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Using power-law equations in driftFluxFoam

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Old   September 21, 2016, 10:50
Post Using power-law equations in driftFluxFoam
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Elena Valle
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Hello
I'm using driftFluxFoam to model a secondary settling tank. I want to use a power-law function, (V0, x and q are constants)

Udm_ = (rhoc_/rho())*V0_/(1 + Foam:: pow((alphad_/x_), q_));

but when I start the simulation I get this error

p { margin-bottom: 0.25cm; line-height: 120%; }a:link { } 0 Foam::error:: printStack(Foam::Ostream&) at ??:?
[5] #1 Foam::sigFpe::sigHandler(int) at ??:?
[5] #2 in "/lib/x86_64-linux-gnu/libc.so.6"
[5] #3 in "/lib/x86_64-linux-gnu/libm.so.6"
[5] #4 pow in "/lib/x86_64-linux-gnu/libm.so.6"
[5] #5 Foam:: pow(Foam::Field<double>&, Foam::UList<double> const&, double const&) at ??:?
[5] #6 Foam::tmp<Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> > Foam:: pow<Foam::fvPatchField, Foam::volMesh>(Foam::tmp<Foam::GeometricField<doub le, Foam::fvPatchField, Foam::volMesh> > const&, Foam::dimensioned<double> const&) at ??:?
[5] #7 Foam::relativeVelocityModels::diehl::correct() at ??:?
[5] #8
[5] at ??:?
[5] #9 __libc_start_main in "/lib/x86_64-linux-gnu/libc.so.6"
[5] #10
[5] at ??:?
[julien-TERRA-PC:05300] *** Process received signal ***
[julien-TERRA-PC:05300] Signal: Floating point exception (8)
[julien-TERRA-PC:05300] Signal code: (-6)
[julien-TERRA-PC:05300] Failing at address: 0x3ea000014b4
[julien-TERRA-PC:05300] [ 0] /lib/x86_64-linux-gnu/libc.so.6(+0x36d40) [0x7fca49befd40]
[julien-TERRA-PC:05300] [ 1] /lib/x86_64-linux-gnu/libc.so.6(gsignal+0x39) [0x7fca49befcc9]
[julien-TERRA-PC:05300] [ 2] /lib/x86_64-linux-gnu/libc.so.6(+0x36d40) [0x7fca49befd40]
[julien-TERRA-PC:05300] [ 3] /lib/x86_64-linux-gnu/libm.so.6(+0x15a95) [0x7fca4a1aaa95]
[julien-TERRA-PC:05300] [ 4] /lib/x86_64-linux-gnu/libm.so.6(pow+0x1c) [0x7fca4a1bb9ac]
[julien-TERRA-PC:05300] [ 5] /opt/openfoam231/platforms/linux64GccDPOpt/lib/libOpenFOAM.so(_ZN4Foam3powERNS_5FieldIdEERKNS_5UL istIdEERKd+0x42) [0x7fca4aeb0e12]
[julien-TERRA-PC:05300] [ 6] /home/elenavalle/OpenFOAM/elenavalle-2.3.1/platforms/linux64GccDPOpt/lib/libdriftFluxRelativeVelocityModels.so(_ZN4Foam3pow INS_12fvPatchFieldENS_7volMeshEEENS_3tmpINS_14Geom etricFieldIdT_T0_EEEERKS8_RKNS_11dimensionedIdEE+0 x176) [0x7fca4de6a656]
[julien-TERRA-PC:05300] [ 7] /home/elenavalle/OpenFOAM/elenavalle-2.3.1/platforms/linux64GccDPOpt/lib/libdriftFluxRelativeVelocityModels.so(_ZN4Foam22re lativeVelocityModels5diehl7correctEv+0x59) [0x7fca4de68db9]
[julien-TERRA-PC:05300] [ 8] diehldriftFluxFoam() [0x43bada]
[julien-TERRA-PC:05300] [ 9] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf5) [0x7fca49bdaec5]
[julien-TERRA-PC:05300] [10] diehldriftFluxFoam() [0x440dbb]
[julien-TERRA-PC:05300] *** End of error message ***

Seeing some coments, this is a mathematical error because alphad_ turns into negative values (I do not know why).

So, can somebody help me, telling me how can I avoid this error?

Thank you so much
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Old   March 10, 2017, 12:33
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Denys Wickens
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alpha_ routinely goes small and negative in driftFluxFoam. It looks like rounding errors due to the limited precision available in 'double' variables. To overcome this I used a temporary variable thus:

volScalarField X = sqrt(sqr(alpha_));

However, I also note your equation involves rho. Are you sure? As I look at slurry.C, driftFluxFoam uses mu not nu and applies a calculated mixture rho in the code that calls the selected transportModel.
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