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what does "Solution Convergence" actually mean?

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Old   November 11, 2015, 14:34
Default what does "Solution Convergence" actually mean?
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Prince Abraham
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I am new to fluent. I am working in PEMFC module.

I can't understand the actual meaning of convergence of solution.
Many says, its the balance of the energy, momentum etc.,

But i'm still not clear about that.

A converged solution will have correct geometry, material zones, boundary conditions and all other parameters?
& a A solution which doesn't converged, will have Incorrect geometry, material zones, boundary conditions and all other parameters?

On which it depends?
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Old   November 12, 2015, 01:56
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Convergence is defined purely based on the solution value and nothing to do with balances or anything else. Convergence is not a measure of accuracy.

It's helpful to review some basic calculus of sequences & series. As you iterate from one iteration to the next, the solution values forms a sequence. You like to stop iterating when the solution has converged. For example this sequence converges to 1.

0.9000 0.9900 0.9990 0.9999 1.0000 1.0000 1.0000 1.0000 1.0000

Now if the actual solution is 2, then my sequence converges to an incorrect result but it converges nonetheless.

Now replace my sequence of numbers with solution values (local x-velocities, y-velocities, z-velocities, pressure, temperature, etc) but only their values.

A good solution will of course be converged and be accurate, but those are two different concepts. You must check for accuracy separately from convergence. Once you have determined whether or not your solution is converged, then you can check for balances, etc and judge whether your solution is of reasonably quality.
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Old   November 12, 2015, 12:08
Default convergence graph
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Prince Abraham
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Thank you so much Lucky Tran..

What can we infer from the convergence graph?
Please see the attached graph, the profiles are repeating again and again!

What can we infer from it?
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File Type: png graph.PNG (24.3 KB, 118 views)
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Old   August 3, 2018, 17:35
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Thank You. I had the same question
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Old   February 2, 2022, 12:44
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Mahima Pareek
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I had the same question, could someone check in one the image that has been sent and tell us what to infer?
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Old   February 2, 2022, 18:08
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If all you have is a residual plot, I can infer that you haven't actually checked any solution values
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