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標題: | 離岸風機基座淘刷數值研究 Numerical simulation of scour around foundation of offshore wind turbine |
作者: | Huan-Wei Kuo 郭桓瑋 |
指導教授: | 周逸儒(Yi-Ju Chou) |
關鍵字: | 局部沖刷,大渦流模擬,虛擬網格沉浸邊界法,移動網格法,馬蹄形渦漩,尾跡渦漩,護基石堆, local scour,large eddy simulation (LES),ghost-cell immersed boundary method (GCIBM),arbitrary Lagrangian-Eulerian scheme (ALE),horseshoe vortex,lee-wake vortex,riprap, |
出版年 : | 2017 |
學位: | 碩士 |
摘要: | 為了瞭解流體經過結構物造成的局部沖刷現象,使用大渦流模擬結合虛擬網格沉浸邊界法與移動網格法來進行數值模擬。我們使用大渦流模擬解析出流場中較細微的瞬時紊流運動以模擬出底床形貌隨時間演進的動態變化。固體邊界使用虛擬網格沉浸邊界法產生,此方法可以在卡式座標網格下定義複雜幾何邊界,且相較於傳統的貼體法較為節省計算資源。移動網格法計算網格速度使流域邊界隨著底床形貌的變化而移動。
數值模擬的結果分為四個部分:第一個部分模擬穩態流流經不同幾何斷面之結構物,並觀察到銳體能夠有效降低底床淘刷;第二個部分透過因次相似模擬在現地波浪條件下的沖刷現象,由模擬結果發現在現地條件Keulegan-Carpenter數(KC)範圍內主要的淘刷機制為尾跡渦漩;第三個部分加上護基石堆進行模擬,由模擬結果發現流場中不對稱的尾跡渦漩運動使得淘刷在護基石堆左側較為劇烈;第四個部分模擬在長週期波浪下的沖刷現象,由模擬結果發現在入流速度相同時,隨著震盪週期增加,圓柱前後緣形成明顯的馬蹄形渦漩,和小KC數時淘刷主要發生在圓柱兩側時的情形不同,最後形成圍繞圓柱的淘刷坑洞,與穩態流淘刷的情形相似。 In this study, we employ large eddy simulation (LES) along with ghost cell immersed boundary method (GCIBM) and arbitrary Lagrangian-Eulerian scheme (ALE) to simulate local scour induced by flow over a wall-mounted structure. In order to simulate the instantaneous evolution of the bed form, we use LES to resolve the detailed flow features. The GCIBM is used to model the geometry associated with the complex solid boundaries without much computational effort. Moreover, the ALE scheme incorporates the grid velocity such that the domain boundary is able to follow the time-dependent bed form geometry. The numerical study comprises four parts. The first part presents the steady current passing an idealized structure with the different shape. Our simulation results show that the sharp-nosed body effectively reduces the bed erosion. In the second part, simulations of the bed scour under field conditions are presented, by means of the law of similarity. The main erosion mechanism within the range of the field Keulegan-Carpenter number (KC) is due to lee-wake vortices. The third part considers the bed scour around a cylinder with the riprap protection. Results show that due to asymmetric motion of lee-wake vortices, scour is more vigorous at the left side of the riprap. The fourth part presents the simulation of scour during a long-wave period. When the wave period increases, the formation of horseshoe vortices around the cylinder is evident. As a result, the scour pattern is different from that in the small KC case. In the latter case, erosion mainly occurs at the left and right sides of the cylinder. In the former case, the scour hole forms around the cylinder, which appears to be a feature similar to the case of the steady current. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/20691 |
DOI: | 10.6342/NTU201702141 |
全文授權: | 未授權 |
顯示於系所單位: | 應用力學研究所 |
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