[mehdi kamyabi]

Dear OpenFoamers

I'm already trying to write a code for simulating conformational rheological problems.
my code is complied well but when I try to use it this error appears:

--> FOAM FATAL ERROR:
Argument of trancendental function not dimensionless

From function trans(const dimensionSet&)
in file dimensionSet/dimensionSet.C at line 480.


I found the source of error may exist in these lines of my code:

//size of shear rate tensor (which is dimensioned scalar)
volScalarField sizegamadot = Foam::sqrt ( 0.5 * (twoD && twoD) );

//ci is a non-dimensioned variable which is calculated by this
//formula : ci = ((-0.0076*ln(sizegamadot) + 0.0385)/0.1876)^1.998

volScalarField ci = Foam:ow( ((-0.0076 * Foam::log (sizegamadot)) + 0.0385) / 0.1876 ) ,1.998 );

// solving equation for a.
tmp<fvSymmTensorMatrix> aEqn
(
fvm::ddt(a_)
== keisi * ( (twoD & a_) + (a_ & twoD) ) + 4 * ci * sizegamadot * (I_ - 3*a_)
);

aEqn().relax();
solve(aEqn);


where keisi is a dimensionless scalar ,a_ is dimensionless tensor , twoD is shear rate tensor ( dimesnion = grad velocity = 1/s ) and I_ is identity tensor(dimensionless)

although ci is dimensionless in real world but this formula makes openFoam to consider it as a dimensioned scalar.(I don't know really why it happens?!! )

however, my question is how i should convert ci in to a dimensionless scalar which can be use in the aEqn?
any help would be appreciated.

[cpro]

Originally Posted by mehdi kamyabi

--> FOAM FATAL ERROR:
Argument of transcendental function not dimensionless

//size of shear rate tensor (which is dimensioned scalar)
volScalarField sizegamadot = Foam::sqrt ( 0.5 * (twoD && twoD) );

//ci is a non-dimensioned variable which is calculated by this
//formula : ci = ((-0.0076*ln(sizegamadot) + 0.0385)/0.1876)^1.998

volScalarField ci = Foam:ow( ((-0.0076 * Foam::log (sizegamadot)) + 0.0385) / 0.1876 ) ,1.998 );

The formula for ci looks like it should be dimensionless. However, it looks like sizegamadot has dimensions of 1/s, which means it isn't a valid argument for log. That may be what the error message means. Hope that helps.

[Lieven]

Cpro is right, sizegamadot is not dimless and this is causing the problem.

The easiest way of solving this, is by writing something as

volScalarField sizegamadot =  Foam::sqrt ( 0.5 * (twoD && twoD) );

dimensionedScalar one = ("one",1/sizegamadot.dimensions(),1.0);

volScalarField ci = Foam::pow( ((-0.0076 * Foam::log (one*sizegamadot)) + 0.0385) / 0.1876 ) ,1.998 );

Normally however, correlations are usually set up such that the transcendental functions arguments are dimensionless. Before applying the fix above, make sure this is not the case for you (cause the fix is basically bypassing the dimensions check in OF).

Cheers,

L

[mehdi kamyabi]

Dear cpro & Lieven

thank you so for your valuable answers...it helped me so much.