| 中文摘要 |
The interaction between structures and fluid flow receives more attention in offshore engineering in the past decades. For example, the simulation of an oscillatory flow past a cylinder array is used to predict the hydrodynamic loading of a tension-leg platform (TLP) from progressive waves. A TLP usually has more than one cylinder as the framework to encounter oscillatory flow form waves. However, the design of an array of three cylinders in a regular triangle arrangement in oscillatory flow is rarely studied. Therefore, the main objective of this study is to present the simulation of the interaction between the oscillatory flow and arrays of three cylinders in a triangular arrangement using the direct forcing immersed boundary method. A virtual force base on the rate of momentum changes of a solid body is added to the momentum equations of fluid. Consequently, this method can solve the force caused by the solid body immersed in fluid cells. In this study, the results include the effects of Keulegan-Carpenter number (KC), pitch ration (P/D), and symmetry of the arrangement. The difference between arrays of three and four cylinders is investigated. The arrangement of the array of four cylinders is similar to the array of three cylinders that all cylinders are symmetric with respect to the in-line direction. The proposed approach can be useful for scientists and engineers who would like to understand the interaction of the oscillatory flow with the cylinder array or to estimate hydrodynamic loading on the array of cylinders.
近年來流固耦合的問題在離岸工業上受到高度重視，其中較為常見的應用為利用圓柱列在振盪流場中模擬離岸工作平台在週期性海流衝擊下的影響。大部分的海洋工作平台都是利用多於一根的圓柱做為受到海流衝擊的骨架，然而採用三根圓柱的設計卻是相當少見的，所以本研究主要利用直接施力沉浸邊界法模擬振盪流與正三角形配置圓柱列的流固耦合現象。直接施力沉浸邊界法主要是將一虛擬力加入動量方程式中，透過固體與流體的動量差可得到此虛擬力，最後藉此求解此固體對流體造成的作用力。本篇研究將探討Keulegan-Carpenter number（KC）、圓柱間距和圓柱配置對稱性對於流場的影響，最後還會比較三根圓柱列和四根圓柱列列在振盪流中的差異，其中四根圓柱列的配置是與三根圓柱列相似的。本研究藉由分析振盪流流經三根圓柱模擬海洋工作平台，瞭解真實結構物與周圍流場的受力情形，可提供設計海洋平台者做為參考。 |
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