[volker]

Hi all,

I have a problem with a task, which seemed to be straight-forward to solve at first.
I need to program an if-loop in order to compare one volScalarField (P1) to another one (P2), and for each grid point, where P1 >= P2, a certain value (d) has to be written to another volScalarField (N) at exactly the same grid point.
I wrote something like:
(a, b, c, d are placeholder for arbitrary volScalarFields)

volScalarField P1 = a;
volScalarField P2 = b;
volScalarField N = c;

    if (P1 >= P2)
    {
    N = d;
    }
    else
    {
    N = -d;
    }

The problem is that the code in the actual version does not compare the values for every single grid point and hence does not write the value (d) to (N) for all the grid points where the logical expression is true (P1 >= P2).
It's more that it just compares just one (the first?!) point of P1 with P2.
Right now, I don't have any idea how to get rid of that problem, though it seems to be a very silly one.
Thanks for any idea.

greets, volker

[alberto]

Hi,

you have to loop over your cells to compare information in each point:

forAll(P1, cellI)
{
  if (P1[cellI] > P2[cellI])
  {
    N[cellI] = ...
  }
  else
  {
    ...
  }
}

Best,

[volker]

hi alberto,

so many thanks for your help!!! It worked great.
I wasn't aware of that class 'cell'.

Do you know if there is a way to loop over the boundary patches as well?

best
volker

[alberto]

Originally Posted by volker

hi alberto,
so many thanks for your help!!! It worked great.
I wasn't aware of that class 'cell'.

It's not a class, it's just an index created locally by the forAll loop

Do you know if there is a way to loop over the boundary patches as well?

Yes, let's assume you want to loop over the boundaries of a field p:

forAll(p.boundaryField(), patchi)
    {
        // Check if it's zeroGradient (optional, depending on your case)
        if (isA<zeroGradientFvPatchScalarField>(p.boundaryField()[patchi]))
        {
            otherFieldA.boundaryField()[patchi] = 0.0;
            otherFieldB.boundaryField()[patchi] = 0.0;
        }
    }

Best,

[volker]

perfect, big thanks to you!

[alberto]

You're welcome

[tooran]

I am tyring to change a viscoisty model. I need to campare strain rate with a constant parameter (gama)


if strainrate is greater than the gama then do....
so I write :



************************************************** *******************



Foam::viscosityModels::MyHerschelBulkley::calcNu() const
{
dimensionedScalar tone("tone", dimTime, 1.0);
dimensionedScalar rtone("rtone", dimless/dimTime, 1.0);

tmp<volScalarField> sr(strainRate());


forAll(calcNu.internalField(), cellI)
{
if (sr[cellI]< gama_.value())

{


......
It shows me the error:
error : calcNu’ does not have class type forAll(calcNu.internalField(), cellI)


could you please help me?


MyHerschelBulkley.C

MyHerschelBulkley.H

[tooran]

Can any one help me?