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Title: 水中浮體音場輻射虛擬共振頻率現象之研究
A Study on the Radiated Fictitious Resonant Frequencies in the Acoustic Field of a Buoy Body
Authors: 張建仁
Contributors: NTOU:Department of Systems Engineering and Naval Architecture
Date: 2000
Issue Date: 2011-06-28T08:19:32Z
Publisher: 行政院國家科學委員會
Abstract: 本研究旨在釐清以各種邊界元素法求解半無窮域邊界上的輻射體或散射體是否會產生虛假頻率。我們提出一個理論來解釋發生虛假頻率的現象,由此我們可以來檢驗各種邊界元素法在針對所處理的問題時,是否會發生虛假頻率。由理論與數值的結果驗證出來,使用截斷法雖有數值誤差的假放大現象發生,但是假放大的頻率會隨著元素的切密而往高頻移動,這並不是真正的虛假頻率。使用平面波假設當作遠域的假想邊界條件時,並不會發生任何的虛假頻率。但是,當映象法使用時,則會發生虛假頻率。
In this research, whether or not fictitious eigenvalues will appear in dealing a radiator or a scatter located on the boundary of a semi-infinite domain is examined. A unified mathematical theory is proposed to explain the fictitious eigenvalue. From this theory, one can verify whether or not fictitious ei- genvalues exist in the BEM. Using theoretical results and numerical results, it is concluded that a direct BEM in conjunction with the truncated-length method do not result in ficti- tious eigenvalues. Although numerical un- reasonable amplifications exist in such method, the wave number where amplifica- tion occurs shifts to high wave number range while a finer mesh is used. Using the plane wave boundary condition as the far-filed ap- proximate boundary condition, the direct BEM then shows no fictitious eigenvalue. However, when an image method is used the fictitious eigenvalue can be observed.
Relation: NSC89-2611-E019-036
Appears in Collections:[Department of Systems Engineering and Naval Architecture] Research Reports

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