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arXiv · 2408.10226

A nonconforming P3 and discontinuous P2 mixed finite element on tetrahedral grids

Xuejun Xu·Shangyou Zhang
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Abstract

A nonconforming $P_3$ finite element is constructed by enriching the conforming $P_3$ finite element space with three $P_3$ nonconforming bubbles and six additional $P_4$ nonconforming bubbles, on each tetrahedron. Here the divergence of the $P_4$ bubble is not a $P_3$ polynomial, but a $P_2$ polynomial. This nonconforming $P_3$ finite element, combined with the discontinuous $P_2$ finite element, is inf-sup stable for solving the Stokes equations on general tetrahedral grids. Consequently such a mixed finite element method produces quasi-optimal solutions for solving the stationary Stokes equations. With these special $P_4$ bubbles, the discrete velocity remains locally pointwise divergence-free. Numerical tests confirm the theory.

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Xuejun Xu, Shangyou Zhang. 2024-08-02. A nonconforming P3 and discontinuous P2 mixed finite element on tetrahedral grids. https://arxiv.org/abs/2408.10226

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