Grid-Nesting is a common method of local refinement when using structured quadrilateral grid in estuarine models. Nevertheless, various issues need to be improved, such as the Courant-Friedrichs-Lewy (CFL) limitations of external gravity wave and information exchange between two-way nesting grids. Based on the material conservation law, a novel scheme with Implicit, Grid-Nesting Elevation Solution (IGNES) and matched Nesting Boundary Flux Conservation Interpolation (NBFCI) was developed in this paper. The unstructured quadrilateral grid, finite-differencing, estuarine and coastal ocean model (UFDECOM) was update to UFDECOM-i. The gravity wave propagation experiment shows that the IGNES can relax the CFL limitations. Compared to traditional i-j two-direction strip refinement, the new scheme has higher computational efficiency. When the root-mean-square-error of elevation and current velocity increases by less than 0.05% and 0.2%, the calculation time is reduced by 40%. When simulating vortex motion, it overcomes the problem of simulation collapse caused by errors in nested boundaries. When simulating material transport, NBFCI scheme has smaller errors at the nesting boundary compared to quadratic interpolation, the high-order spatial interpolation at the middle temporal level (HSMIT) parabolic interpolation, upwind Advection-Equivalent interpolation, and HSIMT Advection-Equivalent interpolation scheme. The simulation results of the severe saltwater intrusion in the Changjiang Estuary in the late summer and early autumn of 2022 demonstrate that the UFDECOM-i with NBFCI and IGNES has higher computational efficiency and accuracy.

中文翻译：

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河口模型中双向嵌套四边形网格的新方案


网格嵌套是在河口模型中使用结构化四边形网格时进行局部细化的常用方法。然而，各种问题需要改进，例如外部重力波的Courant-Friedrichs-Lewy（CFL）限制以及双向嵌套网格之间的信息交换。基于材料守恒定律，本文提出了一种隐式网格嵌套高程解（IGNES）和匹配嵌套边界通量守恒插值（NBFCI）的新方案。非结构化四边形网格有限差分河口和沿海海洋模型 (UFDECOM) 已更新为 UFDECOM-i。重力波传播实验表明IGNES可以放宽CFL的限制。与传统的ij双向条带细化相比，新方案具有更高的计算效率。当高程和海流速度均方根误差增加小于0.05%和0.2%时，计算时间减少40%。在模拟涡运动时，克服了嵌套边界误差导致的模拟崩溃问题。在模拟物质输运时，与二次插值、中时间水平高阶空间插值（HSMIT）抛物线插值、迎风平流等效插值和HSIMT平流等效插值方案相比，NBFCI方案在嵌套边界处的误差更小。 2022年夏末秋初长江口严重海水入侵的模拟结果表明，结合NBFCI和IGNES的UFDECOM-i具有更高的计算效率和精度。