CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > OpenFOAM > OpenFOAM Running, Solving & CFD

initial residual and final residual

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   September 5, 2022, 06:19
Question initial residual and final residual
  #1
Senior Member
 
Sangho Ko
Join Date: Oct 2021
Location: South Korea
Posts: 130
Rep Power: 3
FluidKo is on a distinguished road
Hello everybody~!

I was wondering what is initial residual and final residual.
So I've searched these things in CFD Online and Youtube.
I've seen video at below link.
https://www.youtube.com/watch?v=OOILoJ1zuiw&t=1s
And I've found this post
SIMPLE: Difference between initial and final residuals

At upper link, 'Zbynek' has said that
"When your final residual is low enough, you update the matrix and repeat the whole process I just described (called outer iteration). Voila, you get a new initial residual that has naturally a larger value than the previous final residual."

I'm wondering two points.

1. Deos 'Ax=b' means Navier-Stokes equation?
https://youtu.be/OOILoJ1zuiw?t=281
At this link, MU=-\triangledown p is representing Navier-Stokes equation. So I've thought 'Ax=b' that Zbynek is referring is meaning Navier-Stokes equation and same to MU=-\triangledown p.
Is it right?

2. If 'Ax=b' means Navier-Stokes equation, then how A can be updated during outer iteration?
What I've guessed is below.
At below link,
https://youtu.be/OOILoJ1zuiw?t=360
MU=-\triangledown p can be transformed into Au-H=-\triangledown p.
And this means H=AU-MU can be expressed like below link.
https://youtu.be/OOILoJ1zuiw?t=410
Also H=AU-MU means H can be changed by U.
Because H is changed by U and H is component of MU, if U is updated M must be changed.
And M is same thing to A in 'Ax=b'
Is it right? I'm not sure...
Eventhough we've updated only x then substitute it into MU=-\triangledown p,
how M(same thing to A in 'Ax=b') can be updated?

Thank you~!
FluidKo is offline   Reply With Quote

Reply

Tags
pimple, residual, simple algorithm

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
laplacianFoam with source term Herwig OpenFOAM Running, Solving & CFD 17 November 19, 2019 14:47
Segmentation fault when using reactingFOAM for Fluids Tommy Floessner OpenFOAM Running, Solving & CFD 4 April 22, 2018 13:30
chtMultiRegionSimpleFoam turbulent case Aditya Patil OpenFOAM Running, Solving & CFD 6 April 24, 2017 23:13
simpleFoam error - "Floating point exception" mbcx4jc2 OpenFOAM Running, Solving & CFD 12 August 4, 2015 03:20
calculation stops after few time steps sivakumar OpenFOAM Running, Solving & CFD 7 March 17, 2013 07:37


All times are GMT -4. The time now is 02:25.