UEqn.relax()

mugi · December 7, 2011, 09:35

In the PIMPLE algorithm the momentum equation is defined and afterwards used by UEqun.relax(). As far as I could figure out this means that an underrelaxation is applied, but what does this relax do exactly or where is it defined in the code?

Thanks for any help!
Maike.

giack · June 20, 2013, 05:11

Hi,
Do you find the answer at your question? I have the same question. Moreover in my fvSolution file I don't specify any under relaxation factor..
Thanks

santiagomarquezd · July 2, 2013, 23:14

http://foam.sourceforge.net/docs/cpp/a04763_source.html, line 524

immortality · July 3, 2013, 01:41

it isn't clear how the relaxation is applied even in the code.
Where alpha is defined?
Can we set it and whats alpha at all?
How relaxation is applied?

Bernhard · July 3, 2013, 01:51

See line 658 of the same file, the relax() member function without argument is defined. Then, the parameter are read from a file, as here http://foam.sourceforge.net/docs/cpp...ce.html#l00313

Note that on the docs, you can search for member functions that you want to find (I used it on "equationRelaxationFactor")

giack · July 3, 2013, 05:17

So if I don't specify any relaxation factor in fvSolution file the relaxation is not applied to equation,it's right?

immortality · July 3, 2013, 08:39

its not obvious enough to find out how automatically this relaxation is implemented yet,how can avoid relaxation?

cfdonline2mohsen · July 3, 2013, 13:06

Thanks Santiago & Bernhard
If you don't specify any under relaxation factor then the default is zero

Code:

00099         eqnRelaxDefault_ = 
00100         eqnRelaxDict_.lookupOrDefault<scalar>("default", 0.0);

December 7, 2011, 09:35	UEqn.relax()	#1
mugi New Member Maike Join Date: Dec 2010 Posts: 8 Rep Power: 15	In the PIMPLE algorithm the momentum equation is defined and afterwards used by UEqun.relax(). As far as I could figure out this means that an underrelaxation is applied, but what does this relax do exactly or where is it defined in the code? Thanks for any help! Maike. immortality likes this.

June 20, 2013, 05:11		#2
giack Member Join Date: Mar 2013 Posts: 98 Rep Power: 13	Hi, Do you find the answer at your question? I have the same question. Moreover in my fvSolution file I don't specify any under relaxation factor.. Thanks immortality likes this.

July 2, 2013, 23:14		#3
santiagomarquezd Senior Member Santiago Marquez Damian Join Date: Aug 2009 Location: Santa Fe, Santa Fe, Argentina Posts: 452 Rep Power: 23	http://foam.sourceforge.net/docs/cpp/a04763_source.html, line 524 cfdonline2mohsen, Tobi and ScarFace like this. __________________ Santiago MÁRQUEZ DAMIÁN, Ph.D. Research Scientist Research Center for Computational Methods (CIMEC) - CONICET/UNL Tel: 54-342-4511594 Int. 7032 Colectora Ruta Nac. 168 / Paraje El Pozo (3000) Santa Fe - Argentina. http://www.cimec.org.ar

July 3, 2013, 01:41		#4
immortality Senior Member Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,208 Rep Power: 26	it isn't clear how the relaxation is applied even in the code. Where alpha is defined? Can we set it and whats alpha at all? How relaxation is applied? __________________ Injustice Anywhere is a Threat for Justice Everywhere.Martin Luther King. To Be or Not To Be,Thats the Question! The Only Stupid Question Is the One that Goes Unasked.

July 3, 2013, 01:51		#5
Bernhard Senior Member Bernhard Join Date: Sep 2009 Location: Delft Posts: 790 Rep Power: 21	See line 658 of the same file, the relax() member function without argument is defined. Then, the parameter are read from a file, as here http://foam.sourceforge.net/docs/cpp...ce.html#l00313 Note that on the docs, you can search for member functions that you want to find (I used it on "equationRelaxationFactor") cfdonline2mohsen, ScarFace and nepomnyi like this.

July 3, 2013, 05:17		#6
giack Member Join Date: Mar 2013 Posts: 98 Rep Power: 13	So if I don't specify any relaxation factor in fvSolution file the relaxation is not applied to equation,it's right? immortality likes this.

July 3, 2013, 08:39		#7
immortality Senior Member Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,208 Rep Power: 26	its not obvious enough to find out how automatically this relaxation is implemented yet,how can avoid relaxation? __________________ Injustice Anywhere is a Threat for Justice Everywhere.Martin Luther King. To Be or Not To Be,Thats the Question! The Only Stupid Question Is the One that Goes Unasked. Last edited by immortality; July 3, 2013 at 15:10.

July 3, 2013, 13:06		#8
cfdonline2mohsen Senior Member Mohsen KiaMansouri Join Date: Jan 2010 Location: CFD Lab Posts: 118 Rep Power: 16	Thanks Santiago & Bernhard If you don't specify any under relaxation factor then the default is zero Code: 00099 eqnRelaxDefault_ = 00100 eqnRelaxDict_.lookupOrDefault<scalar>("default", 0.0); immortality, giack, ScarFace and 2 others like this. __________________ “If you have an apple and I have an apple and we exchange these apples then you and I will still each have one apple. But if you have an idea and I have an idea and we exchange these ideas, then each of us will have two ideas.”