黃良雄臺灣大學：土木工程學研究所黃學美Huang, Hsueh-MeiHsueh-MeiHuang2007-11-252018-07-092007-11-252018-07-092007http://ntur.lib.ntu.edu.tw//handle/246246/50235物體經由一微小角度掀起，克服與底床面間之吸附力，而至完全脫離底床之過程可稱為突破現象(breakout phenomenon)。Mei et al. (1985) 延續Foda (1982) 之研究，以水平間隙與楔型夾角兩種情形探討突破現象所需之時間與作用力關係。然解析過程並未包含短時間尺度下之瞬時突破(sudden breakout)效應，並以潤滑理論之平行流方式簡化黏流作用下夾角內部流場，為分析不盡完整處；再者，Mei et al. (1985) 文中採用Beavers & Joseph (1967) 提出之部分滑移邊界條件，連接至底床符合達西定律之孔隙流體，由於達西定律無法完全反應流體黏滯效應，故此作法將忽略底床中由黏滯效應引起的邊界層速度。 短時間尺度下瞬時突破效應主要反映於夾角內部流體對物體之巨大吸附力，本文以勢流理論清楚呈現此一現象，並以正規擾動展開法分析，提出此時夾角內部流體與底床流體之可能流況。長時間尺度下之突破效應主要反應於流體黏滯性開始發揮作用後，不同於勢流作用下，夾角內部及底床孔隙流體之流場分布。本文以低雷諾數流理論輔正規擾動展開法及邊界層修正法，找出底床以壓力梯度驅動之非旋性速度，及存在於邊界層特性尺度內，源自上層流體剪應力之旋性速度，說明達西定律無法完全反映流體黏滯性之缺憾。而由流場分析結果得知長時間尺度下，夾角頂點處有一能量點源存在，使得物體在掀起過程中有滑動之虞，擬可應用於實際工程參考。Breakout phenomenon is the whole process that an object is tilting lifted up from rest at first, and finally separated from the seabed. In the process, the object has to overcome the huge adhesive force exerted by the fluid flowing into the gap at the time it was formed. The force-time relation of breakout phenomenon was discussed in Mei et al. (1985), through cases of a horizontal gap and a wedged gap. However, the analysis was carried out by a few assumptions, which made the study somewhat incomplete -- the vertical velocity was neglected; the inertia term exhibiting the transient effect under small time scale of breakout was absent -- owing to the adoption of lubrication theory. Moreover, the boundary layer was left out in the seabed because of the employment of Darcy’s law, which was unable to reflect the viscosity perfectly. The sudden breakout effect under small time scale was mainly characterized by the huge adhesive force exerted by the fluid in the gap, the potential flow theorem was introduced in the present study to deal with the sudden time effect accordingly. The huge force was found successfully, and the possible flow field in the gap and porous seabed was brought up as well. After some time later, the viscosity started to work out, whence the flow pattern under long time scale was different from the one under small time scale. The low Reynold’s number flow theory was accordingly adopted to describe the flow filed in the present study. On the aid of regular perturbation method and the boundary correction method, the irrotational velocity driven by pressure gradient in the seabed as well as the rotational one coming from the shear stress were cleared up. Meanwhile, through the analysis of such flow field, it was inferred that the object at the apex of the gap was likely to move during the lifting process, which might be helpful to the practical engineering.誌謝　　　　Ⅰ 中文摘要　　III Abstract　　Ⅳ 目錄　　　　V 表目錄　　　Ⅷ 圖目錄　　　X 符號說明　　XⅡ 第一章 導論 1 1.1 研究動機與目的 1 1.2 文獻回顧 2 1.3 章節介紹 4 第二章 Mei et al. (1985) 置於多孔介質底床上物體之掀起作用理論與回顧 5 2.1邊界值問題 5 2.1.1控制方程式 5 2.1.2 邊界條件 6 2.1.3夾角內部流場之解析 7 2.2 討論 9 第三章 物體掀起作用短時間尺度下之勢流理論 10 3.1 流場各區速度勢函數 10 3.1.1 控制方程式 10 3.1.2 邊界條件 11 3.2 正規擾動法展開之邊界值問題 13 3.2.1 流場之擾動尺度與各區速度勢函數之正規擾動展開式 13 3.2.2 各區之邊界值問題 14 3.2.3 流場各區之首階解 16 3.3 結果與討論 20 3.3.1 解之限制 20 3.3.2 流場分佈 20 3.3.3 作用力 21 第四章 物體掀起作用長時間尺度下之低雷諾數流理論 23 4.1 邊界值問題 23 4.1.1 控制方程式 23 4.1.2 邊界條件 25 4.2 正規擾動法展開之邊界值問題 29 4.2.1 流場之擾動尺度及量階探討 29 4.2.2 各區速度之正規擾動展開式 32 4.2.3各區之邊界值問題 32 4.2.4流場各區之首階解 36 4.3 結果與討論 41 4.3.1 流場 42 4.3.2 邊界層 43 4.3.3 作用力分析 44 第五章 結論與建議 46 5.1 結論 46 5.2 建議 47 參考文獻 49 附錄A 拉普拉氏方程式通解之推導 70 附錄B Moffatt Solution 旋性與非旋性部分拆解之過程 732322522 bytesapplication/pdfen-US突破效應掀起大型物體多孔介質底床勢流低雷諾數流breakout phenomenontilting lift up of a large objectporous bedpotential flowlow Reynold number flowthesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/50235/1/ntu-96-R94521312-1.pdf