1、如何設定瞬時問題?電子散熱分析中，通常以穩態(Steady State)結果作為分析依據，在此狀況下可以觀察到整個模型熱場流場穩定后的結果。如需觀察溫度隨時間變化的曲線圖，則必須設定隨時間變化的熱源(Transient Attribute)、瞬時時間網格(Transient Grid)，以便觀察各時間點整體計算區域的熱量傳遞速度及流體擾動狀態。以下以一實際案例解釋FLOTHERM中瞬時設定的流程。瞬時問題建立流程：一、模型建立與幾何尺寸設定：模型建立請參照本公司之”FLOTHERM基礎課程訓練教材”一書。以下為幾何尺寸設定二、PCB板熱源設定：三、瞬時熱源設定：Enclosure的六個面上均提

2、供如上圖之發熱量隨時間變化的Transient Source。四、數值結果顯示及說明：由上圖結果可以得知，在350秒的時候NC1芯片已超過最大容許溫度攝氏125度，所以在350秒的時候此裝置已無法正常運作。五、圖形化后處理：問答集Question 1：使用FLOTHERM解決瞬時問題需注意的事項。Answer：(1) 必須設定材質的密度(Density)及比熱(Specific Heat)。一般求解穩態的案例中，因密度及比熱不隨時間的變化，所以可以忽略不設定。(2) 時間網格( Transient Grid )。FLOTHERM為一自動網格系動熱流仿真軟件，當設定瞬時熱源以后，軟件本身會自動設

3、定其時間網格。所以當求解瞬時問題時，可先設定瞬時熱源再設定時間網格。Question 2： 如何設定瞬時熱源?!Answer：瞬時熱源顧名思義為發熱量隨時間而改變，FLOTHERM中提供以下幾種熱源設定。Question 3： 瞬時收斂性的問題。Answer：瞬時問題收斂性有關于模型本身物理性的網格與時間性網格的設定。當無法收斂的時候兩者都必須作網格收斂性的測試。詳情請參閱Flomerics 網站( )中的技術文件”Convergence and Transient Simulation”何謂局部加密?       

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5、0;                                   <TOP>局部網格加密理論            &#

6、160;                              Validation - 1D Conduction Without validation of the most basic of cases there is no way trust can be gained in the local

7、ized grid solution of more complex models. This model shows that a perfect linear variation in T in this conduction only analysis is predicted both with and without the use of localized grid. It is my belief that if this case was set up and solved in competitive codes that offered such a gridding ca

8、pability there would be kinks in the T profile, kinks that are highly sensitive to the quality of the grid. Validation - 2D Conduction, Getting slightly more complex.Validation - 2D Convection,The first graph indicates that there is a difference. The second graph is for a much finer grid both localized and non-localized. This therefore demonstrates that the difference observed in the first graph was because BOTH localized and non-localized were not gr