[mykkujinu2201]

Dear Forums,

I have a problem with developing code.
Though I have used OpenFOAM for several years,
I know how basic codes work such as pimpleFOAM, pisoFOAM and interFOAM.
However, I am really de-facto new to modify the code myself.

When I find articles, I can get time discretized equations or space discretized equations.
What should I do if I wanna use the formulations in discretized equations?
As far as I know, discretization can be controlled at fvScheme but some expressions seem not to be achieved through fvScheme.
For example, if I have time discretized equation as below, how can I formulate a system of equations?


I know this is second-order time discretized equation.
However, I do know how to exactly construct the system of equations as given.

I really appreciate it if you give me any advice or any guide to solving this issue.

Best regards,
Jun

[mAlletto]

Have a look at the programmer guide. Equations look like this

fvm::ddt(C) + fvm::div(phi,C)

Over the fvschemes dictionary you specify the type of discretication

[mykkujinu2201]

Dear Alleto,

First of all, thank you so much for your reply.

Well, I already know how to construct matrix with fvm, fvc, and fvScheme.

My problem is that whenever I encounter equations in analytic form with information about their discretization scheme, I can handle it.
However, I do not know how to construct matrix from "discretized equation".
Do you know how to handle for this purpose?

Best regards,
Jun

[mAlletto]

When you encounter a dircetized equation you have to choose the corresponding scheme in the fvschemes. There is no other easy way. You can program you scheme by your self of course.

[dlahaye]

Maybe like so:

int main(int argc, char *argv[])
{
#include "setRootCase.H"
#include "createTime.H"
#include "createMesh.H"
#include "createFields.H"

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

//Construct linear solver and preconditioner only once, for re-use later
fvScalarMatrix TEqn
(
fvm::laplacian(k, T)
);
autoPtr<fvScalarMatrix::fvSolver> solver(TEqn.solver());
solverPerformance solverPerf;

for (int i=0; i<10; i++)
{
TEqn.source() = mesh.V() * (- su - fvc::Sp(sp, T));
solverPerf = solver->solve();

runTime++;
runTime.write();
}

Info<< nl;
runTime.printExecutionTime(Info);

Info<< "End\n" << endl;

return 0;
}

[Hughtong]

https://www.tfd.chalmers.se/~hani/ku...s/fvMatrix.pdf

[Kaley2]

When faced with a discretized equation, you must select the appropriate scheme in the fvschemes. There's no simpler alternative. Of course, you always have the option to program your own scheme if needed.