臺灣博碩士論文加值系統

台灣河川坡陡流急，故需在河川中建造堰壩等水工建造物以達到水資源利用及穩定河川之成效。堰壩有許多不同種類的破壞，攔河堰型結構之最常見為溢洪道表面之破損，係由水流挾帶石塊沖擊所致，嚴重時可侵蝕內部結構，導致結構物強度不足。天然河川流路蜿蜒曲折，若堰壩上游經轉彎產生一夾角入流，水流斜向撞擊堰體將產生水平與垂直組合渦流，受渦流之牽引力作用將位於堰體前底床之石塊往上帶起通過堰體撞擊溢洪道表面。堰體安全與破壞之相關研究甚多，卻鮮少探討上游流況對砂石牽引與撞擊堰體表面之影響。鑑此，本研究針對上游水流與堰體非垂直入流情況，進行定床與動床情況下之流場量測，並應用質點影像測速法(PIV)在堰體上游不同水深分層量測其水平流場特性，藉此探討堰體與水流入流夾角之情況下之流場變化。
研究成果顯示，在堰前因導流而形成渦流區與直接通過堰體之流況，其中，靠近渠道中間之水流，可快速通過堰體往下游流動。另一為渦流區，其形成係因水流通過堰體之流速差異大，造成水流擾動與不穩定現象，於導流後方會形成渦流區。迴流區因垂直與水平交錯渦流影響，該區流況相當紊亂，渦流強度隨入流角度與速度增強衰退。渦流本身亦會由小成長至大渦流、能量消散至消失，形成一循環系列。流入迴流區水流會隨著流量加大流速變快且角度擺盪幅度減小，使渦流強度增加。下游沖刷因上游水流之非垂直入流，產生水流往一側集中現象，在下游造成沖刷坑偏移與碰撞邊界後反射產生交替砂洲。

Due to Taiwan’s rivers being steep with rapid flood flow, dams and weirs are usually built for the purpose of water resources supply and river stabilization. There are many types of damage to the dams or weirs, and the damage on the spillway surface is the most common type. The damage comes from the collision of coarse sediments on the spillway surface, which will erode the internal structure and finally endanger the safety of the weir/dam. When the weir is built on a meandering river, the incoming flow will be not perpendicular to the weir axis and thus result in additional vortex flow. This vortex flow will pull up the bed material before the weir and the collision will occur during the passage of the flow. There are few in the literature on this topic. Therefore, this study focuses on the inflows not perpendicular to the weir axis, and uses the PIV to measure the horizontal flow fields at different vertical levels, under fixed- and movable-bed conditons.
This study result reveals that upstream flow field can be divided into two parts: one flows fast to the downstream, the other becomes recirculation before the dam due to the large difference in the flow velocities. In recirculation region, size of vortex grows with water depth and flow discharge. Intensity of vortex depends on the inflow angel and velocity. Being in a cycle series, vortex grows from small to strong and then disappears due to energy disspipation with duration time between 1 to 1.8 seconds. The range of inflow angel narrows down with rising the flow rate.Upstream bed deforms amd grows as a dune and thus makes vortex concentrated and strong. Due to inclined inflow, the flow shifts forward the bank of the flume after passing the weir. The downstream scour hole shifts away from the centerline and the alternative bars occur.

摘要 III
Abstract I
誌謝 II
目錄 III
表目錄 V
圖目錄 VI
符號說明 XIII
第一章 緒論 1
1.1 研究動機 1
1.2 研究目的 2
1.3 文獻回顧 3
1.3.1 堰壩表面破壞因素 5
1.3.2堰壩下游沖刷相關研究 6
1.3.3溢洪道流場相關研究 9
1.3.4質點影像測速法 10
1.4 研究方法 11
1.5 本文組織 12
第二章 試驗佈設規劃與分析方法 13
2.1 試驗佈置規劃 13
2.1.1試驗儀器佈置 13
2.1.2因次分析 22
2.1.3試驗條件 23
2.1.4 試驗步驟 48
2.2 PIV質點影像測速法理論簡介 49
第三章 試驗結果與討論 57
3.1流況概述 57
3.2上游流場PIV量測結果 60
3.2.1水深方向量測結果 60
3.2.2水深方向量測結果討論 61
3.2.3水流方向量測結果 79
3.2.4水流方向量測結果討論 80
3.3下游沖刷坑結果與討論 85
3.4水流角度相關因子分析 92
3.4.1　PIV量測結果中相關因子討論 92
3.4.2 快速傅立葉轉換之頻率分析結果 93
3.4.3 表面入流角量測結果 96
第四章 結論與建議 98
4.1結論 98
4.2建議 99
參考文獻 101
附錄一 流場結果展示 103

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