吳富春2006-07-252018-06-292006-07-252018-06-2920052005-10-31http://ntur.lib.ntu.edu.tw//handle/246246/10782本研究探討近床有序流結構對非均勻 砂礫啟動機率之影響。本研究利用四階 Gram-Charlier 機率密度函數(GC pdf)描述 近床流速隨機分布，並納入亂流突暴之高 階相關性係數。本研究結果較先前之常態 與對數常態分布模式結果具有更高之精確 度，可用來預測均勻或非均勻粒徑砂礫在 部分運移與全運移情況之啟動機率。本研 究結果亦顯示在粗糙河床時三階GC pdf 可 替代四階GC pdf，但在光滑河床時須使用 四階GC pdf 納入高階相關性之影響。The effects of near-bed coherent flow structures on the entrainment probabilities of mixed-size sediment are investigated in this study. The 4th-order Gram-Charlier probability density function (GC pdf) of near-bed streamwise velocity is employed to account for the higher-order correlations associated with turbulent bursting. As compared to the previous models using normal and lognormal pdfs, the present results demonstrate significantly improved agreement with the observed data for the unisize and mixed-size sediments under partial- and full-transport conditions. The results also reveal that for fully rough beds the 3rd-order GC pdf approximates the 4th-order one, however, for smooth beds the 4th-order GC pdf must be used to capture the effects of higher-order correlations.application/pdf935670 bytesapplication/pdfzh-TW國立臺灣大學生物環境系統工程學系暨研究所啟動機率亂流突暴近床有序流結構非均勻砂礫Entrainment probabilityturbulent burstingnear-bed coherent flow structuresmixed-size sedimentreporthttp://ntur.lib.ntu.edu.tw/bitstream/246246/10782/1/932211E002022.pdf