Study on the influence of the moonpool on the smooth water resistance performance of the ship

Modeling Techniques and Control Strategies for Jack-Up Rig: A State of the Art and Challenges

Hydrodynamic Study on Water Column Oscillation of Varying Cross-Section Moonpool and Its Effect on Resistance of a Drill Ship

A moonpool is meant for access to underwater part from onboard ship. It is located mostly at the midship region of the drillship for under water operations either in square or rectangular in shape. In drillship, these openings are used for supply the raiser and other drilling equipment through it. This drillship moonpool is mainly subjected to two types of motions of water mass inside the column namely, piston mode and sloshing mode. The piston mode is a type of water particle motion where the water particles can be seen as a “plug” which oscillates in the vertical direction. In sloshing mode the movement of water plugs in the horizontal direction and makes a standing wave effect on the side wall of the moonpool. This piston and sloshing mode play a major role in vessel’s surge and heave motion while the drill ship in operation/transit and its lead to a larger quantity of green water on the weather deck. In the case of rectangular moonpool the dominating mode is sloshing where as in square moonpool the piston mode of oscillation is the dominant one. Because of this water motion inside the moonpool the drillship regular activities may be affected. Also this water motion is the reason for a large quantity of sea water can enter on to the continuous deck of the vessel. If this quantity of water added with the green water at the deck because of the waves then the net effect may be cause critical situation of the vessel. Also this water entry leads to the down time period of the drillship, because the crew members working on the drillship feel instability over the deck. Therefore this entry of water to the deck should be minimized to better performance of the drillship.

CFD simulation of the moonpool on the total resistance of a drillship

Moonpools are openings right through the hull from continuous deck to bottom of the ship, allowing equipment or mini-submarines to be put into the water at a location on the vessel with minimum ship motion. Open moonpools in a drillship are causing additional resistance when the ship is in forward speed. It was shown that the water inside the moonpool started to oscillate at forward speed. The water mass in the moonpool is subjected to sloshing and piston modes. The vertical motion is piston mode and the longitudinal one is called as sloshing mode. This water particle motion inside the moonpool is mainly depended on the geometry, moonpool depth, and encountered wave frequency. Out of this, moonpool geometry is one of the key factors for the performance of the moonpool. The varying cross-section geometry is one of the practically possible and economically feasible solutions to reduce the oscillation to a considerable level is attempted in this paper. Also the resistance caused by the moonpool and the free surface generated around the hull is investigated with the use of computer simulation.

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Surendran Sankunny

Papers

Hydrodynamic Study on Water Column Oscillation of Varying Cross-Section Moonpool and Its Effect on Resistance of a Drill Ship

CFD simulation of the moonpool on the total resistance of a drillship

Influence of moonpool on the total resistance of a drillship by the effect of water motions inside the moonpool