论文标题

基于有效优化的正交正交非局部问题的变异离散化

Efficient optimization-based quadrature for variational discretization of nonlocal problems

论文作者

Pasetto, Marco, Shen, Zhaoxiang, D'Elia, Marta, Tian, Xiaochuan, Trask, Nathaniel, Kamensky, David

论文摘要

以各种形式施放非局部问题并使用有限元(FE)方法使它们离散,这有助于使用非局部矢量计算来证明此类方案的良好性,收敛性和稳定性。采用FE方法还促进了复杂的域几何形状的网络,并与FE方法结合了局部问题。但是,非局部弱问题涉及一个双综合性的计算,这在计算上昂贵,并提出了几个挑战。特别是,与刚度矩阵相关的变异形式的内部积分是在Fe网状元素与半径$δ$的相交的相交中定义的,其中$δ$是非局部相互作用的范围。识别和参数化这些交叉点是一个非平凡的计算几何问题。在这项工作中,我们提出了一种正交技术,其中使用分布在完整球上的正交点进行内部积分,而无需考虑其相交元素的方式,并根据广义移动最小二乘法计算重量。因此,与所有先前使用的方法相反,我们的技术不需要逐元元素积分,并且完全规避了元素 - 球相交的计算。本文考虑了分段线性连续Fe近似的一维实现,重点是元素大小H和非局部半径$δ$是比例的,这是实用计算的典型情况。当仔细处理边界条件并准确地计算变量形式的外部积分时,使用均匀和非均匀的网格,所有维度的一阶收敛至少在l^2中均为$ h \simδ\至0 $渐近地兼容。

Casting nonlocal problems in variational form and discretizing them with the finite element (FE) method facilitates the use of nonlocal vector calculus to prove well-posedeness, convergence, and stability of such schemes. Employing an FE method also facilitates meshing of complicated domain geometries and coupling with FE methods for local problems. However, nonlocal weak problems involve the computation of a double-integral, which is computationally expensive and presents several challenges. In particular, the inner integral of the variational form associated with the stiffness matrix is defined over the intersections of FE mesh elements with a ball of radius $δ$, where $δ$ is the range of nonlocal interaction. Identifying and parameterizing these intersections is a nontrivial computational geometry problem. In this work, we propose a quadrature technique where the inner integration is performed using quadrature points distributed over the full ball, without regard for how it intersects elements, and weights are computed based on the generalized moving least squares method. Thus, as opposed to all previously employed methods, our technique does not require element-by-element integration and fully circumvents the computation of element-ball intersections. This paper considers one- and two-dimensional implementations of piecewise linear continuous FE approximations, focusing on the case where the element size h and the nonlocal radius $δ$ are proportional, as is typical of practical computations. When boundary conditions are treated carefully and the outer integral of the variational form is computed accurately, the proposed method is asymptotically compatible in the limit of $h \sim δ\to 0$, featuring at least first-order convergence in L^2 for all dimensions, using both uniform and nonuniform grids.

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