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arXiv 0802.0527math.NAcs.NA
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浅水变分自由拉格朗日方法的守恒性质

Conservative Properties of the Variational Free-Lagrange Method for Shallow Water

UC Davis(加州大学戴维斯分校);Los Alamos National Laboratory(洛斯阿拉莫斯国家实验室)

Matthew Dixon, Todd Ringler

AI总结:

本文评估了变分自由拉格朗日方法在正则化浅水中的长时间守恒性质,通过辛积分器和离散算子构造实现了能量和位涡的无长期漂移。

摘要:

浅水的变分自由拉格朗日(VFL)方法是一种自由拉格朗日方法,其额外性质是保留了浅水的变分结构。VFL方法最初由\cite{AUG84}在此背景下推导,他们用自由拉格朗日数据结构离散了哈密顿作用原理。本文的目的是评估VFL方法在正则化浅水中的长时间守恒性质,这些性质对气候模拟有用。长时间正则化浅水模拟表明,VFL方法在(i)通过辛积分器应用的能量误差和(ii)通过构造满足半离散散度和位涡守恒定律的离散旋度、散度和梯度算子得到的位涡误差中,均无长期漂移。这些诊断性半离散方程通过描述拉格朗日框架中各自的无旋和螺线管分量的演化,补充了VFL方法的描述。与连续方程一样,前者包含一个$\text{div}^2\mathbf{U}$项,表明流动具有很强的趋向纯旋转状态的趋势。数值结果表明:(i)在纯旋转正则化浅水中,初始径向对称涡对保持形状和强度;(ii)Voronoi图如何保留流场历史;(iii)能量守恒至$\mathcal{O}(\Delta^2)$,位涡误差在5%以内,且在50年期间无长期增长。

英文摘要:

The variational free-Lagrange (VFL) method for shallow water is a free-Lagrange method with the additional property that it preserves the variational structure of shallow water. The VFL method was first derived in this context by \cite{AUG84} who discretized Hamilton's action principle with a free-Lagrange data structure. The purpose of this article is to assess the long-time conservation properties of the VFL method for regularized shallow water which are useful for climate simulation. Long-time regularized shallow water simulations show that the VFL method exhibits no secular drift in the (i) energy error through the application of symplectic integrators; and (ii) the potential vorticity error through the construction of discrete curl, divergence and gradient operators which satisfy semi-discrete divergence and potential vorticity conservation laws. These diagnostic semi-discrete equations augment the description of the VFL method by characterizing the evolution of its respective irrotational and solenoidal components in the Lagrangian frame. Like the continuum equations, the former exhibits a $\text{div}^2\mathbf{U}$ term which indicates that the flow has a very strong tendency towards a purely rotational state. Numerical results show (i) the preservation of shape and strength of an initially radially symmetric vortex pair in purely rotational regularized shallow water and (ii) how the Voronoi diagram retains the history of the flow field and (iii) that energy is conserved to $\mathcal{O}(Δ^2)$ and potential vorticity error to within 5% with no secular growth over a 50 year period.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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