Issue with volTensorField calculation
 

Hello everyone,
I am trying out different ways to calculate Lyapunov exponents for my current calculations.
For one of them I am interested in calculating jacobian of particle positions, as a test I started using the cell centres as my positions
volVectorField Ct = mesh.C();
volTensorField gradCt = fvc::grad(Ct);

However as I run the code (in parallel), I get the error message below.
Having looked at similar things being done in Openfoam where for example the velocity field U is used, I don't understand why it happens.

Any help would be greatly appreciated. Thanks

[25] --> FOAM FATAL ERROR:
[25] Not implemented
[25]
[25] From function slicedFvPatchField<Type>::snGrad()
[25] in file lnInclude/slicedFvPatchField.C at line 171.

This isn't a solution, simply a diagnosis so apologies if you've already figured this out.

First, as you've found out slicedFvPatch field does not have snGrad defined (not most others). Check out:

and you'll find many of the members functions and constructors are not implemented.

If you dig into the mesh.C() you'll find it creates a slicedVolVectorField which has internal and boundary fields, the later the cause of the error. Check out line 138 in:

You'll have to figure out an alternate way to compute the gradients of the cell centers that doesn't create a slicedGeometricField. Sorry I'm not more helpful.

Thanks for the help!
Indeed I did looked at that in the end, and those "sliced" fields will just have to go..... or maybe not....
Anyway, I'll find a way.

Just thought of something, since (I think) you're interested in the Jacobian of _only_ the cell centers of the volume mesh, you could just try returning the internalField of the volume mesh and apply the gradient to that, i.e.:

I haven't looked at the code and can't confirm it'll work. I'm assuming it's only the undefined snGrad that's not defined so it's just a guess.

Sorry, Chris, no: internalField is just a field and you need a volField to calculate a gradient.

Please make a plain field; make a COPY of the field C and called grad. However, you are just testing discretisation errors: grad(x) = 1 (in 1-D).

I think you need something different...

Hrv

Hello Hrvoje, thank you for your response.

What do you mean by "plain field" and then use the COPY of the mesh.C() field?

volVectorField centres
(
IOobject
(
"centres",
runTime.timeName(),
mesh,
IOobject::NO_READ,
IOobject::NO_WRITE
),
mesh,
dimLength
);

centres == mesh.C();

fvc::grad(centres) should now work.

Hrv