In the last years hydrodynamic interaction between two vessels in side-by-side configuration is one of the hot issues in offshore floating body dynamics. The paper investigates the hydrodynamical aspects of a floating two body system. The topic is geared towards analysing the influence of the vessel’s draft in side-by-side configuration and in head sea condition. The need to solve this problem arises when one wants to study the hydrodynamic variation for the various stages of a offloading process with a defined operational gap. The system is composed of a barge and a prismatic geosim with a fixed gap value and with two barge’s draft values. Regular wave tests have been performed in the model basin of CEHINAV-Technical University of Madrid (UPM). The motion for the geosim was restricted to the surge, heave and pitch motions (just motions on the vertical plane), whereas the barge was kept fixed. The costant gap value is guaranteed during the tests. A numerical model has been created with WAMIT and with an in-house time-domain Rankine Panel Method (TDRPM). In each case the numerical and experimental response amplitude operators (RAOs) are obtained and compared, researching the limitation of the numerical codes for the gap flow modeling. In the past the gap effects on the numerical results have been studied varying the gap value finding resonant behavior in terms of motion and wave amplitude RAOs. Now the draft value contribution on the hydrodynamic effects is investigated. Also in this case the numerical results indicate a resonant behavior in determined frequencies in motion as well as in wave in the gap, that is not found in the tests. In order to overcome this problem, a procedure for introducing an external damping factor that attenuates the wave amplitude along the gap in the time-domain RPM is evaluated based on the experimental data.

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