運用管線於輸送各種流體在煉油、石化工廠、發電廠及燃氣工業中為一相當普及的設備，而在設置管線時經常會利用彎管以改變管線之路徑，增加空間利用的便利性和經濟上的效益，構築出一個龐大而繁忙的原物料運輸網路，大幅提升各類流體於廠區間的輸送效率，有效地增進工廠的生產效能。針對此類管線狀況的檢測，近年來以導波法為受到工業上推薦使用的非破壞檢測技術，其能快速並大範圍的針對管線進行整體性的檢查，評估管線的使用狀況及壽命。然而，使用彎管雖能有效提升管線網路的使用效益，但其特殊的幾何造型卻使得導波傳遞路徑改變，且經過波式轉換後衍生的各種高階非對稱型模態將互相影響，此皆使得其訊號變得複雜而難以預料。
　　本研究將針對導波T(0,1)扭矩模態行經彎管後所產生之局部聚焦現象，以及其對於缺陷檢測的影響分為兩部份，各自以有限元素法模擬和實際量測的方式進行探討。首先於聚焦行為的討論將擷取彎管後不同的位置的穿透訊號，經由分析不同距離時圓管上各個圓周方位上通過的訊號強度，得以瞭解導波通過彎管後，在管線上傳遞時波傳分布的強弱差異。在瞭解導波聚焦的行為之後，接著便於管線上設置缺陷，探討缺陷位置對檢測結果的影響，同時亦將其結果與導波聚焦行為進行比對，瞭解缺陷檢出結果與導波聚焦行為間的關聯性。
　　由研究結果顯示，造成其聚焦行為之因素主要包含彎管的幾何特性、各種模態疊加之結果以及頻散現象。於低頻時由於波式轉換所產生的模態較少，且模態間波速差異較明顯，因此低頻之聚焦行為較為單純，且波傳較快回復平穩。相對地在高頻時，各種高階模態相繼出現，使得聚焦的型式變得複雜，且各模態間波速相近，此也使得聚焦之行為將持續的更久。針對彎管後缺陷的檢出結果，利用有限元素法模擬證實缺陷的回波訊號會受到其分布位置的不同而有所改變，且其變化相當符合導波聚焦之結果。本研究藉由分析彎管後不同距離時的聚焦情況繪製出導波聚焦地圖，其直觀的顯示彎管後管線上導波聚焦的行為特性，並可以此預估缺陷回波訊號受到波傳聚焦的影響，對於缺陷嚴重度的判定提供良好的參考依據。

Pipelines system is generally use in petrochemical industry to transporting fluid or gas. In order to further the efficiency of economic and space applications, elbow parts provide good benefit to connect pipes and change the direction of pipelines. The guided wave method has proved to be a useful and cost-effective NDE technique in inspecting pipelike structures. However, after the guided wave has come through the elbow, propagation path changes and mode conversion happens due of its asymmetric geometric, and will cause the wave characteristic become complex and hard to predict. The guided wave are no longer spread symmetrically but local focusing on part of pipelines. These factors may influence the testing results and estimate the wrong evaluation of defects.
The thesis consists of two parts: the study of the T(0,1) guided wave focusing behavior beyond elbow, and the effect on defect testing by these wave focusing. To understand the focusing behavior after guided wave goes through the elbow, the transmission signal of guided wave are captured from pipe beyond elbow. By analyzing the signals on different distances and different circumference positions of pipes, the variations of guided wave signal amplitude shows the different intensity distribution while guided wave has passed through the elbow. After knowing the focusing behavior beyond the elbow, the defects are set to be proved the relation between the focusing behavior and the defect testing results. The study will proceed with both numerical simulation and experiment.
The study results show that factors cause the focusing behavior include the geometrical characteristics of elbows, the overlapping of different modes, and the dispersion phenomena. Since there are less modes exist at low frequency, and the difference between modes velocity are less as well. So the focusing behavior at low frequency are much simpler and also can be restored to stable quicker. While the frequency becomes higher, more modes appear to cause the focusing behavior that becomes more complex. The wave velocity of each mode come closer at high frequency also cause the focusing behavior keep longer. Furthermore, through the defect testing shows great directly related between guided wave focusing behavior and the defect reflection coefficient, which means the guided wave focusing results can use to predict if the defect signal were magnified or minified. The thesis bring up the focusing map which can easily to display the wave focusing distribution and its characteristic on pipe, that can provide inspectors as a reference when estimating the level of defects beyond the pipe.

中文摘要 i
英文摘要 ii
目錄 iv
表目錄 vi
圖目錄 vii
中英對照檢索 xi
第一章 緒論 1
1.1前言 1
1.2研究動機與目的 2
1.3文獻回顧 4
1.4研究方法 7
1.5論文結構 9
第二章 基本理論 11
2.1導波於圓管傳遞之波動方程式 11
2.1.1縱向模態 12
2.1.2扭矩模態 13
2.1.3撓曲模態 13
2.2頻散曲線 13
2.3波形結構 16
2.4有限元素法 18
第三章 導波於彎管後聚焦現象 25
3.1有限元素暫態模擬 25
3.1.1模型設定與網格劃分 26
3.1.2圓管導波訊號激發 27
3.1.3訊號擷取 28
3.2彎管及彎管後導波聚焦模擬結果 29
3.2.1激振頻率10 kHz之聚焦現象 30
3.2.2激振頻率30 kHz之聚焦現象 33
3.2.3激振頻率100 kHz之聚焦現象 36
3.3導波於彎管後聚焦現象實驗 40
3.3.1導波法檢測儀器系統 40
3.3.2實驗設定及步驟 42
3.3.3實驗結果與討論 44
3.4導波於彎管後聚焦行為總結 47
第四章 導波經彎管後聚焦現象對缺陷檢測的影響 95
4.1導波聚焦分佈圖 95
4.2有限元素法模擬彎管後不同位置缺陷回波訊號 97
4.2.1模擬設定 97
4.2.2模擬結果 98
4.3彎管後缺陷檢測之實驗 101
4.3.1實驗設定 101
4.3.2實驗結果 102
4.4導波經彎管後聚焦行為對缺陷檢測影響之結論 104
第五章 結論與未來展望 118
5.1結論 118
5.2未來展望 120
參考文獻 123

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