Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/15097
標題: 波浪作用下土壤內埋管之有限元素分析模式
Finite element model for wave-induced force on buried pipeline
作者: 張淇銘
Chang, Chi Ming
關鍵字: Finite Element model;有限元素法;海底埋管
出版社: 土木工程學系
摘要: 
摘要
本文目的在建立波浪作用下土壤內埋管之二維有限元素分析模式,模式主要利用Biot''s 壓密理論、彈性力學之力平衡方程式及彈性下應力應變線性關係式,因波浪作用有週期性之特性先將時間變數自方程式及邊界條件分離,再利用Galerkin 法建立有限元素法模式進行分析。
波浪作用下土壤埋管應為一無限邊界問題,但由於波浪作用下之土壤應力及孔隙水壓力受埋管影響之範圍有限情形下,因此以一有限邊界範圍進行分析,首先由波浪作用下而無埋管時之不同長度土壤分析區域所得的邊界結果,以此邊界條件做為不同長度分析區域有埋管之邊界條件,由不同長度分析區域收斂性變化找出正確結果。
本文中將針對不同之埋管深度、埋管材料、埋管直徑、土壤狀況、波浪之波相的影響進行分析,同時探討管線周圍加上保護層所造成之影響,由分析結果對不同條件下在埋管附近之土壤孔隙壓力、土壤應力應變、埋管受波浪作用下所產生上舉力及埋管應力分佈等變化有更一步瞭解,同時可針對不同埋管設計進行差異性比較,經由本文所建立之模式及分析結果,可供工程界在進行海洋埋管設計時做為參考。

Abstract
Submarine pipelines have been extensively used to transport hydrocarbons across a stretch of water. There are also widespread applications of pipelines for the disposal of municipal waste. To protect the pipeline from possible damages caused by waves, currents and anchor dropping/dragging, it is customary to bury the pipeline. The cost of artificial trenching and refilling is high, and the expenditure often accounts for a large proportion of the total budget of a pipeline project.
Design of marine pipelines regarding their stability is a rather complicated problem. One of the important factors that must be taken into account is the seabed instability around the pipeline. When gravity waves propagate over the ocean, they exert fluctuations of wave pressure on the sea floor. These fluctuations further induce excess pore pressures and effective stresses, which have been recognized as a dominant factor in analyzing the instability of a seabed. Once the wave-induced seabed instability occurs near the pipeline, the phenomenon of pipe floating may occur. Thus, the evaluation of the wave-induced soil response, including pore pressure, effective stresses and soil displacements, is particularly important for marine geotechnical engineers involved in the design of foundations for offshore pipelines.
Although the importance of the wave-seabed-pipe interaction problem has been recognised in the past, the whole problem have not been fully understood until now. Foe example, structural engineers have been concerned with the stress distributions of the pipe itself from the aspect of structural engineering, while geotechnical engineers focused on the wave-induced soil response in the vicinity of a pipe from the aspect of geotechnical engineering. In this study, we attempt to couple these two different areas to solve the whole problem of the wave-seabed-pipe interaction problem.
In this study, a two-dimensional Finite Element Model (FEM) is proposed to investigate the mechanism of wave-seabed-pipe interaction. Since the whole boundary value problem is an infinite domain, it has been the major obstacle in numerical modelling for such a problem. In this study, the principle of repeatability has been employed to obtain the lateral boundary conditions for the whole problem.
A comprehension verification of the present model against previous experimental data has been performed in this study. Based on the proposed FEM model, the wave-induced seabed response in the vicinity of a buried pipe has been investigated, as well as the distribution of stresses within pipe itself.. Effects of buried depth, pipe radius, soil types and wave phases on the distribution of stresses have been examined. Finally, a more practical problem for the protection of a buried pipeline, effects of a cover layer, has been considered. The results of this thesis will provide a design guide of pipeline stability for engineers.
URI: http://hdl.handle.net/11455/15097
Appears in Collections:土木工程學系所

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