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  • 學位論文

FLOW-3D模式運用於異重流運移數值模擬

Numeric Simulation of The Density Current Transport by FlOW-3D model

指導教授 : 曾志民

摘要


台灣雖然年平均雨量達2,500公釐,但山高坡陡,河川流短湍急,降雨又集中於梅雨與颱風季節,因此多以水庫來儲存水資源。颱洪期間高濃度挾砂水流進入水庫後,往往容易形成異重流。異重流前端流動過程對於底泥造成之沖刷捲昇,容易擾動庫區細微泥砂形成之底泥,產生高濁水現象。異重流運移過程之泥砂濃度受到入流流量、入流泥砂濃度、泥砂沉降捲昇及下游出流等因素之影響而變化。本研究以三維數值模式FLOW-3D分析異重流運移與底部高濃度淤泥層間之濃度交換情形。 本研究數值計算以陳秉鈞 (2007)之渾水異重流定床試驗成果作為測試驗證對象。並分別利用大渦流模式、RNG模式與k-ε模式測試並與實驗數據比較,其中大渦流模式不論是濃度剖面、頭端速度或濃度沿程變化都與實驗數據較為接近,因此選用大渦流模式模擬渾水異重流之運移過程。網格測試方面,由於大渦流模式網格大小會影響到紊流之黏滯係數,因此針對大渦流模式進行不同網格大小之模擬,以固定X、Y、Z其中兩軸長度並調整第三軸網格長度之方法,得知以大渦流模式與網格大小6cm×2cm×1.5cm之搭配較能描述試驗室尺度異重流之特性。 運用大渦流模式與6cm×2cm×1.5cm之網格大小模擬底部存在高濃度懸浮底泥時,對於異重流運移過程濃度變化之影響。模擬成果顯示當底部存在淤泥層時,因異重流與底部淤泥層之濃度擴散交換,使異重流運移過程前鋒濃度有明顯變化,且增加幅度與Cin/Cb之比值呈負相關關係,Cin/Cb值愈小,則沿程濃度增加幅度愈大,異重流濃度沿程變化可以雙曲正切函數加以描述。

並列摘要


Although average annual rainfall reaches as high as 2,500 mm in Taiwan, building water reservoirs are indispensable for water storage because of highly steep hills and mountains, short length of rivers and streams featuring torrents and rainfall concentration during Taiwan Spring rain season and typhoons. There usually create density currents after water flows landed with high density of sand flood into water reservoirs. The frontal flow of density currents will cause turbidity currents and surge currents, disturbing the sediment mud composed of fine sand in the water reservoirs and high turbidity water. The density current flowing will be affected by inflow volume, inflowing sediment load, sand deposition and boiling and downstream outflow volume. The three-dimensional numerical model (FLOW-3D) is adopted in this research for analyzing the density exchange between density current motion and high-density deposition in the bottom. The turbidity current and density current in the fixed bed experiment established by Chen, B. C. (2007) is adopted as the numeric calculation for this research to examine the researched objects. LES (Large eddy simulation), RNG model and k-ε model were compared with experimental statistics. The comparison statistics show that the concentration profiles, initial flow speed or density of current movement of LES are highly similar to experimental statistics. The LES is thus adopted for simulating the current movement of turbidity current and density current. As the grid porosity of the LES will affect the viscosity of turbulent current, simulations were conducted by using various sizes of grid porosity. On the condition that the lengths of 2 axles of X, Y & Z axles are fixed, and the length of the third axle is adjusted, the result shows that the portfolio of using LES with grid size of 6cm× 2cm×1.5cm can have better measurement performance of the features of density current in term of laboratory scale. The LES combined with grid size of 6cm×2cm×1.5cm is applied for simulating how high density of drilling bed mud will interact with density change of current movement of turbidity current. The simulation testing results show that when there have bed mud deposition, the density diffusion and exchange between density current and bed mud deposition will cause significant change in the initial flow density of density current movement and there is a reverse relationship between the increase ratio and specific value of Cin/Cb. It means that the smaller the value of Cin/Cb, the higher the density of the current movement. The movement change of density current can be illustrated by Hyperbolic Function.

參考文獻


16.楊政翰 (2008)。FLOW-3D應用於土石流防砂壩前流場及衝擊力研究。碩士論文,成功大學水利及海洋工程學系,台南市。
11.陳建宇 (2007)。環圈堆保護橋墩之試驗及其三維流場之數值模擬。碩士論文,成功大學水利及海洋工程學系,台南市。
14.曾仁彥 (2008)。水庫異重流運移過程之數值模擬。碩士論文,長榮大學土地管理與開發學系,台南縣。
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被引用紀錄


彭椿榮(2012)。電視台駐地記者在休閒參與、工作壓力休閒調適與休閒效益之研究〔碩士論文,國立臺灣師範大學〕。華藝線上圖書館。https://www.airitilibrary.com/Article/Detail?DocID=U0021-1610201315275129

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