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題名 | 層流波動邊界層之速度量測與底部剪應力之評估探討=Measurement of Velocity and Evaluation of Bottom Shear Stress in the Laminar Wave Boundary Layer |
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作者 | 林呈; 鄭中南; 顏光輝; 蔡清標; | 書刊名 | 力學 |
卷期 | 12:2 1996.06[民85.06] |
頁次 | 頁267-278 |
分類號 | 440.137 |
關鍵詞 | 光纖雷射杜普勒測速儀; 層流波動邊界層; 速度梯度; 底部剪應力; 摩擦係數; Fiber-Optic laser doppler velocimeter; Laminar wave boundary layer; Velocity gradient; Bottom shear stress; Friction factor; |
語文 | 中文(Chinese) |
中文摘要 | 本文旨在於提出一種既可量測速度場、又能方便且精確地以微分方法來計算波動 底部剪應力之相位變化的量測分析法。為此,本研究首先運用光纖雷射杜普勒測速儀,針對 均等水深下層流波動邊界層的內外,進行水平速度場的量測探討; 然後,藉由距底床 0.08 ∼ 0.20 mm 各量測點處之速度變化,利用各量測點與底床間之速度的線性微分運算, 據以 評估底部剪應力的相位變化。經由本文的研究,吾人可發現:於邊界層內外,經修正相位平 均及富立爾分析處理之任一相位的量測速度剖面均能予以組合重建;且其變動趨勢乃與使用 量測波長代入線性波動理論中所計算的結果十分吻合;又經分析之無因次化極值速度與相位 差對無因次化高度 (z/ δ ) 的變化,亦皆與前人的研究成果甚相一致。再者,經與前人有 關於摩擦係數對雷諾數之變化分析結果的比較,本文建議能用以量測速度、且同時可據以計 算求得(最大百分誤差不超過 4%) 底部剪應力之相位變化的無因次高度為 z/ δ�� 0.2。 |
英文摘要 | The purpose of the present study is to introduce a method that can be used to measure the velocity field as well as to analyze the phase variation of bottom shear stress. The precise measurements of horizontal velocity field in and near the laminar boundary layer, induced by waves propagating over uniform water depth, were first performed by a fiberoptic laser Doppler velocimeter. The phase variation of bottom shear stress was then evaluated by linear differentiation of velocity between some measuring point, 0.08 ∼ 0.20 mm away from bottom, and the origin. It is found that the variation tendencies of velocity profile at various phases are not only well reconstructed by the modified phase average method and Fourier (harmonic) analysis, but also very consistent with the calculated results of linerar wave theory. Moreover, the measured variations of the nondimensionized maximum velocity and phase lag are quite in agreement with those of previous studies. Finally, after comparing the relationship between calculated friction factor and Reynolds number of the present investigation with those analyzed by past work, a criterion of nondimensional height of z/ δ�� 0.2 for measuring velocity and feasibly determining bottom shear stress, with a maximum error of about 4%, is proposed in this study. |
本系統之摘要資訊系依該期刊論文摘要之資訊為主。