In this paper, uniformly unconditionally stable first and second order finite difference schemes are developed for kinetic transport equations in the diffusive scaling. We first derive an approximate evolution equation for the macroscopic density, from the formal solution of the distribution function, which is then discretized by following characteristics for the transport part with a backward finite difference semi-Lagrangian approach, while the diffusive part is discretized implicitly. After the macroscopic density is available, the distribution function can be efficiently solved even with a fully implicit time discretization, since all discrete velocities are decoupled, resulting in a low-dimensional linear system from spatial discretizations at each discrete velocity. Both first and second order discretizations in space and in time are considered. The resulting schemes can be shown to be asymptotic preserving (AP) in the diffusive limit. Uniformly unconditional stabilities are verified from a Fourier analysis based on eigenvalues of corresponding amplification matrices. Numerical experiments, including high dimensional problems, have demonstrated the corresponding orders of accuracy both in space and in time, uniform stability, AP property, and good performances of our proposed approach.
翻译:在本文中,为diffusive 缩放中的动能传输方程式制定了统一、无条件、第一和第二级固定差异方案。我们首先从分配功能的正式解决方案中得出一个宏观密度的近似进化方程,然后通过运输部分的以下特性而分离,半半Lagrangian 方法采用后限差异半Lagrangian 方法,而 diffusive部分是隐含的离散。在提供宏观密度后,即使完全隐含时间离散,分配功能也可以有效解决,因为所有离散速度都是分解的,造成每个离散速度的空间离散的低维线系统。考虑在空间和时间上的第二级离散化,由此产生的计划可以显示在差异限度内是偏差性保存(AP),统一而无条件的稳定性从基于相应增殖矩阵的叶值的四级分析中得到核实。包括高度问题在内的大量实验在空间和时间方法、统一性能、AP属性和拟议的良好性能方面显示了相应的精确性。