[e-nikookar]

how can i use explicit & implicit methode to solve the problems?
which file must be edited?

[Annier]

Hi ebrahim,
These methods are defined in the application/solvers files and their numerical settings is presented at fvSolution file of the tutorial test examples.
For example,
In the available solver icoFoam in
OpenFOAM/OpenFOAM-2.3.x/applications/solvers/incompressible/icoFOAM/
you can open icoFoam.C and createFields.H files, and you can see the term "PISO" defined there which means Pressure implicit with splitting of operator algorithm.

Now, the numerical settings of these PISO algorithm is given in the fvSolution file of /tutorials/icoFoam/cavity/ test as:

PISO
{
    nCorrectors     2;
    nNonOrthogonalCorrectors 0;
    pRefCell        0;
    pRefValue       0;
}

1. In reality, for practical numerical implementation, we will have to create all these files and solvers on our own (similar to these solvers such as icoFoam), wherein we have to mention our algorithm for pressure and velocities (for example).
2. If we just want to build test examples for standard solvers in OpenFOAM,we will already be using predefined explicit or implicit methods of the existing solvers.

Yours
Anil Kunwar