Parametric roll prediction of the KCS containership in head waves with emphasis on the roll damping and nonlinear restoring moment

Abstract

The quantitative prediction of parametric roll of a KCS containership are conducted using a 5-DOF nonlinear time domain model based on the potential flow. In the model, linear radiation and diffraction forces are calculated by the STF method and transferred into time domain using IRF approach, while nonlinear restoring and F–K forces are calculated through pressure integration over instantaneous wetted surfaces. Roll damping is estimated using the Ikeda's method. The sensitive analysis on roll damping is conducted. Five different models for nonlinear restoring and F–K forces are discussed.It is confirmed that the five models overestimate the parametric roll amplitude. Model A considering only the nonlinearity of restoring forces caused by instantaneous ship position under still water is suitable for parametric roll prediction among five models. Moreover, accurate estimation of pitch motions is vital for parametric roll prediction. Through the sensitive analysis, it is found that roll damping affects parametric roll amplitudes but has no effect on the speed region where parametric roll occurs. The sensitivity of nonlinear quadric damping against parametric roll is small, while the sensitivity of linear damping is large. The sensitivity of roll damping against parametric roll for cases close to the speed threshold is significant.