Coupling non-conforming NURBS patches in isogeometric analysis of complex thin shell structures

Isogeometric analysis allows the use of shell formulations without rotational degrees of freedom, but describing complex geometries typically requires multiple NURBS patches, that are often non-conforming. This work presents a flexible method for coupling such multipatch geometries in isogeometric frameworks and applies it to rotationless Kirchhoff-Love shell analysis. The rotationless formulation requires the enforcing of C-1-continuity across patch interfaces. The present work does this by satisfying interface constraints in a master-slave formulation, where the interface constraints can be derived using only the mesh information. Eliminating the slave variables from the system of equations results in a reduced system matrix. Whereas the C-0-part of the coupling is a global coupling in the weak form, the C-1-continuity is enforced by a strong point-wise coupling in certain well-chosen collocation points along the interface. The proposed method can be applied without any user interaction, both for conforming and for non-conforming patch configurations. This is demonstrated for a set of problems of dynamic shell analysis. Together with the rotationless character of the isogeometric shell formulation, the coupling method allows analysing complex shell structures in a computationally efficient manner.