Estimation of characteristic snow loads on offshore structures in the Barents Sea

Abstract

Snow accumulating on offshore structures can reduce freeboard and stability, block equipment and valves, and reduce operability of the platform or ship. It is thus important to assess risk related to snow accumulation prior to offshore operations in cold climates. However, offshore snow conditions in the Barents Sea are largely unquantified.In the present study, methods are developed to investigate snow loads on offshore structures in the Barents Sea. A model to establish time series of snow loads using a 10-day snowfall model, with or without snow transport by wind has been implemented. Methods to estimate extreme value statistics have also been applied, specifically using the generalized extreme value distribution. These models have been used with input from meteorological data from NORA10 hindcast grid points covering the entire Barents Sea to provide estimates of extreme snow loads. The results for a 10-day snowfall model without drift show 100-year return levels of snow load to be in the range 0.7kPa to 1.15kPa in large parts of the Barents Sea. Indication of a declining trend in the extreme values has also been found in the southern Barents Sea. In this area, the trend indicates a 20% decrease in extreme snow accumulation during the 58years of study. The hindcast archive NORA10 was validated against observations to evaluate uncertainties in the hindcast. NORA10 estimates on average more precipitation than observed at all locations, but the distribution of extreme precipitation is similar to the observations. Due to an expected undercatch of snow in the observations, it is likely that NORA10 underestimates extreme precipitation.