Investigation of moonpools as pitch motion reducing device

Abstract

Moonpools as a device for reducing pitch motion is investigated experimentally, numerically and by an approximate theory. A two-dimensional study is carried out of a rectangular body with two moonpools. Forced heave and pitch motion, as well as freely floating body in regular waves are studied. The body geometry is varied; two drafts and five different moonpool inlet configurations are considered; rounded and squared inlets, as well as vertical plates (appendages) extending below the inlet with three different depths. The outer corners of the body are square. There is a resonance as well as cancellation period in both pitch and heave, where the cancellation is the desired effect. By cancellation period we refer to a narrow period range where the pitch motion is nearly cancelled, due to the pressures induced by the moonpool piston-mode resonance. Our investigation reveals that the cases with rounded and square moonpool inlet geometries are most efficient in cancelling the pitch motions.