以CFD模擬二維橋樑斷面之氣動力參數及顫振導數研究

Investigations of aerodynamic coefficients and flutter derivatives of bridge decks by using CFD Approach

林紘毅(Hung-Yi Lin)

指導教授 ： 林堉溢

淡江大學/工學院/土木工程學系碩士班/碩士(2018年)

https://doi.org/10.6846/TKU.2018.00138

摘要

因橋梁工程技術的進步，橋梁漸趨狹長，受風反應越來越明顯，因此風洞試驗受到重視，但風洞試驗在進行試驗時，消耗時間大，成本也高，相較於以往只能以風洞試驗擷取所需數據，如今數值模擬方法漸趨成熟逐漸成為主流。
本研究以數值計算為主風洞斷面試驗為輔，模擬二維幾何斷面橋體在均勻來流下之鄰近紊流流場與結構運動行為。本研究分為三部分，第一部分為利用數值模擬對寬深比B/D=10的矩形斷面進行風力係數及顫振導數分析；第二部分利用前述所選用之參數，對寬深比B/D=5、B/D=20的矩形斷面進行分析；第三部分為利用前述所選用之參數，對高屏溪斜張橋進行風力係數及顫振導數分析。本研究使用計算流體力學的前處理器Pointwise進行模擬風洞試驗的計算域配置、網格繪製以及邊界條件設定，再以ANSYS開發的計算流體力學套裝軟體FLUENT進行分析。
透過B/D=10進行參數測試，將參數測試結果套用在B/D=5、B/D=20上進行風力係數分析，在小攻角±4區間趨勢預測上都有良好的結果，在大攻角時有些微誤差；於高屏溪斜張橋上進行風力係數分析時，整體趨勢預測良好，在風攻角5°時有些微誤差存在。於B/D=5、B/D=20上進行顫振導數分析，所得結果整體趨勢大致良好；於高屏溪斜張橋上，直接導數的預測上與風洞試驗相較下吻合度良好，但在耦合項誤差稍大。
根據本文之研究結果，將可提供對橋梁斷面之CFD模式建立及模擬方法，透過快速的數值模擬，以做為風洞試驗前風力係數及顫振導數之評估參考，並為接下來的CFD氣動力及氣彈力模擬做好初期基礎工作。

關鍵字

橋樑 ； 計算流體力學 ； CFD ； 風力係數 ； 顫振導數 ； FLUENT

並列摘要

Duo to the improvement of bridge engineering technology, the bridge span is getting longer and the wind response is more significant. Therefore, the wind tunnel experiments of long-span bridges have become more important. But the time consuming and the high costing are the weak points of wind tunnel experiments. Contrary to wind tunnel experiments, CFD simulations can obtain full-field physical variables with time and be becoming one of the mainstreams in wind engineering.

In this study, the main methodology is 2D CFD simulation associated with the wind tunnel experiments to investigate the aerodynamic behavior of bridge decks. The method of flutter derivatives identification is based on forced vibration. This study is divided into three parts, the first one is to use CFD simulation to analyze the wind force coefficients and the flutter derivatives of a rectangular cross-section with B/D=10. The second part is using the similar configurations of the B/D=10 to analyze the bridge decks with B/D=5 and B/D=20. The third part is adopting the similar parameters to analyze the Kao-Ping-Hsi cable-stayed bridge. In this study, we use the preprocessing software Pointwise to arrange the calculating domains and then generate the meshes and set up the boundary conditions. Then we use the Ansys Fluent to simulate flow fields around the bridge decks.

Through the tests of the parameters in the case of B/D=10, the optima parameters are identified which are then used to analyze the force coefficients in B/D=5 and B/D=20. There are good agreements in angles of wind attack between 4 and -4 degrees, but with some error in the larger attack angles. The force coefficients of Kao-Ping-Hsi cable-stayed bridge have similar trends with the results of wind tunnel experiments. However the larger errors occur when the wind attack angles are more than 5°. The results of the flutter derivatives in the case of B/D=5 and B/D=20 show that the overall trends are fairly well. Compared to the experiments the flutter derivatives of the Kao-Ping-His Bridge have good agreements with the wind tunnel experiments in the direct flutter derivatives but have some discrepancies in the cross flutter derivatives.

According to the above comparative results, this study provides a reliable CFD approach for 2D simulations of bridge decks. A rapid 2D CFD simulation can be as the preliminary assessment of aerodynamic coefficients and flutter derivatives before the wind tunnel experiments are performed.

並列關鍵字

Fluent ； CFD ； Bridge

參考文獻

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