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標題: | 移動式射流引致海床挖掘:實驗及理論 Seabed trenching by moving point jets: experiments and theory |
作者: | Chiun-Chau Su 粟群超 |
指導教授: | 卡艾瑋(Hervé Capart) |
關鍵字: | 侵蝕,捲增,沈降,水下土壤液體式剝落,溢流,淺水方程,溝渠挖掘,遙控載具, erosion,entrainment,deposition,breaching,overspill,shallow flow,trenching,ROVs, |
出版年 : | 2008 |
學位: | 碩士 |
摘要: | 本研究檢視單一移動式射流的簡化案例來了解水下射流挖掘載具挖掘海床的過程。在小尺度實驗,我們使用可控制履帶來移動一個傾斜且沿著水平海床的針頭射流。引起的水流以及溝渠的切割被觀察到從側面以及俯視(藉由鏡子反射),因此量測到溝渠的深度以及寬度剖面。接下來的物理過程被觀察到:沙床的侵蝕、靜止水被捲增、沙顆粒的沈降、濁流的溢出以及側面牆壁水下土壤的流體式剝落。藉由簡化的物理以及幾何假設,我們導出淺水方程式來描述以上現象。一個理論推導的重要結果是由於在溝渠內的液體密度分層用來解釋紊流減弱的理查森數。此模式用來計算溝渠的形狀由於不同流量的射流以及移動速度。深度以及寬度的計算結果亦和實驗量測之結果比較。同意的是在溝渠的深度上較佳,但是在溝渠的寬度上則較不精確。此模式的限制備註名在未來工作中藉由改善溝渠牆壁側邊水下土壤的流體式剝落。 To understand seabed trenching by underwater jet trenching vehicles, the present research examines the simple case of a single moving jet. In small-scale laboratory experiments, we use a driven carriage to move an oblique needle jet along a horizontal sand bed. The resulting flow and trench incision are observed from the side and top (using a mirror), permitting measurements of both the depth and width profiles of the trench. The following physical processes are observed: sand bed erosion, ambient water entrainment, sand grain settling, turbid current overspill, and side wall breaching. Under simplified physical and geometrical assumptions, we derive shallow flow equations to describe these phenomena. A key result of the theoretical derivation is the definition of a Richardson number accounting for turbulence damping due to density stratification inside the trench. The model is used to compute trench shapes for a range of jet flow rates and speeds of advance. Depth and width profiles are then compared with the experimental measurements. Agreement is good for the trench depth, but less accurate for the trench width. This limitation of the model could be addressed in the future by improving the description of the lateral breaching of trench walls. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/27055 |
全文授權: | 有償授權 |
顯示於系所單位: | 土木工程學系 |
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