Field measurement of the reduction in local pressure from ice management

摘要

Local ice pressures are an important design consideration for vessels performing offshore stationkeeping operations, particularly in the late spring and early fall shoulder seasons when they tend to govern over global loading in the development of operating limits. This paper presents analysis of full-scale data that demonstrates the reduction in local pressures provided by ice management. The data was collected during the Oden Arctic Technology Research Cruise in 2015. The distinguishing aspect of this program was the use of two icebreakers,OdenandFrej, which provided the unique opportunity to conduct a full-scale stationkeeping trial in realistic managed ice conditions. Previous local ice pressure data collection programs have occurred during transit in unmanaged ice, ramming of multi-year ice and bergy bit impacts. These have been used to establish recommendations for local design pressures, however they are not completely representative of conditions while stationkeeping in managed ice. In this study the up-crossing rate method was used to analyze local pressure data collected from strain gaged load panels on theFrej'shull. The results indicate that local pressures from stationkeeping in managed ice are two to four times lower than the transiting cases most analogous to previous data. This provides a sound basis for advocating local design pressures that are lower than current recommendations, and also more representative of actual operating conditions. This can potentially extend the operating envelope of offshore vessels leading to significant savings, while still maintaining limits consistent with accepted risk profiles.