A STUDY OF MOTION MINIMIZATION DEVICES OF FPDSOS

One of the important aspects of FPDSO is seakeeping performance since the operability and safety is directly affected by this performance. The design of riser and mooring system lifetime is also related to this performance in the sea. In Turret FPDSO, the Turret position is normally located on the forward position of the ship to provide a weather vane characteristic, decreasing the environmental forces on the ship.
On the other hand, as far is the turret position from the ship center of gravity, higher vertical motion due to heave and pitch motions will occur. Even for DICAS system, the mooring lines are located on the extreme fore and aft part of ship. Therefore, the minimization of motions is desirable to reduce induced vertical motions on the top of mooring and riser lines. The moonpool is necessary for drilling operation and could be used to pass through risers to the production units. Some studies showed that if it is given an appropriate dimension and a restriction of area in the bottom, the moonpool could work as a passive tank to reduce the vertical motions. Another device that is frequently used to roll motion minimization is the bilge keel. Since there is no concern with the advance resistance, the bilge keel size could be extended to a “structured skirt”. Therefore, this paper will present some numerical and experimental studies concerned with moonpool and “structured skirt” effects on the new hull FPDSO motions.