Rogue Wave by Prof Frederic Dias
A new project jointly led by a UCD researcher will literally shed light on the mysteries behind freak waves in the ocean - by looking at how such waves can arise in optical systems. Freak or ‘rogue’ waves can arise rapidly in deep waters and are distinct from the more familiar tsunamis, which follow a disturbance of the seabed and tend to pose a threat to ports, shallower areas and shores.
Rogue waves had long been reported by mariners and suspected in the loss of some vessels, but their existence was measured scientifically only in the 1990s. Today the origins of rogue waves still remain mysterious, but the MULTIWAVE project to be funded by the European Research Council hopes to use light waves to learn more about the deep ocean phenomenon. “What is really nice about this project is that it combines hydrodynamics and optics,” says Prof. Frédéric Dias, an applied mathematician at the UCD School of Mathematical Sciences, who specialises in ocean waves and hydrodynamics.
He is jointly leading the €1.8 million study with optics expert Prof. John Dudley from the Departments of Physics and Optics at the University of Franche-Comté and the CNRS in France. “Waves in hydrodynamics and optics share some common properties, such as dispersion and non-linearity,” explains Prof. Dias. “And the combination of these two properties can lead to the formation of some extreme waves.”
In the ocean, these are the extreme or rogue waves that can damage vessels unfortunate enough to be in their path. “You can have a relatively quiet sea, then you could have one or two or three much larger waves over a small area, typically one kilometre squared, and it typically happens over a short period of minutes,” says Prof. Dias.
So why use laser-based experiments to try and understand how extreme waves form in the ocean? “A rogue wave is fortunately a rare event in the ocean, so we don’t have that many data on the hydrodynamics,” says Prof. Dias. “And it’s difficult and impractical to do experiments - we can form these waves in the lab but they are under very idealised conditions.” A light-based system offers a much more practical test-bed in the lab, he notes. “In optics we can have the same kind of extreme wave event, so the main idea is to understand better the generation of these events and their propagation. And in optics, experiments are quicker and simpler to perform.”
The plan is to gather data from the optical experiments and look for clues about how the extreme waves form and grow. “In optics we can repeat the experiments over and over, hundreds or even thousands of times, and through statistics we can better understand the probability of occurrence,” says Prof. Dias. The investigators hope that findings from the four-year project will feed into better forecasting of freak waves at sea by identifying early-warning signatures linked to their occurrence.
"As part of the forecasting for the ocean, you have some forecasting on the likelihood of having rogue waves in the area but it is not very precise,” says Prof. Dias. “We want to improve on this and it has important application, because if the occurrence of rogue waves is quite likely, then captains will avoid the area.”
The ERC-funded project also plans to develop an ‘optical wave farm’ to look at the potential impacts of rogue waves on future wave farms of energy-harnessing devices at sea. “If there is an extreme wave that damages the devices in the farm, then maybe the design of the devices would have to take this into consideration,” says Prof Dias.
UCD collaborators on the MULTIWAVE project include Prof. Peter Lynch, Met Éireann Professor of Meteorology, Prof. Chris Bean, Associate Professor in the School of Geological Sciences, Dr Ted Cox, School of Mathematical Sciences, Dr Miguel Bustamante, School of Mathematical Sciences and Dr Lennon O'Naraigh, School of Mathematical Sciences. The grant will also support a PhD student, a post-doc and a research fellow and attract a senior professor from overseas to UCD work on the project.
