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|標題:||Hydraulic Mechanics and Topography of Bending Vegetation in different Density|
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|摘要:||本研究探討植物在不同疏密程度情況下，植株彎曲後對於周圍流場與底床變化的特性，研究中設計渠槽定床試驗與渠槽動床試驗各別探討植株水理與地形沖淤特性。實驗配置方面，變更植株前後的距離以作為疏密程度的依據，試驗中用五個不同的間距。渠槽試驗的水流條件均使用低於底床粒徑的啟動流速。彎曲植株為人工製模型，使用塑膠管彎曲成90度模擬倒伏的植株莖幹，尾端插入塑膠片模擬植株葉片。流場特性量測儀器使用超音波流速剖面量測儀(Ultrasound Velocity Profiler)，量測植株倒伏後對周圍的流速影響與紊流強度，並觀察不同密度下的流場特性；動床沖淤試驗為擬實際植株群分布，將數個倒伏植株埋入10cm石英砂中模擬植株群，並用平行與交錯兩種排列方式，三種密度來進行試驗。試驗過程與結果分別使用縮時攝影機與雷射測距儀紀錄歷程與量化床面地形，並針對特定點位使用UVP量測水理特性，以利床面型態分析之依據。
The study investigated the effects of bending vegetation in different canopy density on distribution of flow field and topography of bed. A fixed bed channel experiment and a movable bed experiment were de-signed for studying flow characteristics and topography of bed, respec-tively. In experiments, canopy density depended on a longitudinal dis-tance between two bending plants by five types. Flow condition in ex-periments was below the threshold velocity of sediment. A bending plant was composed of plastic pipe regarded to stem and P.P.C. film re-garded to blades. The study used Ultrasound Velocity Profiler (UVP) to measure flow field and turbulence intensity around bending vegetation in different density. In movable bed, bending vegetation in three types of density was placed in 10cm quartz sand in channel. Additionally, vegetation arrangement divided into parallel and staggered pattern. The development of topography was recorded by camera and the results of bedform were measured by the laser distance meter. After experiments, the relation between flow characteristics and topography was analyzed in bending vegetation of different density. The results showed that interval zones existed strong turbulence, up-ward flow and transverse flow in sparse canopy that was bent by flow. Strong turbulence and vertical flow in interval zones caused depression inside bending sparse vegetation. In contrast, plant bent and covered other plant in dense canopy. A shear boundary was induced in the sur-face of bending vegetation. Consequently, the shear boundary avoided flow flowing toward bed and reduced the flow velocity. The depth of erosion inside dense canopy could reduce up to 60%. The significant result occurred due to covering motion with bending vegetation pre-vented bed from flow and bending blades made flow downstream quickly. Total volume of scour and deposition in bending sparse canopy was higher than dense ones.
|Appears in Collections:||水土保持學系|
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