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arXiv 2202.11549math.NAcs.NA
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基于离散水平集函数的二维和三维浸入式Crouzeix-Raviart有限元法

An immersed Crouzeix-Raviart finite element method in 2D and 3D based on discrete level set functions

Haifeng Ji

摘要:

本文主要研究三维浸入式有限元方法的构造和分析。与二维情况不同的是,界面与四面体边的交点通常不共面,这使得基于界面的分段线性逼近的二维IFE方法推广到三维情况并不简单.我们解决这个共面性问题的方法,通过离散水平集函数的接口近似。从计算的角度来看,这种方法是非常方便的,因为在许多实际应用中,确切的接口往往是未知的,只有一个离散的水平集函数是可用的。由于这种方法也没有被认为是在2D IFE方法,在本文中,我们提出了一个统一的框架,为2D和3D的情况。我们考虑一种基于传统Crouzeix-Raviart单元的IFE方法,该单元使用面上的积分值作为自由度。所提出的IFE的新颖之处在于,即使对于各向异性界面问题,任意三角形/四面体上的基函数也没有任何角度限制,这比使用节点值作为自由度的IFE更有利。在形状规则三角剖分上证明了IFE插值误差的最优界。对于IFE方法,最佳的先验误差和条件数估计与常数无关的接口相对于未拟合网格的位置。本文还讨论了张量系数各向异性界面问题的推广。数值例子支持的理论结果。

英文摘要:

This paper is devoted to the construction and analysis of immersed finite element (IFE) methods in three dimensions. Different from the 2D case, the points of intersection of the interface and the edges of a tetrahedron are usually not coplanar, which makes the extension of the original 2D IFE methods based on a piecewise linear approximation of the interface to the 3D case not straightforward. We address this coplanarity issue by an approach where the interface is approximated via discrete level set functions. This approach is very convenient from a computational point of view since in many practical applications the exact interface is often unknown, and only a discrete level set function is available. As this approach has also not be considered in the 2D IFE methods, in this paper we present a unified framework for both 2D and 3D cases. We consider an IFE method based on the traditional Crouzeix-Raviart element using integral values on faces as degrees of freedom. The novelty of the proposed IFE is the unisolvence of basis functions on arbitrary triangles/tetrahedrons without any angle restrictions even for anisotropic interface problems, which is advantageous over the IFE using nodal values as degrees of freedom. The optimal bounds for the IFE interpolation errors are proved on shape-regular triangulations. For the IFE method, optimal a priori error and condition number estimates are derived with constants independent of the location of the interface with respect to the unfitted mesh. The extension to anisotropic interface problems with tensor coefficients is also discussed. Numerical examples supporting the theoretical results are provided.

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