Breaking the ice

A wave generator devised by a Canadian marine engineer could bring relief to ships stranded due to heavy ice formation in winter

Published: Monday 30 September 1996

winter ice, which severely disrupts shipping in colder climes, may no longer pose a problem. A Canadian marine engineer, Per Andersen, claims that he has found a technique to control ice formation. His wave generator projector could prevent sea water from freezing, by producing artificial waves ( New Scientist , Vol 151, No 2043).

When sea water is mechanically agitated, the deeper, warmer water gets mixed with the colder surface water. Andersen has tested his prototype in Canada. The machine is 7.5 m long. It consists of a floating helical roller -- similar to a large corkscrew -- supported at either end by pontoons. The roller is rotated in the water by an electric motor and this creates a train of electric waves several hundred millimetres high. According to Andersen, artificial waves could be made to have a higher height-to-length ratio, when compared to natural waves, and this helps them displace more water. As a result, greater amounts of water are drawn up from the warmer depths of the sea. According to Andersen, the maximum mixing occurs at the surface, just where the de-icing is needed the most. With the conventional propeller-driven de-icing system, mixing is less effective because particle velocities tend towards zero near the surface.

The testing of Andersen's system at Oshawa harbour in Ontario, Canada, produced artificial waves nearly 150 millimetres (mm) in height, exceeding Andersen's theoretical projections. The wave measured over 15 m in width and 100 m in length and definitely proved to be an impediment to ice formation. Moreover, the whole process use very little energy to produce waves.

In Toronto harbour, a single access channel makes ferry berths rather vulnerable to ice. Ken Lundy, manager of works and chief engineer with the Toronto Harbour Commissioner says that Andersen's wave generator could be used in areas where the build-up of ice in the berths tends to damage the quay.

"Most conventional machines such as bubbler systems and wind-driven turbines have an effect on just the vertical columns of water," says Andersen. His device should work over much wider areas. The mixing action of the artificial waves extends to a depth which measures half the wavelength, which is equivalent to around 600 mm for the wave generator projector. So the device should not stir up sediments from the lake bed, he adds.

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