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Old   November 7, 2013, 00:55
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Srivathsan N
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Hi Philip,

I have been trying to re-write valueFraction for each face of my patch as symm(n*n). I have a very basic doubt.
Is it better to write a new BC (derived from directionMixed (maybe?)) where this definition of valueFraction is changed as symm(n*n) while looping over all faces of the patch? If yes, where do I make the changes? In the 'updateCoeffs' section?

Thanks.
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Srivaths
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Old   September 15, 2014, 11:28
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Hi,

Quote:
Originally Posted by hjasak View Post
4) If this is not enough for you (there is another possibility), I have written a newDirectionMixedFvPatchField boundary condition, with 4 components. Unlike the above one, this b.c. allows both the normal and tangential condition to be mixed separately between the fixedValue and fixedGradient b.c. with two blending factors. You need this kind of thing for contact problems with friction and large deformation and similar. In my version, the stuff lives in:
OpenFOAM-1.2/applications/solvers/newStressAnalysis/materialModels/newDirectionM ixed
In my problem, I would like to specify on one of my boundaries:
- a zero gradient for the normal component of the displacement
- a zero displacement in the tangential direction
The newDirectionMixed looked like the perfect solution. However, when I ran it with my solver, I got the following error:

Code:
--> FOAM FATAL IO ERROR: 

    Cannot find 'value' entry on patch symr of field U in file "/home/salwa/OpenFOAM/salwa-extend-3.0/run/tutorials/solidMechanics/elasticThermalSolidFoam/flosse_test1/0/U"
    which is required to set the values of the generic patch field.
    (Actual type newDirectionMixed)

    Please add the 'value' entry to the write function of the user-defined boundary-condition
    or link the boundary-condition into libfoamUtil.so

file: /home/salwa/OpenFOAM/salwa-extend-3.0/run/tutorials/solidMechanics/elasticThermalSolidFoam/flosse_test1/0/U::boundaryField::symr from line 64 to line 69.

    From function genericFvPatchField<Type>::genericFvPatchField(const fvPatch&, const Field<Type>&, const dictionary&)
    in file fields/fvPatchFields/basic/generic/genericFvPatchField.C at line 71.

FOAM exiting
Adding a 'value' entry gave this error:
Code:
gradientInternalCoeffs cannot be called for a genericFvPatchField (actual type newDirectionMixed)
    on patch symr of field U in file "/home/salwa/OpenFOAM/salwa-extend-3.0/run/tutorials/solidMechanics/elasticThermalSolidFoam/flosse_test1/0/U"
    You are probably trying to solve for a field with a generic boundary condition.

    From function genericFvPatchField<Type>::gradientInternalCoeffs() const
    in file fields/fvPatchFields/basic/generic/genericFvPatchField.C at line 811.

FOAM exiting
This is my U file:
Code:
symr
    {

        type                                newDirectionMixed;
        refValue                           uniform    0;
        refGrad                            uniform    0;
        nHat                               (1 0 0);
        normalValueFraction            0;
        tangentialValueFraction       1;
        value                               uniform (0 0 0);
  }
Does anyone know where the problem might come from? Is there something wrong with my U file?

Thanks,
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Old   September 17, 2014, 10:02
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Hi Sliwa,

Quote:
In my problem, I would like to specify on one of my boundaries:
- a zero gradient for the normal component of the displacement
- a zero displacement in the tangential direction
directionMixed can do this: the capabilities of newDirectionMixed have essentially been included in the current directionMixed boundary condition, as valueFraction is a symmTensor now instead of a scalar.

To achieve what you want, use directionMixed like this:
Code:
myPatch
{
    type              directionMixed;
    refValue          uniform ( 0 0 0 );
    refGradient       uniform ( 0 0 0 );
    valueFraction     uniform ( 0 0 0 1 0 1 ); // (I - sqr(n))
    value             uniform ( 0 0 0 );
where I have assumed n = ( 1 0 0 ) above.
You can see that to fix the value in the normal direction valueFraction = sqr(n), whereas to fix the value in the tangential directions valueFraction = I - sqr(n).

Best regards,
Philip
tom ato and meth like this.
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Old   September 17, 2014, 10:03
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Philip Cardiff
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Quote:
Originally Posted by Sherlock_1812 View Post
Hi Philip,

I have been trying to re-write valueFraction for each face of my patch as symm(n*n). I have a very basic doubt.
Is it better to write a new BC (derived from directionMixed (maybe?)) where this definition of valueFraction is changed as symm(n*n) while looping over all faces of the patch? If yes, where do I make the changes? In the 'updateCoeffs' section?

Thanks.
Hi Srivaths,

yes you should derive a new boundary condition from directionMixed and set the valueFraction in the constructor or, if the mesh is moving/changing, in updateCoeffs.

See for example, fixedDisplacementZeroShear in $FOAM_SRC/solidModels.fvPatchVectorFields in foam extend.

Best regards,
Philip
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Old   September 18, 2014, 10:55
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Thank you, Philip! That worked.
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Old   August 9, 2015, 21:10
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Hi Dear Foamers

I'm trying to use no-stress wall boundary condition

and I used:

Code:
        type            directionMixed;
        refValue        uniform (0 0 0);
        refGradient     uniform (0 0 0);
        valueFraction   uniform (0 0 0 1 0 0);
and now I'm getting wrong answers

I would appreciate if anyone could help me
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Old   August 12, 2015, 11:09
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any answer guys ?
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Old   August 12, 2015, 11:13
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Philip Cardiff
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I think the slip boundary condition already does what you want.

See here.

Philip
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Old   August 12, 2015, 11:48
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Thanks a lot Philip
It was very Helpful
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Old   December 3, 2015, 19:02
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Quote:
Originally Posted by bigphil View Post
Hi Nicolas,

Yes it is possible, using directionMixed, to give every face on a boundary patch a different gradient in the tangential direction. I would do something like this in a header file at the start of a time-step (although it might be possible to use groovyBC but I am not sure):

Code:
label patchID = mesh.boundaryMesh().findPatchID("patchOfInterest");
if(patchID == -1)
 {
    Info << "patch not found" << endl;
    return 0;
 }

directionMixedFvPatchVectorField& Upatch =
        refCast<directionMixedFvPatchVectorField>
        (
         U.boundaryField()[patchID]
         );

//- patch face normals      
vectorField n = mesh.boundary()[loadingIndex].nf();
      
//- set value fraction so as to have fixed value in patch normal direction
Upatch.valueFraction() = symm(n*n);

//- set fixed value
Upatch.refValue() = vector (0, 0, 0); //- put what ever vectorField you want here

//- set fixed gradient (as a function of position and time as an example)
const vectorField& patchFaceCentres = mesh.boundaryMesh()[patchID].faceCentre();
Upatch.refGradient() = patchFaceCentres * runTime.value();
By the way, "U" is my solution variable above.

Hope this helps,
Philip
Hi Philip
Interesting explanation for the changing the refGradient in the directionMixed BC. If we include this code in the data can we give any values in directionMixed condition in the 0/U file? Is it possible to set a nonuniform value for the valuefraction in a similar manner using tensor fields.

Thank you.

Saurabh
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Old   December 3, 2015, 19:07
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Hi Philip

Just another doubt. Can we use funkySetFields with directionMixed BC. I am getting an error when I try to do that. This is the error:

--> FOAM FATAL IO ERROR:
"ill defined primitiveEntry starting at keyword 'valueFraction' on line 29 and ending at line 41"

Thank you.
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Old   December 4, 2015, 20:40
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Yes Saurabh you can do this,

If you want to this you want to define a summetric tensor field as a variable initialize it corectly with all the constructors and add it to the maping function if you want to be able to use it in parallèle.

You can always look at boundary condition source code to give you great exemple, ther is plenty of them.

But valueFraction is alrethy a symmTensorField !?? I'm not shure what is your objectif in creating your new dirrectionMixed boundary condition.

I dont konw about funkysetfield I did not use it yet.

Out of curiosity why do you want to do this ? What are you tring to accomplish ?

Not shur what you mean by including the code in the data ?

Hope this was usfull
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Old   December 4, 2015, 22:09
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[QUOTE=ubald;576267]Yes Saurabh you can do this,

If you want to this you want to define a summetric tensor field as a variable initialize it corectly with all the constructors and add it to the maping function if you want to be able to use it in parallèle.

You can always look at boundary condition source code to give you great exemple, ther is plenty of them.

But valueFraction is alrethy a symmTensorField !?? I'm not shure what is your objectif in creating your new dirrectionMixed boundary condition.

I dont konw about funkysetfield I did not use it yet.

Out of curiosity why do you want to do this ? What are you tring to accomplish ?

Not shur what you mean by including the code in the data ?

Hi Nicolas

Thank you for replying so quickly. I will take a look the deifnition of the codes and see if I can compile my own BC. I am trying to use openFoam for magnetic decay simulations and my BC doesnot have a symm tensor in value fraction. Please peruse my post:

http://www.cfd-online.com/Forums/ope...groovy-bc.html

This might give you more context to what I am trying to do. Thanks again for the help.
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Old   October 20, 2016, 00:36
Default directionMixed for fluid-fluid interface
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Hello,

I am trying to use the conjugate heat transfer solver to compute phase change at a liquid-vapor interface. I have implemented the phase change models into the solver with just a normal velocity at the interface for the phase change. However, I have vapor flow over the interface which would create a viscous shear on the surface of the liquid. The boundary condition for the problem is essentially equal tangential velocities on either side of the interface and equal tangential shear stresses. Added to this is the fixed value in the normal direction. I was thinking that this would be possible to be implemented using the directionMixed boundary condition. However I am not sure how the value fraction would look for such a scenario.

Is it possible to use directionMixed for such a BC? I am hoping someone with some experience would be able to direct me in the right direction. As far as I know there does not seem to be any similar boundary conditions in OF.

Thanks so much for your time

Praveen
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