虛擬曲折波線追跡法在土木構件斷層掃描之研究

Computational tomography of structural elements by pseudo-bending ray tracing method

林佳慧(Chia-hui Lin)

指導教授 ： 王安培

中原大學/工學院/土木工程學系/碩士(2008年)

https://doi.org/10.6840/cycu200900255

摘要

斷層掃描方法已應用在許多領域的檢測工作，在醫學、地球科學中皆有相當成熟的應用與發展，但是在土木構件的非破壞檢測上卻尚未發展出實用的模式，由於土木構件斷面屬於高度非均質斷面，且缺陷孔洞的尺寸較小，因此波在其中的傳遞路線較為複雜。
本文使用震波斷層掃描法對土木構件進行非破壞性檢測，並以虛擬曲折波線追跡法作為震波斷層掃描法的正算模式，探討虛擬曲折線追跡法應用在土木構件的斷層掃描效果。
本文中所使用的震波斷層掃描中有兩個重要的步驟，分別是計算波行路徑及波徑走時的正算模式，以及由正算模式所得的資料來反推波速模型的反算模式。在正算模式中本文採用虛擬曲折波線追跡法，此演算法的原理為猜測一初始波線，依已知的波速模型進行擾動，直到波徑走時為最小。由正算模式計算出波行路徑後，再以SIRT 反算法（Simultaneous IterativeReconstruction Technique）及LSQ 反算法（Least Square method）兩種反算方法進行波速模型的重建，最後計算出的結果利用影像重製技巧處理後以灰階圖的形式輸出，藉由此灰階影像便可判讀出土木構件的斷面組成。
除了探討虛擬曲折波線追跡法在土木構件的斷層掃描效果之外，尚比較了SIRT 反算法及LSQ 反算法的波速重建效果，結果顯示SIRT 反算法使用在顯示混凝土中的損壞區塊以及混凝土中的鋼筋位置皆有不錯的效果，反之LSQ 反算法無法有效的顯示混凝土中的鋼筋位置。

關鍵字

震波斷層掃描 ； 非破壞性檢測 ； 虛擬曲折波線追跡法

並列摘要

Tomography has applied in testing in many domains. In the medicine and geoscience both has quite mature application and development, but actually not yet develops practical pattern in the non-destructive testing for structural elements. Because the structure element cross section belongs to highly non-isotropic cross section, and the size of flaw is smaller. Therefore the ray path is more complex.
This article use seismic tomography method proceed to the non-destructive testing for the structural elements, and use pseudo-bending ray tracing method to be the forward modeling of seismic tomography. Discuss the effect of tomography of structural element by pseudo-bending ray tracing method.
The seismic tomography contains two important procedures. The first one is the forward modeling for given ray path and travel time. The second is the inversion for updating the model of wave velocity. In forward modeling, this article use pseudo-bending ray tracing method. The principle of this algorithm is assumed an initial ray path. The initial guess of the ray path is iteratively perturbed by known model of wave velocity until the travel time along the path is minimized. Calculates ray path by forward modeling, then reconstructs the model of wave velocity by SIRT inversion technique and LSQ inversion technique. Finally, process the result by image replot technique, and then output it by gray scale chart. By the gray scale chart can ascertain the components of the structural elements.
Besides discusses the effect of tomography of structural elements by
pseudo-bending ray tracing method, also compares the effect of reconstruct the model of wave velocity by SIRT inversion technique and LSQ inversion
technique. The result demonstrates that to display the damage region and
position of steel bar in concrete by SIRT inversion technique, both has good
effect. Otherwise, LSQ inversion technique is unable the effective to display
position of steel bar in concrete.

並列關鍵字

Pseudo-bending ray ； Seismic tomography ； Non-destructive testing

參考文獻

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