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研究生:劉奕良
研究生(外文):Yi-Liang Liu
論文名稱:動床試驗模型時間比尺與變量流底床質運動特性之研究
指導教授:李光敦李光敦引用關係
指導教授(外文):Kwan Tun Lee
學位類別:碩士
校院名稱:國立海洋大學
系所名稱:河海工程學系
學門:工程學門
學類:河海工程學類
論文種類:學術論文
論文出版年:2002
畢業學年度:90
語文別:中文
論文頁數:145
中文關鍵詞:模型時間比尺變量流渠槽試驗底床質運動
外文關鍵詞:model time scaleunsteady flowflume experimentbed-load transport
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水利工程設計一般常以理論推導或數值模擬方式進行分析;然而若問題之影響因素過於複雜,則須藉模型試驗或野外現地量測等方式以進行工程設計。由於天然河川中泥砂輸送現象與水流特性間之力學關係仍未能明確瞭解,因此工程上常採用模型試驗方式,以探討颱洪過程之泥砂輸送現象。模型試驗之首要工作係決定模型比尺;研究中首先推導以福祿數定律為基準之時間比尺,並運用底床質運動之連續方程式與八種輸砂公式,推導以底床質運動為考量觀點之時間比尺,進而對上述二時間比尺,進行分析與探討。此外本試驗研究藉一系列上游不加床質之變量流動床試驗,探討變量流與定量流流況下底床質運動特性之差異,以瞭解變量流特性對底床質輸送量之影響。
研究結果發現,唯有採以天然砂為試驗材質,且模型比尺為等比之情況下,由泥砂運動觀點推導之泥砂運動時間比尺與以福祿數定律推導之水流運動時間比尺方為相等。若模型試驗採用不等比模型,在不等比比例K<3,且模型試驗砂使用天然砂時,仍可由福祿數定律所推導之水流運動時間比尺,作為設計模型時間比尺之依據。
試驗分析結果發現,由於變量流歷程流量尖峰時刻所生成之砂丘規模,無法在退水初期即時消退,造成變量流輸砂率歷線之尖峰到達時刻有一時間上之延遲現象,約佔變量流歷程之6%。因延遲現象之影響,使得昇水時期之輸砂總量較退水時期為小,其比值約為0.75。此外研究顯示,實測之輸砂率尖峰量為預測值之1.3倍,而輸砂總量為預測值之1.6倍。是以變量流實測之底床質輸送率於除去振盪現象後之特性,可由定量流預測之底床質輸送率特性予以估算。
The design work of water resource engineering is usually conducted through theoretical analysis and/or numerical modeling simulation. Nevertheless, it may need to investigate through flume experimental study or field measurement for some physical complex problems. Since the relationship between sediment transport behavior and flow characteristics is still unclear, sediment transport phenomena are usually investigated through flume tests. A prior work for laboratory experiments is to determine the model scale. In this study, a hydraulic time scale based on Froude number law was firstly derived. By using sediment continuity equation and eight selected empirical formulas, the sedimentation time scale for sediment transport was also obtained. The discrepancy between the hydraulic time scale and the sedimentation time scale was detailed discussed in this study. Furthermore, a series of flume experiments, which had different inflow hydrographs without sediment supply from upstream, were carried out to investigate the sediment transport characteristics under unsteady flow conditions.
The analytical results show that the only possibility to have the same model time scale, i.e. the hydraulic time scale equal to the sedimentation time scale, is that the model horizontal length scale should be equal to the vertical length scale, and the specific weight of the experimental sediment should be the same as that of in natural streams. The analytical results show that while model employed natural sediment and the model length-scale distortion ratio is lesser than 3, the model time scale derived from Froude number law can be applied for model design.
The experimental results indicate that a temporal lag was found between the flow hydrograph peak and the sediment hydrograph peak because large dune height was lasting for a long while in falling segment of the flow hydrograph. The temporal lag was found about equal to 6 % of the flow hydrograph duration. Due to the temporal lag, the bed-load discharge in the rising segment was only 0.75 times that in the falling segment. Furthermore, the bed-load peak discharge for unsteady flow condition was 1.3 times that was predicted by using the steady flow experiments results, and the total bed-load discharge for unsteady flow condition was 1.6 times that under steady flow condition. It is expected that the experimental results can be used to estimate the sediment transport characteristics under unsteady flow conditions.
中文摘要 i
英文摘要 ii
目 錄 iv
表 錄 vii
圖 錄 viii
照 錄 xiii
第一章 導論 1
1.1 研究目的 1
1.2 前人研究 2
1.2.1 模型比尺之相關研究 2
1.2.2 底床質輸送問題之相關研究 3
1.3 研究方法 5
1.3.1 模型時間比尺之研究方法 5
1.3.2 底床質輸送問題之研究方法 6
第二章 泥砂運動之理論分析 7
2.1 動床渠道之基本方程式 7
2.2 底床質輸送公式 9
2.2.1 定量流底床質輸送公式 9
2.2.2 變量流底床質輸送公式 15
2.3 因次分析 17
2.4 變量流底床質輸送率資料之處理方法 18
第三章 動床試驗模型比尺之理論分析 21
3.1 模型相似性 21
3.1.1 模型相似條件 21
3.1.2 模型相似律 23
3.1.3 福祿數定律 23
3.1.4 不等比模型 25
3.2 底床質運動時間比尺 26
3.2.1 由底床質運動連續方程式推導出時間比尺 26
3.2.2 由底床質起動相似條件推導床質粒徑比尺 27
3.2.3 不同底床質輸送公式之時間比尺 28
3.3 時間比尺之討論 35
3.3.1 等比模型 35
3.3.2 不等比模型 35
第四章 試驗設備與方法 37
4.1 試驗設備及功能簡介 37
4.2 試驗條件 41
4.2.1 研究集水區概述 41
4.2.2 決定模型之尺度 42
4.3 試驗步驟 44
4.3.1 試驗前之準備 44
4.3.2 試驗操作程序 44
第五章 試驗結果與討論 46
5.1 定量流試驗分析 46
5.2 變量流試驗結果分析 50
5.2.1 水位 50
5.2.2 水面坡降 51
5.2.3 累積之底床質輸送量 52
5.2.4 底床質輸送率 52
5.3 變量流底床質運動特性實測值與估計值之討論 53
第六章 結論與建議 57
6.1 結論 57
6.2 建議 58
參考文獻 59
附 表 62
附 圖 72
附 照 132
符號說明 139
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