Periodic boundary element technique for acoustic and aeroacoustic applications

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Copyright: Karimi, Mahmoud
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Abstract
Two major hurdles associated with simulation of exterior acoustic problems are the memory requirement and computation time. A vast amount of memory is required to simulate and analyse a large 3D acoustic problem, particularly at high frequencies. Acoustic scattering problems are commonly solved using the boundary element method (BEM). For complex structures, the frequency-dependent BEM coefficient matrices are very large and there is little that can be done to alleviate the computational and storage requirements. However, applying the BEM to periodic structures leads to formation of a structured coefficient matrix due to translational invariance of the free-space Green's function. This thesis shows when using the boundary element method to solve 3D acoustic scattering problems for periodic structures, the coefficient matrix can be represented as a block Toeplitz matrix. By exploiting the Toeplitz structure, the computational time and storage requirements to construct the coefficient matrix are significantly reduced. It is also demonstrated that using the BEM, a multi-directional periodic acoustic problem can be formulated as a multilevel block Toeplitz (MBT) matrix. To ensure fast and stable convergence, the generalized minimal residual (GMRES) algorithm is used to solve the MBT matrix. A multi-dimensional discrete Fourier transform is employed in the GMRES method to accelerate the matrix-vector product and to obtain the acoustic pressure. The technique is implemented for a range of acoustic and aeroacoustic applications. To verify and evaluate the efficiency of the periodic BEM technique, the acoustic performance of a sonic crystal barrier with periodicity in one, two or three directions is initially examined. The noise reduction mechanism of a flat plate under flow noise source excitation is investigated by comparing results from unserrated and serrated trailing edges. Flow-induced noise by turbulent flow past a flat plate is also studied using a hybrid computational fluid dynamics (CFD) - periodic BEM technique. The hybrid technique is further extended to efficiently predict acoustic scattering with non-uniform potential flow effects for structures with rotational/translational symmetries. The effect of background mean flow on aerodynamic noise from turbulent flow past a circular cylinder is presented, whereby the numerical results obtained from the technique developed in this thesis are validated by comparison with experimental data from literature.
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Author(s)
Karimi, Mahmoud
Supervisor(s)
Kessisoglou, Nicole
Coraker, Paul
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Publication Year
2016
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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