Two-dimensional moonpool resonances for interface and surface-piercing twin bodies in a two-layer fluid

•Hydrodynamic problem of interface and surface-piercing twin bodies in a two-layer fluid has been investigated.•A numerical model is proposed to compute the hydrodynamic coefficients and radiated surface and internal wave elevation.•Parametric studies have been performed to examine the effects of moonpool geometry and density stratification on the resonant fluid motion and hydrodynamic behavior.•It is found that the higher-order resonant modes are either correlated with standing waves, on the free surface or interfacial surface.

We study the moonpool resonances of two interface and surface-piercing rectangular bodies in a two-layer fluid due to forced harmonic heave motion. The problem is solved by employing a domain decomposition scheme with an eigenfunction matching approach. Heave added mass and damping coefficients, as well as inner and outer region (far-field) radiated wave elevations, are computed to examine the hydrodynamic behavior of the twin floating bodies. The numerical solutions have been compared with those for the case investigated by Zhang and Bandyk [1], where the floating bodies remain in the upper layer fluid. The present analyses reveal that there exist both Helmholtz and higher-order, also called sloshing mode, resonances in the two-layer fluid. It is found that, for an interface and surface piercing twin bodies, the higher-order resonances are closely related with both the free surface and internal waves inside the moonpool gap. Moreover, it is also found that low frequency forced motion can excite higher-order resonances through forming standing internal waves inside the moonpool. Parametric studies have been performed to identify the dependence of hydrodynamic behavior and resonant characteristics on geometry and density stratification.