Iceberg management and impact on design of offshore structures

The subject ice management has been studied with the main objective to deduce a methodology that incorporates the effect of ice management on the structural reliability of offshore installations. This was done by first studying Arctic projects in the past and summarizes the learning’s. All available reports were unanimous and highlighted ice management as a key for the successes in the projects. Based on the reported experiences, an unambiguous definition of ice management was made: “Ice management is the sum of all activities where the objective is to reduce or avoid actions from any kind of ice features” Despite the number of similarities between sea ice management and iceberg management, it was decided to study each of the fields individually. The motivation for doing so was that iceberg management in general focus on reducing the frequency of impacts between icebergs and installations while sea ice management generally focus on reducing the sizes in the ice floe distributions and thereby reduces the severity of the ice actions. One methodology for including iceberg management and one for including sea ice management in the offshore installation design process has been proposed. In order to develop the models for ice management efficiency a number of studies of the various elements were conducted. Individual papers regarding subsurface ice intelligence, iceberg drift modelling, iceberg deterioration, iceberg deflection in ice and ice load variability has been published and are included in this thesis. Each of these papers is of importance for the proposed models for ice management efficiency. The possibility to disconnect an installation and escape the site has been considered both in the methodologies for iceberg management and sea ice management. When considering the number and magnitude of uncertainties both with respect to load calculations from icebergs and sea ice, it is concluded that disconnection capabilities should be considered in all Arctic projects. It was shown that icebreakers not necessarily are sufficient to reduce extreme or abnormal loads on a structure. However, there may still be a number of reasons for why icebreakers also should be considered in Arctic projects. The methodologies presented in this work provide adequate tools for evaluating the effect of various icebreaker fleets and iceberg management systems. However, the approaches rely on a number of tools and formulations with inherent weaknesses and advantages. The weaknesses are discussed and recommendations for further work in order to improve the models have been proposed.