本文主旨係以實驗方法探討規則波浪通過潛堤時，反射率、透射率的變化，並挑出八組發生碎波之造波條件，使用水中聲學儀器及光纖探針陣列，探討波浪通過潛堤發生碎波時，空氣捲入所產生之氣泡特性。氣泡特性一般常以氣泡大小、數量、分佈以及體積分率來表示。
反射率與透射率的實驗量測，係利用分別置於潛堤前端以及潛堤末端的電容式波高計，量測不同造波條件下，波浪通過潛堤時之波高資料，並藉此計算反射率以及透射率結果。從實驗結果得知在潛堤高度與水深比大於0.6時，透射率容易受到波浪尖銳度、相對水深以及相對堤寬影響而有明顯衰減。由反、透射率的實驗觀察，挑出八組產生碎波之造波條件，探討碎波捲入產生之氣泡特性。在水中氣泡噪音實驗中，主要是利用水中麥克風量測碎波發生時，氣泡輻射出之聲音訊號，在濾除環境噪音後，利用Gabor 轉換，將時域訊號轉換為時間－頻率域訊號，並由此分析出氣泡之大小及數量，進一步得出碎波氣泡之機率密度譜。本文造波條件中所估算出之氣泡半徑分佈介於0.1 mm－7.6 mm之間，大約在氣泡半徑0.8 mm處，Hinze Scale將氣泡團區分成兩部分。光纖感測實驗則是利用陣列式光纖探針量測碎波帶內的光訊號，並求出訊號受氣泡影響之時間分率比 (time fraction ratio)。經由圓柱管氣泡率定實驗，可藉由時間分率比判識出氣泡體積分率，光纖探針感測實驗可以彌補以水中聲學方法在計算體積分率上的不足。比較波浪通過潛堤時，因為碎波所造成之能量損失以及碎波產生之氣泡數量後發現，碎波捲入產生之氣泡數量與所造成的能量損失之間存在一線性關係。

In this study, wave gauges, the underwater acoustic instruments and an array of fiber optic sensor were used to explore the characteristics of the air bubbles entrained by breaking waves near a submerged breakwater. The characteristics of air bubbles are discussed in terms of bubble size, numbers, probability density and air void fraction.
In the experiments of wave reflection and transmission, wave gauges were mounted 1 m away from the front and rear sides of the submerged breakwater, to measure the water surface elevation. The experimental data revealed that when the relative height of the breakwater is more than 0.6, an obvious decreasing trend is observed at the transmission coefficient. In order to excavate more about the characteristics of entrained bubbles, eight different wave conditions were selected and carried out in the acoustical and fiber optical experiments.
The hydrophone was utilized to detect the noise radiated from the air bubbles. The time-series data of the underwater sound were transformed into the time-frequency domain for capturing the information of the bubbles, such as the bubble size and numbers. The probability density function of the bubbles was also determined. The results of this study reveal that the radius of the bubbles entrained by the breaking waves near a submerged breakwater ranges between 0.1 mm and 7.6 mm. The probability density function of the bubble shows a different slope with a Hinze scale of 0.8 mm. The number of air bubble increases along with the incident wave height and the width of submerged breakwater.
Array of fiber optic probe is deployed in the surf zone to monitor the optic signals. The time fraction ratio of signals affected by air bubbles was then obtained. A calibration experiment was carried out in a cylindrical tank to establish the rating curve between the time fraction ratio and the void fraction. The rating curve enables the transfer of the time fraction ratio into the void fraction. In the void fraction measurement experiment, distributions of void fraction along the lee side of the breakwater are also presented in the text. There is a nice agreement after comparing the results of energy loss with entrained air bubbles.

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