Free surface and internal periodical waves generated by an oscillating floater in two-layer fluids using fully nonlinear numerical wave tank

Abstract

This study simulated free-surface and internal periodical waves generated by an oscillating floater in two-layer fluids using a numerical wave tank (NWT) with dual-fluid domains. Each domain was based on the potential flow and boundary element method (BEM). To validate the present NWT, the simulated results were compared with Kashiwagi's theoretical and experimental data, which results in good agreement. The fully nonlinear NWT results were compared systematically with the linear results to quantify their differences through higher-order components in barotropic (or surface wave) and baroclinic (or internal wave) modes both in the surface and internal waves. Free-surface and internal waves were analyzed systematically in terms of the two wave modes, respective-order components, several density ratios, and body-oscillation amplitudes and frequencies. For the present NWT(FN-NWT) with dual fluid domains, three different approaches for updating the instantaneous free surface and interface in the mixed Eulerian-Lagrangian (MEL) method were compared to cross-check the robustness of the developed schemes. When the forced oscillation amplitude and density difference are large, both surface and internal waves have strong nonlinearity, especially in the low-frequency region mainly due to the increased effects of the baroclinic mode. On the other hand, for the surface wave, the increased effects of primary and higher-order components from the barotropic mode are observed, particularly in high frequencies.