UBC Theses and Dissertations

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UBC Theses and Dissertations

Acoustic pulse diffraction by curved and planar structures with edges Zhang, Qin


Efficient and accurate solutions of acoustic wave diffraction by a rigid step discontinuity and a curved half-plane are derived by the uniform geometrical theory of diffraction. These solutions can be used in seismic data processing to evaluate and, eventually, to improve the existing data processing procedures. They can also find applications in electromagnetics, microwave antenna design, acoustic design and sound engineering. The rigid step discontinuity solution given in this thesis is more accurate than the existing solutions which are based on Kirchhoff theory of diffraction. This solution removes the previous restriction on the source and the receiver arrangement. It also provides high efficiency by the use of ray theory. This solution is further generalized to two offset half-planes and an inclined wedge. Solutions for more complicated structures can be obtained by superposition of these solutions with added interactions. The complex source position method is used to extend the omnidirectional point source solution to a beam source solution. The effect of changes of the directivity and orientation of the beam source is studied. Time-domain single and double diffraction coefficients are determined through direct Fourier transforming and convolution. An infinite impulse response filter is applied to the time-domain direct computation of single diffraction. This combination achieves a total saving of 75% of computing time over the frequency-domain approach. Diffraction by a curved half-plane is analyzed with the inclusion of creeping wave diffraction and second order edge diffraction. An acoustic model of a curved half-plane is designed to verify the theory. The experimental results obtained by Mellema have verified the existence of the creeping wave diffraction and weak traces of the second order edge diffraction.

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