Modelling the ballistics and thermodynamics of bow spray droplets for marine icing

Abstract

In preparation to the SALTO JIP (Safe Arctic Logistics, Transport & Operations) work was done towards developing an improved model for icing due to sea spray at the bow of a ship. The so-called SHIPICE model may be used in a probabilistic risk-based approach and consists of two main segments:
1. Probabilistic modeling of spray water volumes and the break-up in droplets rising above the freeboard, and
2. Modeling the ballistic and thermodynamic processes of these droplets when falling and freezing to the ship.
The present paper deals with the second phase of the SHIPICE model. The modeling of marine spray shows that spray is a phenomenon with sharply increasing volumes with speed and sea state. Furthermore, the droplet size of spray rising above the freeboard has a distinctive effect on the distribution of the spray volume landing on deck. The thermodynamic freezing model takes into account intermittent wetting and run-off, and depends also on the droplet size distribution due to in-flight cooling of the droplets when falling to the ship. The results from the model seem realistic when computed icing growth is compared with two measured icing events reported in literature. The development of SHIPICE will allow users to dimension pre-cautions to the area and time of operation. Additionally, it will provide an improved basis for regulations and guidelines (e.g. ISO TC 67 SC8). For ship owners, it will help evaluate the susceptibility of their ship to marine spray icing.