導波法可以快速檢測長距離的管線，經由分析反射回波訊號及波式轉換現象可指出缺陷或其他特徵的存在，但對於孔蝕這類型腐蝕仍有檢測困難度與盲點。故本研究之目的係探討導波T(0,1)模態遭遇孔蝕之反射回波現象，並利用小波時頻分析技術來提高腐蝕訊號的判讀能力。
為了瞭解孔蝕反射回波訊號之特性，本論文先以有限元素法模擬T(0,1)模態導波入射至孔蝕所產生之反射訊號，藉由有限元素法模擬與實驗法來研究單一孔蝕在不同孔徑及深度變化下，其導波反射訊號及頻率響應之特性；其次進行多孔規則型及隨機型孔蝕之討論，探討多孔規則型孔蝕區之軸向距離與激發頻率波長之關係，同時也針對四區人工腐蝕程度不同之隨機孔蝕區所產生之回波訊號進行分析。實驗乃藉由環狀探頭激發T(0,1)模態於3吋碳鋼管件上，採收發合置，分析各案例中的孔蝕區回波訊號特性。
由模擬的結果顯示，孔蝕因幾何形狀影響容易散射，導致回波訊號較弱，因此在操作頻率範圍內選擇較高頻者，以取得較大的單一孔蝕反射回波訊號。而由實驗結果可知，當腐蝕截面積損失比小於2 %時，由於訊號過小導致被淹沒於雜訊之中，以目前導波技術尚無法檢測出來。但輔以小波時頻分析後，該結果可有效提高訊號判讀的能力，使訊號得以分離出來；針對多排規則型孔蝕區之研究結果發現，孔蝕區之軸向間距為入射波長0.66倍時發生建設性干涉現象，使得反射訊號有最大值，且由於孔蝕區具有非軸對稱特徵，波式轉換易伴隨而生。針對隨機孔蝕腐蝕區，其反射回波訊號隨頻率變化特性則不像規則型孔蝕一樣受干涉現象影響較深，該回波乃隨頻率升高而反射訊號下降；在不同腐蝕程度下之孔蝕區經小波時頻分析後可有效地定義其腐蝕程度。藉由本研究成果了解T(0,1)模態與孔蝕之交互作用現象，配合訊號處理分析，將有助於提高導波於管線孔蝕檢測之能力。

Using ultrasonic guided waves can achieve long range inspection along the pipeline rapidly. The presence of defect or other features on the pipe were identified by analyzing the reflected echoes as well as mode conversion phenomena. However, it is difficult for guided wave to find a minor corrosion, such as pitting. Therefore, a study of the reflection of torsional T(0,1) mode from pits on the pipe has been carried out and an advanced signal processing method wavelet transform is adopted to process the reflected echoes in this study.
In order to understand that characteristic of the reflected echoes of pits, the propagation of guided wave T(0,1) through pits was simulated by the finite element method. The frequency response of the signal reflected from the pits with different sizes was discussed both by finite element method and experimental method. Then, we discuss two types of pitting including regular- distributed pitting and the random-distributed pitting. We not only discuss the relation between the axial length of regular pitting and wave length of the T(0,1) mode, but also the reflected singal of four random pittings. The experiments were performed on 3 inch carbon steel pipe for measuring the reflected signals from different pittings with different frequencies.
The results of the simulation, indicate that the wave was easily scattered by pitting because the shape of geometry. It is the reason of reducing the amplitude of reflected signals. To receive a dominate signal reflected from pitting, the excitation with higher frequency was choosen within the frequency range of interest. The experimental results indicate that the signals would be too weak to be detected by guided waves when the estimated cross sectional loss of the pitting is less than 2 percent. However, the results after wavelet transform showed the feasibility of improving the abilities of detecting minor pitting. In the case of regular pitting, the maximu value of the reflected signal appeared when the axial length of the pitting equals to the 66 % of the wavelength. It is because the constructive interference. The mode conversion phenomena is another behavior of the reflected signal cased by the non-axissymetric geometry of the pitting. As for the random pitting, The reflected echo shows different behavior with the regular pitting. The amplitude of the signal is bigger with lower frequency we use. The different level of random pitting on the pipe were also identified successfully by wavelet transform. Understanding the phenomena of interaction between the guided wave and the pitting is helpful to the guided wave inspection.

中文摘要................................................................................................................i
英文摘要……………………………………………………………………… iii
目錄……………………………………………………………………………v
表目錄………………………………………………………………………viii
圖目錄……………………………………………………………………x
第一章緒論.........................................................................................................1
1.1 研究背景……………………………………………………………1
1.2 文獻回顧……………………………………………………………2
1.3 研究方法……………………………………………………………5
1.4 本文架構……………………………………………………………5
第二章基本理論.................................................................................................7
2.1 導波基本概念........................................................................................7
2.2 導波基本理論與分析............................................................................7
2.2.1 導波於圓管中之波動方程式.....................................................7
2.2.2 頻散曲線.....................................................................................9
2.2.3 波形結構...................................................................................10
2.3 小波轉換法..........................................................................................11
第三章 實驗架構與模擬設定...........................................................................17
3.1 實驗架設..............................................................................................17
3.1.1 實驗儀器設備[43] ....................................................................17
3.1.2 實驗管件規格...........................................................................19
vi
3.1.3 實驗步驟與方法…...................................................................20
3.2 導波波傳模擬......................................................................................21
3.2.1 有限元素暫態模擬...................................................................21
3.2.2 有限元素法模型設定...............................................................21
3.2.3 施加負載與後處理部份...........................................................22
3.3 缺陷尺寸與截面積損失比之計算......................................................23
3.3.1 單孔、規則型孔蝕模型之建立及截面積損失比之計算.......23
3.3.2 規則型與隨機型孔蝕模型之建立...........................................24
第四章 單一孔蝕之結果與討論.......................................................................40
4.1 單一孔蝕與凹槽模擬結果與討論......................................................40
4.1.1 凹槽尺寸變化之影響...............................................................40
4.1.2 單一孔蝕模擬結果...................................................................41
4.1.3 孔蝕與凹槽模擬討論...............................................................42
4.2 實驗結果與討論..................................................................................43
4.2.1 單一孔蝕………………………………………………………43
4.2.2 重覆性實驗..............................................................................45
4.3 小波時頻分析結果..............................................................................46
第五章 規則型與隨機孔蝕研究成果 ..............................................................73
5.1 規則型與隨機孔蝕模擬結果與討論..................................................73
5.1.1 規則型孔蝕模擬結果與討論...................................................73
5.1.2 隨機型孔蝕模擬結果與討論...................................................75
5.2 規則型與隨機孔蝕實驗結果與討論..................................................75
5.2.1 規則型孔蝕實驗結果與討論...................................................75
vii
5.2.2 隨機型孔蝕實驗結果與討論...................................................76
5.3 小波時頻分析......................................................................................77
第六章 結論與建議.........................................................................................110
6.1 結論....................................................................................................110
6.2 未來展望............................................................................................111
參考文獻...........................................................................................................112

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