Study Reveals Ocean Waves Can Surpass Known Limits, Reaching Heights Four Times Steeper Than Expected
Fresh insights into extreme ocean waves could help engineers develop more resilient offshore structures, such as tidal turbines, experts say.
When ocean waves meet each other from different directions they can reach heights of up to four times steeper than previously thought possible, scientists have discovered.
Waves are often assumed to be two-dimensional – travelling and breaking in one direction – an assumption which underlies the design and safety of many marine structures today.
Yet in reality ocean waves can travel in many directions and rarely fit this simplified model, scientists say.
3D waves
An international team of researchers used the University of Edinburgh’s FloWave tank to recreate so-called three-dimensional waves, which have complex, multidirectional movements.
Three-dimensional waves occur when waves spread in different directions. At its most extreme, this results in a phenomenon known as crossing, where different wave systems meet and overlap. This can happen when the wind changes direction or during a hurricane.
The more spread out the directions of these waves, the larger the resulting wave can become, the team found.
New heights
Three-dimensional waves – which often occur offshore in deeper water – can be twice as steep before breaking compared to two-dimensional waves.
To the team’s surprise, 3D waves continue to grow even steeper even after breaking, the study found.
By rewriting the understanding of how waves behave, the new insights could advance weather forecasting and climate modelling, the team says.
The findings could also affect knowledge of ocean processes such as the transport of microplastics, plankton and how oceans absorb carbon emissions.
Measuring complexity
The research builds on the team’s previous work recreating complex waves at FloWave – including a famous freak wave which mirrored Japanese artist Hokusai’s iconic Great Wave off Kanagawa.
The study, published in Nature was funded by the Engineering and Physical Sciences Research Council (EPSRC) and the Science Foundation Ireland.
Creating the complexities of real-world sea states at laboratory scale is central to the mission of FloWave. This work takes this to a new level by using the multi-directional capabilities of the wave basin to isolate these important wave breaking behaviours.
Dr Thomas Davey
Principal Experimental Officer, FloWave, University of Edinburgh.
This is the first time we’ve been able to measure wave heights at such high spatial resolution over such a big area, giving us a much more detailed understanding of complex wave breaking behaviour.
Ross Calvert
Research Associate, School of Engineering, University of Edinburgh.
Unlike unidirectional (2D) waves, multidirectional waves can become twice as large before they break. Wave breaking plays a pivotal role in air-sea exchange including the absorption of C02, whilst also affecting the transport of particulate matter in the oceans including phytoplankton and microplastics.
Dr Sam Draycott
Senior Lecturer in Ocean Engineering, University of Manchester.