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Hydrodynamic simulation of density current and muddy lake for Shihmen reservoir
|Authors: ||Jian, Da-Jun|
|Contributors: ||NTOU:Department of Harbor and River Engineering|
density current;muddy-lake;numerical model;water entrainment coefficient;total drag coefficient
|Issue Date: ||2017-05-24T08:40:35Z
|Abstract: ||台灣地區山坡陡峭水流湍急，颱風時期因降雨集中，導致水庫上游集水區產生劇烈的沖蝕與大規模崩坍形成高濃度的含砂水流運移至水庫庫區。含砂水流與庫區清水間有密度差異，在適當條件下含砂水流會潛入至庫底形成底層異重流並往壩址運移。本研究使用MacCormack (1969)二階精度差分方法建置變量異重流數值模式，模擬含砂水流因達潛入條件而潛入庫底，形成異重流運移至壩址之運動情形。研究中分析石門水庫多場颱風放水口之濃度歷線，並配合質量守恆之觀念建立概念化渾水潭模式，模擬異重流運移至壩址形成渾水潭後，水庫放水之泥砂濃度。 本研究首先使用定量鹽水異重流實驗之數據，檢定異重流模式中之捲水係數(Ew)與總阻力係數(Cd)，以瞭解參數對於異重流厚度、平均濃度及平均速度之敏感度；並使用變量鹽水異重流實驗之數據進行模式驗證，利用上述之測試結果調整模式參數，使模擬結果與實驗數據相近；最後採用石門水庫集水區之資料，以數場颱風事件進行模擬分析，比較放水口實測之放水濃度與模擬之渾水潭出流濃度。|
Hillsides in Taiwan are usually steep with rapid flow. Large scale landslide and severe erosion usually occur in concentrated rainstorms, which result in a large amount of sediment flowing through overland areas to channel network and then to downstream reservoir to reduce the useful life of reservoir. Since sediment laden flow and reservoir ambient flow conform to the plunge condition, the turbidity flow plunges into the reservoir bottom as a density current. A one-dimensional unsteady density current model was built by second-order MacCormack scheme to simulate the turbidity current plunging into the reservoir bottom and move to the dam site. A conceptual muddy-lake model based on the analysis of Shihmen sediment observations and mass conservation was also developed for reservoir operation to estimate the reservoir outflow concentration. Water entrainment coefficient (Ew) and total drag coefficient (Cd) were calibrated using the data from series saline-density-current flume tests. Sensitivity analysis was conducted to realize the influences of the coefficients on the thickness, velocity, and concentration of the density current. Good similarity can be found between the simulated and the recorded data using the calibrated and . Moreover, hydrological records from typhoons in the Shihmen reservoir of Taiwan were collected to demonstrate the capability of the proposed model for density current simulation. The model is promising to provide valuable information to authorities for reservoir operating to reduce reservoir sedimentation.
|Appears in Collections:||[河海工程學系] 博碩士論文|
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