[Algis]

Hi,

I need to change conditionally fvVectorMatrix (UEqn for example) independently on fvOptions. For example, can I do like that:

Foam::fvVectorMatrix UEqn
(
Foam::fvm::div(phi, U)
- Foam::fvm::laplacian(nu, U)
==
fvOptions(U)
);

if(f_include_turbulence) UEqn += Foam::turbulence->divDevReff(U);
if(f_include_gravity) UEqn -= g;

UEqn().relax();


Or in other words, how do "-=" and "+=" work for fvVectorMatrix, what rules are? How to be sure that operators "-=" and "+=" will change UEqn.A or UEqn.H, or rhs?


Thanks in advance.

[alexeym]

Hi,

it depends on rhs of += or -= operator.

Since UEqn is fvVectorMatrix, look for meaning of operators, for example, at http://foam.sourceforge.net/docs/cpp...31bccd419a176b. Basically you are able to add another matrix, so it will be sum of matrices, or you can add volume field, in this case field will be added to equation source term.

[Algis]

Hi,

I did an experiment. Add gravity (defined as uniformDimensionedVectorField g) by two ways: 1) in definition of UEqn and 2) after definition of UEqn:

1)
fvVectorMatrix UEqn_1
(
fvm::ddt(U)
fvm::div(phi, U)
- fvm::laplacian(nu, U)
==
-g
);

2)
fvVectorMatrix UEqn_2
(
fvm::ddt(U)
fvm::div(phi, U)
- fvm::laplacian(nu, U)
);
UEqn_2 -= g;

and then compared both UEqn_1 and UEqn_2. The result was that A(), H1, source() and residual() were the same for UEqn_1 and UEqn_2, while H() was different. Why H() was different?

Thank you very much in advance,

Algis

[demichie]

Hi Algis,
please can you try with:

UEqn_2 += g;


Ciao
Mattia

[Algis]

Hi Mattia,

I did it and now there is no difference in H() and others. So, analog of

fvVectorMatrix UEqn
(
fvm::ddt(U)
fvm::div(phi, U)
- fvm::laplacian(nu, U)
==
-g
);

is
fvVectorMatrix UEqn_2
(
fvm::ddt(U)
fvm::div(phi, U)
- fvm::laplacian(nu, U)
);
UEqn_2 += g;

but not "UEqn_2 -= g";

Thanks Mattia, now I see in what was my misunderstanding.

Best regards,

Algis

Originally Posted by demichie

Hi Algis,
please can you try with:

UEqn_2 += g;


Ciao
Mattia