應用白噪音強制振動於橋面板之顫振導數系統識別

Identification of Flutter Derivatives of Bridge Decks by White-Noise Forced Oscillation Method

劉韋成(Wei-Chen Liu)

指導教授 ： 吳重成

淡江大學/工學院/土木工程學系碩士班/碩士(2005年)

https://doi.org/10.6846/TKU.2005.00667

摘要

在風工程的領域中，以傳統的自由振動的方法求得橋樑顫振導數之實驗方式與技巧已趨成熟，此種方法在實驗上容易施作，而且所獲得的結果也大都可以達到需求。但根據前人經驗，自由振動的實驗結果有時候會因為渦流顫振(Vortex Shedding)或操作上不嚴謹而產生不可靠的情形。
為改善上述缺點，本文嘗試研擬出一套新的橋樑顫振導數之識別方法，以白噪音強制振動的實驗方式，將橋面版結構連接至一振動平台，透過伺服馬達給予振動平台一白噪音強制振動，量測橋面版受風之後的反應，經由傅立葉轉換後求得橋面版在白噪音強制振動下受風之氣彈互制轉換函數，配合理論的推導分析以及藉助基因演算法求取最佳參數，進行顫振導數之識別。
以寬深比25之削角流線型平板為例，在淡江大學土木系風洞進行顫振導數之識別試驗，並與理論值Theodorsen函數進行比較。識別結果顯示，垂直向顫振導數 、 在各風速下相當一致且 （氣動力阻尼）非常接近理論值；而扭轉向顫振導數 、 則會隨著風速而改變且與理論值差距頗大，其中原因仍待後續研究進一步釐清。

關鍵字

橋樑 ； 顫振導數 ； 氣動力阻尼 ； 白噪音強制振動 ； 氣彈互制 ； 基因演算法

並列摘要

In wind engineering application, the conventional technique using free oscillation method to obtain flutter derivatives of bridge decks has become more mature. This method is easy to use and results are mostly satisfactory in the application. However, based on our past experimental experience, the test results from this method are sometimes unreliable under the circumstances when the influence of vortex shedding is significant or the operations during tests are not cautious.
To improve the reliability of test results, this thesis proposed a new approach of determining the flutter derivatives that uses forced oscillation technique. In the forced oscillation tests, the bridge deck section is connected to a two-axis shaking table driven by two servo-motors, which produces white-noise forced vibration actions in two degree of freedom to the deck. By measuring the response of bridge deck under various wind speeds, the aero-elastic transfer functions of the responses can be computed by using Fourier analysis. The results were curve-fitted to those from theoretical formulation by minimizing the error between each other, in which the Genetic Algorithm is used to locate the optimal parameters. Consequently, the flutter derivatives can be thus derived.
For demonstration, a chamfered bridge deck with width/depth ratio of 25 is constructed and tested in the wind tunnel following the proposed approach. The experimental results show that the flutter derivatives and are consistent for different wind speeds; in particular the aerodynamic damping matches Theodorsen function quite well. However, the flutter derivatives and are not consistent with the wind speed varied. In the future study, further investigations shall be conducted to clarify such an inconsistency.

並列關鍵字

Bridge ； Flutter Derivatives ； Aerodynamic Damping ； White-Noise Forced Vibration ； Aeroelasticity ； Genetic Algorithm

參考文獻

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