[sharonyue]

Hi guys,

In my code I have this We definition:

volScalarField We(2*rho2*pow(epsilon,0.6667)*pow(d,1.6667));

Then I define:

volScalarField Web(-1.5*(1/We));

It compiles okay, and actually I only define this Web, I even dont use it in function. But when I run a case it said:

#0  Foam::error::printStack(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  void Foam::divide<Foam::fvPatchField, Foam::volMesh>(Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh>&, Foam::dimensioned<double> const&, Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> const&) at ??:?
#5  Foam::tmp<Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> > Foam::operator/<Foam::fvPatchField, Foam::volMesh>(Foam::dimensioned<double> const&, Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> const&) at ??:?
#6  Foam::tmp<Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> > Foam::operator/<Foam::fvPatchField, Foam::volMesh>(double const&, Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> const&) at ??:?
#7  
 at ??:?
#8  __libc_start_main in "/lib/x86_64-linux-gnu/libc.so.6"
#9  
 at ??:?
Floating point exception (core dumped)

I tried another definition:

volScalarField Web(-1.5*(pow(We,-1));

It compiles okay too, but when I run it said:

#0  Foam::error::printStack(Foam::Ostream&) at ??:?
#1  Foam::sigFpe::sigHandler(int) at ??:?
#2   in "/lib/x86_64-linux-gnu/libc.so.6"
#3   in "/lib/x86_64-linux-gnu/libm.so.6"
#4  pow in "/lib/x86_64-linux-gnu/libm.so.6"
#5  Foam::pow(Foam::Field<double>&, Foam::UList<double> const&, double const&) at ??:?
#6  void Foam::pow<Foam::fvPatchField, Foam::volMesh>(Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh>&, Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> const&, Foam::dimensioned<double> const&) at ??:?
#7  Foam::tmp<Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> > Foam::pow<Foam::fvPatchField, Foam::volMesh>(Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> const&, Foam::dimensioned<double> const&) at ??:?
#8  Foam::tmp<Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> > Foam::pow<Foam::fvPatchField, Foam::volMesh>(Foam::GeometricField<double, Foam::fvPatchField, Foam::volMesh> const&, double const&) at ??:?
#9  
 at ??:?
#10  __libc_start_main in "/lib/x86_64-linux-gnu/libc.so.6"

So I think this core dumped is caused by this definition. How should I do? Thanks.


PS. If I define it like this:

volScalarField Web(-1.5*(pow(We,1));

It runs with out error.

[alexeym]

Hi,

as the error is in division, it seems that We is zero somewhere.

[sharonyue]

Originally Posted by alexeym

Hi,

as the error is in division, it seems that We is zero somewhere.

Solved! You do pretty good in OpenFOAM, everytime you know the solution.!

[alexeym]

This time it's just common sense

[Amjad Asad]

hallo
how did u solve this problem plz

[sharonyue]

Originally Posted by Amjad Asad

hallo
how did u solve this problem plz

Just like Alexey have said,

when you are using pow() function. Watch out your denominator, it can not be zero. So if you wanna use this function as this: pow(e,-1). You'd better define a small number like SMALL=1e-6, and write it as pow(e+SMALL,-1). This worked for my problem.

Regards,

[Amjad Asad]

I am trying to write a code to estimate the turbulence intensity in openfoam. the code does not work, when mag (U) is equal to zero.
volScalarField Intensity
(
IOobject
(
"Intensity",
runTime.timeName(),
mesh,
IOobject::NO_READ

),


sqrt((2.0/3.0)*k)/mag(UMean)



);

[alexeym]

Hi,

instead of

Originally Posted by Amjad Asad

sqrt((2.0/3.0)*k)/mag(UMean)

you can use

sqrt((2.0/3.0)*k)/max(SMALL, mag(UMean))

[Amjad Asad]

thanks for ur reply but i have a new problem now, I get

--> FOAM FATAL ERROR:
Arguments of max have different dimensions
dimensions : [0 0 0 0 0 0 0] and [0 1 -1 0 0 0 0]

thanks

[alexeym]

Oh, forgot about dimensions. Then it should be something like:

sqrt((2.0/3.0)*k)/max(dimensionedScalar("uSMALL", dimVelocity, SMALL), mag(UMean))

[Amjad Asad]

thanks it is working very good now

[Amjad Asad]

hi again,
but i still get strange values at the wall where the velocity zero

[alexeym]

And by strange values you mean? What BCs did you use for k on this wall with non-slip BC for velocity?

[Amjad Asad]

i meant with strang values that they are too hight 1e+13. and the BCs is fixed wall and i used wall function here for K

[alexeym]

OK.

Let's forget for a moment about volume fields. If you have expression y/x in your model, rewriting it as y/(x + small) will help you to resolve a problem with 0/0. But it will give you very high values if y is non-zero.

Now returning to OpenFOAM. You've got non-slip BC for velocity at the wall and you've got non-zero value of k at the same wall. Why? If there's no motion why there is turbulence? If you're using kqRWallFunction for k, it's actually simple zero-gradient boundary condition and you have to use appropriate mesh so k go to 0 at the wall. Or maybe your solution is not converged. Or maybe your initial conditions do not make sense. Or ...

First fix your model, then fix code.

[Amjad Asad]

thanks for ur help, I think there is no proplem with K. the problem is mag(U) because it too small
at the wall, them K/mag(u) will be too high.
my code is attached.