted to a duct, comprising of coplanar quarter wavelength resonators that aims to slow the speed of sound at selective resonance frequencies. A good agreement between theoretical analysis and experimental measurements is demonstrated.

The second technique is based on acoustic porous foam and it is about modeling and characterization of a novel porous metallic foam absorber inside ducts. This material proved to be a similar or better sound absorber compared to the conventional porous absorbers, but with robust and less degradable properties. Material characterization of this porous absorber from a simple transfer matrix measurement is proposed.The last part of this research is focused on impedance of perforates with grazing flow on both sides. Modeling of the double sided grazing flow impedance is done using a modified version of an inverse semi-analytical technique. A minimization scheme is used to find the liner impedance value in the complex plane to match the calculated sound field to the measured one at the microphone positions.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. 69 p.
Series
TRITA-AVE, ISSN 1651-7660 ; 58
Keyword
Locally resonant materials, slow sound, acoustic impedance, metallic foam, low frequency noise, mufflers, lined ducts, grazing flow, flow duct, impedance eduction.
National Category
Vehicle Engineering
Research subject
Vehicle and Maritime Engineering
Identifiers
urn:nbn:se:kth:diva-192927 (URN)978-91-7729-119-0 (ISBN)
Public defence
2016-10-21, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
EU, FP7, Seventh Framework Programme, 289352
Note

QC 20160923

Available from: 2016-09-23 Created: 2016-09-23 Last updated: 2016-09-23Bibliographically approved

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Farooqui, Maaz

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