Water motion in moonpools - Empirical and numerical approach
Author Gaillarde G. and Coteleer A.
Title Water motion in moonpools - Empirical and numerical approach
Conference/Journal ATMA - Association Technique Maritime et Aeronautique, Paris, France
Month June
Year 2004

A moonpool is a large wall-sided hole in the bottom of a ship through which, for instance, equipment can be lowered into the sea or through which pipes (riser, cables or drills) are going. When properly designed and located on the vessel, the outside horizontal forces as well as vertical motion of the water are suppressed to allow safe subsea operations.
Vessels equipped with moonpools are drilling vessels, pipe-laying vessels, rock dumping vessels, survey vessels or diving support vessels.

The column of water inside the moonpool can, however, be excited at its own natural frequency resulting in large vertical motions described in the literature as piston mode. Internal sloshing can also occur, resulting in transverse breaking waves that are added to the vertical motions. Water motions in the moonpool can be excited through different mechanisms, in waves or in calm water with forward speed of the vessel.
This dynamic magnification can cause slamming on diving bells or ROVs that are launched, green water over the edge of the moonpool which can be dangerous for the crew, or can increase drastically the resistance of the vessel in transit conditions.

This paper presents the different conditions in which oscillations of the moonpool will hamper the operations of the vessel. Moonpool motions have been studied since a long time (see references [1] to [30]). Hereafter a summary is presented of the phenomenon, of the empirical solutions applied during model tests and on existing vessels, as well as new techniques to solve the problem numerically.

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