[vtAM]

Hi all,


Ive been reading this forum a lot and have drawn many useful information for developing my new solver. Close to finishing, I am now stuck and looking for some help.

What I want to do: I want to rotate the components of a vector respectively a tensor field. By rotation I mean just rotate the vectors or tensor by changing theirs components. I dont want to rotate the mesh here nor do I want to change the cell center locations or anything.

What I do have:

• The reference to the mesh "mesh_"
• A quaternion "rotationquaternion" that describes the rotation i want to perform

This is my code:

 

            // Print a vector before rotation (debugging)
             Info<<mesh_.lookupObjectRef<volVectorField>
            (
                "U"
            ).ref()[1] << nl << endl;

            // Rotation to be performed
            vector rotaxis(0, 0, 1);        // about z axis
            scalar rotangle(3.14159/2.0) ; // around 90°
            quaternion rotationquaternion(rotangle,rotaxis);
            
            // Perform rotation
            Foam::transform
            (
                rotationquaternion,
                mesh_.lookupObjectRef<volVectorField>
                (
                    "U"
                ).ref() 
            );

            // Print a vector after rotation (debugging)
            Info<<mesh_.lookupObjectRef<volVectorField>
            (
                "U"
            ).ref()[1] << nl << endl;

However, the first vector of the field I print out to check if the transformation was done remains unchanged. The output I get:

(-3.89156e-05 1.63329e-05 -2.96595e-05)

(-3.89156e-05 1.63329e-05 -2.96595e-05)

The output I want:

(-3.89156e-05 1.63329e-05 -2.96595e-05)

(-1.63329e-05 -3.89156e-05 -2.96595e-05)

I need to use the lookup because later on I want to rotate any field (not just "U") dynamically without hardcoding their names.


Any help is highly appreciated! Thank you!


vtAM

[vtAM]

Just managed to solve. This is working as inteded:

            

            // Print a vector before rotation (debugging)
            Info<<mesh_.lookupObjectRef<volVectorField>
            (
                "U"
            ).internalField()[678] << nl << endl;

            // Rotation to be performed
            vector rotaxis(0, 0, 1);        // about z axis
            scalar rotangle(M_PI_2) ; // 90°
            quaternion rotationquaternion(rotaxis, rotangle);
            Info<< "quaternion " << rotationquaternion << nl << endl;

            // Perform rotation
            Foam::transform
            (
                                mesh_.lookupObjectRef<volVectorField>
                (
                    "U"
                ).ref(),
                rotationquaternion,
                mesh_.lookupObjectRef<volVectorField>
                (
                    "U"
                ).internalField() 
            );

            // Print a vector after rotation (debugging)
            Info<<mesh_.lookupObjectRef<volVectorField>
            (
                "U"
            ).internalField()[678] << nl << endl;

There are three changes made.

1. Correct initialization of the quaternion. The axis goes first, the angle second
2. Use internalField() instead of ref(). Both work, but internalField() is a static reference and recommended for speed, see src/OpenFOAM/fields/GeometricFields/GeometricField/GeometricField.H
3. Use Foam::transform(ref to field, quaternion, ref to field) to actual change the field itself. I am not a C++ pro but from my understanding the previous Foam::transform(quaternion, ref to field) would only return a copy of the rotated field.

Hope this helps someone in the future. Thanks to everybody who was about to help.


Cheers,


vtAM