非破壞檢測技術中的導波法可以檢測長距離的管線，經由判斷其反射波以及波式轉換現象可指出缺陷或其它特徵的存在。為了研究導波定量管線沉積物的可行性，本文藉由有限元素暫態模擬分析導波T(0,1)模態遇管內存在非對稱層的散射現象，結合二維傅立葉轉換與小波轉換等訊號處理技術來了解該現象。數值分析顯示了以下的現象，其一，T(0,1)模態導波於圓管上傳遞時，若遭遇如沉積物一般之非對稱層於波傳路徑上，局部波傳能量將洩漏至管內非對稱層內，並轉換成非對稱層與圓管所形成的複合管，其模態進行傳遞；其二，非對稱層於管線內部，會對傳遞而至的T(0,1)模態產生反射回波，該回波模態包含T(0,1)模態本身與其它周向高階模態。擷取反射訊號在不同截面積比例下所產生之反射回波，其相對應反射頻譜響應乃與非對稱層於管內的百分比參數息息相關；於本研究結果亦藉由小波轉換的時頻分析技術，將反射波中的T(0,1)扭矩模態做為定量沉積物之預測工具。

Ultrasonic guided waves having the ability to inspect long distance pipeline is one of the non-destructive testing methods. The reflected echoes as well as mode conversion phenomena indicate the presence of defect or other features on the pipe. To study the feasibility of guided wave quantification of sludge inside pipes, this thesis applies the transient simulation by finite element method to analyze the scattering of the guided T(0,1) mode by non-axisymmetry layer inside a pipe. Both the Two-dimensional Fourier transform and Wavelet transform were used to process the signals to understand the scattering behavior. The numerical analyses revealed the following phenomena. First, partial energy of the T(0,1) mode will leaky into the asymmetric layer when T(0,1) mode propagates along the pipe and impinge onto the asymmetric layer inside a pipe named a composite pipe. The T(0,1) mode will convert to the propagating modes of the composite pipe model. Secondly, the composite pipe will reflect the T(0,1) and modes of higher circumferential order. The percentage of asymmetric layer inside a pipe is one of the parameter controlling the reflection spectrum response. To sum up, in this study, the reflection spectrum response could used to predict the quantified accumulation of sludge by wavelet transform through time-frequency analysis.

中文摘要 i
英文摘要 ii
目錄 iii
表目錄 v
圖目錄 vi
第一章、緒論1
1.1前言 1
1.2文獻回顧 1
1.3本文架構 4
第二章、基本理論 5
2.1導波的基本概念 5
2.2導波基本理論與分析 5
2.2.1導波於圓管中的波動方程式 5
2.2.2頻散曲線 7
2.2.3波型結構 9
2.3有限元素法 9
2.4二維傅立葉轉換法 10
2.5小波轉換法 11
第三章、導波波傳行為模擬分析 17
3.1有限元素暫態模擬 17
3.1.1網格建立 18
3.1.2邊界條件設定 18
3.1.3求解與分析結果 19
3.2波傳模態辨識 20
3.3反射訊號分析 21
3.4振動模態分析 23
3.5本章結論 24
第四章、T(0,1)模態對管內非對稱層的散射行為 36
4.1結構規劃與模擬訊號擷取 36
4.2穿透波討論 37
4.3反射波討論 39
第五章、結論與建議 66
5.1結論 66
5.2建議與未來展望 67
參考文獻 68

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