CEE Research Conversations: Why Rogue Waves Are Bigger Than We Thought
Summary
- Rogue waves, waves that are significantly larger than their neighbouring ones, threaten coastal and offshore safety, causing vessel capsizing, sinking of large ships, and destruction of structures.
- Along with his team, Assistant Professor Saulo Mendes at NTU School of Civil and Environmental Engineering analysed the impact of opposing and forward tidal currents on rogue waves.
- Unlike traditional models, the study found that rogue waves are both more likely to happen and reach greater heights under opposing and forward flows, offering insights into wave-current interactions.
- These perspectives provide the potential benefits of improving marine predictions, strengthening shoreline risk evaluations, and supporting offshore structure planning.
Rogue waves endanger coastal and offshore safety, resulting in vessel capsizing, sinking of large ships, and destruction of structures, highlighting the need for better forecasting to protect lives and infrastructure.
These powerful waves are linked to ocean processes at the coast and in the open sea. In either zone, interferences caused by complex ocean processes such as shoaling, crossing seas or current interactions disrupt the wave statistics, increasing the likelihood and intensity of rogue waves.
Researchers use simulations and laboratory studies to investigate the mechanisms that amplify the frequency and intensity of rogue waves. However, modelling the interaction between waves and tidal currents remains challenging.
Conventional models suggest that opposing tidal flows, where ocean currents are moving in the opposite direction of the waves, increase wave heights. In contrast, forward flows, where ocean currents travel in the same direction of the waves, reduce them.
A pictorial illustration of tides in motion
However, how this plays out in the complex conditions of the ocean is poorly understood.
Insights from the Southern North Sea
To bridge this gap, Assistant Professor Saulo Mendes and the team carried out a long-term observational study by collecting wave and current data from wind farms at the North Sea. The data was recorded between 2019 and 2022 at the FINO1 research platform.
Through analysing this data, the team examined the impact of opposing and forward tidal flows on rogue waves. This is the first long-term observational statistical study to do so.
Their discoveries provide new insights into wave-current interactions and were recently published in the Journal of Fluid Mechanics by Cambridge University Press.
Amplified waves
A key finding is that rogue waves are both more likely to occur and reach greater heights under opposing and forward flows, compared to conditions without any underlying coastal current.
The finding observed under forward flows challenges previous assumptions and came as a surprise to the research team.
“When we saw the data on following (forward) tides, we were shocked by the results because it was the opposite of what the textbook tells us,” explained Assistant Professor Mendes.
Both opposing and forward tidal currents lead to an increase in wave height followed by a decrease
These enhanced perspectives translate into potential real-world benefits such as improving marine predictions, strengthening shoreline risk evaluations, and supporting offshore structure planning.
Looking ahead
The team will next conduct controlled experiments at NTU’s School of Civil and Environmental Engineering (CEE) Hydraulics Laboratory to replicate their findings. By carrying this out in laboratories, they aim to better understand the factors influencing these wave-current interactions and ultimately improve the accuracy of predictive models.
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