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arXiv 1807.09894math.NAcs.NA
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一个用于求解两相斯托克斯问题混合有限元方法的虚拟域方法

A fictitious domain approach for a mixed finite element method solving the two-phase Stokes problem with surface tension forces

Institute for Mathematics and Scientific Computing, Karl-Franzens-Universität(格拉茨大学数学与科学计算研究所)

Sébastien Court

AI总结:

本文研究了一种混合有限元格式,用于求解带有表面力的斯托克斯问题,这些力在将域分成两个子域的界面处引起应力张量法向迹的跃变。假设界面处速度相等。通过乘数考虑界面条件。引入了一个合适的拉格朗日泛函以推导问题的弱形式。该工作的特色是使用虚拟域方法考虑界面。后者受XFEM方法启发,使用截断函数,但更易于实现,因为没有提供奇异函数的富集。在该背景下,获得定义在界面上的对偶变量的收敛性是非平凡的。为此,一种增广拉格朗日技术稳定了乘数的收敛性,这对于确定不稳框架中界面的动力学至关重要。理论分析表明,对于稳定化格式,满足与网格尺寸无关的离散inf-sup条件。这保证了最优收敛率,我们通过数值测试观察到。该方法的能力通过鲁棒性测试和一个用于测试界面变形的不稳模型得到验证,这些变形对应于二维中的椭球形状。

摘要:

在本文中,我们研究了一种混合有限元格式,用于求解带有通用表面力的斯托克斯问题,这些力在将域分成两个子域的界面处引起应力张量法向迹的跃变。假定界面处速度相等。界面条件通过乘数来考虑。引入了一个合适的拉格朗日泛函以推导问题的弱形式。该工作的特色是使用虚拟域方法考虑界面。后者受XFEM方法启发,使用截断函数,但更易于实现,因为没有提供奇异函数的富集。在该背景下,获得定义在界面上的对偶变量的收敛性是非平凡的。为此,一种增广拉格朗日技术稳定了乘数的收敛性,这对于确定不稳框架中界面的动力学至关重要。理论分析表明,对于稳定化格式,满足与网格尺寸无关的离散inf-sup条件。这保证了最优收敛率,我们通过数值测试观察到。该方法的能力通过鲁棒性测试和一个用于测试界面变形的不稳模型得到验证,这些变形对应于二维中的椭球形状。

英文摘要:

In this article we study a mixed finite element formulation for solving the Stokes problem with general surface forces that induce a jump of the normal trace of the stress tensor, on an interface that splits the domain into two subdomains. Equality of velocities is assumed at the interface. The interface conditions are taken into account with multipliers. A suitable Lagrangian functional is introduced for deriving a weak formulation of the problem. A specificity of this work is the consideration of the interface with a fictitious domain approach. The latter is inspired by the XFEM approach in the sense that cut-off functions are used, but it is simpler to implement since no enrichment by singular functions is provided. In that context, getting convergence for the dual variables defined on the interface is non-trivial. For that purpose, an augmented Lagrangian technique stabilizes the convergence of the multipliers, which is important because their value would determine the dynamics of the interface in an unsteady framework. Theoretical analysis is provided, where we show that a discrete inf-sup condition, independent of the mesh size, is satisfied for the stabilized formulation. This guarantees optimal convergence rates, that we observe with numerical tests. The capacity of the method is demonstrated with robustness tests, and with an unsteady model tested for deformations of the interface that correspond to ellipsoidal shapes in dimension 2.

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