# vectorField Uwall(Up.patchInternalField() - Up)

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 January 25, 2013, 13:23 vectorField Uwall(Up.patchInternalField() - Up) #1 New Member   Join Date: May 2012 Posts: 17 Rep Power: 7 Dear Foamers, I am trying to understand the calculation of the dynamic contact angle in dynamicAlphaContactAngleFvPatchScalarField.C and I am having trouble to understand the line: vectorField Uwall(Up.patchInternalField() - Up); I know Up is U_.boundaryField()[patchi], but why subtract the velocities on patchi from their values next to patchi ("Up.patchInternalField()")? Thanks, Arnout chery1986 likes this.

 January 25, 2013, 17:48 #2 Senior Member   Lieven Join Date: Dec 2011 Location: Leuven, Belgium Posts: 297 Rep Power: 16 It seems to me that Uwall is the relative velocity with respect to the wall. I expect that Up = 0 for fixed walls and nonzero for moving walls. You can easily verify this by adding Info << Up << endl; to the code Cheers, L vigneshTG likes this.

 January 27, 2013, 18:15 #3 New Member   Join Date: May 2012 Posts: 17 Rep Power: 7 I had not thought of the possibility of moving walls. Now it makes sense. Thanks for your reply!

 July 10, 2014, 08:42 #4 Member   Vignesh Join Date: Oct 2012 Location: Darmstadt, Germany Posts: 66 Rep Power: 7 Boeleman !! I am also trying to understand the dynamic contact angle model implemented in the openfoam. I want to know whether "patch().nf()" refers to face unit normals or something else? Also, whats the difference between nf and nhat ? Regards Vignesh

 July 17, 2014, 15:36 #5 New Member   Join Date: May 2012 Posts: 17 Rep Power: 7 nf(), does indeed refer to the face unit normal, so Uwall -= (nf & Uwall)*nf;calculates the velocity parallel to the wall, by subtracting the normal component from the complete velocity vector. nhat() is the normal to the interface of the two phases. vigneshTG likes this.

 August 15, 2014, 15:11 #6 New Member   Anjishnu Choudhury Join Date: Jul 2014 Posts: 4 Rep Power: 5 Hey, I am really not getting the physical meaning of the term vectorField Uwall(Up.patchInternalField() - Up); Uwall seems to be of type vectorField, but what does the term in brackets mean ? Thanks in advance!

August 15, 2014, 18:02
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Vignesh
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Quote:
 Originally Posted by Anjishnu Choudhury Hey, I am really not getting the physical meaning of the term vectorField Uwall(Up.patchInternalField() - Up); Uwall seems to be of type vectorField, but what does the term in brackets mean ? Thanks in advance!
Up contains the values of U in the boundary and Up.patchInternalField is the values of U in the cells next to the boundary. Their difference gives the relative velocity !!

Hope this helps
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Vignesh

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