Higher order Bernstein–Bézier and Nédélec finite elements for the relaxed micromorphic model

Abstract

The relaxed micromorphic model is a generalized continuum model that is well-posed in the space X=[H1]3×[H(curl)]3. Consequently, finite element formulations of the model rely on H1-conforming subspaces and Nédélec elements for discrete solutions of the corresponding variational problem. This work applies the recently introduced polytopal template methodology for the construction of Nédélec elements. This is done in conjunction with Bernstein–Bézier polynomials and dual numbers in order to compute hp-FEM solutions of the model. Bernstein–Bézier polynomials allow for optimal complexity in the assembly procedure due to their natural factorization into univariate Bernstein base functions. In this work, this characteristic is further augmented by the use of dual numbers in order to compute their values and their derivatives simultaneously. The application of the polytopal template methodology for the construction of the Nédélec base functions allows them to directly inherit the optimal complexity of the underlying Bernstein–Bézier basis. We introduce the Bernstein–Bézier basis along with its factorization to univariate Bernstein base functions, the principle of automatic differentiation via dual numbers and a detailed construction of Nédélec elements based on Bernstein–Bézier polynomials with the polytopal template methodology. This is complemented with a corresponding technique to embed Dirichlet boundary conditions, with emphasis on the consistent coupling condition. The performance of the elements is shown in examples of the relaxed micromorphic model.