Freak waves are so called because of their unexpectedly large size relative to the population of smaller waves in which they occur. The 84-foot- (25.6 m) high Draupner wave, observed in the North Sea on the 1st of January 1995, was one of the first confirmed field measurements of a freak wave. Now, a team of scientists from the Universities of Oxford and Edinburgh, UK, has recreated the famous wave.
Freak waves are unexpectedly large in comparison to surrounding waves. They are difficult to predict, often appearing suddenly without warning, and are commonly attributed as probable causes for maritime catastrophes such as the sinking of large ships.
University of Oxford’s Dr. Mark McAllister and colleagues set out to reproduce freak waves under lab conditions.
The researchers successfully achieved this reconstruction by creating the wave using two smaller wave groups and varying the crossing angle — the angle at which the two groups travel.
“The measurement of the Draupner wave in 1995 was a seminal observation initiating many years of research into the physics of freak waves and shifting their standing from mere folklore to a credible real-world phenomenon,” Dr. McAllister said.
“By recreating the Draupner wave in the lab we have moved one step closer to understanding the potential mechanisms of this phenomenon.”
It was the crossing angle between the two smaller groups that proved critical to the successful reconstruction.
The scientists found it was only possible to reproduce the freak wave when the crossing angle between the two groups was approximately 120 degrees.
When waves are not crossing, wave breaking limits the height that a wave can achieve. However, when waves cross at large angles, wave breaking behavior changes and no longer limits the height a wave can achieve in the same manner.
“Not only does this laboratory observation shed light on how the famous Draupner wave may have occurred, it also highlights the nature and significance of wave breaking in crossing sea conditions,” said University of Oxford’s Professor Ton van den Bremer.
“The latter of these two findings has broad implications, illustrating previously unobserved wave breaking behavior, which differs significantly from current state-of-the-art understanding of ocean wave breaking.”
To the researchers’ amazement, the wave they created bore an uncanny resemblance to ‘The Great Wave off Kanagawa,’ a woodblock print published in the early 1800s by the Japanese artist Katsushika Hokusai.
Hokusai’s image depicts an enormous wave threatening three fishing boats and towers over Mount Fuji which appears in the background. Hokusai’s wave is believed to depict a freak wave.
The laboratory-created freak wave also bears strong resemblances with photographs of freak waves in the ocean.
“We hope that this study will lay the groundwork for being able to predict these potentially catastrophic and hugely damaging waves that occur suddenly in the ocean without warning,” the scientists said.
The findings appear in the Journal of Fluid Mechanics.
M.L. McAllister et al. 2019. Laboratory recreation of the Draupner wave and the role of breaking in crossing seas. Journal of Fluid Mechanics 860: 767-786; doi: 10.1017/jfm.2018.886