UNCERTAINTY OF A METHODOLOGY TO ESTIMATE GLOBAL SHIP LOADS DURING INTERACTION EVENTS WITH ICE FEATURES

摘要

This paper describes a methodology to estimate uncertainty of global ice loading from measured accelerations, velocities and displacements. The global load can be estimated by the principle of rigid body dynamics of the ship during interaction events with different ice features. The accuracy of the methodology and estimated load levels were studied with uncertainty analysis. The challenges for the global load calculation from ship motions and challenges related to the uncertainty analysis are discussed extensively. An example case of global ice load and its uncertainty calculated from ship motions is presented. Ship motions in six degrees of freedom were measured using a motion reference unit during interaction events with different ice types during the ice trials of South African research icebreaker S.A. Agulhas Ⅱ in the Bay of Bothnia in the Baltic Sea in March 2012. The highest calculated peak load was 109 kN ± 17 kN with 95 % level of confidence. The analysis indicates that the uncertainty calculation can be applied to the global load calculation method. The uncertainty analysis is most sensitive to the changes in added mass and damping uncertainty. There are challenges related to the global load calculations from ship motions during impact with ridges or rubble fields so further study on the effect of the ship - ice interaction during these impacts is needed.