[fisch]

Hello,

i found a lot of posts in the forum where some solver tolerances within openFOAM are suggested as accurate. For example in the fvSolution file for solving the p-equation is "tolerance 1e-6", "1e-4" or "1e-8".
I wanted to figure out how this tolerance number is calculated to estimate a number for my simulations, but i can't get it out of the code. Is there any explanation what this residual number / norm means or which norm is taken from the residual vector!?

A little example would be very nice (for example in relative error if i would have only one cell ... or something else)

Thanks a lot.
rupert

[bastil]

Well,

the relTol is the relative tolerance between the initial and the final residual. Both are reported by the solver:
GAMG: Solving for p, Initial residual = 0.0334352, Final residual = 0.000941545, No Iterations 17

if you specify a relTol of 0.1 the solver will stop iterating if the final residual falls below 0.1*0.0334352=0.00334352.
The absolute tolerance you refer to with "tolerance" in fvSolution is the value the Final residual need to fall below.

Regards Bastian

[fisch]

Thanks for the reply Bastian,

but the question is still how the (total) residuum is calculated or what it means..
Do you know that?

[alberto]

Please check here: http://www.cfd-online.com/Forums/ope...d-solvers.html

Google knows ;-)

[fisch]

thank you alberto

[amin_jalalian]

Originally Posted by bastil

Well,

the relTol is the relative tolerance between the initial and the final residual. Both are reported by the solver:
GAMG: Solving for p, Initial residual = 0.0334352, Final residual = 0.000941545, No Iterations 17

if you specify a relTol of 0.1 the solver will stop iterating if the final residual falls below 0.1*0.0334352=0.00334352.
The absolute tolerance you refer to with "tolerance" in fvSolution is the value the Final residual need to fall below.

Regards Bastian

Thanks about this post, But I have 2 question.

1- O.F uses relTol or tolerance for stop iteration?
2- What is difference between tolerance in for example "U" and "UFinal"?

Thanks.

[c.vasseur]

1- O.F uses relTol or tolerance for stop iteration?

I think both of them are used. Both conditions have to be respected.
(as read in this article).

[sfernaferna]

Hi amin_jalalian, I'm a bit late, but a new user might appreciate the answer. About your second question, I believe UFinal is used for transient algorithms for the final iteration of each inner loop (inside the same timestep). Not 100% sure, though.