Open thin-walled rectangular cross section profile (a longitudinal cut is performed at the lateral wall center line, whose kerf (width) is negligible), 120x40mm outer dimensions, 2mm wall thickness. (Dimensions at the midsurface: 118x38mm), element size ranging from ~10mm to ~20mm.
At the A cross section, a skew-symmetry material continuity constraint is applied.
The kinematic constraint at the B point (sphere in cylinder joint) is a positioning constraint, along with the $w_A=0$ axial constraint in A.
A twist per unit length equaling 0.001 radiant/mm is imposed to the profile, i.e. a $\psi_B=0.001 \cdot l$ (it was, erroneously, $\psi_B=0.0005 \cdot l$) rotation is imposed at each end, where $l$ is the $z$ axial coordinate of the endpoints, being z=0 at the skew-symmetry plane.
The reaction moment associated with the constraint will determine the applied torque $T$.