Researchers from the HSE campus in Nizhny Novgorod, together with scientists from Australia and Japan, have built a model explaining the occurrence of abnormally high waves on the sea surface. Also known as rogue waves or killer waves, they often lead to accidents in the sea. The study findings are published in Physical Review Letters. The paper was selected as the Editor's Suggestion for its significance, novelty, and wide application. The research was financed by a megagrant from the Russian government as part of the 'Science and Universities' National Project and a grant from the Russian Foundation for Basic Research (RFBR).
Abnormally high waves known as rogue waves occur unexpectedly and often cause tragic accidents involving ships and platforms on high seas and off the coast. Unlike tsunamis, which are formed as a result of submarine earthquakes or landslides, the occurrence of rogue waves is not associated with catastrophic geophysical events. Instead, rogue waves have been explained by the physical mechanism of self-modulation, when intense and short wave groups formed without any external impact generate unexpectedly high waves.
Back in the 1960s, Soviet scientists of the 'Gorky school' (Gorky was the name of Nizhny Novgorod at the time) were among the first to study wave self-focusing and self-modulation. The effects they discovered are widely used in physics today. The new study findings substantially generalise the applicability of the existing wave self-modulation theory and suggest analytical solutions such as rogue wave prototypes.
The researchers used laboratory experiments and direct numerical modelling to demonstrate that counterpropagating waves do not have the effect of weakening the amplification of a rogue wave. The study shows that rogue waves can occur in the fields of standing waves that form when waves approaching the shore are reflected from obstacles such as stationary structures or steep cliffs.
The experiments were conducted at the University of Sydney in a laboratory equipped with a wave generator. The first wave train generated by a moving paddle ran through the flume, was reflected from the opposite wall, and ran against the second generated wave train. The second wave train produced a disturbance as it moved, which evolved into a short group incorporating very high waves.
Numerical modelling was conducted using the full system of hydrodynamic equations as well as within a simplified framework which still takes into account the key physical effects. This approach made it possible to simulate waves' evolution at longer distances than those available in laboratories worldwide.
This result has been achieved thanks to a longstanding collaboration between international teams. We were able to simulate a theoretically predicted effect on the actual water surface under realistic marine conditions. We assume that the detected effect may also be characteristic of other physical environments.
The researchers plan to continue their study by examining related effects in more complex wave configurations (cross-wave systems, waves of varying lengths, and others).
Text author: Agafon Selitrennikov
Co-author of the paper, Leading Research Fellow, International Laboratory of Dynamic Systems and Applications