Icing Rate on Stationary Structures Under Marine Conditions

摘要

Icing on stationary structures such as oil rigs is becoming an increasingly serious problem as offshore drilling operations in the subpolar regions become more common. Little information exists on this subject. Extensive observations have been made of icing on the upper structures of moving ships, but the complexity of this problem makes analysis of the results very difficult. Even the generation of water drops in this case involves many factors, such as windspeed, wave direction relative to the bearing of the ship, and size and free-board of the ship. On stationary structures, however, the problem is much simpler, since the major factor in drop generation is whitecaps produced by wind, and no motion of the structure is involved. In the present study, a theoretical calculation was made by combining the data available on the generation of drops by wind with data on the proportion of ice frozen from the collected water. The rate of ice accumulation on stationary structures was calculated using published data. The results were compared with icing measured on board ships. Although the general trend of this calculation indicated parallelism with the onboard measurements, the measured ice accumulation rate on ships needed a 5 to 8 m/s higher windspeed to correspond with the calculated rate for stationary structures.