The impact of piston and sloshing motions on added resistance from moonpool configurations

Moonpools are vertical watertight openings employed in the decks and lower structures of marine vessels and offshore platforms to allow drilling pipes and risers to be lowered into the sea. In the present work, the resistance performance of a drillship with varied moonpool configurations under calm water and regular wave conditions is investigated using a shear-stress transport (SST) k-ω model based on OpenFOAM. It is confirmed by comparing experimental and numerical results that this method can accurately predict the resistance of a ship with a moonpool. The numerical results suggest that the added resistance caused by a moonpool can be effectively reduced by optimally arranging the notch on the recess. A significant variation in the local flow field of the moonpool accounts for this. The implementation of the notch affects the development of vortices structures, thus transforms the free surface evolutions as well as the fluid resonance. Finally, the variation in pressure distribution contributes to a decline in the added resistance associated with the moonpool.