Abstract

When polar ship navigates in the Arctic region, the ship side structure may be impacted by different shapes of ice floes, which may produce certain permanent plastic deformations. Therefore, based on a simplified ice-side structure collision scenario, a series of laboratory model tests of ice-plate impact are conducted to investigate the dynamic responses of plate and ice damage. In these tests, the ice geometries are changed by using different shapes of the front end of ice models. The parametric analysis for different ice shapes is carried out to study the mechanisms of the influences of ice crushing characteristics on plastic deformations of plates under ice impacts. Besides, the critical load case and ice impact scenario can be found by comparing the plastic deformations of plate specimens obtained from the model tests, providing some guidance for strength assessment of ship plates under ice floe impacts.

Introduction

Due to global warming, more and more voyages will cross the Arctic water nowadays, while ice floes in the polar channels give a great potential threat to them. Statistics show that ice collision is one of the main causes of the polar ship accidents. According to the Hänninen's report (2005), 30% of the damages were caused by ice-ship interaction and 15% of hull damages occurred in the ice regions under compression in the severe winter during 2002-2003. During the ice and ship impact process, much of the energies will be absorbed by the ship in a short time, which will produce the permanent plastic deformations or damages of ship plates. Moreover, different shapes of the ice floes impacting the plate will cause different degrees of damage due to different ice crushing characteristics.

Much works has been done to study the dynamic behavior of ship structures under ice impact by full-scaled tests or scaled model tests. The full-scaled test can predict really the dynamic responses of ship structures under ice impact. Gagnon (2008) used a new Impact Panel to measure forces and pressures during collisions of a ship (CCGS Terry Fox) with bergy bits and a small iceberg, and found that pressure on the hard zones increased as the hard zone area increased. Johnston et al (2008) described the forces that were measured on the CCGS Terry Fox during just over 50 collisions with glacial ice. Ritch (2008) carried out a field test program with the CCGS Terry Fox. From the pressures measured, pressure-area curves were developed, total forces were calculated and the correlation between various parameters such as velocity and bergy bit mass was analyzed.

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