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Issue one 2012 - Issue #15


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Perfect storm

Story by James Hutson

View articles in related topics: Ocean Engineering, Sustainability & The Environment, Physics


Alexander Babanin
Professor Alexander Babanin. Photo: Eamon Gallagher

Swinburne leads an international conversation about predicting and protecting against extreme weather events.

Four of the world’s seven tropical cyclone formation basins directly affect Australia and South-East Asia. The impact of these severe storms can be devastating to local communities and nations both in terms of injury, loss of life and property damage.

 

Satellite data and sophisticated computer modelling has significantly improved knowledge of how these extreme weather systems develop and their behaviour in the past 20 to 30 years. However, predicting cyclone intensity remains a challenge, which is impacting on efforts to better protect people and property, according to Professor Alexander Babanin.

 

“Apparently some physics is missing,” says Babanin, Director of Swinburne’s Centre for Ocean Engineering, Science and Technology, based at the Hawthorn campus in Melbourne.

Surprisingly, what’s missing are waves. Currently wave physics exists only as an outlying parameter in the vast majority of climate models. But sufficiently large waves that occur in extreme events, like tropical storms and cyclones, can mix the upper layer of the ocean with the cooler deeper parts, exchanging heat and carbon dioxide with the atmosphere, which affects weather and climate.

 

It’s this desire to better protect people, property and the environment by patching and refining the science behind current large-scale weather and climate predictions that is the unifying theme of much of the centre’s research at both the Hawthorn campus in Melbourne and Sarawak campus in Malaysia.


Big storms aren’t the only cause of large waves. The same mechanisms that cause the formation of wind-generated waves may help explain a maritime legend.

 

Nine-storey waves

In 1995 marine scientists and engineers were presented with proof of a monster. Video and lasers measured a 26-metre (nine storeys) high rogue wave passing the Draupner oil platform in the North Sea. Improbably rare, freakishly tall waves once regarded as unlikely myths were suddenly acknowledged to be all too real.

 

But extreme wave heights are not simply the result of waves adding together to form bigger waves. Babanin and his colleagues were investigating the non-linear mechanisms which are responsible for the formation, steepness and breaking of wind-generated waves in the open ocean. They found their model could also account for the formation of rogue waves up to 30 metres (10 storeys) tall.

 

Rogue waves are not tsunamis. A tsunami is a vast displacement of water caused by earthquake or submarine landslide. Tsunamis are rarely noticeable in the open ocean, but can wreak havoc over huge areas only when the volume of fast-moving water approaches the shore. Rogue waves are almost the opposite. They usually arise in open sea, are very localised and very noticeable. The giant wave described in Sebastian Junger’s book The Perfect Storm and later depicted in the movie of the same name, was a rogue wave.

 

In 2004 the European Space Agency suggested rogue waves associated with severe weather were the mostly likely cause of the loss of 200 supertankers and container ships exceeding 200 metres in length during the last two decades.

 

Offshore engineering

Swinburne lecturer and researcher in water, port engineering and oceanography, Dr Alessandro Toffoli, found when a stable group of waves enters an ocean current, it can trigger processes that cause one wave in the group to rapidly increase in size and go rogue.

 

This helps highlight likely rogue wave areas beyond the known trouble spots like Cape Agulhas of South Africa, Kuroshio off Japan and the Gulf Stream off the eastern United States.


“The work we’ve done is very much theoretical; in principle it can be applied in offshore engineering, for example. As we’re predicting rogue waves, this has safety implications for marine operations, but it can also help design practices to properly account for the wave-load on structures.”

 

It is this relatively frequent risk that rogue waves pose to offshore infrastructure that has industry’s attention. Woodside, a Swinburne ocean engineering partner, manages platforms and pipelines in sites such as the North West shelf that must be designed and engineered to withstand not just rogue waves every few years, but one in five thousand year events.

 

Swinburne’s predictions can calculate maximum wave heights, which will determine the design of offshore platforms and can also advise as to the day-to-day wear and tear of ordinary wave interactions. This is particularly useful if local wave patterns begin to vary under the influence of climate change. And there is no doubt, the oceans are changing.


Bigger waves, faster winds

The most comprehensive study of its kind has recently found that oceanic wind speeds and wave heights increased significantly over the last 25 years.

 

Swinburne and Australian National University researchers used satellite altimeter data sets from around the globe spanning 23 years from 1985 to 2008, recently developed by the Swinburne team of Babanin, Professor Ian Young, now Vice-Chancellor of the Australian National University, and Dr Stefan Zieger.

The study found the change especially true of the high winds and the big waves. For extremely high winds, speed increased by a yearly average of 0.75 per cent. In some parts of the ocean, extreme waves increased by up to one per cent per annum. 

 

“For example, today the average height of the top one per cent of waves off south-west Australia’s coastline is around six metres. That’s over one metre higher than in 1985,” Babanin says. 

 

Future research

Babanin has a clear vision of where the centre’s research will lead. “Right now small-scale wave physics and large-scale climate modelling exist separately. To improve prediction, large-scale models will have to be coupled with wave models. Right now very few centres have taken this approach. In 10 years it will be everyone.”

 

As these integrated models are improved and refined, he hopes they can be used to inform other oceanographic disciplines like ecology. Ocean and atmospheric mechanisms don’t occur in isolation. Rainfall and drift affect sedimentation, changes in wave climate affect the movement of nutrients and these in turn impact on the biodiversity and sustainability of a marine community.

 

Swinburne is bringing this expertise to discussions with some 50 collaborating research groups across Australia, Europe, North America and Asia, including Malaysia, where the university has a campus. Malaysia has low-lying coast regions, diverse and productive ocean environments and offshore extractive industries, all of which are vulnerable to extreme weather and changes in the climate. The insights gained through Swinburne’s Centre for Ocean Engineering, Science and Technology’s work may open up new monitoring, research and consulting opportunities with benefits for communities and industry in the region and beyond.

 

Wave energy

Dr Richard Manasseh is a mechanical engineer specialising in vibrations, waves and oscillations in fluids.

A newcomer to Swinburne, Manasseh’s background is ideal for applying the wave physics and climate modelling knowledge of Babanin and his team to the fundamental mechanical engineering of wave-energy harnessing devices.


Here he outlines a few of the challenges:

 

The amount of energy available from waves is vast. Waves dump power on the Great Australian Bight coastline equivalent to over 50 Snowy Mountains hydroelectric schemes.

But waves are not like wind. Wave momentum reverses direction (reciprocates) continually and no two waves are the same. They vary wave to wave and day to day. That doesn’t sound like a big deal, but in practice it is. So while simple, land-based, one direction at a time wind power has windmill-like turbines, wave power still has no such standard device.

 

You also have the added difficulties of having to ship wave power devices offshore, deploy and maintain them in big seas and stop them from becoming fouled by marine organisms.

Swinburne’s Centre for Ocean Engineering, Science and Technology’s wave physics research provides invaluable data about likely wave heights, location and the complicated mix of wave frequencies and wavelengths that the devices must be tuned to in order to work efficiently.

 

Once wave-power devices are deployed in sufficient numbers in one location, Swinburne’s modelling should also help predict what the resulting removal of wave energy will do to local currents and conditions.

And even when physics and engineering challenges are solved, wave power devices will require appropriate and coordinated testing, standards and government regulation.

 

The big blow

Australia’s cyclone timeline

 

Each summer, on average 11 to 12 tropical cyclones form in the Australian region. Based on Bureau of Meteorology records, here is a timeline of the most powerful and destructive tropical cyclones to hit Australia since Cyclone Tracy obliterated Darwin in 1974.

 

Christmas Day December 1974

Tracy kills 71 people and flattens more than 90 per cent of Darwin’s houses.

 

March–April 1978

Alby kills five people in Western Australia and causes widespread property and environmental damage.

 

February 1995

Bobby kills eight people (including seven on two fishing trawlers) as it sweeps across northwest Australia’s coast from Darwin to Exmouth.

 

March 1997

Justin, after killing at least 30 people in Papua New Guinea, causes the deaths of five people offshore when their yacht is destroyed and two people on land with major damage between Cairns and Townsville in Queensland.

 

March 2006

Larry, the season’s 17th cyclone to form in the region crosses the Queensland coast just south of Cairns. No lives are lost but damage to farmland reaches a record $1.5 billion.

 

April 2006

Monica, the strongest cyclone recorded in Australia before Yasi, with sustained wind speeds of 155 miles per hour hit remote northern Cape York Peninsula causing property loss estimated at $6.6 million and devastating vegetation across 7000 square kilometres.

 

February–March 2007

George kills three people and causes $8 million property damage to Port Hedland and numerous isolated mining camps in northwest Australia.

 

March 2010

Ului was one of the fastest intensifying tropical cyclones on record and caused Queensland infrastructural damage estimated at $20 million and agricultural losses of $60 million.

 

January–February 2011

Yasi built to be the most intense and widespread cyclone recorded. Queensland authorities estimated the property loss at $3.5 billion. Remnants of Yasi, as a tropical low, caused widespread floods devastating communities and property across Queensland, New South Wales, Victoria and South Australia.

 

 

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