圓柱橋墩結構之計算流體力學模擬研究

淡江大學機構典藏 > 工學院 > 土木工程學系暨研究所 > 學位論文 > Item 987654321/74487

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题名:	圓柱橋墩結構之計算流體力學模擬研究
其它题名:	The study of computationa fluid dynamics on cylindrical piers structure
作者:	鄭凱仁;Cheng, Kai-Jen
贡献者:	淡江大學土木工程學系碩士班張正興;Chang, Cheng-Hsin
关键词:	CFD;k-ε;V.O.F
日期:	2011
上传时间:	2011-12-28 18:44:23 (UTC+8)
摘要:	颱風來襲時洪水挾帶泥沙、土石使得橋墩沖刷，斷橋事件頻傳。過度的盜採砂石，使得下游橋墩造成不平衡沖刷，危及橋樑下部結構，當洪水侵襲時便造成橋墩損壞。水工結構物造成水理特性的改變而造成橋墩周圍底床形成倒錐形的局部沖刷。對於水利工程方面多半以水工試驗作為研究主體，搭配數值模擬做驗證，但多半為討論流場及沖刷深度的變化。本研究希望透過CFD模擬出三維流場中橋墩周圍流場及橋墩之受力情形，在省時省力情況下提供初步評估。本研究數值模擬分為兩部分；第一部分為數值模型驗證部分以四種模式紊流模式Standard k- ε、RNG k- ε 、realizable k- ε 、RSM進行流場模擬，並與試驗數據比較。第二部分則進行不同流場條件之數值模擬，並討論橋墩周維流場及橋墩受力情況。研究顯示：經由Fluent軟體模擬橋墩周圍流場，在水工試驗尚未進行前，可先經由數值模擬了解流場特性(如速度、壓力之分佈)；也可利用模擬所得床底剪應力帶入由相關公式推估橋墩周圍沖刷深度。以水工試驗後之試驗資料進行數值模擬比對合理後，則可對試驗無法量測處利用數值模擬結果進行探討；水工試驗多討論流場特性及沖刷深度，因此橋墩受力之資料上有所不足。本研究針對水工試驗不常探討橋墩受力狀況之情形，針對橋墩基底之受力進行分析，比較不同流量與不同床形下之受力狀況，希望未來能夠擴展到模擬洪水衝擊下之受力狀況。 This study is divided into two parts, the first part is validating numerical models using four kinds of turbulence models (standard k-ε, RNG k-ε, realizable k-εand RSM) to simulate the flow field around bridge piers and to compare the results of the four models with experimental data. The better model was chosen for the second part of the research. The second part is setting different boundary conditions to run numerical simulations. In this part, the characteristics of the flow field around bridge piers and the stress on the piers were studies and discussed. Before hydraulic tests, software "Fluent" can be used to simulate the flow field around bridge piers to obtain flow field characteristic data (e.g., velocity and pressure distribution), and simulated bed shear stress can be used to estimate the scour depth around piers. When the results of numerical simulation match the data from previous hydraulic tests, unmeasured locations can be investigated using numerical simulations. In hydraulic tests, the focuses are on the characteristic of flow field and scour depth, and usually not enough data regarding the forces on the piers. Therefore, in this study, different boundary conditions (e.g., flow depth, velocity and bed shape) were used in the numerical simulations and analysis of the forces on the piers. It is hoped that the results of this thesis can be extended in the future to simulate the loading condition of piers subjected to flood impact.
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