Numerical modelling of marine icing on offshore structures and vessels

Abstract

A numerical model for predicting icing on offshore structures and vessels has been developed and implemented. The model calculates the icing caused by freezing sea spray, and focuses on two distinct sources of spray - spray from droplets blowing off whitecaps on the sea surface, and spray from waves colliding with the vessel. The implementations of both wind-induced and wave-induced sea spray are based on existing theoretical models, and are combined with a thermodynamic model for the icing process. The model may be used to calculate icing on reference objects or structures on the vessel. In addition, algorithms have been developed so that the model can be applied to polygon-based vessel geometries, calculating the icing distribution over the entire vessel. The model has been applied to meteorological observations and hindcast data for locations in the Norwegian Sea and Barents Sea, in particular at the locations of the Norne field and the undeveloped Skrugard and Shtokman fields. The results indicate that the icing will be comparable at the locations of Skrugard and Shtokman, and that both the frequency and severity of icing events will be far greater for these two locations than for Norne. Although conditions at Shtokman are colder than at Skrugard, the higher winds and waves near Skrugard will increase the available sea spray in the model, thus making the number of severe icing events more similar for the two locations.