OpenFoam: changing STL position lead to undefine behaviour or crash

Question

I am testing example of the Magnus Effect for OpenFoam-9 https://drive.google.com/file/d/1J2rKIRU8DAZadORyjUfd6OBBcfR-9rLo/view?usp=sharing

What I got from https://holzmann-cfd.com/community/training-cases/magnus-effect

And it works fine:

But when I change STL object with shifted a little position in STL file then simulation is breaking

snappyHexMeshDict:
geometry
{
    cylinder_x01y0z0.stl
    {
        type triSurfaceMesh;
        name cylinder;
    }
};

Please help to understand why a little position shifting in STL file breaks simulation.

Thank you in advance.

Answer 1

Try to change the code in 0.orig/U for your cylinder boundary condition as follows (See the comments):

    cylinder 
    {

        type            codedFixedValue;
        value           uniform (0 0 0);
        name            myBC;

        code
        #{
            const scalar time = this->db().time().value();

            const fvPatch& boundaryPatch = patch(); 

            const vectorField& Cf = boundaryPatch.Cf(); 

            vectorField rot(Cf.size(), vector(0,0,0));
            
            const vector CENTER(0.1,0.0, 0.0); // <<<< Add this line and add it below

            const scalar rotate_speed_max = 10.0;
            const scalar rotate_time_start = 0.0;

            scalar rotate_speed = 0.5 * (time - rotate_time_start) * (time - rotate_time_start);
            rotate_speed = rotate_speed > rotate_speed_max ? rotate_speed_max : rotate_speed;

            //- Start motion of the wall after 15s
            if (time > rotate_time_start)
            {
                rot = rotate_speed * vector(0,0,1) ^ (Cf- CENTER); //<<<< Added here
                // std::cout << __func__ << ":" << __LINE__ << " rotate_speed=" << rotate_speed <<std::endl;
            }

            operator==(rot);

        #};
    }