Trenching of underwater sand beds by steadily moving jets
Date Issued
2006
Date
2006
Author(s)
Perng, Arthur Tzyy-Hsuang
DOI
en-US
Abstract
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.
Subjects
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
Underwater dredging
Trenching jet
Erosion
Entrainment
Internal hydraulic jump
Shallow flow model with interface transfer
ROVs
Type
thesis
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