# Equation for scalar source

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 September 15, 2005, 04:43 Halleluja! Another one saved #1 Super Moderator     Niklas Nordin Join Date: Mar 2009 Location: Stockholm, Sweden Posts: 693 Rep Power: 22 Halleluja! Another one saved by the dimensionality check As you can see from your error message you have incompatible dimensions. fvm::ddt(scal) has 1/s, which means that all the other terms must have the same dimension. However, your sv-term has (1/m)*(m^2/s)^(.5) = s^-0.5, so you should check your terms, they are obviously incompatible, or there is a dimension in w1. N

 September 15, 2005, 04:47 Dimension checking - does exac #2 Senior Member   Gavin Tabor Join Date: Mar 2009 Posts: 181 Rep Power: 10 Dimension checking - does exactly what it says on the tin! If your scal is dimensionless then when you take a time derivative you get something with dimensions [0 0 -1 0 0 0 0]. On the rhs you took a square root. This is either wrong, or you need a prefactor to this term with the dimensions [0 0 -0.5 0 0 0 0] to be physically correct. Gavin

 September 15, 2005, 06:04 Hi guys, Got that, and indee #3 Member   Radu Mustata Join Date: Mar 2009 Location: Zaragoza, Spain Posts: 97 Rep Power: 10 Hi guys, Got that, and indeed the w1 should have dimension of s^-0.5. Then how do I define w1 with the right dimension? Thanks, Radu

 September 15, 2005, 06:17 something like this... dime #4 Super Moderator     Niklas Nordin Join Date: Mar 2009 Location: Stockholm, Sweden Posts: 693 Rep Power: 22 something like this... dimensionedVector w1 ( "w1", dimensionSet(0,0,-0.5,0,0), vector(-1,1,-1) );

 September 15, 2005, 06:25 I've been trying to see how to #5 Senior Member   Gavin Tabor Join Date: Mar 2009 Posts: 181 Rep Power: 10 I've been trying to see how to do this implicitly. The easiest way would be to do this: solve ( fvm::ddt(scal) + fvm::div(phi,scal) - fvm::laplacian(sgsModel->nuEff(),scal) == fvm::Sp(sv1/scal,scal) ); A more elegant way would be to expand your term to get at least one involving (thing)*scal, and discretise that implicitly. Gavin

 September 15, 2005, 06:27 Thanks Niklas, So far so goo #6 Member   Radu Mustata Join Date: Mar 2009 Location: Zaragoza, Spain Posts: 97 Rep Power: 10 Thanks Niklas, So far so good. Seems to work fine now. Of course this is just a small part of what I want to do. Will get back later, hopefuly with no so easy questions. Radu

 September 15, 2005, 06:31 Or use that... hope my math-sk #7 Super Moderator     Niklas Nordin Join Date: Mar 2009 Location: Stockholm, Sweden Posts: 693 Rep Power: 22 Or use that... hope my math-skills are all forgotten. grad(a) dot V = div(aV) - a *div(V) and since V is constant... div(aV) = grad(a) dot V hence, fvc::grad(...) = div(...,scal) Henry or Hrv will correct me if im wrong N

 September 15, 2005, 07:13 Actually, V is not constant, s #8 Super Moderator     Niklas Nordin Join Date: Mar 2009 Location: Stockholm, Sweden Posts: 693 Rep Power: 22 Actually, V is not constant, since nuEff is in there, V=nuEff*w1, so you cant drop that term. It'll be something like fvc::grad(...) & w1 = fvm::div(..., scal) -fvm::Sp(div(V), scal) Anyway, im leaving the details to you. You do the math. (hehe, I love to say that) N

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