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Scientists Model Rogue Waves

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By MarEx 2015-12-20 18:50:38

Mariners have long spoken of walls of water appearing from nowhere in the open seas, but some scientists have disregarded the stories and suggested that rogue waves build up gradually and have relatively narrow crests.

New research from the U.K. University of Oxford in collaboration with the University of Western Australia, however, supports the anecdotal evidence. Rather than coming at the end of a series of increasingly large waves, rogue (or freak) waves emerge suddenly, being preceded by much smaller waves.

The mathematical modelling also demonstrates that the crests of these rogue waves are longer than the smaller waves that surround them.

Professor Thomas Adcock, of Oxford’s Department of Engineering Science, said: “The waves we’re dealing with here occur in deep water in the open ocean – very different from the waves you’ll see if you go to the beach, which is what most people are familiar with.

“In deep water, where waves are much less regular, you expect a larger wave from time to time. Our paper shows that, in contrast to what was previously thought, if you’re the observer on a ship, rather than seeing a gradual build-up of waves, the rogue wave will come seemingly out of nowhere.

“This happens because large waves tend to move to the front of the wave group.”

The research made use of mathematical modelling based on non-linear physics. The investigators used hundreds of simulations of random waves to analyze the differences between linear and non-linear wave dynamics.

“These findings fit the anecdotal evidence you hear from mariners,” said Adcock. “They often describe “walls of water” coming at them in the open ocean that are impossible to steer around – an observation supported by our modelling, which shows that rogue waves tend to have a much broader crest than traditionally predicted by linear theory.

“All of this means that in a very rough storm, you can’t simply assume you’ll get a warning before a freak wave hits. Seafarers need to be aware that a large wave may appear out of nowhere.”

Recent Documented Encounters (source Wikipedia)

MS Bremen and Caledonian Star (South Atlantic, 2001) encountered 30-meter (98 feet) freak waves. Bridge windows on both ships were smashed, and all power and instrumentation lost.

U.S. Naval Research Laboratory ocean-floor pressure sensors detected a freak wave caused by Hurricane Ivan in the Gulf of Mexico, 2004. The wave was around 27.7 meters (91 feet) high from peak to trough and around 200 meters (660 feet) long.

On April 16, 2005, after sailing into rough weather off the coast of Georgia, Norwegian Dawn encountered a series of three 70-foot (21 meter) rogue waves. The third wave damaged several windows on the 9th and 10th decks and several decks were flooded. Damage, however, was not extensive and the ship was quickly repaired. Four passengers were slightly injured in this incident.

Footage of Aleutian Ballad, (Bering Sea, 2005) in what is identified as a 60-foot (18 meter) wave appears in an episode of Deadliest Catch. The wave strikes the ship at night and cripples the vessel, causing the boat to tip for a short period onto its side. This is one of the few video recordings of what might be a rogue wave.

In 2006, researchers from U.S. Naval Institute theorize rogue waves may be responsible for the unexplained loss of low-flying aircraft, such as U.S. Coast Guard helicopters during search and rescue missions.

On January 24, 2009 the Augusto González de Linares buoy, located 22 miles north of Santander, Spain reported a wave of 26.13 meters, equivalent to 8 floors high, during a storm.

MS Louis Majesty (Mediterranean Sea, March 2010) was struck by three successive 8-metre (26 feet) waves while crossing the Gulf of Lion on a Mediterranean cruise between Cartagena and Marseille. Two passengers were killed by flying glass when a lounge window was shattered by the second and third waves. The waves, which struck without warning, were all abnormally high in respect to the sea swell at the time of the incident.

The Spanish Deepwater Buoys Network, in January 2014, measured a wave height of 27.81 meters (91.2 feet). The data was taken at the buoy Vilán-Sisargas (Cape Vilan) in Galicia (Spain) during the winter storms, which were particularly severe in Atlantic waters.

MS Marco Polo was struck by a rogue wave in the English Channel (February 2014), and killed a 85-year-old man and injured a woman in her 70s.