Investigating the Feasibility and Stability for Modeling Acoustic Wave Scattering Using a Time-Domain Boundary Integral Equation with Impedance Boundary Condition

<p>Reducing aircraft noise is a major objective in the field of computational aeroacoustics. When designing next generation quiet and environmentally friendly aircraft, it is important to be able to accurately and efficiently predict the acoustic scattering by an aircraft body from a given noise source. Acoustic liners are an effective tool for aircraft noise reduction and are characterized by a frequency-dependent impedance. Converted into the time-domain using Fourier transforms, an impedance boundary condition can be used to simulate the acoustic wave scattering by geometric bodies treated with acoustic liners</p> <p>This work considers using either an impedance or an admittance (inverse of impedance) boundary condition to allow for acoustic scattering problems to be modeled with geometries consisting of both unlined and lined surfaces. Three acoustic liner models are discussed: the <em>Extended Helmholtz Resonator Model</em>, the <em>Three-Parameter Impedance Model</em>, and the <em>Broadband Impedance Model</em>. In both the <em>Helmholtz</em> and <em>Three-Parameter</em> models, liner impedance is specified at a given frequency, whereas the <em>Broadband</em> model allows for the investigation of multiple frequencies simultaneously. The impedance and admittance boundary conditions for acoustic liners are derived for each model and coupled with a time-domain boundary integral equation. The scattering solution is obtained iteratively using a boundary element method with constant spatial and third-order temporal basis functions.</p> <p>Time-domain boundary integral equations are unfortunately prone to numerical instabilities due to resonant frequencies resulting from non-trivial solutions in the interior domain. When reformulated with the Burton-Miller method, the instabilities are eliminated. Using a Burton-Miller reformulation, the stability of the boundary element method assuming a liner boundary condition is assessed using eigenvalue analysis. The stability of each liner model is discussed, and it is shown that the <em>Three-Parameter</em> and <em>Broadband </em>models are sufficient for modeling an acoustic liner on the surface of scattering bodies. The <em>Helmholtz</em> model demonstrates strict limitations for stability, whereas the <em>Three-Parameter</em> and <em>Broadband</em> models are stable for most cases.</p> <p>Also included in this work is an assessment of the spatial accuracy of the time-domain boundary element method with respect to the surface element basis functions, as well as a performance study of the numerical algorithm.</p>

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Mathematics & Statistics

Year dc:date.available

2020

Author dc:creator

• Rodio, Michelle E.

Contributors dc:contributor

• Fang Q. Hu
• Douglas M. Nark
• Yan Peng
• John Tweed
• Ruhai Zhou

• Acoustic liners
• Aeroacoustics
• Eigenvalue
• Numerical methods
• Quadrature
• Sparse matrices
• Acoustics, Dynamics, and Controls
• Applied Mathematics
• Computer Sciences

Statement dc:rights

• <p>In Copyright. URI: <a href="http://rightsstatements.org/vocab/InC/1.0/">http://rightsstatements.org/vocab/InC/1.0/</a> This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).</p>

Identifier

9798641756578

OAI identifier oai:identifier

oai:digitalcommons.odu.edu:mathstat_etds-1113