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 vijay January 30, 2006 23:02

convergence

Hi,

I have a problem while running an unsteady case using coupled implicit scheme. The continuity and x,y,z velocity residuals are fluctuating between a constant minimum and maximum. They are going horizontally and parallely without converging. Does it mean that the grid should be refined further or is there something else to be done? Please suggest.

 Muhammad Shakaib January 30, 2006 23:57

Re: convergence

you can try with smaller time steps

 vijay January 31, 2006 01:46

Re: convergence

Hi,

Thanks for ur reply. But I tried with smaller time steps as well. Eventually after coming to the time step I required i.e. smaller time step multiplied with number of time steps, the fluctuations are starting again. Hope u have understood what I mean. Kindly suggest an alternative.

Thanks

 Muhammad Shakaib January 31, 2006 06:29

Re: convergence

What type of fluctuation you have noticed. Typically there is convergence in 20-30 iterations for every time step i.e. residuals drop alteast an order of magnitude and if you have placed a surface monitor it becomes constant in these no. of iterations. Alongwith refining the grid you can test some more things; using different options of solution controls. Also use surface monitors to check whether convergence is acheived for each time step

 HS January 31, 2006 08:35

Re: convergence

Are you sure the minimums and maximums are actually constant? I think the coupled implicit solver can make the residuals look like they're oscillating when they are in fact decreasing over a longer number of iterations (much depending on your Courant number).

/Henrik

 vijay January 31, 2006 11:38

Re: convergence

Hi,

The fluctuations are remaining without any deterioration. Even after large number of iterations they are present. I tried again by refininig the grid but it did not work out. Can u suggest anything?

Thanks

 kharicha February 1, 2006 04:04

Re: convergence

Please refine your boundary layer if you have....not the entire domain. If it doesn't work detail a bit your geometry and phenomena you want to model...

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