Numerical Investigation of Internal–External Coupled Free-Surface Flow in a Liquid-Containing Tank

This study numerically investigates the internal–external coupled free-surface flow in a liquid-containing cylindrical tank using STAR-CCM+ and the Volume of Fluid (VOF) method. Three dimensional models were established, including an external wave-field model, an internal sloshing model for a baffled tank under horizontal harmonic excitation, and an internal–external coupled model. The external model was used to simulate the interaction between incident waves and a partially submerged cylindrical tank, while the internal model was employed to analyze the free-surface response of the liquid inside the tank. Based on these two models, the coupled model was further developed to examine the transmission of external wave excitation into the internal liquid domain. The results show that the proposed method can effectively reproduce both the external wave evolution and the internal sloshing behavior within a unified numerical framework. In the internal sloshing model with the elliptical baffle, the maximum free-surface wave height reaches 0.08 m, where as in the coupled case the internal free-surface response is about 0.002 m under the present simulation condition. Although these values correspond to different models and are not directly comparable, they indicate that the internal liquid exhibits distinct response characteristics under imposed excitation and external-wave-induced coupled excitation. These findings demonstrate that the STAR-CCM+–VOF framework is a reliable numerical tool for analyzing coupled wave–sloshing problems and can provide useful support for the hydrodynamic assessment of liquid-containing marine structures under wave excitation.