CFD Online Discussion Forums - Stress analysis--BC's on non-planar surface

CFD Online Discussion Forums (https://www.cfd-online.com/Forums/)

- OpenFOAM Running, Solving & CFD (https://www.cfd-online.com/Forums/openfoam-solving/)

- - Stress analysis--BC's on non-planar surface (https://www.cfd-online.com/Forums/openfoam-solving/137886-stress-analysis-bcs-non-planar-surface.html)

Stress analysis--BC's on non-planar surface

Hi there,

I'm having trouble figuring out a way to prescribe a stress condition on a non planar boundary. For example, if we consider the Plate With A Hole example from the documents and wish to prescribe a pressure condition of 10kPa pushing outward on the hole instead of the (planar) plate boundary, how can I actually do this? In particular, my problem arises from the fact that I cannot see how to employ the tractionDisplacement boundary condition to do this:

Code:

right 

{ 

    type            tractionDisplacement; 

    traction        uniform ( 10000 0 0 ); 

    pressure        uniform 0; 

    value           uniform (0 0 0); 

}

the "traction" is clearly expected to have the a vector value prescribed, but I'm not seeing something like "normal to the surface" available.

Thanks in advance for all help!

Hi the.drizzle,

I am a newbie on OpenFOAM because I use it for 1 month. I use sometimes the solver solidEquilibriumDisplacementFoam and I think traction and pressure are in Pa, traction runs in the x,y, and z directions and pressure runs in the normal direction on the plane.

Try this:
hole { type tractionDisplacement; traction uniform ( 0 0 0 ); pressure uniform 10000; value uniform (0 0 0); }
Good luck! :cool: I wait your results.

Jeff.

Hi Jeff,

Thanks for the reply! I don't have my OF-equipped computer handy, but I don't think that will work--I think I already tried exactly that approach already. I think. Maybe not though, I will try again later today to be sure.

It would make sense if it did work though, as the we have from the tutorial:

Quote:

The other patches are traction boundary conditions, set by a specialist traction boundary type. The traction boundary conditions are specified by a linear combination of: (1) a boundary traction vector under keyword traction; (2) a pressure that produces a traction normal to the boundary surface that is defined as negative when pointing out of the surface, under keyword pressure. The up and hole patches are zero traction so the boundary traction and pressure are set to zero. For the right patch the traction should be (1e4,0, 0) Pa and the pressure should be 0 Pa.

except even from this, I'm not quite seeing how this works as it should also work (by this reasoning) to define the BC on the right wall as:

Code:

right

{ 

    type            tractionDisplacement; 

    traction        uniform ( 0 0 0 ); 

    pressure        uniform 10000; 

    value           uniform (0 0 0); 

}

which I'm quite sure won't work...

3 ways to model your exemple and not the same results

Hi the.drizzle,

Good to hear from you!

As to model the traction of the right planar surface, I try three differents BC details with the exemple of the plateHole.

Ont the first one, we applied a traction of 10000 Pa on the positive direction.

Code:

right

    {

        type            tractionDisplacement;

        traction        uniform ( 10000 0 0 );

        pressure        uniform 0;

        value           uniform (0 0 0);

    }

The second one:

Code:

right

    {

        type            tractionDisplacement;

        traction        uniform ( 0 0 0 );

        pressure        uniform 10000;

        value           uniform (0 0 0);

    }

The same results from the first example but sigmaXX(1st ex) = - sigmaXX(2nd ex)
I thought the pressure in on the opposite direction. That's why I try a last example on the other direction:

Code:

right

    {

        type            tractionDisplacement;

        traction        uniform ( 0 0 0 );

        pressure        uniform -10000;

        value           uniform (0 0 0);

    }

This time, the results aren't the same as the 1st example but there are closed and not in the opposite values.

What's wrong :confused:? I don't know ...

Please find attached the pics from my tests on OpenFOAM.

See you,

Jeff.

A mistake from me :D

In the third example, I stop my atteinment at the first increment. That's why I haven't the same results as the first exemple :rolleyes:.

Please see the real result of the sigmaXX on the third one. It is the same as the first one.

So, the pressure is like a traction if you apply it on the opposite direction.

Now, I'm waiting your results on the hole.