# Question about the fvm::SuSp, and fvm::Sp

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

 June 6, 2012, 09:37 Question about the fvm::SuSp, and fvm::Sp #1 Member   Charlie Join Date: Dec 2010 Location: USA Posts: 82 Rep Power: 8 Sponsored Links Hi Foamers! When I'm programming with the OpenFOAM, I got confused with the difference between fvm::SuSp, and fvm::Sp, could anybody tell me the difference? As far as I know, fvm::SuSp(a,b) will calculate a*b implicitly or explicitly according to the sign of a, however, when a is positive, is fvm::Sp explicit or implicit? fvm::Sp(a,b) will calculate a*b implicitly anyway. The second question is related to a phenomenon I found when I'm solving the continuity equation, the exact form should be : ddt(alpha) + div(phia, alpha) - alpha * div(phia) ==0 This supposed to be solving ddt(alpha) + U_a*grad(alpha) =0, and the implementation I made in the code is : (alpha is a scalar, volume fraction) fvScalarMatrix alphaEqn ( fvm::ddt(alpha) + fvm::div(phia, alpha, scheme) - fvm::Sp(fvc::div(phia), alpha, schemer) ); where phia = fvc::interpolation(Ua) *mesh.Sf() Interestingly, after this, I got that alpha does not change with time anymore, which means that the equation reduced to ddt(alpha) =0, which is clearly not true if we take the definition of fvm::Sp(). However, my worry is that, in the momentum equation, they are solving : fvm::ddt(Ua) + fvm::div(phia, Ua, "div(phia,Ua)") - fvm::Sp(fvc::div(phia), Ua) == ........ I'm wondering if this fvm::Sp( ) makes a difference between the scalar source and vector source. Thanks!!!! Any idea would be appreciated!!

 June 6, 2012, 10:06 Sorry for the mistake I made in the continuity equation #2 Member   Charlie Join Date: Dec 2010 Location: USA Posts: 82 Rep Power: 8 Hi I made a mistake, I think the exact form for continuity equation should be: ddt(alpha) + div(alpha*phia) =0 not : ddt(alpha) + U_a*grad(alpha) =0 So, forget about the continuity equation I described, however, the question about the difference between fvm::SuSp() and fvm::Sp() is still valid, Thanks! Zhen

 October 10, 2014, 04:52 A bit late, but however... #3 New Member     Damiano Natali Join Date: Mar 2013 Location: Genova, Italy Posts: 17 Rep Power: 6 A bit late, but however...this page on the wiki helps a lot in clarifying! hansh34, beatlejuice, serles and 1 others like this.

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules