水下移動式射流引致輸砂及水躍現象

Trenching of underwater sand beds by steadily moving jets

彭子軒(Arthur Tzyy-Hsuang Perng)

指導教授 ： 卡艾瑋

國立臺灣大學/工學院/土木工程學研究所/博士(2006年)

https://doi.org/10.6342/NTU.2006.00235

摘要

隨著水下海事工程的日漸發達，諸如挖砂及埋管等工作需求不斷，操控水下遙控載具的精準度也相對要求提高。本論文針對長期工作之載具其利用射流所造成的自挖填之相關問題，模擬移動式水射條件輔以實驗室量測及觀察水射對輸砂的影響，其中包含了砂與水複雜的互制行為、射流的捲增效應、沖刷及淤積現象等。除了實驗配置外並研究淺水波理論之於射流模擬之可行性，理論之建立除了架構於傳統的連續方程及動量守恆更嘗試聯立能量方程。初步以水面均勻射流及水下異重射流做理論根基的基礎，整合介面分層以及傳輸理論將統御方程延伸應用在曲線座標裡。並針對水下穩定的作業提供一維穩定解之操作模式。理論計算將和實驗資料一一驗證，除了寄望對於沖刷深度及長度等工程實際問題提供有效之模式預測，並發現模式可能之侷限性。雖然模式得以驗證水射之於輸砂具薄層流及水躍行為，經由實驗觀察，移動式水射所造成之溝渠流仍有可能發生超出模式之分離流等。

關鍵字

水射 ； 輸砂 ； 捲增效應 ； 淺水理論 ； 介面傳輸理論 ； 曲線方程 ； 水下遙控載具 ； 溝渠流水躍

並列摘要

Underwater activities such as extracting sand beds or burying pipelines are getting more and more widespread and remotely operated vehicles (ROVs) are being increasingly used to reach deeper areas. The present thesis examines the behaviour of jetting onto the sediment sand bed by using a trencher-like machine. Complex phenomena of the interaction between water and sand are observed experimentally, including physical processes of erosion, suspension, entrainment and breaching. Starting with two simpler cases of surface current and bottom plume with a slope break, extensions of shallow flow theory are first presented and validated with analytic solutions. To further extend the theory to eroding turbid currents, interface transfer theory and concept of sub-layered shallow flow are integrated in a mathematical curvilinear formulation. The governing equations include conservation laws for continuity, momentum and energy. Simulating the steady flow, numerical calculations and approximate solutions are obtained in moving coordinates attached to the travelling jets. Comparison of theory and experiments include is made for the bed response profiles. Both in the model and the experiment, two possible pattern of flow are observed, with and without an internal hydraulic jump. In some of the experimental runs, however, phenomena such as flow separation and sand face breaching are observed, which exceed the current scope of the proposed theory.

並列關鍵字

Underwater dredging ； Trenching jet ； Erosion ； Entrainment ； Internal hydraulic jump ； Shallow flow model with interface transfer ； ROVs

參考文獻

Aderibigbe, O.O., and Rajaratnam, N. (1996) Erosion of loose beds by submerged circular impinging vertical turbulent jets. J. Hydr. Res. 34(1), 19-33.

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Capart, H., and Young, D.L. (1998) Formation of a jump by the dam-break wave over a granular bed. Journal of Fluid Mechanics 372, 165-187.

Charbeneau, R.J. (2000) Groundwater Hydraulics and Pollutant Transport. Prentice-Hall.

Ellison, T.H., and Turner, J.S. (1959) Turbulent entrainment in stratified flows. J. Fluid Mech. 6, 423-448.