The interest in Arctic waters has been increasing in recent years under the influence of high oil prices and a decrease in sea ice extent and thickness. Production and drilling operations will likely more progressively towards the north where sea ice has retreated during the summer season. Some of these areas are also closer to calving glaciers and the possibility of encountering icebergs could be higher. Drillships and moored production vessels are considered as a possible way of developing Arctic hydrocarbon resources especially in areas where seasonal ice or icebergs are present. Hydrocarbon development in the Barents Sea will prove especially challenging. Iceberg or bergy pit collision with a moored production vessel can cause high impact loads to ship structures and mooring systems. The problem of iceberg collision is a major design consideration for vessels of this type. Iceberg movement is influenced by wind, waves and currents. Iceberg kinetic energy is consumed in a collision event until either the iceberg movements cease or it is no longer in contact with the ship hull. Energy can also be absorbed in deformation of the iceberg and the ship hull, ship movements and stresses in the mooring system. Mooring and riser system responses are crucial for a second vessel in station keeping and securing safe production. The paper describes the modeling of the capabilities of the moored ship to resist iceberg collision. Existing software packages are applied to help solve combined response of iceberg and ship local structure deformation and mooring system stresses. Probabilities of bergy encounters for a selected location in the Barents Sea are presented. Also, a preliminary assessment of shell plating for bergy pit impact is presented.

The paper describes different strategies for establishing current design profiles from sea bed to water surface, for use in analysis of subsea installation activities, e.g. during a pipe laying process or for dynamic analysis of risers. Measured data covering a period of 3–4 years for more than 20 measurement depths are used in the study. We investigate 4 strategies for depth profiles: General Purpose Profile: an envelope of the set of n-year speeds for individual depths, with unidirectional current at all depths. Empirical Event Profile: essentially a measured current profile which is deemed to be “serious,” i.e. potentially governing for design, scaled to adequately reflect a required return period. Whether a profile is “serious” or not would depend on the application. Response Based Profile: defined as the most probable profile causing an extreme response. It is obtained from design point current speeds from a reliability analysis of a selected response, while applying a detailed stochastic current model. Alternatively, an envelope of most probable profiles might be used.

Laboratory experiments on the growth of sea ice in a very thin plastic tank filled with salt water, cooled from above and insulated with thermopane, clearly show the formation and development of brine drainage channels. The sea-water freezing cell is 0.3 cm thick by 35 cm wide by 50 cm deep; the thermopane insulation permits the ice interior to be photographed. Experimentally, we observe that vertical channels with diameters of 1 to 3 mm and associated smaller feeder channels extend throughout the ice sheet. Close examination of the brine channels show that their diameter at the ice-water interface is much narrower than higher up in the ice, so that the channel has a “neck” at the interface. Further, oscillations occur in the brine channels, in that brine flows out of the channel followed by a flow of sea-water up into the channel. Theoretically, a qualitative theory based on the difference in pressure head between the brine inside the ice and the sea-water provides a consistent explanation for the formation of the channels, and the onset of a convective instability explains the existence of the neck. Finally, an analysis based on the presence of the brine-channel neck provides an explanation for the observed oscillations.