̽��ֱ�� of Cambridge - BP Institute for Multiphase Flow (BPI)

A new model could help stall shifting sand dunes, protecting infrastructure and ecosystems

cmm201 — Tue, 26 Oct 2021 16:33:55 +0000

̽��ֱ��team’s experiment – which featured mock-up obstacles of varying size and shape – shows that large obstacles are the most effective at halting the migration of a dune, especially when they are ridge-shaped, like a wall, rather than smooth and cylindrical, like a pipeline.

̽��ֱ��model, published in Physical Review Fluids, is the first to describe interactions between sand dunes and obstacles.

By analysing how currents are deflected in the presence of an obstacle, they were also able to develop an efficient, data-driven tool that aims to forecast how a dune will interact with its surroundings.

̽��ֱ��research could help in the design of more effective barriers that can, for instance, stop sand dunes from invading agricultural land. It could also be used to protect sand dunes and their unique ecosystems from damage.

“Moving sand dunes impact people and their livelihoods directly; across the world and in a range of environments,” said lead author Karol Bacik, who conducted the experiments as a PhD student in Cambridge’s Department of Applied Mathematics and Theoretical Physics (DAMTP). “By revealing the physics behind dune-obstacle interactions, this work gives us the guiding principles we need to divert or halt dunes – mitigating damage.”

As deserts continue to expand, sand dunes pose an increasing risk to the built environment: swallowing up roads and houses whole as they engulf the land. In a similar way, dunes on the seabed can block shipping routes and even compromise the safety of underwater cables and pipelines.

But in certain locations, rather than stopping the sand dune moving, it can be preferable for a dune to move through an obstacle as quickly as possible. Take pipelines, for instance, which can be damaged if buried under the weight of a stationary dune for too long.

Bacik’s work shows how obstacles of varying design should be selected to fit the desired outcome, “If you want the dune the pass, make the obstacle as smooth and rounded as possible – if you want to halt it, make it as sharp as possible,” said Bacik.

̽��ֱ��research is one of a series of experiments Nathalie Vriend - who is based jointly at Cambridge’s BP Institute for Multiphase Flow, the Department of Earth Sciences and DAMTP - has been leading experiments to understand why sand dunes move like they do. “Sand is fascinating: pour some from your hand and it flows like a liquid….then, when it lands, it makes a solid heap,” she said. “But toss it into the air and it blows along like a gas. Its ability to morph between states like this makes it a real challenge to model how sand moves.”

̽��ֱ��team made a ring-shaped tank to contain their sand dunes, which can travel in circuits, almost like a ‘merry-go-round’. By submerging the dunes in water, and disturbing the flow with paddles, they were able to reconstruct how the dunes are moved by water currents. They then put obstacles of varying size and shape in the path of the moving dunes to observe their effect.

“We can see evidence of sand dunes moving right in front of us, but what’s fascinating is their movement is all down to the hidden flow of water currents or wind patterns,” said Bacik, “You can’t see the curling tails of turbulence until you use a visualisation technique…and it's only then, once you have done a fluid analysis, that you can really understand why sand dunes move like they do.”

̽��ֱ��researchers’ ultimate goal is to model sand dune movements in more complex and realistic, three-dimensional, landscapes in addition to exploring the wind-blown dunes found in deserts. Ideally, they would like to be able to pinpoint a location on a map, input information on weather, air or water currents, and predict whether a dune would pass over a specific obstacle. Although these numerical simulations would be more complex, their new experiments serve as an important validation benchmark for continued exploration.

Reference:
Bacik, KA, Canizares, P, Caulfield, CP, Williams, MJ, Vriend, NM, Dynamics of migrating sand dunes interacting with obstacles, Physical Review Fluids, DOI: 10.1103/PhysReFluids.00.004300

PBS Terra Documentary, 'What makes These Dunes Sing': release date 20 October

Cambridge scientists have used downscaled laboratory models to show how sand dunes move through a landscape, revealing the conditions that determine whether they will pass through hurdles in their path – like pipelines or walls -- or get stopped in their tracks.

We can see evidence of sand dunes moving right in front of us, but what’s fascinating is their movement is all down to the hidden flow of water currents or wind patterns

Karol Bacik

What Makes These Dunes Sing? (ft. @It's Okay To Be Smart)

Pixabay

Desert under blue sky

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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Sand dunes can ‘communicate’ with each other

sc604 — Tue, 04 Feb 2020 01:00:00 +0000

Using an experimental dune ‘racetrack’, the researchers observed that two identical dunes start out close together, but over time they get further and further apart. This interaction is controlled by turbulent swirls from the upstream dune, which push the downstream dune away. ̽��ֱ��results, reported in the journal Physical Review Letters, are key for the study of long-term dune migration, which threatens shipping channels, increases desertification, and can bury infrastructure such as highways.

When a pile of sand is exposed to wind or water flow, it forms a dune shape and starts moving downstream with the flow. Sand dunes, whether in deserts, on river bottoms or sea beds, rarely occur in isolation and instead usually appear in large groups, forming striking patterns known as dune fields or corridors.

It’s well-known that active sand dunes migrate. Generally speaking, the speed of a dune is inverse to its size: smaller dunes move faster and larger dunes move slower. What hasn’t been understood is if and how dunes within a field interact with each other.

“There are different theories on dune interaction: one is that dunes of different sizes will collide, and keep colliding, until they form one giant dune, although this phenomenon has not yet been observed in nature,” said Karol Bacik, a PhD candidate in Cambridge’s Department of Applied Mathematics and Theoretical Physics, and the paper’s first author. “Another theory is that dunes might collide and exchange mass - sort of like billiard balls bouncing off one another - until they are the same size and move at the same speed, but we need to validate these theories experimentally.”

Now, Bacik and his Cambridge colleagues have shown results that question these explanations. “We’ve discovered physics that hasn’t been part of the model before,” said Dr Nathalie Vriend, who led the research.

Most of the work in modelling the behaviour of sand dunes is done numerically, but Vriend and the members of her lab designed and constructed a unique experimental facility which enables them to observe their long-term behaviour. Water-filled flumes are common tools for studying the movement of sand dunes in a lab setting, but the dunes can only be observed until they reach the end of the tank. Instead, the Cambridge researchers have built a circular flume so that the dunes can be observed for hours as the flume rotates, while high-speed cameras allow them to track the flow of individual particles in the dunes.

Bacik hadn’t originally meant to study the interaction between two dunes: “Originally, I put multiple dunes in the tank just to speed up data collection, but we didn’t expect to see how they started to interact with each other,” he said.

̽��ֱ��two dunes started with the same volume and in the same shape. As the flow began to move across the two dunes, they started moving. “Since we know that the speed of a dune is related to its height, we expected that the two dunes would move at the same speed,” said Vriend, who is based at the BP Institute for Multiphase Flow. “However, this is not what we observed.”

Initially, the front dune moved faster than the back dune, but as the experiment continued, the front dune began to slow down, until the two dunes were moving at almost the same speed.

Crucially, the pattern of flow across the two dunes was observed to be different: the flow is deflected by the front dune, generating ‘swirls’ on the back dune and pushing it away. “ ̽��ֱ��front dune generates the turbulence pattern which we see on the back dune,” said Vriend. “ ̽��ֱ��flow structure behind the front dune is like a wake behind a boat, and affects the properties of the next dune.”

As the experiment continued, the dunes got further and further apart, until they form an equilibrium on opposite sides of the circular flume, remaining 180 degrees apart.

̽��ֱ��next step for the research is to find quantitative evidence of large-scale and complex dune migration in deserts, using observations and satellite images. By tracking clusters of dunes over long periods, we can observe whether measures to divert the migration of dunes are effective or not.

Reference:
Karol A. Bacik et al. ‘Wake-induced long range repulsion of aqueous dunes.’ Physical Review Letters (2020). DOI: 10.1103/PhysRevLett.124.054501

Even though they are inanimate objects, sand dunes can ‘communicate’ with each other, researchers have found. A team from the ̽��ֱ�� of Cambridge has found that as they move, sand dunes interact with and repel their downstream neighbours.

We’ve discovered physics that hasn’t been part of the model before

Nathalie Vriend

Sand dunes can ‘communicate’ with each other.

Karol Bacik, Nathalie Vriend

Sand dune

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Size matters: if you are a bubble of volcanic gas

sc604 — Mon, 06 Aug 2018 11:13:18 +0000

A team of scientists, including a volcanologist and mathematician from the ̽��ֱ�� of Cambridge, discovered the phenomenon through detailed observations of gas emissions from Kīlauea volcano in Hawaii.

At many volcanoes around the world, gas emissions are monitored routinely to help with forecasting eruptions. Changes in the output or proportions of different gases - such as carbon dioxide and sulphur dioxide – can herald shifts in the activity of a volcano. Volcanologists have considered that these chemical changes reflect the rise and fall of magma in the Earth’s crust but the new research reveals that the composition of volcanic gases depends also on the size of the gas bubbles rising up to the surface.

Until the latest spectacular eruption opened up fissures on the flank of the volcano, Kīlauea held a vast lava lake in its summit crater. ̽��ֱ��behaviour of this lava lake alternated between phases of fiery ‘spattering’ powered by large gas bubbles bursting through the magma, and more gentle gas release, accompanied by slow and steady motion of the lava.

In the past, volcanic gases have been sampled directly from steaming vents and openings called fumaroles. But this is not possible for the emissions from a lava lake, 200 metres across, and at the bottom of a steep-sided crater. Instead, the team used an infrared spectrometer, which is employed for routine volcano monitoring by co-authors of the study, Jeff Sutton and Tamar Elias from the Hawaiian Volcano Observatory (US Geological Survey).

̽��ֱ��device was located on the edge of the crater, pointed at the lava lake, and recorded gas compositions in the atmosphere every few seconds. ̽��ֱ��emissions of carbon- and sulphur-bearing gases were measured during both the vigorous and mild phases of activity.

Each individual measurement was used to compute the temperature of the volcanic gas. What immediately struck the scientists was that the gas temperatures ranged from 1150 degrees Celsius – the temperature of the lava – down to around 900 degrees Celsius. “At this temperature, the lava would freeze,” said lead author Dr Clive Oppenheimer, from Cambridge’s Department of Geography. “At first, we couldn’t understand how the gases could emerge much colder than the molten lava sloshing in the lake.”

̽��ֱ��clue to this puzzle came from the variation in calculated gas temperatures – they were high when the lava lake was placid, and low when it was bubbling furiously. “We realised it could be because of the size of the gas bubbles,” said co-author Professor Andy Woods, Director of Cambridge’s BP Institute. “Larger bubbles rise faster through the magma and expand rapidly as the pressure reduces, just like bubbles rising in a glass of fizzy drink; the gas cools down because of the expansion.” Larger bubbles form when smaller bubbles bump into each other and merge.

Woods and Oppenheimer developed a mathematical model to account for the process, which showed a very good fit with the observations.

But there was yet another surprising finding from the gas observations from Hawaii. As well as being cooler, the emissions from the large gas bubbles were more oxidised than expected – they had higher proportions of carbon dioxide to carbon monoxide.

̽��ֱ��chemical balance of volcanic gases such as carbon dioxide and carbon monoxide (or sulphur dioxide and hydrogen sulphide) is generally thought to be controlled by the chemistry of the surrounding liquid magma but what the new findings showed is that when bubbles get large enough, most of the gas inside follows its own chemical pathway as the gas cools.

̽��ֱ��ratio of carbon dioxide to carbon monoxide when the lava lake was in its most energetic state was six times higher than during the most stable phase. ̽��ֱ��scientists suggest this effect should be taken into account when gas measurements are being used to forecast major changes in volcanic activity.

“Gas measurements are critical to our monitoring and hazard assessment; refining our understanding of how magma behaves beneath the volcano allows us to better interpret our observations,” said co-author Tamar Elias from the Hawaiian Volcano Observatory.

And there is another implication of this discovery – not for eruptions today but for the evolution of the Earth’s atmosphere billions of years ago. “Volcanic emissions in Earth’s deep past may have made the atmosphere more oxidising than we thought,” said co-author Bruno Scaillet. “A more oxygen-rich atmosphere would have facilitated the emergence and viability of life on land, by generating an ozone layer, which shields against harmful ultraviolet rays from the sun.”

Reference:
Clive Oppenheimer et al “Influence of eruptive style on volcanic gas emission chemistry and temperature” Nature Geoscience (2018). DOI: 10.1038/s41561-018-0194-5

Inset image: Clive Oppenheimer in Hawaii. Credit: Clive Oppenheimer

̽��ֱ��chemical composition of gases emitted from volcanoes – which are used to monitor changes in volcanic activity – can change depending on the size of gas bubbles rising to the surface, and relate to the way in which they erupt. ̽��ֱ��results, published in the journal Nature Geoscience, could be used to improve the forecasting of threats posed by certain volcanoes.

At first, we couldn’t understand how the gases could emerge much colder than the molten lava sloshing in the lake.

Clive Oppenheimer

Kīlauea eruption, 2018

Yes

BP Institute for Multiphase Flow

lw355 — Sat, 01 Aug 2009 15:10:59 +0000

Endowed by a £22 million donation from BP, the BP Institute for Multiphase Flow (BPI) was created in 2000 with the explicit intent of hosting research teams from five departments within the ̽��ֱ��: Applied Maths and Theoretical Physics, Chemical Engineering, Chemistry, Earth Sciences and Engineering.

Today, a multidisciplinary team of almost 40 academics and students is working to understand how gases and fluids move. Multiphase flow is an area of great interest to BP as it underpins all parts of its business: from enhancing oil recovery to delivering it to customers, and from refining hydrocarbons to investing in a low carbon future.

For the BPI, engagement with BP enriches research in a very practical sense, as Professor Andy Woods, Director, explained: ‘Our close working relationship with BP gives us in-depth exposure to technical challenges in the industry as well as unparalleled access to field data that would be impossible for us to collect. This means that we can frame research directions that are fundamentally interesting to us as academics and can also solve problems that are of relevance to the industry.’

Currently, a large pan-Institute project is analysing the interactions between fluids and solids in oil fields to understand the physical chemistry that controls how much oil can be recovered as a function of the salinity of the water used to pump it from the well. Other projects vary from analysing the molecular basis of how lubricants work to understanding how volcanoes erupt, and from addressing questions about the long-term storage of CO₂ in redundant oil wells to determining how you can control heat transfer in buildings through natural convection. This latter research theme led in 2006 to the spin-out company E-Stack, which was set up to commercialise a low energy ventilation system that uses natural convection to keep the interior temperature of buildings buffered from exterior changes.

Professor Woods sees the link between basic research and industrial applications as key to research at BPI. ‘We determine our own research programme and our prime interest is in answering fundamental questions about flow. But we’re also looking at how this impacts on ‘real world’ applications because this in turn informs a whole new set of fundamental questions and, if we’re lucky, the development of unforeseen applications.’

For more information, please contact Professor Andy Woods (andy@bpi.cam.ac.uk) or visit www.bpi.cam.ac.uk/

Understanding flow – whether it’s of oil, air, lubricants, lava, seawater or CO2 – lies at the heart of Cambridge’s BP Institute.

Our prime interest is in answering fundamental questions about flow. But we’re also looking at how this impacts on ‘real world’ applications because this in turn informs a whole new set of fundamental questions and, if we’re lucky, the development of unforeseen applications.

Professor Andy Woods

̽��ֱ�� of Cambridge

BP Institute

Energy giant BP looks to its engagement with universities like Cambridge to help stay connected to cutting-edge research in science and technology.

‘As head of BP’s research and technology portfolio, my job is to ensure that BP has the technology it needs to contribute to the world’s future energy demands,’ said David Eyton, BP Group Head of Research & Technology and Executive Sponsor for Cambridge. ‘As part of this, we work closely with a handful of excellent academic centres like Cambridge to keep us plugged into the fast-changing world of science and technology.’

BP’s relationship with the ̽��ֱ��, which stretches back through the past century, was recently formalised by the signing of a Memorandum of Understanding (MoU). ‘ ̽��ֱ��MoU,’ David Eyton explained, ‘embraces all of our current interactions with Cambridge at a strategic level – from research activities, through policy development and training, to recruitment – as well as laying the groundwork for mutual support and development so that the relationship can fulfil its greatest potential.’ These interactions are being overseen by Andy Leonard in his role as BP’s Vice-President for Cambridge.

Valuing research

BP’s annual spend for 2009 across the ̽��ֱ�� is £3.6 million, of which approximately £1 million is funding technical research and the remainder is principally funding endowments and scholarships.

̽��ֱ��company’s main channels of engagement are the BP Institute for Multiphase Flow, established in 2000 with a £22 million endowment from BP, and Judge Business School through the Centre for India and Global Business and the Cambridge Centre for Energy Studies. BP has also had long and fruitful collaborations elsewhere in the ̽��ֱ��, especially with the Bullard Laboratories within the Department of Earth Sciences.

Several areas of applied research activities in Cambridge have brought world-class expertise to bear on practical issues that have reaped immediate benefits for BP, from exploration through to fuels and lubricants. But BP also views fundamental research as strategically important: ‘Although fundamental research can take years from invention to commercialisation, it also has the potential to yield something truly significant,’ said Eyton. ‘ ̽��ֱ�� ̽��ֱ�� has a fabulous track record of creating important knowledge and that is one of the reasons we are investing in Cambridge. As a business, we have to stay competitive and invest in areas that we believe will benefit our shareholders.’

Recruiting the best

Recruitment is very much part of the strategic relationship with Cambridge. ‘ ̽��ֱ��people we recruit today could have a profound impact on the company over many decades,’ explained Andy Leonard, ‘so we need to ensure that the highest quality students are exposed to the range of employment opportunities within BP.’ Also of importance, partly from a recruiting perspective, is the large number of scholarship programmes BP runs for research students, mainly in collaboration with the Cambridge Commonwealth and Overseas Trusts. This year, BP has made job offers to 20 graduates and 17 interns in Cambridge, as well as partially funding 49 research scholarships.

Recognising opportunities

‘ ̽��ֱ��key to success in strategic relationships is to create situations where there is genuine mutuality,’ said Eyton. ‘We want the relationship with Cambridge to achieve its greatest potential and to progress the strategic aims of the ̽��ֱ�� and BP.’ ̽��ֱ��company is also keen to support the strengthening of links between universities such as Cambridge, the Massachusetts Institute of Technology (MIT) and Tsinghua ̽��ֱ�� in Beijing, predominantly with regard to finding new forms of low carbon energy and moving towards a more sustainable energy landscape in the world.

‘I am a big believer in investing in places like Cambridge that have a proven record of success,’ explained Eyton. ‘I also think that we have even more to discover in terms of opportunities for productive interactions. I’m delighted to say that we are on this journey.’

For more information about BP, please visit www.bp.com/

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