论文标题

部分可观测时空混沌系统的无模型预测

Arbitrary Order Energy and Enstrophy Conserving Finite Element Methods for 2D Incompressible Fluid Dynamics and Drift-Reduced Magnetohydrodynamics

论文作者

Holec, Milan, Zhu, Ben, Joseph, Ilon, Vogl, Christopher J., Southworth, Ben S., Campos, Alejandro, Dimits, Andris M., Pazner, Will E.

论文摘要

在完全离散的环境中维持保护定律对于数值模拟的准确行为至关重要,并且需要考虑时空和时间的离散保护属性。本文得出了任意订单有限元的外观外部计算空间离散,用于二维(2D)Navier-Stokes和漂移还原的磁性水力学方程,当与通常的符号时间融合方法耦合时,可以将能量和递减的能量递给机器精度。连续和不连续的 - 加加尔金(DG)弱制剂都可以确保保存,但通常只有同骨的时间整合方法,例如隐式中点方法,可以及时进行精确保护。此外,符号隐式中点方法在显式方案上产生了一个数量级的加速顺序。该方法是使用MFEM库实施的,并为二维中性流体湍流测试问题进行了广泛的套件进行验证。数值解决方案通过与半分析线性特征索的比较以及有限的差异全局漂移气球(GDB)代码进行了比较。然而,发现保存能量和肠子的湍流模拟往往在高波数中具有过多的功率,并且该部分应通过重新引入人工耗散来控制频谱的这一部分。 DG公式允许向对流操作员升级,该对流操作员消散了胚胎,同时仍保持节能。将上环的DG与隐式互合成整合结合在一起,似乎提供了允许中距离波数字达到适当振幅的最佳折衷方案,同时仍控制光谱的高波动部分。

Maintaining conservation laws in the fully discrete setting is critical for accurate long-time behavior of numerical simulations and requires accounting for discrete conservation properties in both space and time. This paper derives arbitrary order finite element exterior calculus spatial discretizations for the two-dimensional (2D) Navier-Stokes and drift-reduced magnetohydrodynamic equations that conserve both energy and enstrophy to machine precision when coupled with generally symplectic time-integration methods. Both continuous and discontinuous-Galerkin (DG) weak formulations can ensure conservation, but only generally symplectic time integration methods, such as the implicit midpoint method, permit exact conservation in time. Moreover, the symplectic implicit midpoint method yields an order of magnitude speedup over explicit schemes. The methods are implemented using the MFEM library and the solutions are verified for an extensive suite of 2D neutral fluid turbulence test problems. Numerical solutions are verified via comparison to a semi-analytic linear eigensolver as well as to the finite difference Global Drift Ballooning (GDB) code. However, it is found that turbulent simulations that conserve both energy and enstrophy tend to have too much power at high wavenumber and that this part of the spectrum should be controlled by reintroducing artificial dissipation. The DG formulation allows upwinding of the advection operator which dissipates enstrophy while still maintaining conservation of energy. Coupling upwinded DG with implicit symplectic integration appears to offer the best compromise of allowing mid-range wavenumbers to reach the appropriate amplitude while still controlling the high-wavenumber part of the spectrum.

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