本文關鍵詞： 龍卷風 高層建筑 風荷載 沖擊效應 數(shù)值模擬　出處：《中國科學技術大學》2015年碩士論文　論文類型：學位論文

【摘要】：龍卷風具有較強的破壞力,是抗風減災工程重要的防范對象之一。近年來,隨著地球環(huán)境的惡化,龍卷風襲擊大型城市的災害時有發(fā)生,針對城市中高層建筑的龍卷風災害研究開始受到重視。已有的研究多集中于實驗尺度模型和準靜態(tài)荷載,而對龍卷風動態(tài)沖擊全尺寸高層的研究還比較少,特別是現(xiàn)行建筑設計規(guī)范仍沒有針對龍卷風給出結構設計及安全方面的具體要求和方法,迫切需要從理論模擬及實驗等多方面開展研究。本文首先建立了動態(tài)運動龍卷風的數(shù)值風場模型,應用大渦模擬(LES)方法開展了龍卷風動態(tài)沖擊高層建筑的非定常過程模擬,對其漩渦演化及對高層建筑的沖擊風荷載特性開展了初步研究,并與實驗室尺度下的荷載特征進行了比較研究,進一步搞清了龍卷風沖擊不同尺度和形狀的高層建筑流場差異和荷載產(chǎn)生機理,主要獲得如下結論：1)在模擬龍卷風動態(tài)運動的數(shù)值風場模型中,簡單采用動態(tài)速度邊界條件較難保持龍卷風在運動過程中的形態(tài)和強度不變,采用預設旋轉強度和速度保持恒定的數(shù)值驅動區(qū)是一種較簡便且高效的計算方法。2)實驗室尺度下的數(shù)值模擬結果表明：龍卷風動態(tài)沖擊高層建筑,其荷載響應特性與建筑尺度有關。建筑尺度較小時,沖擊荷載呈雙峰特征,沖擊效應和時變效應相對較小。相反,沖擊荷載呈多峰特征,時變性強,沖擊效應明顯。同時,龍卷風在沖擊較大尺度建筑時,主渦會發(fā)生破裂,形成多個漩渦。多漩渦之間以及與建筑尾渦相互作用和耦合將導致更大的沖擊荷載。這種力學現(xiàn)象在國內(nèi)外龍卷風研究中尚未發(fā)現(xiàn)類似報道。3)全尺寸龍卷風沖擊高層建筑的載荷響應特性與實驗室模擬尺度下的載荷響應特性存在相似特性與尺度效應。其相似性體現(xiàn)在：當龍卷風尺度與建筑尺度比相似時,其荷載變化規(guī)律和特征存在一定相似性。不過其具體載荷系數(shù)及峰值響應位置卻存在較大差異,這反應了龍卷風的尺度效應。4)全尺寸模擬結果表明：當建筑模型的高度相同,尺度相近時,建筑的外形跟載荷響應的大小有一定的關系。綜合不同建筑的龍卷風載荷載荷響應特性上看,矩形建筑的龍卷風載荷響應系數(shù)相對較大,且與龍卷風襲擊攻角有關。
[Abstract]:Tornadoes have strong destructive power, which is one of the important protection objects of wind disaster mitigation engineering. In recent years, with the deterioration of the earth environment, tornadoes frequently hit large cities. The research on tornado disasters of high-rise buildings in cities has been paid more attention. Most of the existing researches focus on the experimental scale model and quasi-static load, but the research on tornado dynamic impact on the full scale high-rise is relatively rare. In particular, the current building design code still does not give the specific requirements and methods of structural design and safety for tornadoes. There is an urgent need for theoretical simulation and experimental research. Firstly, the numerical wind field model of dynamic moving tornadoes is established in this paper. The unsteady process of tornado dynamic impact on high-rise buildings is simulated by means of large eddy simulation (les) method. The vortex evolution and impact wind load characteristics of high-rise buildings are studied preliminarily. Compared with the load characteristics of laboratory scale, the flow field difference and load generation mechanism of high-rise building with different scale and shape of tornado impact are further understood. The main conclusions are as follows: 1) in the numerical wind field model of simulating tornado dynamic motion, it is difficult to maintain the shape and intensity of tornado in the course of motion by simply adopting dynamic velocity boundary condition. Numerical driving region with preset rotation strength and constant velocity is a simple and efficient calculation method. 2) numerical simulation results at laboratory scale show that tornadoes impact on high-rise buildings dynamically. The load response characteristics are related to the building scale. When the building scale is small, the impact load is bimodal, while the impact effect and time-varying effect are relatively small. On the contrary, the impact load is multi-peak and time-varying. The impact effect is obvious. At the same time, when tornadoes impact large scale buildings, the main vortex will break down. The formation of multiple whirlpools. The interaction and coupling between multiple whirlpools and building trailing vortices will lead to larger impact loads. This mechanical phenomenon has not been reported in tornadoes at home and abroad. The load response characteristics of full-scale tornado impact high-rise buildings are similar to those of laboratory simulation scale. When the scale of a tornado is similar to that of a building. The law and characteristics of load variation are similar, but the load coefficient and peak response location are different. This reflects the scale effect of tornadoes. 4) the full-scale simulation results show that when the height of the building model is the same and the scale is similar. The shape of the building has a certain relationship with the size of the load response. Considering the tornado load response characteristics of different buildings, the tornado load response coefficient of rectangular buildings is relatively large. And with tornadoes attack angle of attack related.
【學位授予單位】：中國科學技術大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TU973.213

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