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change timestep after a certain iteration number

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Old   May 31, 2007, 05:03
Default change timestep after a certain iteration number
  #1
Sans
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Hi, I observe that my problem starts to diverge after say 60-70 iterations, but it is soon rectified when I reduce the timestep. But during a batch run I would like to do the same. Is it possible to change the timestep after a specified iteration during a batch run (command line)?

Thanks...

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Old   May 31, 2007, 08:12
Default Re: change timestep after a certain iteration numb
  #2
Gert-Jan
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I do it every day....

Physical Timescale = min(1e-2[s],max(5e-3[s],2e-2[s]-citern*1e-4[s]))

Plot it in Pre to find out how it looks like.

Gert-Jan

www.bunova.nl

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Old   June 1, 2007, 00:58
Default Re: change timestep after a certain iteration numb
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Sans
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Thanks a lot Gert-Jan,

Now it strikes me...or inturn I can also use a fuction in PRE
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Old   June 1, 2007, 03:27
Default Re: change timestep after a certain iteration numb
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Jack
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Hi! Gert-Jan, I think This is also useful to me, could you please explain the meaning of "min(1e-2[s],max(5e-3[s],2e-2[s]-citern*1e-4[s]))", since I am quite new to CFX. Thanks
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Old   June 1, 2007, 04:56
Default Re: change timestep after a certain iteration numb
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Gert-Jan
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It is mathematics. The only unknown thing is citern which is the current iteration number. You can also use aitern which is the accumulated iteration number.

Just play around in Pre or a spreadheet to see what the function does...

Gert-Jan

www.bunova.nl
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Old   June 3, 2007, 05:17
Default Re: change timestep after a certain iteration numb
  #6
Sameer
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Hi. There is another way is to use step function. suppose timestep upto 60th iteration is 0.025 [s] and after 60th iteration it is tobe reduced to 0.002 [s], you may use following step function, Timestep = 0.025[s]*step(aitern-60)+0.002[s]*step(60-aitern).

Sameer
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