Simulating true ocean waves for the first time


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We are barely 20 years into this century, and already scientists have unravelled some of Earth’s biggest mysteries, from observing gravitational waves to discovering the Higgs boson.

And yet, there are fundamental processes sustaining life on our planet that we still don’t fully understand.

Perhaps surprisingly, there are still unsolved mysteries within one of science’s most well-known concepts: the water cycle.

Scientists can’t accurately quantify how much water evaporates from the ocean to form clouds, and how this may change under different weather conditions, or in different locations. By extension, their understanding of the role of clouds in a warming climate remains limited (although it is improving).

This is due to a bigger unknown. While we know that wind creates waves and causes evaporation (think of air blowing over a puddle), we don’t know what happens, exactly, when the wind interacts with the ocean to create waves.

Solving this puzzle is difficult, for the simple reason that taking wind and wave measurements in the middle of the ocean is challenging (to say the least).

“It’s unbelievably hard,” says Professor Jason Monty, a University of Melbourne expert in fluid mechanics.

“It’s hard to get there in the first place – there are not many research vessels in the world. And they tend to be reluctant to sail into storms.”

It’s also too expensive to put instrumentation on platforms, satellites can’t provide the required measurements of ocean winds, and computer modelling isn’t powerful enough. And then there’s the problem of scale; measurements need to be taken across the globe to gain a complete understanding of air-sea interaction.

A problem we need to solve

But this is a problem we need to solve. Essential processes happen thanks to activity in the ‘atmospheric boundary layer’ between the ocean and the atmosphere, where waves and wind meet.

This doesn’t just include evaporation to form clouds, but also processes like sequestering a large proportion of the Earth’s CO2 and regulating the ocean’s temperature.

So, Professor Monty and his team at the University of Melbourne are planning the “next best option” after direct ocean measurements: simulated ocean measurements, conducted in a laboratory.

“That’s also really tricky because you need such big facilities,” he says.

“You can’t simulate the ocean on a benchtop facility. In fluid mechanics, scaling processes down doesn’t often give you the right answers.”

But at the new University of Melbourne campus at Fishermans Bend, the team will be able to build a facility at a much larger scale, closer to true ocean wave conditions.

The campus, which is due to open in 2025 at the urban renewal site just south of Melbourne’s CBD, will be home to the world’s first ‘Extreme Air-Sea Interaction Circuit’.

The new wave tank will simulate the ocean in a state researchers refer to as ‘fully developed’; when waves reach the maximum peak dictated by wind conditions before naturally breaking. In calm conditions, the waves will be small; in stormy conditions they will be big. But they don’t grow infinitely in the ocean – there is always a natural ‘fully developed’ point in the real world.

We’ll be able to simulate whatever we need to, to examine phenomena like CO2 exchange, evaporation, how waves grow and how they impact on engineering structures

It is this point that has been impossible to achieve in the lab – until now.

Professor Monty and his team will maintain a fully developed state in their ocean simulator by using a huge continuous ring of water, a bit like an Olympic racetrack (to 0.5 scale). When they blow air over the ring, the waves will form and travel around the circuit, interacting with one another to maintain their fully developed state.

Conditions from calm to hurricane

The facility will be able to simulate everything from calm to hurricane-like conditions.

“It’s going to be a real engineering showpiece,” says Professor Monty.

“We’ll be able to simulate whatever we need to, to examine phenomena like CO2 exchange, evaporation, how waves grow and how they impact on engineering structures.”

The new wave tank’s ability to directly measure the interaction between the wind and waves will help answer important questions – including the unsolved mystery of how water evaporates to form clouds.

These answers, and more, will help address current unknowns in climate modelling, like how much CO2 is likely to be sequestered in the ocean and where.

The new facility will support other areas of research, too. These include underwater vehicle detection and models to help helicopter pilots land more safely on ocean vessels (the most common cause of injury among Australian military helicopter pilots).

It will even allow researchers to predict performance and advise on location and configuration of offshore wind turbines better than they have previously been able to.

“By modelling the wind / sea interactions we’ll be able to take much of the guess work out of these decisions,” says Professor Monty.

The new wave tank will take pride of place in the new campus building, something Professor Monty is particularly looking forward to.

“It’s spectacular to watch waves you’ve made in the lab,” he says.

“The new facilities will be visible to everyone in the building and, like anything of grandeur, it’s going to bring people together - students, academics and industry.

“And that is going to help not just with our own research, but with wider engineering challenges, too.”

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First published on 26 November 2021.

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