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How the waveguide acoustic black hole works: A study of possible damping mechanisms
Umeå University, Faculty of Science and Technology, Department of Computing Science.
Umeå University, Faculty of Science and Technology, Department of Computing Science.ORCID iD: 0000-0003-0473-3263
Department of Mathematics and Computer Science, Karlstad University, Karlstad, Sweden.ORCID iD: 0000-0001-8704-9584
2022 (English)In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 151, no 6, p. 4279-4290Article in journal (Refereed) Published
Abstract [en]

The acoustic black hole (ABH) effect in waveguides is studied using frequency-domain finite element simulations of a cylindrical waveguide with an embedded ABH termination composed of retarding rings. This design is adopted from an experimental study in the literature, which surprisingly showed, contrary to the structural counterpart, that the addition of damping material to the end of the waveguide does not significantly reduce the reflection coefficient any further. To investigate this unexpected behavior, we model different damping mechanisms involved in the attenuation of sound waves in this setup. A sequence of computed pressure distributions indicates occurrences of frequency-dependent resonances in the device. The axial position of the cavity where the resonance occurs can be predicted by a more elaborate wall admittance model than the one that was initially used to study and design ABHs. The results of our simulations show that at higher frequencies, the visco-thermal losses and the damping material added to the end of the setup do not contribute significantly to the performance of the device. Our results suggest that the primary source of damping, responsible for the low reflection coefficients at higher frequencies, is local absorption effects at the outer surface of the cylinder.

Place, publisher, year, edition, pages
2022. Vol. 151, no 6, p. 4279-4290
Keywords [en]
Acoustic black hole, Finite element method, Helmholtz equation
National Category
Fluid Mechanics and Acoustics Applied Mechanics Computational Mathematics
Identifiers
URN: urn:nbn:se:umu:diva-198676DOI: 10.1121/10.0011788ISI: 000818623100001PubMedID: 35778217Scopus ID: 2-s2.0-85133707077OAI: oai:DiVA.org:umu-198676DiVA, id: diva2:1687981
Funder
Swedish Research Council, Swedish Research CouncilAvailable from: 2022-08-17 Created: 2022-08-17 Last updated: 2023-09-05Bibliographically approved
In thesis
1. Computational analysis and design optimization for acoustic devices
Open this publication in new window or tab >>Computational analysis and design optimization for acoustic devices
2023 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis focuses on material distribution topology optimization for acoustic waveguides. The limitations of the material distribution approach are discussed in the context of acoustic waveguides with extensive viscous and thermal boundary losses. An extension of the material distribution method is introduced which is capable of incorporating these boundary losses in the optimization process. Furthermore, a computational analysis of waveguide acoustic black holes (WABs) is also provided followed by a topology optimization approach for the conceptual design of a WAB with enhanced wave-focusing capabilities, utilizing the novel method introduced in the first part of the thesis.  The thesis commences with a comprehensive literature review to set the context for the subsequent research. The material distribution topology optimization is then discussed in detail, focusing on the design of a transition section for impedance matching between two cylindrical waveguides with different radii to maximize planar wave transmission. The linear wave propagation in the device is modeled using the Helmholtz equation and solved utilizing the finite element method to obtain acoustic pressure distribution. Nonlinear density filters are used to impose a size control on the design, and the design optimization problem is formulated and solved utilizing the method of moving asymptotes (MMA) with the sensitivity information provided through an ad-joint method. Selected results are provided for the considered design optimization problem. We expanded the analysis to encompass viscothermal acoustics and introduced a novel material distribution method capable of incorporating complex interface conditions. The new method is then applied to design acoustic absorbers with the aim of maximizing boundary losses in a targeted frequency range. The selected results represent the effectiveness of the proposed method.  The thesis further explores the limitations of the classical ribbed design of WABs in achieving true wave-focusing capabilities. To address this, a design optimization problem is formulated to obtain a conceptual design of a WAB. Utilizing the novel material distribution method for viscothermal acoustics introduced in this thesis, the optimization problem is solved, and the optimized design is compared with the results of a classical lossless approach and the ribbed design WAB. The numerical simulations demonstrate the superior wave-focusing capabilities of the optimized design, especially when incorporating boundary losses in the optimization process.   

Place, publisher, year, edition, pages
Umeå: Umeå University, 2023. p. 57
Series
Report / UMINF, ISSN 0348-0542 ; 23.05
Keywords
Design optimization, computational analysis, viscothermal acoustics, material distribution topology optimization, acoustic black holes, finite element method
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:umu:diva-214089 (URN)978-91-8070-146-4 (ISBN)978-91-8070-147-1 (ISBN)
Public defence
2023-09-29, NAT.D 300, Naturvetarhuset, Umeå, 09:15 (English)
Opponent
Supervisors
Available from: 2023-09-08 Created: 2023-09-04 Last updated: 2023-09-05Bibliographically approved

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Mousavi, AbbasBerggren, MartinWadbro, Eddie

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