[huyidao]

Hello,
I try to implement a new temperature dependent viscosity model in which nu=a*exp(b/T)+c.Here is my code to calculate the viscosity.

Foam::viscosityModels::TDepLaw::calcNu() constant
{
const volScalarField& T=U_.mesh().lookupObject<volScalarField>("T");
return (a_*exp(b_/T)+c_)
}

But it seems that the exp(b_/T) is not right.How can i calculate the viscosity at every cell by the a*exp(b/T)+c?
Many thanks,
Nemo.

[kebsiali]

return (a_*exp(b_/T)+c_);
try to add the ;

[alexeym]

Hi,

Originally Posted by huyidao

But it seems that the exp(b_/T) is not right.How can i calculate the viscosity at every cell by the a*exp(b/T)+c?

And what are the types of a_, b_, and c_? If b_ is just scalar, then b_/T has units K^-1 and transcendent functions are only defined for dimensionless arguments. Also can you express "But it seems that the exp(b_/T) is not right" in compiler error?

[huyidao]

I am sorry,my carelessness.in the code there is a ; ,and the code can be compiled successfully.

[kebsiali]

why did you change the original post
you make me look stupid lol

[huyidao]

Originally Posted by alexeym

Hi,



And what are the types of a_, b_, and c_? If b_ is just scalar, then b_/T has units K^-1 and transcendent functions are only defined for dimensionless arguments. Also can you express "But it seems that the exp(b_/T) is not right" in compiler error?

In the file transportproperties,I define the a_ and c_ has the same unit with nu,and b_ has the same unit with T.It can be compiled successfully.But when i run a simple Case,here are the errors

Selecting incompressible transport model TDepLaw
#0 Foam::error:rintStack(Foam::Ostream&) at ??:?
#1 Foam::sigFpe::sigHandler(int) at ??:?
#2 in "/lib/x86_64-linux-gnu/libc.so.6"
#3 Foam::divide(Foam::Field<double>&, double const&, Foam::UList<double> const&) at ??:?
#4 Foam::tmp<Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> > Foam:perator/<Foam::fvPatchField, Foam::volMesh>(Foam::dimensioned<double> const&, Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> const&) at ??:?
#5 Foam::viscosityModels::tempDepExp::calcNu() const at ??:?
#6 Foam::viscosityModels::tempDepExp::tempDepExp(Foam ::word const&, Foam::dictionary const&, Foam::GeometricField<Foam::Vector<double>, Foam::fvPatchField, Foam::volMesh> const&, Foam::GeometricField<double, Foam::fvsPatchField, Foam::surfaceMesh> const&) at ??:?
#7 Foam::viscosityModel::adddictionaryConstructorToTa ble<Foam::viscosityModels::tempDepExp>::New(Foam:: word const&, Foam::dictionary const&, Foam::GeometricField<Foam::Vector<double>, Foam::fvPatchField, Foam::volMesh> const&, Foam::GeometricField<double, Foam::fvsPatchField, Foam::surfaceMesh> const&) at ??:?
#8 Foam::viscosityModel::New(Foam::word const&, Foam::dictionary const&, Foam::GeometricField<Foam::Vector<double>, Foam::fvPatchField, Foam::volMesh> const&, Foam::GeometricField<double, Foam::fvsPatchField, Foam::surfaceMesh> const&) at ??:?
#9 Foam::singlePhaseTransportModel::singlePhaseTransp ortModel(Foam::GeometricField<Foam::Vector<double> , Foam::fvPatchField, Foam::volMesh> const&, Foam::GeometricField<double, Foam::fvsPatchField, Foam::surfaceMesh> const&) at ??:?
#10
at ??:?
#11 __libc_start_main in "/lib/x86_64-linux-gnu/libc.so.6"
#12
at ??:?
Floating point exception (core dumped)

[alexeym]

Hi,

As the error is in Foam::divide, in general it is division by zero. Also in general T is greater than zero. In your case it seems not to be the case. To avoid division by zero, you can write denominator as T + Tsmall, where Tsmall is small dimensioned value with temperature units.

Also the error can indicate diverging solution, wrong initial or boundary conditions.

[kebsiali]

I presume you followed the example that implemented the temperature dependant power law
meaning you declared a,b like he did with kslope and Tbase
if not? explain what you did
one more thing, can you specify what you did in transportProperties?

[huyidao]

Hello kebsiali,I implented the viscosity model followed by this http://www.tfd.chalmers.se/~hani/kur...nFoam%20v2.pdf
,and i think i have found my mistake,i set the temperature inlet boundary condition to 0 which is not right.
Thank you so much,alexeym and kebsiali.