Isogeometric collocation with smooth mixed degree splines over planar multi-patch domains

We present a novel isogeometric collocation method for solving the Poisson’s and the biharmonic equation over planar bilinearly parameterized multi-patch geometries. The proposed approach relies on the use of a modified construction of the C s -smooth mixed degree isogeometric spline space [1] for 𝑠 = 2 and 𝑠 = 4 in case of the Poisson’s and the biharmonic equation, respectively. The adapted spline space possesses the minimal possible degree 𝑝 = 𝑠 + 1 everywhere on the multi-patch domain except in a small neighborhood of the inner edges and of the vertices of patch valency greater than one where a degree 𝑝 = 2 ⁢ 𝑠 + 1 is required. This allows to solve the PDEs with a much lower number of degrees of freedom compared to employing the C s -smooth spline space [2] with the same high degree 𝑝 = 2 ⁢ 𝑠 + 1 everywhere. To perform isogeometric collocation with the smooth mixed degree spline functions, we introduce and study two different sets of collocation points, namely first a generalization of the standard Greville points to the set of mixed degree Greville points and second the so-called mixed degree superconvergent points. The collocation method is further extended to the class of bilinear-like G s multi-patch parameterizations [3], which enables the modeling of multi-patch domains with curved boundaries, and is finally tested on the basis of several numerical examples.