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研究生:葉智惠
研究生(外文):Chih-Hui Yeh
論文名稱:水滴撞擊水面產生氣泡之類型及噪音特性之研究
論文名稱(外文):Different types of bubble formation and underwater noise caused by single water drops
指導教授:黃清哲黃清哲引用關係
指導教授(外文):Ching-Jer Huang
學位類別:碩士
校院名稱:國立成功大學
系所名稱:水利及海洋工程學系碩博士班
學門:工程學門
學類:河海工程學類
論文種類:學術論文
論文出版年:2002
畢業學年度:90
語文別:英文
論文頁數:83
中文關鍵詞:氣泡
外文關鍵詞:underwater soundGabor transformbubble
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中文摘要
本研究主要是以實驗方法探討單一水滴降落水面氣泡形成之過程及其產生噪音之特性。實驗分為兩部分,其一是以數位式高速照相機拍攝雨滴撞擊水面時氣泡形成之過程;另一部份則是以水中收音器量測雨滴撞擊水面產生之噪音,並用Gabor transform將瞬時訊號轉換成時間—頻率域進行分析。本實驗水滴大小分布為2.6mm~5.66mm,水滴降落高度為10cm~150cm。
實驗結果顯示水滴撞擊水面產生之氣泡種類,可分為三個類型。第一種類型的氣泡發生在水滴撞擊水面時,水面受力產生一向下的凹面,凹面在收縮過程中形成一氣泡。第二種類型的氣泡可細分為兩種形式,分別為第二種-A型及第二種-B型氣泡。第二種-A型氣泡為衝出水面之水柱在降落的過程產生單一氣泡;第二種-B型氣泡為衝出水面之水柱在降落的過程產生一渦流環(vortex ring),其周圍生成一環狀排列的小氣泡。第三種氣泡則是水柱上方的水珠降落時所生成。其中第一種及第三種類型氣泡所釋放出的頻率約在6~15kHz間;第二種-A型氣泡其頻率在4~8kHz之間;第二種-B型氣泡由於其氣泡大小不一,因此頻域較寬,在7~17kHz之間,且在14kHz左右聲壓最大,由此可看出為何現場水中降雨噪音主頻約在14kHz。實驗中加入鹽水的結果顯示,除了出現前面所討論的氣泡產生形式外,氣泡在形成的過程中也會有一個大氣泡變形分裂成兩個小氣泡的情況產生。
Longuet-Higgins在1989年,利用The Dirichlet hyperboloids推導氣泡形成時圓錐角角度為109.5∘。與本實驗氣泡形成時圓錐角角度相當吻合。
ABSTRACT
The bubble formation and underwater sound produced by a single water drop was investigated experimentally in this study. A CCD camera was set up to photograph the drop impact and the process of bubble formation. Underwater sound was received using a hydrophone connected to a charge amplifier and a data-acquisition system for capturing the main characteristics of the sound. The time-series of the underwater sound was transformed into the time-frequency domain using the Gabor transform. The range of the drop diameter is from 2.6 mm to 5.66 mm. The release height of the drop ranges from 10 cm to 150 cm. The experimental results show that there are three different bubble types generated by the water drops impact. Type I bubble is formed at the base or the apex of the contracting crater produced by the primary impact of the drop. Type II bubbles are entrained by the downward motion of the water column produced during the primary drop impact. Type III bubble is generated by the secondary impact of the small drop above the water column. The angle at the instance of bubble formation is consistent with the theoretical value predicted by Longuet-Higgins (1990). Effect of the salinity on the drop impact was also studied. In the salt water, bubble of relatively large size can be formed and collapses later into two bubbles.
Contents
Chinese Abstract………...……….………………………………..…………………Ⅰ
English Abstract………...……….…………………………….….………………….ⅡAcknowledgement……………………………………………………………………Ⅲ
Contents……………………………………………………………………………...Ⅳ
Table Caption………...……….…………………………….….…………………….Ⅵ
Figure Caption……...……….…………………………….….………………………Ⅶ
Notation………………………………….…………………………….…………….XII
Chapter 1Introduction..….….….…..………………………..…………………...1
1.1Purpose of this study………….……………………………….…1
1.2Literature review……………………….………………………...1
1.3 Outline of this study…………………………………….………..5
Chapter 2The Related Theories…………………………………….……………7
2.1The impact velocity of rain drops………..………………….…..7
2.2Bubble equation and natural frequency of bubble………………9
2.3The angle of the inverted cone…………….……………………12
2.4A physical discussion of the angle of the inverted cone…….….16
2.5Gabor expansion………………………………………………..17
Chapter 3Experimental Set-up………….……...……………………………… 20
Chapter 4Results and Discussions..…..……….………………………………..23
4.1Background noise………….……………………………………23
4.2The bubble formation and the underwater sound produced by a single water drop………………………………………………..23
4.3Effects of the salinity of the water.…………….…………….…28
Chapter 5Conclusions and Suggestions……………………....……………….. 31
5.1Conclusions…….………….……………………….…………...31
5.2Recommendations for Future Research……….…….………….32
References..…….….………….……………………………….…………………33
Appendix 1……….………….……………………………….……….…………..83
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