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Old   January 8, 2006, 09:07
Default Unsteady Case
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Q
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I want to know when I perform unsteady cacluation using fluent. Let us suppose I use fixed time stepping method.

And I use certain delta_t=x1 and maximum number of iteration 20 and I also use maximum number of iteration 10 and 4. What is the difference I will get in the results.

How can I optimze delta_t and maximum number of iteration?

Thanks

Q
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Old   January 8, 2006, 20:00
Default Re: Unsteady Case
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galary
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In my opinion, maximum number of iteration is number of equation iteration solutionin in one time step.Usually you should choose number of iteration to satisfy convergence and get a stable solution in the time step.In face unsteady case in one time step is regarded as steady case.

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Old   January 9, 2006, 02:36
Default Re: Unsteady Case
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Muhammad Shakaib
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Generally if your time step is correct than there is convergence before 30 iterations this means the residuals drop to atleast an order of magnitude and if you have placed a monitoring point for any variable it becomes stable for last few iterations. The no. of iterations '10' appears to be enough for small time step (than needed) but 4 iterations does not seem suitable.
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Old   January 9, 2006, 03:48
Default Re: Unsteady Case
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Q
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Hello I am running a unsteady case I would like to know what kind of message I would be getting during this iterations whether I will get message that the solution is converged in 10 iterations if suppose I am using the maximum number of ietartions to be 30.

Q
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Old   January 9, 2006, 07:50
Default Re: Unsteady Case
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Muhammad Shakaib
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While iterating if the residuals drop below the values (of residuals) that you have set message will be ' solution is converged' and next time step will be started.
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Old   January 9, 2006, 11:24
Default Re: Unsteady Case
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Q
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what is the typical value of residuals you set?
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Old   January 13, 2006, 23:08
Default Re: Unsteady Case *NM*
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Muhammad Shakaib
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Old   January 13, 2006, 23:11
Default Re: Unsteady Case
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Muhammad Shakaib
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Sorry for prevoius empty reply. I just clicked the'post message' due to mistake. I keep my residuals for continiuty 1e-5 for others 1e-3. But these values depends on the case so this may not help you.

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