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arXiv 2106.03260math.NAcs.NA
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Cahn-Hilliard-Stokes-Darcy方程组解耦数值格式的误差估计

Error estimate of a decoupled numerical scheme for the Cahn-Hilliard-Stokes-Darcy system

Wenbin Chen, Daozhi Han, Cheng Wang, Shufen Wang, Xiaoming Wang, Yichao Zhang

摘要:

我们分析了一个完全离散的有限元数值方案的Cahn-Hilliard-Stokes-Darcy系统,模型在耦合的自由流和多孔介质中的两相流。为了避免Cahn-Hilliard方程和流体运动之间的耦合,我们在数值格式中采用算子分裂,使得这两个求解器解耦,从而大大提高了计算效率。证明了在~ \cite{CHW2017}中的唯一可解性和能量稳定性。本文对全离散有限元格式进行了详细的收敛性分析和误差估计,从而在能量范数下建立了最优速率收敛阶,即,在相位变量的$\ell^\infty (0, T; H^1) \cap \ell^2 (0, T; H^2)$范数中,以及在速度变量的$\ell^\infty (0, T; H^1) \cap \ell^2 (0, T; H^2)$范数中。这样的能量范数误差估计导致与对流部分相关联的非线性误差项的消除,这被证明是通过分析的关键步骤。此外,相位变量数值解的离散$\ell^2 (0;T; H^3)$界在误差估计中起着重要的作用,该误差估计是通过有限元中的Gagliardo-Nirenberg不等式的离散形式来实现的。

英文摘要:

We analyze a fully discrete finite element numerical scheme for the Cahn-Hilliard-Stokes-Darcy system that models two-phase flows in coupled free flow and porous media. To avoid a well-known difficulty associated with the coupling between the Cahn-Hilliard equation and the fluid motion, we make use of the operator-splitting in the numerical scheme, so that these two solvers are decoupled, which in turn would greatly improve the computational efficiency. The unique solvability and the energy stability have been proved in~\cite{CHW2017}. In this work, we carry out a detailed convergence analysis and error estimate for the fully discrete finite element scheme, so that the optimal rate convergence order is established in the energy norm, i.e.,, in the $\ell^\infty (0, T; H^1) \cap \ell^2 (0, T; H^2)$ norm for the phase variables, as well as in the $\ell^\infty (0, T; H^1) \cap \ell^2 (0, T; H^2)$ norm for the velocity variable. Such an energy norm error estimate leads to a cancellation of a nonlinear error term associated with the convection part, which turns out to be a key step to pass through the analysis. In addition, a discrete $\ell^2 (0;T; H^3)$ bound of the numerical solution for the phase variables plays an important role in the error estimate, which is accomplished via a discrete version of Gagliardo-Nirenberg inequality in the finite element setting.

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