engleski

An investigation of dynamic instabilities caused by parametric rolling of C11 class containership

The trend of container ship fast growth is due to the fact that the containerized transportation is becoming more and more attractive. The increasing demand in container transportation is met by use of new generation of container ships including Post-Panamax and Malacca-max containers. Unfortunately, this new ships are severely hit by parametric rolling so new loss of containers in seas and accidents of container vessels are continuously reported from many ship-owners. The term parametric roll is used to describe the phenomenon of large unstable roll motion suddenly occurring in head or stern seas. The prime reason for parametric rolling is the variation of the ship’ s stability characteristics because of the constant change of the underwater hull geometry as waves travel past the ship. Hull forms with pronounced bow flare, flat transom stern and wallsided midship section are most vulnerable to parametric roll due to contribution of such features to the variation of the ship’ s stability characteristics. Possible consequences could be very serious ; loss of containers, machinery failure, structural damage, and even capsize. This paper addresses the technical background based on the operational guidelines from ABS classification society in order to outline a method in identifying the effect in coupling of pitch and extreme rolling, as well as to avoid or to reduce the effects of such phenomenon. Brief explanation of the physics of the parametric roll resonance phenomenon which follows the structure of the proposed Guide in longitudinal (head and following) waves is given. Analysis criteria to determine if a particular vessel is vulnerable to parametric roll (susceptibility criteria) is conducted through ABS Guide for the assessment of parametric roll resonance in the estimation of container carriers attainable ship speed and heading. A non-linear, time domain simulation program for predicting ship motions instabilities in waves is utilized to determine how large these roll motions might be (severity criteria), which are needed while considering the influence of vessel operational restrictions on the tendency of containerships towards parametric rolling. This study is conducted for a post-Panamax, C11 class containership which proved to be particularly prone to exhibit this behavior. Comparisons between numerical and experimental (in progress) results were performed in order to demonstrate the validity of the proposed technique for parametric roll prediction in regular as well as in irregular waves.

parametric rolling; containership

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