- 學位論文
風浪表面熱圖像的條痕結構特性
Characteristics of Streaky Structure on Thermographic Images of Laboratory Wind Waves
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摘要
風浪下之邊界層流場存在成對反向旋轉之渦旋結構，且旋轉軸與風場方向平行，即 Langmuir 環流。Langmuir 環流在水面形成匯聚區，而於熱圖像產生沿流向之條痕結構，本研究旨在探討風浪表面熱圖像中的條痕結構特性。因熱圖像含有短波雜訊，故利用數位影像處理之技術，去除雜訊及小尺度的紊流結構對條痕結構的影響，以辨識條痕，統計條痕間距，進一步分析間距分佈之特性。結果顯示平均條痕間距隨風速增加而變小，與前人的研究結果相符，且此特性亦與無滑移邊界之紊流邊界層的條痕特性類似；而以摩擦長度無因次化之平均條痕間距則隨風速而變大，此與無滑移邊界層之無因次平均條痕間距為一定值的結果不同。經卡方適合度檢定，低溫條痕之間距分佈近似於對數常態分佈，與無滑移邊界之紊流邊界層的條痕分佈特性相同。
並列摘要
The counter-rotating streamwise vortex pairs are generated in the free-slip surface boundary layers. The vortical structures, which is also called Langmuir circulations, induce the converging zone at surface and form the streamwisely elongated streaky signatures. In this study, the characteristics of streaky structure on thermographic images of wind wave surface are analyzed. At first, the imaging procession techniques are employed to eliminate the effects of white noises and fine turbulent structures on images. As the positions of streaks are identified, the streak spacings and the corresponding distributions are then derived. The result shows that the mean streak spacing decreases as the friction velocity grows, which is similar to that of the no-slip wall turbulent boundary layer. The non-dimensional mean streak spacing based on friction length, however, increases with the friction velocity, different from that of the no-slip wall turbulent boundary layer, in which the non-dimensional mean streak spacing remains to be constant. Through the method of chi-square goodness-of-fit test, it is found that the distributions of streak spacing are close to lognormal distribution, similar to that of no-slip wall turbulent boundary layer.
參考文獻
[39] 古孟巧，「風浪表面熱圖像的條痕結構辨識與間距特性探討」，碩士論文，
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