風吹落物之軌跡預測與災害風險評估

台灣位處於亞熱帶地區，氣候形態多變，常受西北太平洋颱風之侵襲，而近年來因全球氣候變遷，強烈颱風的數量明顯增加，導致引發的風災更加慘重，除了在山區因強降雨所引發的山崩土石流，以及中下游地區洪水暴漲的可怕場景，颱風所夾帶的強風，同樣也對國人的生命財產造成嚴重的威脅。　　面對如此高的風險，該如何對國土進行有效的管理與運用，以及面對天然災害時的危機處理能力，就成了政府的一項重大課題。目前現行之颱風災損評估模組，主要是針對強降雨所導致之土石流與洪水進行分析，對於強風引發的效應則著墨較少，強風導致的災損規模或許不像洪水或土石流般的龐大，但對於人口密集且環境擁擠的都市區來說，其所造成的災損也是具有相當程度的影響。　　Tachikawa將板狀風吹落物在飛行時的狀態分為三種類型，分別為翻轉模式、平移模式，以及混合模式；而Lin則在其發表的論文中，利用他透過實驗所得到的軌跡方程式，發展出一個可以估算在某一住宅區內，房屋遭受風吹落物破壞的機率的系統，但是Lin在建立軌跡方程式的時候，並沒有特別去區分飛行模式，單純只針對水平向位移來進行分析，而忽略了垂直向軌跡造成的影響。　　但Visscher在其研究中發現，翻轉和平移這兩種模式在飛行的距離上會有明顯的差異，這種差異的產生，主要來自於在不同的飛行模式下，風吹落物的滯空時間並不相同，此即為垂直向軌跡所引起之效應。故將垂直向軌跡造成的影響納入軌跡方程式內，以期得到較符合真實情形的結果，即為本研究的重點所在。　　本研究在實驗設置上，為了找出兩不同飛行模式下的差異，將特別針對風攻角做設定，分別為30度以及75度，並以四種不同風速進行實驗，實驗的對象為內含6種不同材質的20塊板，外型尺寸上除了正方形與長方形各半以外，在厚度上也略有不同。在實驗完成並得到垂直向的軌跡資料之後，便可將最終整理出來的軌跡方程式代入評估系統內進行分析，並計算風吹落物造成破壞的機率。

關鍵字

風吹落物；垂直向軌跡；翻轉模式；平移模式；風險評估系統

並列摘要

Taiwan, located in the subtropical region, has a lot of typhoons, which bring heavy rains and strong winds. It not only causes landslide and debris flow, but also damages houses. Due to the high risk of natural disasters, how to predict disasters is government’s priority. Windborne debris was developed in 1980s, and Tachikawa reported the flying behavior of plate-type debris in 1983. He defined three different kinds of flight mode: auto-rotation, translation, and intermediate. In 2006, Lin used experiment data to form the empirical expressions for estimation the horizontal flight speed and distance, and then designed a risk assessment to estimate the probability of damage. It should be noted that in this system, the vertical trajectory was ignored. But in further research, Visscher pointed that the flight distance has significant difference between auto-rotation and translation. In experiment setup, we choose different types of plates and set the angle of attack to 30 and 75 degrees representing auto-rotation and translation respectively. The wind speed range between 8 and 18 m/s. This paper presents the relation between the flight mode and flight distance. We will use these experiment data to find the vertical trajectory influencing the flight time and flight distance. Finally, these empirical expressions are to calculate the damage probability in risk assessment.

並列關鍵字

Windborne Debris ； Vertical Trajectory ； Auto-rotation ； Translation ； Risk Assessment

參考文獻

2. Tachikawa, M. (1983). Trajectories of flat plates in uniform flow with application to wind-generated missiles. Journal of Wind Engineering and Industrial Aerodynamics, 14(1-3), 443-453. doi:DOI: 10.1016/0167-6105(83)90045-4

3. Tachikawa, M. (1988). A method for estimating the distribution range of trajectories of wind-borne missiles. Journal of Wind Engineering and Industrial Aerodynamics, 29(1-3), 175-184. doi:DOI: 10.1016/0167-6105(88)90156-0

4. Wills, J. A. B., Lee, B. E., & Wyatt, T. A. (2002). A model of wind-borne debris damage. Journal of Wind Engineering and Industrial Aerodynamics, 90(4-5), 555-565. doi:DOI: 10.1016/S0167-6105(01)00197-0

5. Lin, N., Letchford, C., & Holmes, J. (2006). Investigation of plate-type windborne debris. part I. experiments in wind tunnel and full scale. Journal of Wind Engineering and Industrial Aerodynamics, 94(2), 51-76. doi:DOI: 10.1016/j.jweia.2005.12.005

6. Visscher, B. T., & Kopp, G. A. (2007). Trajectories of roof sheathing panels under high winds. Journal of Wind Engineering and Industrial Aerodynamics, 95(8), 697-713. doi:DOI: 10.1016/j.jweia.2007.01.003

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風吹落物之軌跡預測與災害風險評估

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