  The use of trigonometric polynomials as Lagrange multipliers in the harmonic
mortar method enables an efficient and elegant treatment of relative motion in
the stator-rotor coupling of electric machine simulation. Explicit formulas for
the torque computation are derived by energetic considerations, and their
realization by harmonic mortar finite element and isogemetric analysis
discretizations is discussed. Numerical tests are presented to illustrate the
theoretical results and demonstrate the potential of harmonic mortar methods
for the evaluation of torque ripples.
