New understanding of unusually large ocean waves could help inform the design of oil platforms and other offshore structures.

So-called rogue waves – which are exceptionally powerful and dangerous – can be exacerbated when they are produced by two sets of waves crossing at a particular angle, a study has found.

This phenomenon, which has been demonstrated in an experiment for the first time, is believed to have played a part in producing a 25-metre wave, known as the Draupner wave, which struck a North Sea oil platform in 1995. Experiments carried out in a world-leading ocean research facility have shown for the first time how large waves are affected by the angle at which they intersect.

Researchers used the 25-metre circular testing tank to study the complex interactions that occur when waves cross in open water. Researchers showed that when waves intersect at an angle greater than approximately 60 degrees, they cause the surface level of the ocean to rise. This adds to the overall height of the combined wave that results.

Experiments were carried out in the FloWave Ocean Energy Research Facility at the University of Edinburgh, the only testing tank of its type in the world. The tank is able to simulate ocean currents and waves of any type, which are monitored using overhead sensors.

Dr Ton van den Bremer, formerly of the University of Edinburgh’s School of Engineering, who led the study, said: “This improves understanding of rogue waves, decades after this aspect of their behaviour was suggested. The more we know about this dangerous phenomenon, the better equipped we will be to design offshore structures and to navigate the oceans.”

Dr Mark McAllister, formerly of the University of Edinburgh’s School of Engineering, who took part in the study, said: “These experiments provide new insight into how a heightened, or set-up, wave actually forms. They revealed that this behaves like a partial standing wave, which forms underneath waves as they cross. This insight allowed us to create a simple theory to predict when such waves might occur.”

The study, published in the Journal of Fluid Mechanics, was carried out in collaboration with the University of Oxford and supported by the UK’s Engineering and Physical Sciences Research Council.