Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/97353
標題: Analysis and Simulation of Live-Bed Pier Scour Evolutionin Steady and Unsteady Flow Conditions
動床條件下定量流及變量流橋墩沖刷深度變化分析與模擬
作者: Hsun-Chuan Chan
Po-Wei Lin
Jhih -Syong Peng
Jian-Hao Hong
詹勳全
林柏瑋
彭志雄
洪健豪
關鍵字: Live-bed
unsteady flow
local scour
pier
動床
變量流
局部沖刷
橋墩
摘要: This paper aims to analyze temporal evolutions of pier scour in live-bed condition. Five steady flow experiments are conductedwith different flow intensitiesratio of mean velocity to critical velocity varying from 1.18 to 2.21. To find out the effects of unsteady flow on scour depth, different steady flow intensities were combined as four unsteady flow experiments, including: (1) advanced hydrograph, (2) delayed hydrograph, (3) symmetric hydrograph and (4) symmetric hydrograph with low peak. A semi-empirical model proposed by Hong et al. (2014) was used topredict thetemporal variation of pier-scour depth. Moreover, alinear-combination hypothesis, i.e. scour depth hydrograph of unsteady flow can be simulated by a linear-combination ofscour depth hydrographs of steady flows,was proposed to extend Hong et al.'s model inunsteady flow conditions. Comparison of the experimental and model resultsshowed that the present modeldid not perform perfectly on the variation of dune migration velocity with changing flow intensity is changing. Simulation and experiment resultsrevealed a phase difference because of the effect of dune migration velocity.However,the error betweenthe simulatedand experimentalscour depths ranged from 8% to10% , including that the present modelcan estimate the temporal variationof scour depth for cyliderical piersunder unsteady flow conditionsreasonably well.
本研究利用明渠水槽試驗探討定量流況與不同流量歷線鋒型之變量流況,在動床條件下橋墩前方沖刷深度隨時間變化。試驗完成五組定量流流量,其水流強度 (平均流速與臨界流速之比值) 分別為1.18、1.38、1.6、1.91、2.21,以及由前述五組定量流水流強度組合而成之四組不同鋒型變量流之橋墩沖刷,包括:前峰型、後峰型、對稱型 (高洪峰)、對稱型 (低洪峰) 之變量流流量歷線。試驗設計定量流試驗歷時為三小時,變量流試驗歷時則為五小時,變量流每間隔一個小時改變一次水流強度,試驗過程以橋墩內架設之攝影機記錄沖刷歷程。結果分析比較不同水流強度定量流與不同峰型變量流橋墩沖刷歷程外,也將試驗結果引用Honget al.(2014) 發展之半經驗模式進行定量流沖刷歷程預測,並透過線性組合假設,延伸模式應用對變量流沖刷歷程進行推估。研究結果顯示,半經驗模式配合線性組合雖無法完全反應受水流強度變動對砂丘推移速度之影 響,致使模擬與試驗之沖刷歷程在部分時刻有相位差發生的情況,然變量流沖刷深度之變化整體發展趨勢仍為模式所掌握,不同峰型變量流之模擬與試驗沖刷深度平均誤差僅介於8%~10%之間,可推論Hong et al.(2014)半經驗模式配合線性組合假設,能合理推估變量流動床條件下橋墩前方沖刷深度隨時間之變化。
URI: http://hdl.handle.net/11455/97353
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