[D.R.]

Hello Foamers,

I have found that the solvers in openFoam solve using an implicit formulation, something along the lines of,

fvScalarMatrix Eqn_1 //original
(
         fvm::ddt(kappa, A_1)
==
         fvm::laplacian(gamma, A_1)
);

Eqn_1.solve();

I have went through the forums and openfoam documentation and have found mention of explicit solutions to these full equations, however, I can not find any examples in the code where the equation is finally solved explicitly instead of implicitly.

Does anyone have an example of this? i.e.

Solve( fvc::ddt(kappa, A_1)
==
fvc::laplacian(gamma,A_1));

or something along these lines? (Note: my example for fvc::ddt() has been attempted and did not work.)

Any help would be appreciated, thank you for your time.

[MSF]

Hi

If you use

Solve( fvm::ddt(kappa, A_1)
==
fvc::laplacian(gamma,A_1));

It's explicit.

Best Moritz

[D.R.]

Thanks for the help, though I had a typo before, and had to use a lower case,

solve(...);

Is it the same functionality, i.e. is it still explicit, if it is written as,

fvScalarMatrix Eqn_1
(
fvm::ddt(kappa, A_1)
==
fvc::laplacian(gamma, A_1)
);
Eqn_1.solve();

?

[MSF]

Yes. There is no difference regarding explicit or implicit time stepping between these two formulations. You can also look at 2.5.1 Treatment of temporal discretization in OpenFOAM (programmers guide).

Best
Moritz