Numerical modeling of two-dimensional sea spray icing on vessel-mounted cylinders

• A new two-dimensional sea spray icing model
• New formulas for the time-average sea spray mass flux against a trawler and the duration of a single spray
• Finite difference method used to solve the icing equations (extension of the Lax–Wendroff method)
• Comparison between the numerical model results and real icing observations on a trawler

This report presents an important extension of the first Norwegian marine icing model: ICEMOD. That model was one-dimensional in the sense that the brine film covering the accreted ice moved only in one coordinate direction. The improved model, ICEMOD2, presented in this article is two-dimensional. After a thorough presentation of the mathematical model and an outline of the numerical method used the model is applied to cylinders with various diameters. The brine film is acted upon by both wind and spray stress forces and the gravity force. Model results are compared with real icing observations on vertical cylinders placed on the observation vessel “Endre Dyrøy” (former trawler) and satisfactory agreements are obtained. A mean spray mass flux formula based on spray measurements on the same vessel was used. A simple theoretical formula is used to calculate single spray duration. Perhaps somewhat surprisingly it turns out that maximum ice thickness often occurs at some angle away from the stagnation line. But this form of the ice profile has actually been observed by others. Finally, sensitivity tests were done to examine the possible effect of the vessel speed, spray salinity, cylinder heeling angle and relative wind heading. It turns out that variations of the relative wind direction have the most significant effect upon vessel icing. The model tests show that more ice accumulates when the heading increases, the vessel speed increases or the spray salinity decreases. If the cylinder is not vertical ice accumulates slightly asymmetrical around the stagnation line, provided a sufficient wet icing mode is present.