Wave drift forces and moments on two ships arranged side by side in waves

Hydrodynamic interactions are studied between two floating bodies situated side by side and closely as a model of LNG-FPSO system. Main interest is placed on the wave drift forces and moments which are of second order in the wave amplitude and can be computed from quadratic products of the first-order quantities. To solve the first-order radiation and diffraction problems with hydrodynamic interactions taken into account, a higher-order boundary-element method is applied directly to the whole wetted surface of two ships. The second-order wave drift forces on each ship are computed by the near-field method based on the pressure integration, and validity is confirmed by comparing the sum of the forces on each ship with the corresponding value computed by the far-field method. Experiments are also conducted in beam waves for the side-by-side arrangement of a modified Wigley model and a rectangular barge model. Measured results are in favorable agreement with computed results not only for the first-order hydrodynamic forces but also for the second-order steady forces in sway and heave.