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標題: 有限振幅重複波勢能區流場特性之實驗研究
作者: 林呈
關鍵字: 腹點
出版社: 國立中興大學工學院;Airiti Press Inc.
摘要: 有旨在利用流場可視化法與二維光纖雷射杜普勒測速儀,於均等水深之波動水槽內,針對入射?之非線性參數Ur=0.46~40.0及波浪尖銳度Hi/Li=0.010~0.063之不同造波實驗條件,探討有限振幅重複波勢能疑之水位變化與速度場分佈。根據線性或有限振富重複?理論,腹點與節點在入射與竑射方向上應為空間中之固定點,且線性重複波理論之節點是在靜水位處不動。惟於波動水槽實驗中,本研究發現:即使在精密造波機之造波調控下,由於每一造波週期未必完全相同,乃導致入射波列與反射波列中各波之波長亦隨之微幅變動,因而導致此一重複波流場中形成瞬時之最大波高與最小波高的發生位置亦隨時間而有微幅偏移的現象。 其次,本實驗針對有限振幅重複?之最高與最低、及平均水位的空間分佈特性,提出一套判釋的方法,並據以確認真正發生統計平均之最大波高與最小波高處的位置;繼而系統化研討此二特殊位置及介於其間之中點等三個斷面處之水、水平速度與垂直速 度的時序列變化特性,並研究相對應之頻譜變動特性。特別是在發生最小波高處之水位與垂直速度頻譜中所出現的雙位頻與次調和頻率特性,亦有詳實的討論。再者,對於勢能區內水平速度與垂直速度極值之剖面分佈特性,文中也予以闡述歸納。
The characteristics of flow field in the potential region of finite amplitude standing waves are investigated experimentally for Ursell number ranging from 0.46 to 40.0. flow visualization technique and fiber laser Doppler velocimeter (FLDV) was used , respectively, for qualitative observation and quantitative measurement. According to linear standing was theory, the nodes and anti-nodes are fixed points in the space of wave field and the nodes just locate at the still wave level. These specific points, on the contrary, are found to be not fixed in the flow field of wave flume experiment, due to tiny period differences of incident waves generated by a precise wave maker. Therefore, the method which was used to determine the spatial distributions of the highest, lowest, and mean water levels in the finite amplitude standing waves was proposed first. The positions of the maximum and minimum was heights were then determined. The characteristics of the time histories and spectra of the water surface elevation as well as the underlying horizontal and vertical velocities, measured along three sections, are elucidated in detail. Moreover, the characteristics of frequency doubling and subharmonic frequency in the time histories and spectra of both the water surface elevation and the vertical velocity, measured along vertical at the position of the minimum wave height, are depicted. Finally, the profiles of extreme values of the horizontal and vertical velocities below the will water level are also demonstrated in this work.
ISSN: 1017-4397
Appears in Collections:第13卷 第3期



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