what does "Solution Convergence" actually mean?

Prince Abraham · November 11, 2015, 14:34

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?

LuckyTran · November 12, 2015, 01:56

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.

Prince Abraham · November 12, 2015, 12:08

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?

soumitra2102 · August 3, 2018, 17:35

Thank You. I had the same question

iamalwaysconfused · February 2, 2022, 12:44

I had the same question, could someone check in one the image that has been sent and tell us what to infer?

LuckyTran · February 2, 2022, 18:08

If all you have is a residual plot, I can infer that you haven't actually checked any solution values

November 11, 2015, 14:34	what does "Solution Convergence" actually mean?	#1
Prince Abraham New Member Prince Abraham Join Date: Oct 2015 Location: Kovilpatti Posts: 5 Rep Power: 11	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? tianjunjie likes this.

November 12, 2015, 01:56		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,762 Rep Power: 66	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. hulli and daku like this.

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LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,762 Rep Power: 66	If all you have is a residual plot, I can infer that you haven't actually checked any solution values