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Modelling of a ground impedance boundary in a time-domain CAA method

Pol, E. van der (2012) Modelling of a ground impedance boundary in a time-domain CAA method. Master's Thesis / Essay, Mathematics.

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In this thesis the modelling of a ground impedance boundary condition in a time-domain computational aeroacoustic method is investigated. A ground impedance boundary is a boundary that absorbs part of the incoming acoustic wave and reflects the rest. In the literature several models are proposed to model the quantity of absorption, the impedance, for a range of ground types. All of the proposed models are defined in the frequency domain, but the computational aeroacoustic method calculates in the time domain. Unfortunately, the transformation to the time domain is not straightforward, and therefore approximations are proposed. One approximation is a broadband approach and is described by poles, another is a single-frequency approximation. There are several ways to discretize the pole approximation. In the literature a recursive implementation is proposed. However, in this thesis a new implementation is proposed. The implementation is given as a system of ordinary differential equations. This system can be solved with the same fourth-order time-integration method, as is used in the computational aeroacoustic method, which makes the entire system fourth-order accurate. Some two-dimensional test cases show the influence of the ground impedance boundary condition on a sound wave.

Item Type: Thesis (Master's Thesis / Essay)
Degree programme: Mathematics
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 15 Feb 2018 07:50
Last Modified: 15 Feb 2018 07:50

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