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Old   May 29, 2007, 13:47
Default Specifying timestep
  #1
carlos
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Hi all,

Can anyone tell me how to specify using CCL expresions an specific timestep for a given number of iterations and then change it for the rest.

Thanks,

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Old   May 29, 2007, 14:19
Default Re: Specifying timestep
  #2
Robin
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Hi Carlos,

You mean CEL (CFX Expression Language) expression, not CCL.

You can either use a step function or an easier way is to create a 1D profile and use it for your timestep. The input to the step function of profile would be either the current iteration number (citern) or the absolute iteration number (aitern). The absolute iteration number continues to increase across restarts whereas the current iteration number is only for the current run.

Say you wanted to switch from .001 [s] to .01 [s] after 30 iterations, the step function would be:

timestep = .01 [s]*step(aitern-30) + .001 [s]*step(30-aitern)

The argument to a step function must be unitless (which the iteration number is) and returns 0 if the argument is less than zero, 0.5 if it is equal to zero and 1 if it is greater than zero.

Regards, Robin
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Old   June 5, 2007, 15:54
Default Re: Specifying timestep
  #3
hannah
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Hi, Robin, would you like to tell me where I can put this time step function in Pre? I use CFX 10 now?

Thank you for your advice.

Hannah
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Old   June 9, 2007, 08:06
Default Re: Specifying timestep
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carlos
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Hi hannah,

You have to specify this at the solver control manually. On the solver tree, do rigth click on Solver control > Edit in Command Editor and then modify the corresponding line.

Regards,

Carlos.
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Old   June 11, 2007, 09:50
Default Re: Specifying timestep
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hannah
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thanks carlos for your replying. I open the Pre and enter the solver control section.Do I need to modify the whole CONVERGENCE CONTROL section contents with the commands you guys present here?

Thanks for your further comments.

Hannah

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