[tecmul]

Hi all,
The rotational transformation tensors in transform.H seem to be the transpose of the actual transformation tensors.
For example:

//- Rotational transformation tensor about the z-axis by omega radians
inline tensor Rz(const scalar& omega)
{
    const scalar s = sin(omega);
    const scalar c = cos(omega);
    return tensor
    (
        c,  s,  0,
       -s,  c,  0,
        0,  0,  1
    );
}

This is the rotational transformation tensor around the z-axis.


I checked multiple versions of OpenFoam and they all do the same thing. Why is this?

[olesen]

Originally Posted by tecmul

Hi all,
The rotational transformation tensors in transform.H seem to be the transpose of the actual transformation tensors.
...
I checked multiple versions of OpenFoam and they all do the same thing. Why is this?

It is best phrased as a question of perspective. Does the transform represent how to get from a global coordinate orientation to a local coordinate orientation, or how to get from a local coordinate orientation to a global one?


If you can be content with "transform" meaning "how do I transform to get everything into the global reference?", it seems OK.


The axesRotation.C might make the local/global relationship clearer.

https://develop.openfoam.com/Develop...otation.C#L128

[tecmul]

Originally Posted by olesen

It is best phrased as a question of perspective. Does the transform represent how to get from a global coordinate orientation to a local coordinate orientation, or how to get from a local coordinate orientation to a global one?

Ah, I think I understand now. I was thinking in terms of transforming a vector, not the coordinate system. Thank you very much.