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  • 學位論文

水底管線管湧現象預防之最佳配置

The Optimized Arrangement of Prevention for Piping of Underwater Pipelines

指導教授 : 黃良雄
共同指導教授 : 林孟郁

摘要


水底管線現已普遍利用在資源的運輸,若管線所處位置為海底,其環境之惡劣需要相關單位定期的檢測關注,但經常還是有無可預期的破壞發生,維修工作耗費大量人力物力財力,瞭解海底管線損壞原因,將有助於找到解決海底管線失效問題的有效方法。   於張芯瑜(2012)研究中,認為管線放置於海床上,常因海流將管線底部土體沖刷導致管線懸空,進而斷裂、破壞,研判海床底質遭到沖刷之原因為管線下方產生管湧(piping)現象所致,故構想於圓管外包覆透水材質,建立底床上包覆透水層圓管之模型,模擬結果證實包覆透水材質後可舒緩底床之壓力梯度,抑制管湧現象發生。   本研究延續張芯瑜(2012)之概念模型,以勢流理論與達西定律分別探討純流體與多孔介質之流場。由於純流體與多孔介質流體間部分邊界條件等號兩邊量階差異過大,數值計算中可能會遭遇矩陣不良條件(ill-condition)(Wang et al.,2010),故本研究以雙微小參數之正規擾動法將原始問題分階分區成若干個邊界值問題,並使用邊界元素法計算水流流經多孔介質底床上圓管之流況。   本研究為瞭解包覆於圓管外透水層滲透係數大小對流場之影響,將兩多孔介質滲透係數視為不同量階並使用雙微小擾動參數,個別依據兩微小參數之量階關係將物理量進行不同方式之擾動展開。在兩多孔介質滲透係數量階相差甚大之情況下,其交界面之通量連續條件依量階分析將得到無通量邊界條件,此與現實不符合且將無法瞭解包覆透水材質之效用,故對該邊界條件進行修正,假想於相對不透水多孔介質邊界上有一薄層,並由連續方程式證實該薄層存在之合理性。   影響底床上圓管附近流況之物理參數眾多且複雜,不易尋找預防管湧現象之最佳配置,本研究考慮實際工程之情境,亦從初步模擬結果進行分析,討論各參數對於管湧作用減緩之影響,進行有效率的模擬,最後整理出之最佳配置,將可提供工程師往後管線設計與施工之參考依據。

並列摘要


Nowadays, underwater pipeline has been widely applied to transport resources. If the pipeline is located on the sea bed, the related units must maintain the pipeline regularly due to the tough environment. Despite this, there are still lots of unexpected damages and the following maintenance costs much efforts, resources and money. To solve this problem, understanding of the reasons of the injuries would be an effective method.   Above several reasons of the damages, Chang (2012) considered that the scour around the pipes is the main reason and the erosion process could be related to piping effect. Chang came up with an idea that cladding porous media outside the pipe to protect it from the scour of current or wave. The study turned the idea into a numerical model and the results indicated that the increase of permeability of the pipe would significantly reduce the gradient of pressure around the pipe which drive the flow in the porous media.   In this study, we continue to develop the conceptual model created by Chang, potential theory and Darcy’s law are adopted to investigate the potential field in water and in porous media respectively. Use the regular perturbation method to deal with the ill-conditioned problem caused by the permeability of porous media (Wang et al., 2010). We apply multiple parameters perturbation to classify the original problem into several boundary value problems (B.V.P.) based on the order of physical quantities and the regions. Use the boundary element method (B.E.M.) to simulate the potential field, velocity and pressure profile around the pipe on the bed.   We believe there is an important relation between permeability of artificial porous media and flow around the pipe. In this study, we regard these two permeability of porous media as two different order and describe them with two small perturbation parameters. But under the situations that the order difference in these two small parameters is too large to ignore. After executing the order analysis, it turns out that the boundary condition of continuity of mass flux between these two kind of porous media becomes no flux condition. It’s not rational and we will not know the utility of artificial porous media. So we make a correction to the boundary condition and assume there is a thin layer on the boundary of the relatively impermeable porous media. Use the continuity equation to prove the rationality of the thin layer.   There are many physical parameters affect the flow nearby the pipe. It’s hard to search the optimized arrangement of the remedy for piping of pipelines. We both consider the reality of engineering and analysis of the modeling results to reduce the possible parameter combinations and discuss the relation between parameters and piping effect. Further, simulate the limited cases to seek for the optimized arrangement of model. In the end, for the future designs and works, we provide engineers reference materials on the basis of physical theory and numerical results.

參考文獻


19. 張芯瑜. (2012). “底床上圓管管湧現象之減緩方法”. 國立臺灣大學碩士論文.
18. 張正緯,黃良雄,蔡東霖,郭遠錦. (2009). “三維地下水模式之發展與應用”. 中國土木水利工程學刊,第二十一卷,第二期, 頁 169-181.
1. Bear, J. (1972). “Dynamics of Fluids in Porous Media”.
2. Biot, M. A. (1962). “Mechanics of Deformation and Acoustic Propagation in Porous Media”. Journal of Applied Physics, Vol. 33(4), pp. 1482-1498.
3. Brebbia, C. A. ; Telles J. C. F. and Wrobel L. C. (1984). “Boundary Element Techniques-Theory and Applications in Engineering”.

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