Comparative numerical study of repulsive drift forces and gap resonances between two vessels floating side-by-side in proximity in head seas using a discontinuous HOBEM and a constant BEM with boundary matching formulation

The hydrodynamic interaction between two bodies floating side-by-side in close proximity was studied using a nine-node discontinuous higher order boundary element method based on the conventional two-body formulation (9dHOBEM) and a constant boundary element method based on the boundary matching formulation (BM-CBEM). It has been shown that unrealistic peaks on the first-order hydrodynamic coefficients at the first resonant frequency can be attenuated by both BM-CBEM combined with the free surface damping and 9dHOBEM combined with the wetted surface damping. It has also been shown that both the free surface damping and the wetted surface damping have apparent attenuation effects on the amplitude of radiation and scattering waves respectively at the first gap resonant frequency known as the Helmholtz resonant frequency. Almost perfect cancellations between the radiation and scattering waves in the gap between freely floating twin caissons in head seas have been found at the first two resonant frequencies. The significant peaks on the drift forces were found at the frequencies higher than the Helmholtz resonant frequency. Using 9dHOBEM and tuning the wetted surface damping parameter with experimental results, the unrealistically large numerical values of repulsive drift forces in head seas can be reduced reasonably.