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arXiv 2106.13610math.NAcs.NA
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线弹性力学对偶公式的分片光滑和多重网格法

Patch-Smoother and Multigrid for the Dual Formulation for Linear Elasticity

Gabriele Rovi, Rolf Krause

摘要:

线弹性力学的对偶公式与原始公式相反,不受锁定的影响,因为它是以应力为主要未知量的。因此,它是相当有吸引力的几乎不可压缩和不可压缩的材料。用混合有限元离散化将导致--可能很大--具有特定结构的线性鞍点系统。而有效的多重网格方法存在的混合平面弹性问题的解决,据作者所知,没有多重网格方法是现成的一般对偶制定。两个主要的挑战是在构建一个多重网格方法的双重制定线弹性。首先,在不可压缩极限下,与应力有关的矩阵块是半正定的。第二,应力属于$\textbf{H}_{\text{div}}$,并且不能应用标准平滑器,用于$\textbf{H}^1$常规问题。我们提出了一种新的补丁为基础的光滑的对偶制定线弹性。我们讨论了不同类型的局部边界条件的补丁子问题。基于我们的补丁平滑,我们建立了一个多重网格方法的解决方案产生的鞍点问题,并研究其效率和鲁棒性。数值实验表明,罗宾条件最佳拟合多重网格框架,最终导致多重网格性能。

英文摘要:

The dual formulation for linear elasticity, in contrast to the primal formulation, is not affected by locking, as it is based on the stresses as main unknowns. Thus it is quite attractive for nearly incompressible and incompressible materials. Discretization with mixed finite elements will lead to -- possibly large -- linear saddle point systems with a particular structure. Whereas efficient multigrid methods exist for solving problems in mixed plane elasticity, to the knowledge of the authors, no multigrid methods are readily available for the general dual formulation. Two are the main challenges in constructing a multigrid method for the dual formulation for linear elasticity. First, in the incompressible limit, the matrix block related to the stress is semi-positive definite. Second, the stress belongs to $\textbf{H}_{\text{div}}$ and standard smoothers, working for $\textbf{H}^1$ regular problems, cannot be applied. We present a novel patch-based smoother for the dual formulation for linear elasticity. We discuss different types of local boundary conditions for the patch subproblems. Based on our patch-smoother, we build a multigrid method for the solution of the resulting saddle point problem and investigate its efficiency and robustness. Numerical experiments show that Robin conditions best fit the multigrid framework, leading eventually to multigrid performance.

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