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Validation of low frequency noise attenuation using locally resonant patches
2016 (English)In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524Article in journal (Refereed) Published
Abstract [en]

Since conventional silencers in acoustic ducts have problems of size limitations at low frequencies and being prone to high backpressure, locally resonant aluminum patches are introduced in acoustic duct walls aiming at creating frequency stop bands in the low frequency region (below 1 KHz). With these flush mounted patches, promising noise reductions, with no such drawbacks, can be obtained, building on local resonance phenomenon implemented in acoustic metamaterials techniques. The objective of the current paper is to experimentally validate the performance of an array of flexible side-wall-mounted patches inside ducts. The experimental results are compared with Analytical Green's function method as well as Numerical Finite Element Method and a close agreement was found. The results show that the presence of the patches singly or periodically can play a prominent role in designing any acousticbandgap materials. The effect of the arrays of patches on the effective dynamic density and bulk modulushas also been investigated.

Place, publisher, year, edition, pages
Acoustical Society of America (ASA), 2016.
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-192863DOI: 10.1121/1.4950736ISI: 000379164900041Scopus ID: 2-s2.0-84977272653OAI: oai:DiVA.org:kth-192863DiVA: diva2:972574
Funder
EU, FP7, Seventh Framework Programme, 289352
Note

QC 20161017

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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