How accurate are finite elements on anisotropic triangulations in the maximum norm?

Abstract

In [5] a counterexample of an anisotropic triangulation was given on which the exact solution has a second-order error of linear interpolation, while the computed solution obtained using linear finite elements is only first-order pointwise accurate. This example was given in the context of a singularly perturbed reaction-diffusion equation. In this paper, we present further examples of unanticipated pointwise convergence behaviour of Lagrange finite elements on anisotropic triangulations. In particular, we show that linear finite elements may exhibit lower than expected orders of convergence for the Laplace equation, as well as for certain singular equations, and their accuracy depends not only on the linear interpolation error, but also on the mesh topology. Furthermore, we demonstrate that pointwise convergence rates which are worse than one might expect are also observed when higher-order finite elements are employed on anisotropic meshes. A theoretical justification will be given for some of the observed numerical phenomena.

Can Offshore Meteoric Groundwater Generate Mechanical Instabilities in Passive Continental Margins?

“…The linear elements in our groundwater model do account for sediment anisotropy. However, due to the skewness of the elements, errors may be introduced (e.g., Balan et al., 2022; Huang et al., 2017; Kopteva, 2020a, 2020b). Additional numerical simulations we carried out (Figures S5–S7 in Supporting Information S1) suggest that there is no evidence of numerical errors based on grid refinement.…”

“…For this reason, the onshore component of the groundwater systems was not considered, and we were unable to take into account the variability of climatic parameters (e.g., precipitation, temperature, land use, and ice cover). The linear elements in our groundwater model do account for sediment anisotropy. However, due to the skewness of the elements, errors may be introduced (e.g., Balan et al., 2022; Huang et al., 2017; Kopteva, 2020a, 2020b). Additional numerical simulations we carried out (Figures S5–S7 in Supporting Information S1) suggest that there is no evidence of numerical errors based on grid refinement. The generated stratigraphic models are simplified and do not include the fine‐scale heterogeneity observed in field data.…”