Abstract

This study has evaluated the ice-induced fatigue life and analyzed the fatigue damage index.

Recently, the number of ships (icebreakers) such as LNG carriers and oil tankers navigating the ice-covered oceans is increasing. It is necessary to assess the risk of fatigue damage during the ice navigation. Icebreakers are under repeated impact and contact loads by the ice in the process of navigating through the ice on the water. Micro-cracks due to repeated ice loads may lead to a fatigue failure, namely ice-induced fatigue.

Fatigue assessment of icebreakers has become one of important standard evaluations. ISO 19906 states that the fatigue limit state should be considered when designing arctic offshore structures. Lloyd's Register (LR) has recently developed a fatigue design assessment procedure, ShipRight FDA ICE, for the icebreakers. The fatigue damage is estimated by the distribution of the ice-loads and the structural responses due to the loads. The purpose of this procedure is to reduce the risk of fatigue damage, and the LR emphasizes assessment of the structural integrity of the ships. Also they suggested a simplified fatigue criterion.

Field measurements of local ice loads were carried out two times in the Arctic Ocean using the Korean first icebreaking research vessel, the ARAON. In 2010, she navigated ice-covered oceans, performing icebreaking tests repeatedly against a medium-size floe. On August 2013, new field measurements were performed under the similar condition as the 2010 study in the Arctic Ocean. The ice load data was measured for approximately 38.7 hours. The data was measured using a strain gauges system.

The analyses of fatigue damages and fatigue-life measurements on the side-shell in the bow thruster room of the ARAON are reported in this paper. The fatigue analysis is based on the maximum and mean value of the data measured in 2010 and 2013 Arctic voyages.

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