On the hydrodynamic behaviour of second-order harmonic induced sloshing-mode resonance in moonpool

Abstract

Fluid resonance in moonpool formed by two-identical rectangular hulls under the regular-wave action is investigated by employing the Computational Fluid Dynamics (CFD) package OpenFOAM®. In this study, the second-order harmonic induced sloshing-mode resonance occurs simultaneously with the first-order induced piston-mode resonance, generating a significant peak value on the free surface amplitudes in moonpool at the corresponding frequency. One period of piston-mode oscillation and two periods of sloshing-mode oscillation can be identified during one incident wave period. It is confirmed that the piston- and sloshing-mode resonances above are generated by the wave frequency and double frequency of incident waves, respectively. The non-monotonic variations of normalized resonant amplitudes in moonpool with incident wave amplitudes can be observed, which is the combined influence of free surface nonlinearity and energy dissipation on wave responses in moonpool. Finally, the second-order harmonic induced sloshing-mode resonance can also affect horizontal wave forces; while it has insignificant effect on vertical wave forces.