Parameterization of Unresolved Obstacles in the Complicated Characteristic Inlaid Scheme

The presence of small islands and reefs, which are too small to be resolved within a computational grid, is a notable source of error in wave modeling. This study presents an approach that considers subgrid obstacles within the complicated characteristic inlaid scheme (CCIS), a wave propagation algorithm adopted by the WAve Model developed by the Key Laboratory of MArine Science and NUmerical Modeling (MASNUM-WAM) of the Ministry of Natural Resources (People’s Republic of China). While the CCIS can solve for wave energy flux with strong physical meaning, neither of the existing subgrid obstruction algorithms (i.e., GRIDGEN and UOST) can be directly applied within it. To develop this new approach, the transparency rate, estimated using the open-source software alphaBetaLab, is incorporated into the CCIS interpolation procedure. Additionally, a scaling factor is introduced to adjust the rate coefficient for various computational resolutions. Numerical tests, which included the Ryukyu Islands and the Batan and Babuyan Islands, revealed that the deviation in simulated significant wave height (SWH) between coarse and fine grids could be reduced from >0.5 to <0.2 m, with a background SWH of 4 m. Moreover, the mean absolute SWH error was reduced by 40%–70%. These results indicate that the newly proposed subgrid obstruction scheme effectively represents the effects of unresolved obstacles within the CCIS framework used by MASNUM-WAM.