第五章 模式檢定與驗證
6.2 建議
針對本研究至今之成果及不足之處，在此提出建議以供後續研究之參考:
(1) 本研究對二維模式中沖刷公式進行修正，在實務應用上應已足夠表示局部底 床之變化情況。然而橋墩周圍流況相當複雜，若要以微觀之角度對每一種流 場機制對底床沖刷之影響進行研究，則建議搭配擬似三維或全三維之流場模 式進行動床模擬。
(2) 本研究主要針對局部實驗沖刷進行模擬，並未進行現場之模擬應用，而實務 情況之橋墩形狀並非均勻之圓柱，針對此一方面可參考Melville and Raudkivi (1996)等效橋墩寬度之做法加入橋墩形狀之影響進一步改良。
(3) 本研究乃針對均勻沉滓粒徑之定量流之情況進行模擬，然而原二維沖刷模式 已具備有處理非均勻沉滓及變量流之能力，加入本研究成果後之實際使用情 況有待進一步確認。
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Engrg., ASCE, Vol.125, No.1, pp. 59-65(1999).
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附錄一 CFX 模式之數值方法簡介
針對不可壓縮流之壓力項，CFX 使用以下之數值方法求解:
(I) SIMPLE(Semi-implicit Method for Pressure-Lined Equations)法 以二維流體之動量方程式為例做說明:
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(II) SIMPLEC(SIMPLE consistent)法
SIMPLEC 數值方法基本上與 SIMPLE 數值方法的計算流程一致，其不一樣 的地方在於第(A-6)、(A-7)式中保留ue'anb 與ve'anb ，並將anb(unb' ue')以及
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(III) PISO(Pressure-Implicit with Splitting of Operators)法
PISO 數值方法是一種利用 time-marching 的方式來獲得穩態的速度場與壓力 場，在每一個time step 中，PISO 的計算包括一個預測階段(predictor step)與一個 或多個修正階段(corrector step)。為方便解釋，以下變數的上標“*”表示為預測階
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(4)使用第一階段的修正速度值，由第(A-16)式計算第一階段的修正壓力。
(5)利用第(A-15)式計算第二階段的修正速度。
(6)使用第二階段的修正速度值，由第(A-16)式計算第二階段的修正壓力。
(7)前進到下一個 time step，直到速度與壓力場達到穩態。