Roll damping estimation via sway-roll coupled equation and the MOIRC (most often instantaneous rotation center) consideration

Abstract

This work focuses on the roll damping estimation performing free decay roll and regular beam wave for e 2D section of a FPSO in transversal plan. Two terms are concerns of this study, definition of rotation center and sway/roll coupling term effects on the roll damping. A unique pole is defined in condition of free decay roll and is used to develop a robust approach (3rd order approach) that uses system identification techniques to obtain damping properties from the decay tests. The research studies on instantaneous rotation center for free decay test and in regular condition experimentally and numerically, the locus of the IRCs is a frequency dependent straight line and devises a closed form equation for the IRC locus. Surprisingly, the so-called roll center is not a concept well defined for rolling ships or platforms that submitted to a wave field. This research proposes a new definition of MOIRC via Cauchy distribution which provides a deeper and remarkable insight into roll motion and roll damping of FPSO.