adding div(phi)

bluemind · May 31, 2012, 08:11

Hello everybody,

I'm currently working on the implementation of the some equations within the twoLiquidMixingFoam solver and I am facing some trouble when I try to add (in bold) an extra term in this transport equation :

fvScalarMatrix fracVolLVEqn
(
fvm::ddt(fracVolLV)
+ fvm::div(phi, fracVolLV)
- fvm::laplacian
(
Dab + alphatab*turbulence->nut(), fracVolLV,
"laplacian(Dab,fracVolLV)"
)
== fvm::div(phi, fracVolTot)

);

fracVolLVEqn.solve();

(fracVolLV =alpha1 (volumetric fraction of liquid) + alpha2 (volumetric fraction of vapor)
fracVolTot=alpha1 + alpha2+ alpha3 (volumetric fraction of air) ) equal to 1

When I compile, I don't have any errors however when I run the program I have the following error message :

--> FOAM FATAL ERROR:
incompatible fields for operation
[fracVolLV] == [fracVolTot]

Does anyone know how can I solve the problem ?

Thank you for the help,

akidess · May 31, 2012, 08:22

Try using fvc::div.

bluemind · May 31, 2012, 08:48

Thank you for the answer, I have already tried to use fvc :: div (), and the program works (even if the calculation diverge at some point). But I'm confused about using an explicit resolution for this term whereas the other terms are resolved implicitly.

akidess · May 31, 2012, 08:54

You can only have one solution variable per equation. If you use fvm, the solver will see fracVolLV and fracVolTot as solution variables which cannot work.

bluemind · May 31, 2012, 08:58

Thank you for the explanation I understand better now

May 31, 2012, 08:11	adding div(phi)	#1
bluemind New Member Nabil MEAH Join Date: Apr 2012 Posts: 8 Rep Power: 14	Hello everybody, I'm currently working on the implementation of the some equations within the twoLiquidMixingFoam solver and I am facing some trouble when I try to add (in bold) an extra term in this transport equation : fvScalarMatrix fracVolLVEqn ( fvm::ddt(fracVolLV) + fvm::div(phi, fracVolLV) - fvm::laplacian ( Dab + alphatabturbulence->nut(), fracVolLV, "laplacian(Dab,fracVolLV)" ) == fvm::div(phi, fracVolTot)* ); fracVolLVEqn.solve(); (fracVolLV =alpha1 (volumetric fraction of liquid) + alpha2 (volumetric fraction of vapor) fracVolTot=alpha1 + alpha2+ alpha3 (volumetric fraction of air) ) equal to 1 When I compile, I don't have any errors however when I run the program I have the following error message : --> FOAM FATAL ERROR: incompatible fields for operation [fracVolLV] == [fracVolTot] Does anyone know how can I solve the problem ? Thank you for the help,

May 31, 2012, 08:22		#2
akidess Senior Member Anton Kidess Join Date: May 2009 Location: Germany Posts: 1,377 Rep Power: 29	Try using fvc::div. __________________ On twitter @akidTwit Spend as much time formulating your questions as you expect people to spend on their answer.

May 31, 2012, 08:54		#4
akidess Senior Member Anton Kidess Join Date: May 2009 Location: Germany Posts: 1,377 Rep Power: 29	You can only have one solution variable per equation. If you use fvm, the solver will see fracVolLV and fracVolTot as solution variables which cannot work. __________________ On twitter @akidTwit Spend as much time formulating your questions as you expect people to spend on their answer.

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May 31, 2012, 08:48		#3
bluemind New Member Nabil MEAH Join Date: Apr 2012 Posts: 8 Rep Power: 14	Thank you for the answer, I have already tried to use fvc :: div (), and the program works (even if the calculation diverge at some point). But I'm confused about using an explicit resolution for this term whereas the other terms are resolved implicitly.

May 31, 2012, 08:58		#5
bluemind New Member Nabil MEAH Join Date: Apr 2012 Posts: 8 Rep Power: 14	Thank you for the explanation I understand better now