Communications on Applied Mathematics and Computation ›› 2023, Vol. 5 ›› Issue (4): 1323-1338.doi: 10.1007/s42967-022-00201-5
Xiu Ye1, Shangyou Zhang2
Xiu Ye1, Shangyou Zhang2
摘要: A stabilizer-free weak Galerkin (SFWG) finite element method was introduced and analyzed in Ye and Zhang (SIAM J. Numer. Anal. 58: 2572–2588, 2020) for the biharmonic equation, which has an ultra simple finite element formulation. This work is a continuation of our investigation of the SFWG method for the biharmonic equation. The new SFWG method is highly accurate with a convergence rate of four orders higher than the optimal order of convergence in both the energy norm and the L2 norm on triangular grids. This new method also keeps the formulation that is symmetric, positive definite, and stabilizerfree. Four-order superconvergence error estimates are proved for the corresponding SFWG finite element solutions in a discrete H2 norm. Superconvergence of four orders in the L2 norm is also derived for k ≥ 3, where k is the degree of the approximation polynomial. The postprocessing is proved to lift a Pk SFWG solution to a Pk+4 solution elementwise which converges at the optimal order. Numerical examples are tested to verify the theories.
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