Risk of Sea Spray Icing to Offshore Structures

摘要

Severe sea spray icing is a hazard to fixed offshore structures working at subfreezing air temperatures. Spray icing on structures is different from that on ships. Ship icing is caused by water flung into the air when the ship’s bow collides with waves and can be ameliorated by changing course and decreasing speed. Exploration and production platforms, on the other hand, are fixed, and many designs have little area at the waterline to create spray by collision. In these cases, spray drops are generated when bubbles in whitecaps burst or as spindrift when the wind shears water from the crests of waves. Thus, spray icing on fixed offshore structures increases with wind speed and wave height. Spindrift formation, which is associated with very high winds, dramatically increases the liquid water content of the spray. In this paper, we analyze both North American Regional Reanalysis data and data from the National Data Buoy Center to illustrate the variation of sea spray liquid water content and icing severity with wind speed. Air temperatures, wind speeds, and calculated wave heights from the reanalysis data on a 32-km grid provide a regional view of spray liquid water content and icing from 1979 to the present. Data measured at buoys and coastal stations for varying periods of record supply sitespecific results for comparison with the gridded data. We also briefly discuss recent field observations.