Reading field only at the first time folder
 

Hello everyone,
I am implementing a new solver with openfoam, I need to subtract a constant source term from the momentum equation. Since this source term is constant and is pre-obtained, it is better to only save it in the first time step folder. The following is the code (in red) I am using now, but this would end up with saving this term in every time step folder. If anyone hows how to implement it ?

Info<< "Reading field dU0dt\n" << endl;
volVectorField dU0dt
(
IOobject
(
"dU0dt",
runTime.timeName(),
mesh,
IOobject::MUST_READ,
IOobject::AUTO_WRITE
),
mesh
);

ps: Saving this constant term in /constant folder is not an option, since it would work with parallel computing. Therefore, it is better to be saved in the time folder.

Hi yongxiang,

I'm quite new at this, but this looks like it works.

In createFields.H
I wrote the following code snippet:
in the solver, I added the following lines:

Before the while (runTime.run()) loop:
After the first round of calculations (or wherever it is feasible for your code):
I placed it after runTime.write();
and that's it.

After the first time step, it will create a constant (placed in your constant folder) which will then be referred to (and unedited) for following calculations.
--
Note, I am not sure if you need this value for your first timestep, If you do, you should probably initialize it with some approximation.
You could also move the dU0dt.write(); further up in the solver and use READ_IF_PRESENT.
--
Let me know if this helps,

Tony

Hi Tony,
thanks very much for your reply. You provide me an option to complete my desired task. However, the thing is if dU0dt is saved in the /constant folder, there would be problem with parallel computation. As far as I understood, the parallel computation only decompose the /polyMesh folder, where the mesh is stored, into different /processor* folder. Therefore, if dU0dt is stored in the /constant folder, it would not be decomposed, which would make the parallel computing fail.
That's why I think saving dU0dt in time folder would be better, since it would be automatically decomposed for parallel computation. I know function like:

runTime.constant(), and
runTime.timeName(),

but do you know something like:

runTime.startTime() or
runTime.timeName(startTime) or
runTime.timeName().startTime()

which would allow us to read the dU0dt always from the startTime folder. (All the above are not working as I already tried.)

Thanks again for your suggestion.
Yongxiang

Whoops,

Sorry about that...

Note: I accidently posted an incorrect solution.

I'll keep looking for a solution.