教師資料查詢 | 類別: 研究報告 | 教師: 羅元隆 LO, YUAN-LUNG (瀏覽個人網頁)

標題:建築結構於非定常氣流下之風力特性研究(1/3)
學年107
學期2
出版(發表)日期2019/05/01
作品名稱建築結構於非定常氣流下之風力特性研究(1/3)
作品名稱(其他語言)
著者羅元隆
單位
描述
委託單位
摘要傳統的結構風載重設計理論假設在定常性氣流的流場環境中,根據準靜定理論建構風致振動的行為預測。然而根據國外最新研究成果以及淡江大學風工程研究中心過去執行長達十年的實場監測數據來看,非定常性氣流相較於定常性假設更接近於真實,也更應該用以作為預測結構振動行為的外力來源。根據義大利及澳洲學者的文獻來看,主導當地氣候並影響結構設計風載重的主要氣候特徵為雷雨(Thunderstorm)。由實場監測資料看來,雷雨的垂直向風速剖面常會隨時間改變而非遵守固定的冪次法則(Power Law);尤其是剖面高度介於一般高層建築之內,且接近地表時會產生水平向的加速度氣流,造成風速尖峰因子甚至高達7,8以上,遠高於一般假設為高斯特性的3.5。另一方面,台灣淡水中央電台的數據亦顯示出在同一颱風期間,風速剖面亦不全然遵守冪次法則,快速的剖面特性轉換實際上很可能讓建築表面接近地面的風力加大而接近屋頂部分的風力減低。如此一來,過去常見的風壓分布圖僅能列為定常性風壓分布。同理,建築結構的整體風力計算以及建築表面或附屬結構物的設計風壓,也應該予以重新定義。本計畫預計執行期間為三年,第一年進行非定常性氣流流場模擬以及二維鈍體空氣動力學基礎研究。藉由淡江大學於2016年竣工的複數風扇風洞實驗室作為主要流場模擬平台,配合八組熱膜探針系統同步量測,並與CFD數值模擬比對,產生符合實場中各種非定常性氣流的流場環境。接著針對2D氣動力模型進行瞬時風壓量測,討論各種氣流(包含加速氣流及時變性剖面氣流)對於風壓特性的影響。第二年則是進行2D氣彈力模型的振動與風壓同步量測,找出非定常性外力與結構反應之間的關係,重新定義時頻性機械轉換函數與利用小波理論分析時頻變化。此外,製作低矮及高層建築模型進行氣動力風壓量測,了解並重新定義建築表面或附屬結構物的設計風壓。第三年則進行低矮及高層建築模型的風力量測實驗,討論整體風力計算與過去傳統理論之相異處。再利用強制振動系統進行不穩定氣流下的機械轉換函數定義。可視化實驗則配合既有的雷射、煙霧產生器及高速攝影機,進一步觀察流場於模型周圍的分布特性,並與CFD模擬結果比對,提出與傳統假設不同的流固現象觀察結果。複數風扇風洞實驗室在全球風工程相關實驗室寥寥可數,屬於十分具有創新性的實驗機具。除了實踐本計畫所規劃的內容外,期待能在國內激起新一系列的研究主題,提升我國在該學術領域的學術能量。
Conventional theory of design wind loads on structures is assumed to be quasi-static under the stationary flow environment. However, according to the latest research works and field measurement observations by TKU-WERC group, non-stationary flows are, in fact, more suitable to be considered as the driven force on structures rather than stationary ones. For instance, the main meteorological characteristics in Italy and Australia for the consideration of design wind loads are thunderstorms. From the field monitoring results, the vertical wind profile of a thunderstorm does not follow the power law; instead, the profile is time-dependent and is tend to generate a jet flow near the ground. The resultant horizontal accelerated wind sometimes rises the peak factor even up to 7 or 8, which is much higher than the Gaussian one. On the other hand, the monitoring results in Tamsui Central Tower also shows that the vertical profile during a typhoon is rapidly changing with time and such changing feature may significantly reduce the wind force on the top area of the building but enlarge the force on the bottom area, which in other words, the projected wind force characteristics may not be estimated from conventional theory. Therefore, it is strongly believed that, the design wind loads of the main resistant system and design wind pressures of cladding components need further revisions. This project is designed to run for three academic years. In the first year, the simulation of various non-stationary flows and the basic understanding of two-dimensional bluff-body aerodynamics are emphasized. By means of multiple-fan wind tunnel, which was built by TKU-WERC in 2016, along with simultaneous wind speed measurements and CFD numerical simulations, 2D bluff-body immersed in non-stationary flows are examined. In the second year, simultaneous measurements of displacement and wind pressures are conducted to find the relationship between non-stationary excitation and structural response. The mechanical function is revised by time-frequency domain analysis. On the other hand, low-rise and high-rise building models are made for surface pressure measurement in order to discuss the design wind pressures for cladding components. In the third year, forced vibrator is adopted to confirm the relationship between non-stationary excitation and structural response. The design wind load for the main resistant system is concerned. Visualization test and CFD numerical simulation are also conducted to enhance the understanding of flow-solid interaction phenomenon observation.Active-control type wind tunnels, such as the multiple-fan wind tunnel in this project, are rare to seen in wind engineering related laboratories in the world. The advanced technology of high-performance servo motors is expected to stimulate innovative research themes. Except for the planned items in this project, other possible topics may be developed and upgrade our design load criterion to a higher level.
關鍵字非定常性氣流;複數風扇風洞;氣動力風壓;氣彈力振動;加速度風速;時變性風速剖面;Non-stationary flow;Multiple-fan wind tunnel;Aerodynamic pressure;Aero-elastic vibration;Accelerating wind speed;Time-dependent wind profile
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