Page 18: of Maritime Reporter Magazine (August 2015)

EYE ON DESIGN

BY ALBERT AALBERS

Why bother about a bit of spray? In mild climate

Passage to the High North Passage to the High North latitudes rain and spray water is hardly a concern; it will run off and the ship happily car- – – When Spray MattersWhen Spray Matters ries on. But going to the High

North it’s different.

ith the economic develop- This will predict spray volumes and drop that two mechanisms have to be consid- was used. The jet thickness and velocity ment of the High North and sizes and then the thermodynamic and ered: jet forming due to rapid immersion exceeding the bow height are then com-

WArctic areas, partly driven by ballistic process in which the spray wa- of a bow section and jet forming due to puted. Hourly volumes of spray water the reduced ice conditions and partly by ter will develop an ice cover on the ship. impacts. over the bow can be computed by ap- opportunities to develop oil & gas and The generation of spray on a ship in Rapid immersion spray leads to a jet plying this method to a ship transiting in scarce mineral resources, maritime op- waves is a hydrodynamic No Man’s breaking up due to vorticity formed by an irregular sea. There is unfortunately erations in these areas are booming. But Land. In the past year a probabilistic friction along the hull, according to the scarce validation material available, al- safety of the environment, crew and their model was developed, taking into ac- well-known Kelvin- Helmholz instabil- though what we have matches satisfacto- ships is of prime concern. In the Arctic, count the prime elements of spray gen- ity process. The break-up in droplets af- rily. Results were published at the Arctic global warming doesn’t mean milder eration comprising: ter an impact event is much quicker and Technology Conference in Copenhagen conditions. • Ship motions has a close resemblance to the Richtmy- in March 2014, thereby inviting the in-

One of the operational aspects to be • Above water hull shape er-Meshkov instability process from a dustry and other interested parties to pro- considered is icing, formed by precipita- • Bow wave (at speed) shock wave. vide further validation material. tion and through seawater spraying onto • Wave non-linearity The main step in the modelling process The development of a realistic predic- the ship in cold weather. A major hazard A thorough examination of high-speed is matching the ship motions in waves to tion method for bow spray has shown leading to intense icing is a so-called video of large scale waves impacting on a jet generating process. For this, the hy- that the effect of bow shape, speed and ‘Polar Low,’ which are small, low-pres- a wall, thanks to the Sloshel JIP, found drodynamic theory of wedge immersion wave direction are very strong. Previous sure systems developing into storms models could hardly distinguish between with sharp temperature rises – typically ship size and they used only speed and from -20 to -1 °C – and this is combined wind parameters to predict spray forma- with precipitation. A ship in these con- tion at the bow. MARIN believes that for ditions will be cold, plus the seawater this reason it is fair to say that a major is cold and spray and precipitation will step forward has been made in the ability stick. to better predict sea spray induced icing.

Time Domain Simulation

In the SALTO JIP icing is one of the parameters considered in the time do- main simulation for operations in Arctic

The Author conditions. In the metocean modelling, provided by the Danish Meteorological

Albert Aalbers is Senior Researcher of

Institute, precipitation icing is comput- the R&D Department of MARIN, the

Maritime Research Institute Nether- ed, while MARIN has formed a co-oper- lands. ation with Delft University to develop a

E: [email protected] computational model for seawater spray. 18 Maritime Reporter & Engineering News • AUGUST 2015

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