Dornisch, WolfgangStöckler, Joachim2022-04-192022-04-192021-11-13http://hdl.handle.net/2003/40861http://dx.doi.org/10.17877/DE290R-22718We investigate the mortar finite element method for second order elliptic boundary value problems on domains which are decomposed into patches Ωk with tensor-product NURBS parameterizations. We follow the methodology of IsoGeometric Analysis (IGA) and choose discrete spaces Xh,k on each patch Ωk as tensor-product NURBS spaces of the same or higher degree as given by the parameterization. Our work is an extension of Brivadis et al. (Comput Methods Appl Mech Eng 284:292–319, 2015) and highlights several aspects which did not receive full attention before. In particular, by choosing appropriate spaces of polynomial splines as Lagrange multipliers, we obtain a uniform infsup-inequality. Moreover, we provide a new additional condition on the discrete spaces Xh,k which is required for obtaining optimal convergence rates of the mortar method. Our numerical examples demonstrate that the optimal rate is lost if this condition is neglected.en65N3065N5541A15510Text