Abstract The impact of various parameters in the coarse mesh finite difference (CMFD) acceleration method on overall convergence behavior is investigated through numerical calculations using the method of characteristics (MOC). Four parameters appearing in the CMFD acceleration with MOC, i.e., scalar flux distribution in flat flux regions (FFRFlux), the scalar flux distribution in CMFD meshes (CMFDFlux), homogenized cross sections (HXSs) in CMFD meshes, and current correction factors (CCFs), are considered. Parts of these four parameters are fixed to the converged values throughout iterations in order to estimate their impact on convergence. Numerical calculations are carried out for Korea Advanced Institute of Science and Technology’s (KAIST’s) benchmark problem KAIST-2A, which is a heterogeneous and multigroup problem, and the number of outer iterations to reach convergence is evaluated. The impact of geometric heterogeneity and cross-section homogenization in the CMFD acceleration has not been considered in linearized Fourier analysis so far. The calculation results indicate that (1) convergence of HXS has little impact on the overall convergence, (2) convergence of FFRFlux is dominant followed by CCF when a CMFD mesh is optically thin, and (3) convergence of FFRFlux is dominant when a CMFD mesh is optically thick and contains many flat flux regions.

中文翻译：

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多组异构几何中各种参数对MOC CMFD加速收敛性能的影响

摘要 通过使用特征法(MOC) 的数值计算，研究了粗网格有限差分(CMFD) 加速方法中的各种参数对整体收敛行为的影响。CMFD 加速与 MOC 中出现的四个参数，即平坦通量区域中的标量通量分布 (FFRFlux)、CMFD 网格中的标量通量分布 (CMFDFlux)、CMFD 网格中的均质横截面 (HXSs) 和电流校正因子 (CCFs) ）， 被考虑。这四个参数的一部分在整个迭代过程中固定为收敛值，以估计它们对收敛的影响。对韩国科学技术高等研究院 (KAIST) 的基准问题 KAIST-2A 进行了数值计算，这是一个异构和多组问题，并评估达到收敛的外部迭代次数。迄今为止，线性化傅立叶分析中尚未考虑几何异质性和横截面均匀化对 CMFD 加速度的影响。计算结果表明：（1）HXS的收敛对整体收敛影响不大，（2）当CMFD网格光学薄时FFRFlux的收敛占主导地位，其次是CCF，（3）当CMFD时FFRFlux的收敛占主导地位网格在光学上很厚并且包含许多平坦的通量区域。