[[alternative]]Characteristics of near Surface Atmospheric Boundary Layers Developed over Various Terrains

計畫編號：NSC101-2221-E032-030 研究期間：201208~201307 研究經費：777,000[[abstract]]我國的風力規範：「建築物耐風設計規範及解說」，對於建築物設計風力有重要影響 的參數可分為三大類：設計風速及風場特性，風壓（風力）係數，陣風反應因子（順風 向風力）或是風力頻譜（橫風向與扭轉向風力）。其中影響最為重要，且具有本土特性 的是設計風速及風場特性。其中設計風速是根據全國各氣象站的多年風速記錄，經由極 值統計分析所得。所謂風場特性則是包括了在不同地況條件下，平均風速在高度上的分 佈以及紊流特性。由於我國缺乏相關資料，風力規範中所描述的的風場特性是依據 ASCE-7 的相關規定修訂而成。然而，我國的設計風速主要受到颱風的影響，與美國的 大陸型氣候不盡相同，台灣地狹人稠的社會發展型態與地廣人稀的美國都市鄉鎮型態亦 不盡相同，直接採用美國的風場特性，未必能夠正確的反應本土的風場特性。因此進行 相關研究，建立本土的自然風場數據做為未來風力規範的修訂依據，實有其必要性。 自然風場特性的研究方法不外乎實場監測、風洞模擬與數值模擬，三種研究方法各 有其優缺點。實場監測的數據最為真實可信，然而確有設備昂貴、設點不易、量測困難、 強風難求等諸多難處。風洞縮尺實驗最為便捷，然而僅採用風洞試驗進行自然風場之模 擬亦有不及之處。一般風洞實驗室模擬已知風場之特性，多利用人造物之不同組合以製 造出所需之風場。然而對於未知風場特性時，則需使風洞發展段之氣流自行通過足夠長 度之真實地形地物來產生一合理之邊界層。在數值模擬方面，現階段以CFD 數值模擬 根據實際地況發展紊流邊界層特性仍存在極大困難，然而以風工程之發展潛能為出發點， 本計畫仍CFD 數值模擬作為研究風法之一。 本計畫的基本研究內容扼要說明如下： 1. 以實場定點風速量測與遙測方式，量測在符合台灣地區典型地況之平均風速剖面與 紊流參數特性，實測數據除了可以作為風洞與數值模擬之比對驗證依據之外，更是 建立本土風場特性的重要數據。 2. 以風洞縮尺實驗，模擬不同地況（包括實場測點鄰近地況與規範定義之標準地況） 所產生的紊流邊界層特性。 3. 探討以 CFD 數值方法模擬(i)大氣邊界層自然生成，(ii)複雜地形風場之可行性。 整體計畫為期三年，前二年度執行實場監測、監測位址之風洞縮尺試驗、紊流邊界層流 場之CFD 數值模擬。未來一年將持續進行實場量測，並根據前二年研究所得之風洞模 擬與數值模擬方法，探討具有本土特性之自然風場特性。本計畫希望達成下列目標： 1. 建立研究自然風場的系統性方法； 2. 取得台灣地區在颱風與常年季風作用時，在海岸線、鄉村開闊地況、鄉鎮地況與都 會地區等自然風場特性之相關數據。 3. 由於實場監測變數甚多，本研究完成雖然未必能夠立即提出我國風力規範中有關風 速剖面與紊流特性之修訂建議，然而研究所取得之相關數據必然成為未來規範修訂 的重要參考依據。[[abstract]]This research project proposes the preliminary study on the characteristics of the atmospheric boundary layers. It is well known that the characteristics of the nature wind, the wind pressure (force) coefficients and the gust response factors are the three most important factors in the building wind code. Among the three items, the nature wind field exerts probably the most significant impact on the design wind load, and at the same time, is the most localized wind load parameter. Due to lack of local field data, this important and localized factor of wind code was transplanted from the ASCE-7. Taiwan is a mountainous island with complex terrain. The topographic features of the so called “large city”, “suburban” and “country side” in Taiwan are quite different from the continental nation such as the Unite States. Therefore, the terrain category for the wind field of these two different countries may not be the same. Besides of the topographical differences, there are two different types of wind that are important in Taiwan. Every year from July to November is the typhoon season in Taiwan. It averages 3.5 tropical cyclone type of strong wind per year over the past century. From December to February Taiwan has strong North-East Monsoon wind as the result of large scale weather system. It is wind engineers’ interest to investigate the similarity or/and difference on these two different types of wind. Therefore, this research project proposes to perform an in-depth investigation on the characteristics of nature wind through three different approaches, namely, full-scale monitoring, wind tunnel simulation and CFD simulation. For the period of three years, this project will carry out the following tasks: (1) in-situ measurements, by fixed location ultrasonic anemometer and portable Lidar system, of the velocity profiles and turbulence characteristics of near surface atmospheric boundary layer developed over the typical open, suburban and urban terrains in Taiwan; (2) systematic wind tunnel simulation of fully developed neutral turbulent boundary layers developed over terrains with various uniform roughness, terrain similar to the field measurements and complex terrain; (3) developing the techniques of the CFD simulation on fully developed turbulence boundary layer, and application of this technique to the simulations of turbulence boundary layer over uniform terrain and complex terrain. This is a 3-year project. For the previous two years, this project has carried out the field measurement of the atmospheric boundary layers; conducted the wind tunnel simulation on the flow field at full-scale monitoring sites and the LES simulation of turbulent boundary layers. The results of the first two years’ research work will be adopted to perform in-depth investigation on the wind characteristics the developed over terrains reflecting the local topography. This year’s research project is expected to accomplish the following goals: (1) developing a systematic approach for long term on the characteristics of natural wind field in the interest of structural wind engineering, (2) acquire wind data from open, suburban and urban terrains in Taiwan, (3) the results of this project may not be sufficient to proposing a set of new turbulent boundary layer parameters for the wind code revision, nevertheless, it will be an important set of data for the reference of future wind code revision.[[sponsorship]]行政院國家科學委員