# Problems with dimension

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 April 28, 2013, 03:34 Problems with dimension #1 Member   Join Date: Aug 2011 Posts: 74 Rep Power: 5 Hello, hopefully I´ve got an easy question for you I just want to calculate a absolut value of a gradient of a volScalarField (for example epsilon of the k-epsilon-turbulence model) Could somebody help me with the name of the function? Thanks a lot Last edited by idefix; April 29, 2013 at 03:18.

 April 29, 2013, 04:06 #2 Senior Member   Nima Sam Join Date: Sep 2009 Location: Tehran, Iran Posts: 1,123 Blog Entries: 1 Rep Power: 14 Code: `mag(fvc::grad(epsilon))` __________________ Training Course on OpenFOAM at (http://www.isme.ir/) My Weblog (http://openfoam.blogfa.com/)

 April 29, 2013, 04:33 #3 Member   Join Date: Aug 2011 Posts: 74 Rep Power: 5 Thanks but now I get an error because of the dimensions. (--> FOAM FATAL ERROR: LHS and RHS of - have different dimensions dimensions : [0 -1 0 0 0 0 0] - [0 0 0 0 0 0 0] ) I want to calculate ( mag(fvc::grad(alpha1_)) - 1 ) / ( mag(fvc::grad(alpha1_)) - 1.1 ) alpha1_ is the phase volume fraction of the VOF-model Has somebody an idea how I can do it? I thought that this term has no dimension: (metre - 1) / (metre -1 ) = 1 thanks again

 April 29, 2013, 06:06 #4 Senior Member   Nima Sam Join Date: Sep 2009 Location: Tehran, Iran Posts: 1,123 Blog Entries: 1 Rep Power: 14 its some how obvious :P, grad means in simple word d/dx , when you gradient a dimless value! it gets a dimension -1 for meter so you can not add it with a constant number unless you use its value with value() function or give you constant a dimension __________________ Training Course on OpenFOAM at (http://www.isme.ir/) My Weblog (http://openfoam.blogfa.com/)

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