Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/12948
標題: 結構物風吹模型修正與受風顫振行為分析
Correction Factor for Wind Tunnel Test Model and Flutter Analysis of Structures
作者: 李增欽
Lee, Tzen Chin
關鍵字: Wind engineering
風工程
Aerodynamic instability
Wind tunnel test
氣動力不穩定
風洞試驗
出版社: 土木工程學系
摘要: 有鑑於建築物的日漸高層化,使得建築結構物受風力之影響愈來愈重要。尤其是受風力振動所引起之問題,常需借助風洞試驗模擬解決。此外,柔性結構受風作用其氣動力所造成之不穩定問題,亦為分析設計之重點,本文即針對高樓建築之風洞試驗修正係數及柔性結構之顫振分析進行探討。 建築物受風力的振動機理非常複雜,尤其是高樓建築很難藉由擬靜力之規範公式或數值分析的方法求得精確的反應值;工程上一般大都透過風洞試驗求取風吹模型的反應,然後再推算出結構之真正受風反應。風洞剛體模型試驗中,係假設風吹模型的第一振態為線性,且僅有第一振態參與反應,但對一般高層建築結構物而言,此等假設是不適切的。本文首先利用李亞波諾穩定理論,求得風吹模型及結構原型之受風極限類能量,將兩者比較後,可求得原型結構體與模型間之反應修正係數,再依此修正係數乘以模型在試驗中所得之數據,即可求得原型結構在實際風埸下較合理的反應行為。此修正係數與Holmes所提有關高相關性修正係數之公式相同。相對於其他方式,本文之修正係數有下列優點:其一,可改善風洞試驗剛體模型不足之處;其二,亦能將剛體模型之試驗結果修正為原型結構為非線性振態之真實情形。而於不改變結構外形之條件下,若原型結構須變更設計,則祇需求得新的修正係數即可,在進行變更設計時,無須再花費重作風洞試驗,值得提供風洞試驗剛體模型反應修正係數使用之參考。而於柔性結構之風致振動;其中影響最顯著者為顫振與抖振。顫振之分析,一般係依pK-F法求顫振行列式,以分析橋樑之顫振臨界風速。本文主要探討顫振現象對橋樑產生之氣動力效應,並提出以多項式之特徵方程式,依其根之實數部份具正、負號之特性,於複數平面映射得到之f(iy)曲線,作為穩定性判斷之基準,當座標原點位於該曲線行進方向之左邊時,系統處於穩定狀態。而當座標原點位於曲線行進方向之右邊時,則系統處於不穩定狀態。循此準則可以判別系統是否穩定,而可求得顫振之臨界風速。 本文之方法有別於一般的pK-F法。其優點為:不需求解特徵方程式的根,而可直接求得顫振臨界風速,故不受振態耦合的影響。又與pK-F法相較,因其須求解顫振行列式之值,基本上為一種數值分析之方法,其可能無法求得特殊解或跳過某些解而不知,本文所提供之圖解法分析係以複數映射方式作為穩定性判斷之基準,因不需求解顫振行列式之值,故無上述無法求得特殊解或跳過某些解之顧慮。且其過程簡捷可行,值得參考使用。
Strong wind has a great influence on the structural response of high rise buildings. The mechanism of structure response of buildings caused by wind is very complicated. It is difficult to obtain real structure responses of buildings by the quasi-static approaches adopted in design codes or by the approaches of numerical simulation. In general, the experiment of building''s model in wind tunnel may provide some insights of real response of high rise buildings. Conventionally, two fundamental assumptions in the test modeling may not be realistic. First, vibrating mode is assumed as linear fundamental mode and secondly, only that mode is dominating in the building''s dynamic response. In this paper, the Liapunov''s stability theory is used to analysis ultimate energy due to wind for both the wind-tunnel model and prototype building. Then, a comparison is made to determine the correction factor of response spectrum of the model and that of the prototype. This approach may provide a theoretically versatile correction factor than those obtained by other methods. The flutter of a bridge is induced by self-excited force factors such as lift, drag and aerodynamic moment. These factors are associated with flutter derivatives in the analysis of wind engineering. The flutter derivatives are the function of structure configuration, wind velocity and response circular frequency. Therefore, the governing equations for the interaction between the wind and dynamic response of the structure are complicated and highly nonlinearity. Herein, a numerical algorithm through graphical technique for the solution of wind at flutter is design. It provides a concise approach to the solution of wind velocity at flutter.
URI: http://hdl.handle.net/11455/12948
Appears in Collections:土木工程學系所

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