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September 8, 2009, 04:35 |
If my solution is converged ?
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#1 |
New Member
Join Date: Jun 2009
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I want to use the time-dependant solver to get the steady state. And I also monitor some important parameters, such as temperature, vof...
After some iterations, I found these parameters almost do not change, but the residuals remains at a high value(10-2) and goes flat. I wonder if I my problem is converged ? The residula and monitor look like this > vof.JPGresidual.JPG |
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September 9, 2009, 08:28 |
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#2 |
Member
JP
Join Date: Mar 2009
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Residuals becoming flat may indicate:
1. Your solution has converged, or 2. This is the minimum residual possible with your current grid. For further reduction in residuals, you may have to refine or adapt the grid. |
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September 9, 2009, 14:08 |
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#3 |
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Sean Delfel
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Yeah, I agree with srjp. You're going to need to refine your grid. I would recommend plotting contours of mass imbalance (since your continuity residuals didn't converge) and refining where they are high.
-sean |
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September 10, 2009, 01:39 |
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#4 |
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you both wrong.
this is transient solution and if one decrease the time step the residuals will decrease too. you execute 1 ineration on 1 time step? |
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September 10, 2009, 02:03 |
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#5 |
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Maxime Perelli
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the continuity residuals are too high.
reduce your time step
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In memory of my friend Hervé: CFD engineer & freerider |
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September 10, 2009, 09:16 |
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#6 |
Member
JP
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Sorry, I thought it was steady state simulation.
May be after frustration of seeing so many flat residuals !!! Agree with mAx on the timestep reduction. |
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September 10, 2009, 11:00 |
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#7 |
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Sean Delfel
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ditto.
-sean |
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September 11, 2009, 02:51 |
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#8 |
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Yes, 1 interation on 1 time step at beginning, because I want save computation time. And then I increase the interations each time step, and the residuals also remain flat.
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September 11, 2009, 03:39 |
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#9 |
Super Moderator
Maxime Perelli
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forget 1 iteration per time step
try the default settings, eg: 20 iterations per time step I would also recommend you to start your unsteady computation from a well converged steady solution
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In memory of my friend Hervé: CFD engineer & freerider |
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September 11, 2009, 17:46 |
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#10 |
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Ivan
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Most likely you are using a too big time-step. The time in your pictures is 2.4e4. Imagine if time step=1e-6, how many steps it will be....
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September 16, 2009, 09:21 |
Character of success iteration???
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#11 |
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teguh hady
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Hello!!!
I'm a new user in FLUENT. I've read your Post. I wanna know what is the indication that we have success iteration?? I've thought that FLAT graph on the Residual graph is the indication!!! Am I wrong??? |
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September 17, 2009, 04:07 |
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#12 |
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I think when the we get converged solution, the residual will go flat. But at the same time, the residual should fulfill the criterion, such as 10e-4,10e-5...
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September 17, 2009, 06:59 |
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#13 |
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Flat or not it is no matter. If iteration converged then it is. I think so.
Regards. |
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September 28, 2009, 03:29 |
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#14 |
Senior Member
teguh hady
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Is there an equation to prove it?? just to know how much convergence value!!!
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September 29, 2009, 01:33 |
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#15 |
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there is navier-stokes equation.
and http://en.wikipedia.org/wiki/Residua...rical_analysis) regards. |
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