Water motion in moonpools - Empirical and numerical approach

Moonpools are used on many types of vessels: cable-laying vessels, exploration and drilling vessels, production barges, research and offshore support vessels. They are used to launch and retrieve equipment, divers or diving bells, or lay cables or risers, in an environment protected from the waves. This use is valid as long as the column of water does not enter in resonant condition, excited by the waves and the heave motion of the vessel. In resonant condition, the oscillations can reach as much as three to four times the wave height. Another case of oscillation is observed in calm water with forward speed of the ship. The oscillations will cause a dramatic increase in calm water résistance. With large oscillations, the vessel will also start to heave and surge. Despite the research effort conducted on that subject, most of the solutions were found and are still found and validated experimentally. The present paper shows recent solutions applied to reduce the oscillations in the moonpool caused by the forward speed of the vessel. New numerical methods are also presented to solve the problem in transit and stationary conditions in waves, making using in particular of VOF models.