高層建物受風影響之動力行為研究－實場監測與風洞試驗驗證

Field measurement and the validation of wind tunnel test of the tall building

池雅寗(Ya-Ning Chih)

指導教授 ： 鄭啟明

淡江大學/工學院/土木工程學系碩士班/碩士(2007年)

https://doi.org/10.6846/TKU.2007.00985

摘要

本文主要的重點為風工程實場量測相關技術之發展，主要目的在於建立起包含台灣氣候特徵（颱風）之結構受風反應與風場特性資料庫，做為風洞物理模擬、計算流體力學數值模擬以及理論分析結果之最終驗證。並且做有關風洞實驗與實場量測間之比對與探討
於該大樓裝設速度計、加速度計與風速計，量測大樓在不同風速下之受風反應。因此風洞實驗將透過風力量測以及結構動力之計算，求得特定風速下中央百世大樓之振動情形，並與實場監測結果做一比較。 實場風速計之裝設位置受限於大樓景觀之考量，於頂樓架設之高度無法有效脫離該大樓造成之氣流尾跡區域，因此實場量得之風速資料與逼近流實際之風速將有所差別。故於風洞實驗中亦將針對風速之量測進行修正，使實場風速資料能正確反應逼近流場之風速特性。
本研究由實場監測所得到數據可知道，超音波風速計所擺放的位置無法有效的脫離建物本身造成的渦流，而使得其紊流強度過大，無法與風洞試驗之結果做有效的驗證。其中紊流強度會隨著風速的增大而隨之遞減。在頻譜分析上，實場監測所得頻譜和Karman的經驗公式非常吻合，而高頻的部分有受到干擾，其數值也較實驗和文獻之數值低。另外，在識別結構頻率時，Ｘ向和Ｙ向較扭轉向來得準確且穩定。在結構物受風時的微動訊號所計算出來之阻尼比，有一拋物線趨勢，此趨勢到1%左右趨於平穩。風洞試驗所計算出來的位移反應變異數皆較實場監測所得到的結果來得小。造成此現象有兩個原因：在做風洞試驗時，沒有完全的考量到附近的山區和圓盤外較高建物對測點本身造成的影響；在縮尺上的設計，和風洞模擬之流況縮尺不相同造成。

另外，在實場監測和風洞試驗驗證上，有以下兩點結論：
1.位移反應∼在實場和實驗的位移比較上，Ｘ向較為相似，但在Ｙ向的誤差較
Ｘ向大。
2.風速頻譜∼實場和實驗不完全符合是因為紊流強度無法完全的模擬實場。

關鍵字

實場監測 ； 風洞試驗 ； 阻尼識別 ； 颱風 ； 阻尼

並列摘要

This paper mainly focused on the related technology development of the wind engineering field measurements. The aim is to establish a database of Taiwan (Typhoon) climate features, including structures under the wind reaction and wind characteristics, which can be used as the final certification of a physical wind tunnel simulation, computational fluid dynamics, and numerical analysis and simulation results. In addition, the comparison and discussion between the wind tunnel experiments and field measurement are done.

By installation of speed-meter, acceleration-meter and anemometer, we can measure the wind response of the building under different wind speeds. Therefore wind tunnel experiments will give vibration conditions of tall building under a certain wind speed through the measurement of strength of wind and the calculation of structure dynamics, and compare with the actual results of the field measurement. The installation of the anemometer in the building is restricted in locations due to scenery considerations. If installed in the top floor of building, it is hard to effectively depart from the airstream tail regional caused by the building. Therefore, data of wind speed with filed measurement and data of real wind speed of the approaching wind flow will have differences. Consequently, in the wind tunnel experiments the correction to the wind speed measurement is necessary, so that data of wind speed with filed measurement can correctly reflect the properties of the wind speed of the approaching airstream.

By the real monitoring data, this study shows that the placed location of the ultrasound anemometer can not be effectively away from the vortex caused by the building itself, which makes it too much turbulence intensity, therefore, not compatible with the wind tunnel testing results effectively. The intensity of turbulence will decrease as the increasing of the wind speed. Regarding he spectrum analysis, the spectrum by filed measurement matched with Karman’s empirical formula, but yet, the high-frequency part had a disruption, and its value was lower than that of experiments and literatures. Moreover, when identifying the structure frequency, X direction and Y direction are more accurate and stable than the twist direction. The calculated damping ratio by the fretting signals when the structure encounters the wind gives a parabolic trend, and that trend becomes flat at about 1%. The variance of the displacement response calculated by wind tunnel tests is smaller than that of results of the filed measurement. This phenomenon can be explained by two reasons: when doing wind tunnel tests, we failed to consider influences at measuring points caused by the nearby mountains and high buildings outside the disk. Aslo, for the scale in the design, this was caused by the difference of the scale from that in wind tunnel simulation.

Moreover, for the verification of the filed measurement and wind tunnel tests, the following two conclusions are made:
-displacement response: for the comparison of the displacement between the filed measurement and the experimental one, it’s more similar in the X direction, but the error in the Y direction is larger than that in the X direction.
-speed spectrum: Being not completely matched between the filed measurement and the experimental one is because the turbulent intensity can not fully simulate the real situation.

並列關鍵字

Field measurement ； Wind tunnel test ； damping ratio identification ； typhoon ； damping

參考文獻

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