How to deal with ""Program terminated -time step too small"" error message? "
""Time step too small"" is shown when the current time step is less than 10% of the initial time step. You can always decrease the minimum time step to continue the calculation. After loading your problem, go to the Controls panel and select Timestep Options. Change the Minimum Time Step to a very small number, or zero. Zero Minimum Time Step means that the minimum time step size is calculated automatically by the code. The variables affecting the time step are the smallest cell size, gap size, velocity, and sound speed. For Lagrangian type parts, you need to examine the geometry of the parts to see if there are distorted cells. For Eulerian type parts, you need to examine the velocity and sound speed of the parts to see if there are abnormal velocity or sound speeds. If Lagrange-Lagrange interaction is involved in the calculation, you need to check the gap size and gap type. If internal gap is used, the time step is usually calculated from the gap size because it is the smallest. The internal gap size decreases with the decreasing cell length and thus causes the smaller time step size. So the best type of gap is EXTERNAL GAP. Change the gap type to EXTERNAL and run the model again. For Euler calculations, following the instructions help you to prevent a small timestep: 1. Use Internal Energy Transport. This is set in the Controls panel under Transport, by selecting internal for the ALE/Euler Energy option. The default in AUTODYN is Total Energy Transport. In Euler calculations of shaped charges or detonation of explosives where the detonation products escape into a void at high speed, a better result will be achieved using internal energy transport as this provides a more accurate determination of the internal energy in a cell, which in turn is used in the explosive equation of state. 2. Use large relative density cutoffs 1.0E-4 instead of default 1.0E-6. This is set for each material and can be changed in the Material panel by selecting the relevant material from the list and pressing the Modify button. The escaping detonation products are typically at very low density. It is useful to limit the diffusion of extremely small masses which can causes very small time step by increasing this cutoff value. 3. Use a Maximum velocity cutoff of ~10,000 m/sec. Very small masses of explosive escaping into Void can sometimes achieve unrealistic velocities which results in verysmall time step This should be limited by setting the Maximum velocity cutoff in the Controls panel under Global Cutoffs."
當前時間步長小於初始時間步長的10％時，將顯示“時間步長太小”。您始終可以減少最短時間步長以繼續計算。加載問題后，轉到“控制”面板，然后選擇“時間步選項”。將“最小時間步長”更改為非常小的數字，或者為零。最小時間步長為零表示最小時間步長由代碼自動計算。影響時間步長的變量是最小的像元大小，間隙大小，速度和聲速。對於拉格朗日類型的零件，您需要檢查零件的幾何形狀以查看是否存在扭曲的單元。對於歐拉型零件，您需要檢查零件的速度和聲速，以查看是否存在異常的速度或聲速。如果計算中涉及拉格朗日-拉格朗日相互作用，則需要檢查間隙大小和間隙類型。如果使用內部間隙，則時間步長通常根據間隙大小來計算，因為它是最小的。內部間隙尺寸隨着單元長度的減小而減小，從而導致較小的時間步長。因此，最好的間隙類型是EXTERNAL GAP。將間隙類型更改為EXTERNAL，然后再次運行模型。對於Euler計算，請按照說明進行操作以幫助您避免浪費時間：1.使用內部能量傳輸。通過在ALE / Euler Energy選項中選擇internal，可以在“控制”面板中的“運輸”下進行設置。AUTODYN中的默認值為總能量傳輸。在歐拉計算爆炸物的定型裝葯或爆炸時，爆炸產物以高速逃逸到空隙中，使用內部能量傳輸將獲得更好的結果，因為這可以更准確地確定單元中的內部能量，進而將其用於爆炸狀態方程中。2.使用較大的相對密度極限1.0E-4代替默認的1.0E-6。這是為每種物料設置的，可以通過從列表中選擇相關物料並按“修改”按鈕在“物料”面板中進行更改。逃逸的爆炸產物通常處於非常低的密度。限制極小質量的擴散非常有用，這可以通過增加該截止值來導致非常小的時間步長。3.使用〜10,000 m / sec的最大速度截止。
另外幾種建議：
- in analysis setting -->maximum energy error = a big number 1e6 and time step safety factor = 0.5