Exact-curved Lagrange finite elements for the Poisson problem in two dimensions
二维泊松问题的精确弯曲拉格朗日有限元
Hiroki Ishizaka
AI总结 针对二维弯曲域上的泊松问题,提出一种精确弯曲拉格朗日有限元框架,通过分解单元映射为仿射核心与弯曲映射,实现插值分析并证明误差估计。
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我们针对二维弯曲域上的泊松问题,开发了一种精确弯曲拉格朗日有限元框架。单元映射分解为 $F_K=Ψ_K\circΦ_{T_K}$,其中 $Φ_{T_K}$ 将参考三角形映射到仿射核心,$Ψ_K$ 将仿射核心映射到物理弯曲单元。这种分解将仿射缩放与曲率效应分离,使得插值分析可以首先在仿射核心上进行,然后转移到精确弯曲单元。对于协调线性拉格朗日单元,我们在精确弯曲三角形上证明了局部 $L^2$ 和 $H^1$ 插值估计。这些估计用物理单元上的传输方向导数表示,并且在所陈述的半正则性假设下,常数与仿射核心的各向异性形状无关。然后将这些插值估计应用于推导泊松问题的能量范数和 $L^2$ 误差估计。单位圆盘上的数值结果说明了直边与弯曲几何表示之间的差异:弯曲几何显著减少了几何误差,而主导的有限元误差仍然由 $\mathbb{P}^1$ 近似控制。
We develop an exact-curved Lagrange finite element framework for the Poisson problem on two-dimensional curved domains. The element map is factorised as $ F_K=Ψ_K\circΦ_{T_K}$, where $Φ_{T_K}$ maps the reference triangle to an affine core and $Ψ_K$ maps the affine core to the physical curved element. This factorisation separates affine scaling from curvature effects and allows the interpolation analysis to be carried out first on the affine core and then transferred to the exact curved element. For conforming linear Lagrange elements, we prove local $L^2$- and $H^1$-interpolation estimates on exact curved triangles. The estimates are expressed in terms of transported directional derivatives on the physical element, and the constants are independent of the anisotropic shape of the affine core under the stated semi-regularity assumptions. These interpolation estimates are then applied to derive energy-norm and $L^2$-error estimates for the Poisson problem. Numerical results on the unit disk illustrate the difference between straight-sided and curved geometric representations: the curved geometry reduces the geometric error substantially, while the leading finite element error remains governed by the $\mathbb{P}^1$ approximation.