CFD Online Discussion Forums - Ueqn.A() extract the diag. term from the Ueqn??

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Ueqn.A() extract the diag. term from the Ueqn??

I just made a testify, add this code into icoFoam:

Code:

fvVectorMatrix UEqn

        (

            fvm::ddt(U)

          + fvm::div(phi, U)

          - fvm::laplacian(nu, U)

        );



Info<<"UEqn:" << UEqn << endl;

Info<<"UEqn.A():" << UEqn.A()<< endl;

Info<<"UEqn.H():" << UEqn.H()<< endl;        

        //solve(UEqn == -fvc::grad(p));



        // --- PISO loop

Then I run a 9 nodes cavity case. It output this in the first timestep:

Code:

Create time



Create mesh for time = 0



Reading transportProperties



Reading field p



Reading field U



Reading/calculating face flux field phi





Starting time loop



Time = 0.005



Courant Number mean: 0 max: 0

UEqn:Lower triangle = 

12

(

-3e-05

-3e-05

-3e-05

-3e-05

-3e-05

-3e-05

-3e-05

-3e-05

-3e-05

-3e-05

-3e-05

-3e-05

)





diagonal = 9(0.00012 0.00015 0.00012 0.00015 0.00018 0.00015 0.00012 0.00015 0.00012)



Upper triangle = 

12

(

-3e-05

-3e-05

-3e-05

-3e-05

-3e-05

-3e-05

-3e-05

-3e-05

-3e-05

-3e-05

-3e-05

-3e-05

)







[0 4 -2 0 0 0 0]

9{(0 0 0)}



3

(

3((6e-05 6e-05 6e-05) (6e-05 6e-05 6e-05) (6e-05 6e-05 6e-05))

9((6e-05 6e-05 6e-05) (6e-05 6e-05 6e-05) (6e-05 6e-05 6e-05) (6e-05 6e-05 6e-05) (6e-05 6e-05 6e-05) (6e-05 6e-05 6e-05) (6e-05 6e-05 6e-05) (6e-05 6e-05 6e-05) (6e-05 6e-05 6e-05))

0()

)





3

(

3((6e-05 0 0) (6e-05 0 0) (6e-05 0 0))

9{(0 0 0)}

0()

)





UEqn.A():dimensions      [0 0 -1 0 0 0 0];



internalField   nonuniform List<scalar> 9(800 700 800 700 600 700 800 700 800);



boundaryField

{

    movingWall

    {

        type            zeroGradient;

    }

    fixedWalls

    {

        type            zeroGradient;

    }

    frontAndBack

    {

        type            empty;

    }

}



UEqn.H():dimensions      [0 1 -2 0 0 0 0];



internalField   nonuniform List<vector> 9((0 0 0) (0 0 0) (0 0 0) (0 0 0) (0 0 0) (0 0 0) (200 0 0) (200 0 0) (200 0 0));



boundaryField

{

    movingWall

    {

        type            zeroGradient;

    }

    fixedWalls

    {

        type            zeroGradient;

    }

    frontAndBack

    {

        type            empty;

    }

}

So in this log, Why Ueqn.A()'s internal field is not equal to the Ueqn's diag. term? I mark this two in the red.

Thanks in advance,

If A()=diag()/mesh.V(),
this is my mesh:

Code:

convertToMeters 0.03;



vertices

(

    (0 0 0)

    (1 0 0)

    (1 1 0)

    (0 1 0)

    (0 0 0.1)

    (1 0 0.1)

    (1 1 0.1)

    (0 1 0.1)

);



blocks

(

    hex (0 1 2 3 4 5 6 7) (3 3 1) simpleGrading (1 1 1)

);

So V is 0.003*0.01*0.01=0.000003.
but 0.00012/0.000003 does not equal to 800.

Hi,

Ueqn.A()=diag()/mesh.V() holds true only for cells, which do not contact the boundary. E.g. in your example:

600=0.00018/(0.01*0.01*0.003)

[and be careful mesh.V()=3e-7 (not 3e-6)].

At the moment I'm also trying to clarify details about the "Ueqn.A()".

B.r. Martin.

Quote:

Originally Posted by Martin80 (Post 441732)

So this is only true for inner cells, not boundary cells. Thats clear! Thx very much!