請用此 Handle URI 來引用此文件:
http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/44330
標題: | 水下爆炸氣泡在不同邊界附近趨移之研究 The Migration of Underwater Explosion Bubbles Near Different Boundaries |
作者: | Jing-Jia Hwangfu 皇甫敬嘉 |
指導教授: | 洪振發 |
關鍵字: | 水下爆炸,空化氣泡,氣泡動力學,氣泡趨移,噴流,凱爾文衝量,流體結構交互影響, underwater explosion,cavitation bubble,bubble dynamics,bubble migration,bubble jetting,Kelvin impulse,LSDYNA,ALE,fluid-structure interaction, |
出版年 : | 2011 |
學位: | 博士 |
摘要: | 在軍事、機械與醫學領域,結構因附近氣泡崩潰而產生的衝擊破壞,一直是個重要的問題。氣泡的趨移則與破壞有密切的關係,當氣泡朝向結構趨移,將產生較嚴重的破壞。因此,若想消除甚至利用水下爆炸氣泡破壞的威力,瞭解趨移的機制與具有預估趨移方向的能力是十分重要的。然而相關的文獻很少,因而引起作者研究動機。
在空化氣泡的研究中可以找到一些氣泡趨移的理論。由於這兩種氣泡在巨觀上相似,作者假設空化的趨移理論可以應用在水下爆炸氣泡上,由此著手研究。作者以微量炸藥產生的氣泡進行試驗,觀察氣泡在背面是空氣的崁板以及自由液面等邊界附近的行為。將觀察到的行為與用於空化氣泡研究的電火花/雷射氣泡比較,以確認兩者的相似性。試驗數據則代入空化氣泡趨移理論中,包括Kelvin衝量公式、邊界慣量m* 與邊界勁度k*圖表等。結果發現空化氣泡與水下爆炸氣泡是相似的,但是當同時考量邊界質量與勁度時,上述理論無一能全然地預估氣泡趨移方向,只有Kelvin衝量公式可以預估氣泡在自由液面附近的趨移方向。然而由試驗數據發現,邊界反應與氣泡振動的相位關係可以當作趨移的指標。為了獲得更多的資料,作者以模擬進行較密集的探索。 作者先以有限元素法程式LSDYNA模擬試驗場景,藉由調整元素幾何與微調程式指令參數達到模擬與實際相近的結果。當數值模型完成驗証後,便進行改變邊界厚度、材質與爆炸間距的密集探索。經過對氣泡行為與邊界反應的觀察,分析出氣泡趨移的機制。作者發現邊界振動週期對氣泡週期的比值r與氣泡趨移指標BRMIN/L具有線性關係:BRMIN/L=1.55r,由r可利用此關係估算氣泡趨移指標,從而知道氣泡趨移方向。作者還發現氣泡運動並不會受到爆炸產生的主震波的影響,因此上述發現也可用於電火花/雷射及空化氣泡。這些結果對於未來在機械與醫學領域中,消除空化氣泡的破壞,以及在軍事及工程領域利用水下爆炸氣泡破壞威力的研究具有貢獻。 Damage of structures by impacts of nearby collapsing bubbles is an important problem in the military, engineering, and medicine. The migration direction of bubbles is closely related to damage. When a bubble migrates toward a boundary, serious damage can be induced. To neutralize and even utilize this damage, it is essential to understand the mechanism of bubble migration and to be able to predict migration direction. However, related studies are rare, which motivates the interesting of the author. Research in cavitation has produced some results on the subject of bubble migration. Since these bubbles seem similar macroscopically, the author has assumed that these results can be applied to underwater explosion bubbles. To verify this assumption, experiments involving underwater explosion bubbles, produced by small charges, near four side-clamped air-backed metal plates and the free surface, were conducted. The behavior of spark/laser induced bubbles, which have been used in cavitation studies, were compared with underwater explosion bubbles. The author found that the behaviors of these two bubbles are similar. Experimental data were substituted into equations of the Kelvin impulse and charts of boundary inertia m* and boundary stiffness k*, which were developed to predict the migration of spark/laser bubbles. It was found that none of them are able to comprehensively predict the migration when boundary elasticity is considered. However, the Kelvin Impulse can predict the migration direction when the bubble is near the free surface. On the other hand, the author found that the phase between the boundary response and the bubble pulsation could help develop a predictive index. To obtain more information, a detailed investigation was undertaken using simulation methods. The finite element code LSDYNA was adopted for the simulation. The author first simulates the scenario of the experiment. Consistent results were achieved by adjusting meshes and tuning command parameters. After the numerical model was verified, detailed exploration of different boundary thicknesses, materials, and stand-off distances was carried out. By observing the bubble behavior and boundary responses in simulation, the mechanism of bubble migration was analyzed. The author found that the ratio of the boundary vibration period to the bubble period, r, and the normalized bubble migration index, BRMIN/L, are linearly related: BRMIN/L=1.55r. From r and through this relation, we can estimate the migration index and thus find the migration direction of the bubble. The author has also found that the primary shock has no effect on the bubble motions. This indicates that the bubble migration relation mentioned above, can be applied to spark/laser and cavitation bubbles. These results will help to neutralize, or even utilize bubble damage in future studies. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/44330 |
全文授權: | 有償授權 |
顯示於系所單位: | 工程科學及海洋工程學系 |
文件中的檔案:
檔案 | 大小 | 格式 | |
---|---|---|---|
ntu-100-1.pdf 目前未授權公開取用 | 7.18 MB | Adobe PDF |
系統中的文件,除了特別指名其著作權條款之外,均受到著作權保護,並且保留所有的權利。