利用風壓量測求取氣動力參數

Determination of Aerodynamic Coefficients of Bridge Decks Using Wind Pressure Distribution Measurements

徐佳煌(Chia-Huang Hsu)

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(2006年)

https://doi.org/10.6846/TKU.2006.00136

摘要

本篇論文主要在研究矩形斷面之氣動力係數與氣彈力係數，主要在於量測平均風壓與振動模式下的位移，並利用其所得之外力與位移結果推導氣動力參數。在風壓量測方面，藉由了解模型表面壓力孔之壓力，可以推算模型之受力狀況，而利用位移量測則可以了解模型之振動行為，將外力與位移資料代入推導之公式，可以計算出所欲推求之氣動力參數，此方法應可以同時考慮橋體受力與振動反應下之行為。
本論文實驗分為兩大部分，其一為風壓量測實驗，另一為位移量測實驗，在氣動力實驗方面，主要是利用量測矩型斷面在平滑流場下之風壓數值，再利用壓力積分成外力後便可得到斷面所受的外力，經由數值計算便可得到所欲求的風力係數，經由探討風力係數之結果，可以觀察出橋體之運動與受力之行為，本實驗並針對不同風攻角探討其角度變化後的風力係數之趨勢。而氣彈力實驗方面，有別以往之位移分析模式，在本論文中加入了外力的變數，利用外力量測與位移量測的結果再代入自身擾動力的方程式，經由外力頻譜與位移頻譜計算則可以求得所欲求得顫振導數。
在實驗結果之探討方面，由風力係數實驗之結果，無論是拖曳向、垂直向、扭轉向係數都可以得到與力-位移量測計相似之趨勢，而在扭轉向係數方面有較為精確的結果。在顫振導數方面，主要之分析項目為風力頻譜與位移頻譜之計算，藉由頻譜的特性去探討各頻率點下之所有顫振導數之結果，並探討如何選擇適合之頻率點，以決定顫振導數之結果。在以風壓量測時，管線之率定為一重要之步驟，管線之率定可以改善因管線較長所造成訊號的扭曲，與訊號經時間傳遞所產生之相位改變。

關鍵字

風力係數 ； 顫振導數 ； 頻譜 ； 管線率定

並列摘要

The main objective of this thesis is to investigate the aerodynamic and the aeroelastic coefficients of the rectangular bridge deck by using the pressure measurements. The mean pressure distribution and the displacement of the bridge deck were measured when the deck was vibrated. The static force coefficients were obtained by measuring the mean pressure distribution as the bridge deck was stationary. As the bridge was vibrated, the flutter derivatives can be derived by using the relationship between the force and the displacement spectra.
There are two parts in the experiments. One is the measurement of mean pressure distribution and the other is the measurement of displacement. All the tests were conducted in smooth flow. In the aerodynamic experiment, the static coefficients can be obtained by integrating the pressure around the bridge deck. The effect of wind attack angle is also studied. In the aeroelastic experiment, the pressure and the displacement are simultaneously measured as the bridge deck model is in motion. The flutter derivatives can then be derived by using the relationship between the force spectra and the displacement spectra.
It can be seen that from the results of aerodynamic experiments, the trend of the static coefficients, including the drag, the lift and the torsional coefficients, is similar to those obtained from the load cell measurements. It should be mentioned that the torsional coefficient, especially in large wind attack angle, is more reasonable than that obtained from the load cell measurement. From the results of aeroelastic experiment, it can be inspected that the flutter derivatives obtained from this approach are not reasonable compared to those obtained from the classical test. The possible reason is that the force spectra measured not only include the self-excited force but also the turbulence in smooth flow. For better consistency, this method needs to be improved in the future.

並列關鍵字

Aerodynamic coefficients ； Flutter derivative ； Spectra ； Calibration

參考文獻

1、Yasuharu Nakamura, Shigehira Ozono, （1987）, “The effects of turbulence on a separated and reattaching flow.” Journal of Fluid Mech., 178, 477-490.

3、Whitbread﹐R. E.﹐1963 ﹐" Model Simulation of Wind Effects on Structures" Proceeding of the Conference on Wind Effects on Buildings and Structures﹐pp.284-306.

5、Irwin, H. P. A. H., Cooper, K. R., Girard, R.,（1979）, ” Correction of distortion effects caused by tubing systems in measurements of fluctuating pressures.”, Journal of Wind Engineering and Industrial Aerodynamics, 5, 93-107.

6、Da Matha Sant' Anna, F. A., Laneville, A., Trépanier, J.Y., Lű, Z.Y.,（1988）, “Detailed pressure field measurements for some 2-D rectangular cylinder” Journal of Wind Engineering and Industrial Aerodynamics, 28, 241-250.

7、Saathoff, P. J., Melbourne, W. H., （1989）, “The generation of peak pressures in separated reattaching flow.” Journal of Wind Engineering and Industrial Aerodynamics, 32, 121-134.