# refValue in the Boundary Conditions

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 April 7, 2018, 00:07 refValue in the Boundary Conditions #1 New Member   Longism Join Date: Mar 2018 Posts: 7 Rep Power: 3 Hi everyone, Am very newbee to the OpenFoam. And now am looking at the Boundary conditions define. For velocity in the slip condition, it is defined as below: wall { type maxwellSlipU; accommondationCoeff 1; curvature on; Uwall uniform (0 0 0); value uniform (0 0 0); refValue uniform (0 0 0); } Please help what is the differences in U wall, value and refValue. As my understanding, Uwall is the velocity of the wall, value is the initial value of the velocity on the wall, refValue is reference value (from there you can find the absolute value of Uwall and initial velocity) is my undertanding is correct? It is quite confusing. Thanks

 April 7, 2018, 04:20 #2 Senior Member     Uwe Pilz Join Date: Feb 2017 Location: Leipzig, Germany Posts: 590 Rep Power: 7 What is the reason for using maxwellSlipU? I would start at least with a constant value. __________________ Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)

 April 7, 2018, 07:59 #3 New Member   Longism Join Date: Mar 2018 Posts: 7 Rep Power: 3 This is a sample code I found that using maxwell slip condition on the wall. Trying to understand it

 April 11, 2018, 15:42 #4 Senior Member   Lucky Tran Join Date: Apr 2011 Location: Orlando, FL USA Posts: 3,181 Rep Power: 39 Uwall is the wall velocity. U wall is (0 0 0) if your wall is stationary. value is the current solution/value, which is more-or-less the slip velocity. I don't understand the model well enough to understand refValue. It is related to the thermalCreep and curvature options and it looks like it's a calculated variable. Code: ``` if (thermalCreep_) { const volScalarField& vsfT = this->db().objectRegistry::lookupObject(TName_); label patchi = this->patch().index(); const fvPatchScalarField& pT = vsfT.boundaryField()[patchi]; Field gradpT(fvc::grad(vsfT)().boundaryField()[patchi]); vectorField n(patch().nf()); refValue() -= 3.0*pnu/(4.0*pT)*transform(I - n*n, gradpT); } if (curvature_) { const fvPatchTensorField& ptauMC = patch().lookupPatchField(tauMCName_); vectorField n(patch().nf()); refValue() -= C1/prho*transform(I - n*n, (n & ptauMC)); }```

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