[joeeweaver]

I am extending a solver whose final fields are calculated using a collection of intermediate values. Generically, it writes field F, which is the sum A+B+C+D.

I would like to visualize the individual components (per cell) over time to get a feel for their relative contributions under different conditions and in different locations.

While I'm able to just spit a bunch of output to the terminal and parse it, I'm also aware that the better way to do this would be to be output them using the built-in OpenFOAM registry functionality (IOobject) etc.

I'm not particularly familiar with how that part of the code works, particularly in the context of local variables (the A,B,C,D components) within a function.


Following the wiki, I've successfully set up an IOobject for component A

volScalarField A_comp
(
    IOobject
    (
        "A_comp",
        fc_->mesh_.time().timeName(),
        fc_->mesh_,
        IOobject::NO_READ,
        IOobject::AUTO_WRITE
    ),
    fc_->mesh_
);

A_comp = fc_->calculate_A();

The

fc_

object is just a pointer to a class which calculates some of the components and has a handy reference to the mesh. This all compiles and the solver runs to the first time it tries to write. I get the error

--> FOAM FATAL ERROR: 
cannot find file "~/case/0.002/A_comp"

I'm interpreting this as I need to do some additional setup for preparing a file to write the A_comp field. I'm not sure where to go from that point and googling around hasn't provided much illumination.

Note that we have no idea of what the initial values of A,B,C,D are, nor would guesses at those ICs be used in calculating them. I don't think I need to set up blank files in the 0 directory, but could be wrong.

Any guidance would be appreciated.

[Mirza8]

That might be because of the type of the constructor that you use for your volScalarField. According to following lines from GeometricField.H file, this constructor is used when you want to read an object:

//- Construct and read given IOobject
        GeometricField
        (
            const IOobject&,
            const Mesh&
        );

So maybe you need to use another constructor. I usually use something like this:

volVectorField A_comp
(
    IOobject
    (
        "A_comp",
        runTime.timeName(),
        mesh,
        IOobject::NO_READ,
        IOobject::AUTO_WRITE
    ),
    fc_->calculate_A()   // the value of the volScalarField
);

So I use the desired value of the volScalarField instead of fc_->mesh_ that you previously used, in the constructor.

[joeeweaver]

Thanks, this makes sense but revealed a further issue.

It turns out

fc_->calculate_A()

is actually calculating a scalar for a single cell rather than volScalarField. The values get recombined higher up the call stack into a field.

I'll be looking for a better place to run this, unless there's some variant of IOobject where you can insert individual scalars and have it recreate the field.