Navier-Stokes型变分不等式的两水平梯度-散度稳定化方法

Two-Level Gradient-Divergence Stabilization Method for Navier-Stokes Type Variational Inequalities

  • 摘要: 在含摩擦边界条件的定常不可压 Navier-Stoke方程数值求解中,标准的混合有限元方法所得速度近似解的精度依赖于压力,当压力较大且黏性系数较小时,导致速度近似解的精度不够理想。为克服此不足,本文提出一种梯度-散度(grad-div)稳定化的两水平有限元方法。该方法采用分层策略:首先在一粗网格上求解含梯度-散度稳定项的非线性Navier-Stokes 型变分不等式问题,得到一个粗网格解;然后在一细网格上以粗网格解线性化非线性的对流项,求解一个 Ossen、 Stokes或 Newton 线性化问题得到最终解,并利用梯度-散度稳定项抑制压力对速度的影响。我们从理论上估计了该数值方法所得近似解的误差界,并通过数值试验验证了理论结果的正确性和数值方法的有效性。数值结果表明,与标准的两水平有限元方法相比,该方法显著提升了速度近似解的精度。

     

    Abstract: In the numerical solution of steady incompressible Navier-Stokes equations with frictional boundary conditions, the accuracy of velocity approximations obtained by the standard mixed finite element method depends on pressure. When the pressure is high and the viscosity coefficient is small, the accuracy of velocity approximations becomes unsatisfactory. To address this issue, this paper proposes a gradient–divergence (grad–div) stabilized two-level finite element method. The method employs a hierarchical strategy: first, a nonlinear Navier-Stokes-type variational inequality problem with a grad–div stabilization term is solved on a coarse grid to obtain a coarse-grid solution; then, the nonlinear convective term is linearized using the coarse-grid solution on a fine grid, and a linearized problem (Ossen, Stokes, or Newton type) is solved to derive the final solution. The grad–div stabilization term is utilized to suppress the influence of pressure on velocity. Theoretical error bounds for the approximate solutions of this numerical method are derived, and numerical experiments validate the correctness of theoretical results and the effectiveness of the method. Numerical results show that compared with the standard two-level finite element method, the proposed method significantly improves the accuracy of velocity approximations.

     

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