Physically-constrained identification of hydrodynamics for a circular cylinder near the free-surface

This study develops a physically-constrained parametric identification framework for modelling depth-dependent hydrodynamic coefficients of a two-dimensional circular cylinder near a free surface at high Reynolds numbers. OpenFOAM simulations are conducted for varying submergence Gap Ratio. Using extracted CFD data and free-surface–vortex interaction mechanisms, parametric formulations are established for mean drag, mean lift, lift fluctuation amplitude, and vortex shedding frequency. The formulation captures the transition of near-surface flow states and their asymptotic recovery towards the infinite-depth limit. Comparisons with additional simulations and representative external datasets from both numerical and experimental show that the proposed functional structure remains applicable to mean-force-related coefficients, while oscillation-related coefficients are more sensitive to the specific dataset and parameter space.