# Time step UDF for help

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 November 22, 2011, 22:41 Time step UDF for help #1 New Member   Join Date: Apr 2011 Posts: 9 Rep Power: 6 The CFD calculation is so time-consuming, so I want to define the timestep size by udf, and then expect that the calculation can be done automatically, i.e, after a certain steps, timestep size can be changed and go on calculating without taking care manually. I have used the following UDF, but when used it in practice, it does not work well. After calculate for 100 steps, the iteration will stop, then I have to restart the calculate, but it stopped after another 100 steps. Plese help me, thanks in advance. DEFINE_DELTAT(my_timestep,d) { real time_step; real flow_time = CURRENT_TIME; if (flow_time < 0.005) time_step = 0.00005; /*0.00005 100 steps */ else if(flow_time < 0.025) time_step = 0.0001; /*0.0001 200 steps */ else if(flow_time<0.175) time_step=0.0005; /*0.0005 300 steps */ else if(flow_time<1.175) time_step=0.001; /*0.001 1000 steps */ else if(flow_time<5.675) time_step=0.003; /*0.003 1500 steps */ else if(flow_time<10.675) time_step=0.005; /*0.005 1000 steps */ else time_step=0.01; return time_step; }

 November 23, 2011, 05:15 #2 Member     Laurent B Join Date: Jun 2009 Location: Lille, FRANCE Posts: 70 Rep Power: 8 What do you choose for the "Number of Time Steps" under "Run Calculation" ? you must put a number higher than 4600 (total number of steps)

November 23, 2011, 21:43
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 Originally Posted by laurentb What do you choose for the "Number of Time Steps" under "Run Calculation" ? you must put a number higher than 4600 (total number of steps)
Thank youvery much. I think you are right and I have accept your suggestion. Wish to success.

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