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January 20, 2012, 09:41 
conditional solving of transport equation

#1 
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hi people,
I would like to set up a solver for a solidification process with solving a transport equation for a species only in the liquid phase of the sytem. There is a volScalarField alpha which defines the state of phase (0<alpha<1). alpha is the liquid fraction, alpha = 0 > complete solid. How can I define a solver which works only in the non solid part of the domain like: // definition of eq. {liqEqn = ....} // conditional solving of liqEqn if (alpha != 0) liqEqn.solve(); Is there somewhere a similar case/tutorial/documentation reference? thank you for advice, dzi (I use OF 2.01) 

January 22, 2012, 14:10 

#2 
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David Gaden
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It is very difficult to only use portions of the mesh for the matrix solution in OpenFOAM. You'd probably have to create a new temporary mesh, and create new variables on it  then you'd have to create new boundaries where it is cutoff... Rather than that, you probably want to work with the full mesh, and modify the matrix so that the portion from the solid cells reduce to a trivial equation.
I'm thinking you could create a custom preconditioner for your matrix. I don't know exactly what you want to do to the matrix to achieve this, though.
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January 23, 2012, 04:35 

#3 
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Anton Kidess
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I think the easiest solution is to multiply all terms in the equation with alpha.
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January 24, 2012, 11:51 

#4  
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Alberto Passalacqua
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Quote:
volScalarField solveEq(pos(alphaalphaCutOff)); volScalarField doNotEq(1solveEq); which is 1 when alpha > alphaCutOff, and 0 elsewhere. Then there are two possible solutions, depending on what you are trying to do (momentum equation or scalar equation?)  Momentum equation: Code:
fvMatrix UEqn ( solveAlpha* ( //Put your equation here )+ doNotSolve* ( fvm::Sp(coeff,yourVariable) // Set the variable to zero or to a value here ) ); Code:
myEqn.setValues(...) Best, 

January 25, 2012, 04:47 

#5 
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thank you for the replies,
for me the easiest solution is the suggestion from akidess to multiply all, or parts of the equation with alpha. Looks like it can be solved and I get something out which makes sense. The other suggestions also sound interesting. I will try if I come to a limit with the first solution, but on the first glance they seem to be more sophisticated. Thank you again for helping on this topic! dzi 

January 25, 2012, 11:19 

#6  
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Alberto Passalacqua
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Quote:
If you are solving the momentum equation, you will also have to deal with the problem of the central coefficient going to zero, which will lead to a segmentation fault when you calculate H/A. You can check how this problem is addressed in compressibleTwoPhaseEulerFoam. Best, 

January 30, 2013, 02:57 
Solidification in OpenFOAM

#7 
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Hi
I am solving a binary alloy solidification problem with OpenFOAM. For the species equation, which seems to be the most critical equation especially at the region where channels form, I have used zero grad boundary conditions; which causes a flow into the wall. Have you guys also used grad(CL) = 0, and grad(C) = 0 at the boundaries? 

Tags 
conditional, solidification, solving 
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