Introduce a drag model
I wanted to introduce a drag model call "Tam" into the twoPhaseEulerFoam solver in OF v1.7.1. However, the solver made a complain. I added Tam.C to "files" located at the following folder. Please let me know what mistakes I did in Tam.C.
"run/multiphase/twoPhaseEulerFoamMod/interfacialModels/Make/" ====Tam.C======== ... // * * * * * * * * * * * * * * * Member Functions * * * * * * * * * * * * * // Foam::tmp<Foam::volScalarField> Foam::Tam::K ( const volScalarField& Ur ) const { volScalarField beta = max(scalar(1)  alpha_, scalar(1.0e6)); forAll(alpha_, celli) { if(alpha_[celli] > 0.6666) { functAlpha[celli] = 1.0e6; } } return 4.5/(beta*alpha_ + scalar(1.0e6))*phaseb_.nu()/pow(phasea_.d(),2.0)*functAlpha; } ================ Below is what I see on my screen. ===== .... Time = 0.002 DILUPBiCG: Solving for alpha, Initial residual = 0.0021426, Final residual = 5.45235e12, No Iterations 3 Dispersed phase volume fraction = 0.36753 Min(alpha) = 0.0272179 Max(alpha) = 1.00084 DILUPBiCG: Solving for alpha, Initial residual = 8.90552e05, Final residual = 1.62296e12, No Iterations 3 Dispersed phase volume fraction = 0.36753 Min(alpha) = 0.0291739 Max(alpha) = 1.00075 #0 Foam::error::printStack(Foam::Ostream&) in "/home/jeong/OpenFOAM/openfoam171/lib/linuxGccDPOpt/libOpenFOAM.so" #1 Foam::sigFpe::sigFpeHandler(int) in "/home/jeong/OpenFOAM/openfoam171/lib/linuxGccDPOpt/libOpenFOAM.so" #2 Uninterpreted: #3 Foam::sqrt(Foam::Field<double>&, Foam::UList<double> const&) in "/home/jeong/OpenFOAM/openfoam171/lib/linuxGccDPOpt/libOpenFOAM.so" #4 Foam::tmp<Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> > Foam::sqrt<Foam::fvPatchField, Foam::volMesh>(Foam::tmp<Foam::GeometricField<doub le, Foam::fvPatchField, Foam::volMesh> > const&) in "/home/jeong/OpenFOAM/openfoam171/lib/linuxGccDPOpt/libEulerianInterfacialModels.so" #5 Foam::Tam::K(Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> const&) const in "/home/jeong/OpenFOAM/openfoam171/lib/linuxGccDPOpt/libEulerianInterfacialModels.so" #6 in "/home/jeong/OpenFOAM/openfoam171/applications/bin/linuxGccDPOpt/twoPhaseEulerFoamMod" #7 __libc_start_main in "/lib/tls/i686/cmov/libc.so.6" #8 in "/home/jeong/OpenFOAM/openfoam171/applications/bin/linuxGccDPOpt/twoPhaseEulerFoamMod" Floating point exception ===== 
There is somewhere an error in calculating a square root. I suppose the value of K becomes negative in your calculation. Double check your formula or consider bounding the value of K: max(SMALL,4.5/...)
Edit: You can see that your minimum volume fraction is negative (Min(alpha) = 0.0272179), This is not physical but if it works with everything else I would replace all 'alpha' in your code with 'alphaBounded' and add above: volScalarField alphaBounded = min(1.0,max(0.0,alpha)); 
Thank you for your comment.

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