Tag Archives: oceans

On flatness and roughness

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Photograph of aircraft carrier in heavy seas for decorative purposes onlyFlatness is a tricky term to define.  Technically, it is the deviation, or lack of deviation, from a plane. However, something that appears flat to human eye often turns out not to be at all flat when looked at closely and measured with a high resolution instrument.  It’s a bit like how the ocean might appear flat and smooth to a passenger sitting comfortably in a window seat of an aeroplane and looking down at the surface of the water below but feels like a roller-coaster to a sailor in a small yacht.  Of course, if the passenger looks at the horizon instead of down at the yacht below then they will realise the surface of the ocean is curved but this is unlikely to be apparent to the sailor who can only see the next line of waves advancing towards them.  Of course, the Earth is not flat and the waves are better described as surface roughness.  Some months ago I wrote about our struggles to build a thin flat metallic plate using additive manufacturing [see ‘If you don’t succeed, try and try again…’ on September 29th, 2021].  At the time, we were building our rectangular plates in landscape orientation and using buttresses to support them during the manufacturing process; however, when we removed the plates from the machine and detached the buttresses they deformed into a dome-shape.  I am pleased to say that our perseverance has paid off and recently we have been much more successful by building our plates orientated in portrait mode, i.e., with the short side of the rectangle horizontal, and using a more sophisticated design of buttresses.  Viewed from the right perspective our recent plates could be considered flat though in reality they deviate from a plane by less than 3% of their in-plane dimensions and also have a surface roughness of several tens of micrometres (that’s the average deviation from the surface).  The funding organisations for our research expect us to publish our results in a peer-reviewed journal that will only accept novel unpublished results so I am not going to say anything more about our flat plates.  Instead let me return to the ocean analogy and try to make you seasick by recalling an earlier career in which I was on duty on the bridge of an aircraft carrier ploughing through seas so rough, or not flat, that waves were breaking over the flight deck and the ship felt like it was still rolling and pitching when we sailed serenely into port some days later.

The current research is funded jointly by the National Science Foundation (NSF) in the USA and the Engineering and Physical Sciences Research Council (EPSRC) in the UK (see Grants on the Web).

Image from https://laststandonzombieisland.com/2015/07/22/warship-wednesday-july-22-2015-the-giant-messenger-god/1977-hms-hermes-r-12-with-her-bows-nearly-out-of-the-water/

From strain measurements to assessing El Niño events

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Figure 11 from RSOS 201086One of the exciting aspects of leading a university research group is that you can never be quite sure where the research is going next.  We published a nice example of this unpredictability last week in Royal Society Open Science in a paper called ‘Transformation of measurement uncertainties into low-dimensional feature space‘ [1].  While the title is an accurate description of the contents, it does not give much away and certainly does not reveal that we proposed a new method for assessing the occurrence of El Niño events.  For some time we have been working with massive datasets of measurements from arrays of sensors and representing them by fitting polynomials in a process known as image decomposition [see ‘Recognising strain‘ on October 28th, 2015]. The relatively small number of coefficients from these polynomials can be collated into a feature vector which facilitates comparison with other datasets [see for example, ‘Out of the valley of death into a hype cycle‘ on February 24th, 2021].  Our recent paper provides a solution to the issue of representing the measurement uncertainty in the same space as the feature vector which is roughly what we set out to do.  We demonstrated our new method for representing the measurement uncertainty by calibrating and validating a computational model of a simple beam in bending using data from an earlier study in a EU-funded project called VANESSA [2] — so no surprises there.  However, then my co-author and PhD student, Antonis Alexiadis went looking for other interesting datasets with which to demonstrate the new method.  He found a set of spatially-varying uncertainties associated with a metamodel of soil moisture in a river basin in China [3] and global oceanographic temperature fields collected monthly over 11 years from 2002 to 2012 [4].  We used the latter set of data to develop a new technique for assessing the occurrence of El-Niño events in the Pacific Ocean.  Our technique is based on global ocean dynamics rather than on the small region in the Pacific Ocean which is usually used and has the added advantages of providing a confidence level on the assessment as well as enabling straightforward comparisons of predictions and measurements.  The comparison of predictions and measurements is a recurring theme in our current research but I did not expect it to lead into ocean dynamics.

Image is Figure 11 from [1] showing convex hulls fitted to the cloud of points representing the uncertainty intervals for the ocean temperature measurements for each month in 2002 using only the three most significant principal components . The lack of overlap between hulls can be interpreted as implying a significant difference in the temperature between months.

References:

[1] Alexiadis, A. and Ferson, S. and  Patterson, E.A., , 2021. Transformation of measurement uncertainties into low-dimensional feature vector space. Royal Society Open Science, 8(3): 201086.

[2] Lampeas G, Pasialis V, Lin X, Patterson EA. 2015.  On the validation of solid mechanics models using optical measurements and data decomposition. Simulation Modelling Practice and Theory 52, 92-107.

[3] Kang J, Jin R, Li X, Zhang Y. 2017, Block Kriging with measurement errors: a case study of the spatial prediction of soil moisture in the middle reaches of Heihe River Basin. IEEE Geoscience and Remote Sensing Letters, 14, 87-91.

[4] Gaillard F, Reynaud T, Thierry V, Kolodziejczyk N, von Schuckmann K. 2016. In situ-based reanalysis of the global ocean temperature and salinity with ISAS: variability of the heat content and steric height. J. Climate. 29, 1305-1323.

Formula Ocean

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I have had intermittent interactions with motorsport during my engineering career, principally with Formula 1, Formula SAE and Formula Student teams.  The design, construction and competition involved in Formula Student generates tremendous enthusiasm amongst a section of the student community and enormously increases their employability.  As a Department Chair at Michigan State University, I was a proud and enthusiastic sponsor of the MSU Formula SAE team.  However, I find it increasingly difficult to support an activity that is associated with profligate expenditure of energy and resources – this is not the impression of engineering that should be portrayed to our current and future students.  Engineering is about so much more than making a vehicle go around a track as fast as possible.  See my posts on ‘Re-engineering Engineering‘ on August 30th, 2017, ‘Engineering is all about ingenuity‘ on September 14th, 2016 or ‘Life takes engineering‘ on April 22nd, 2015.

There are many other challenges that could taken up by student teams, in competition if that encourages participation, which would benefit human-kind and the planet.  A current hot topic in the UK media is the pollution of oceans by waste plastic [see for example BBC report]; so, engineering undergraduates could be challenged to design, construct and operate an autonomous marine vehicle that collects and processes plastic waste.  It could be powered from the embedded energy in the waste plastic collected in the ocean.  It would need to navigate to avoid collisions with other vessels, coastal features and wildlife, and to locate and identify the waste.  These represent technological changes in chemical, control, electronic, materials and mechanical engineering – and probably some other fields as well.  I have shared this concept with colleagues in Liverpool and there is some enthusiasm for it; maybe some competition from other universities is all that’s needed to get Formula Ocean started.  The machine with the largest positive net impact on the environment wins!

 

The ‘other’ CO2 problem

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163-6306_IMGMost of us are aware of the rising levels of anthropogenic carbon dioxide in the atmosphere and its impact on climate change but what about the potential loss of our oxygen supply? Far fewer of us are aware of what is sometimes referred to as the ‘other’ carbon dioxide problem, which is the acidification of the oceans. Carbon dioxide dissolves in the surface of the ocean when the concentration in the water is lower than in the atmosphere. Joanne Hopkins of the National Oceanography Centre in Liverpool describes this as the reverse of bubbles escaping when you open a fizzy drink, because the concentration of carbon dioxide in the air is less than in the drink. Carbon dioxide is also taken up in the ocean by tiny marine plants, known as phytoplankton, which convert it into organic matter and oxygen. Tiny marine animals, known as zooplankton, eat the phytoplankton and in turn are eaten and so on. Phytoplankton are important not just because they are the bottom of the food chain but also because they produce about half the oxygen that we breathe. The problem is that dissolved carbon dioxide is shifting the pH balance of the oceans which is beginning to cause demineralisation of microorganisms the ocean. At a recent Royal Society Regional Meeting in Bristol, Professor Daniela Schmidt described this as analogous to osteoporosis, a ‘brittle’ bone disease suffered by humans. Many years ago, my research group worked with a pathologist, Dr Dennis Cotton to examine whether it was possible that osteoporosis sufferers could break their leg and fall over rather than fall over and break their leg. In other words, could osteoporosis change the material properties of bone so dramatically that the structural integrity was insufficient for everyday activities such as getting out of bed or walking upstairs? Our answers at the time were inconclusive, at least in the generic case. Professor Schmidt is working with another team of engineers to examine the structural integrity of microorganisms in the oceans and the impact of demineralisation. The concern is that they could become structurally unstable and die and this could lead to a major reduction in our oxygen supply.

Ok, there is a lot of uncertainty about the series of interactions described above, about the magnitude of the effects and about the ability of ecosystems to adapt to the new conditions. However, the potential consequences are so catastrophic that we should not ignore them. Urgent action is needed to reduce our production of carbon dioxide, and since our governments appear incapable of action we have to take individual responsibilty as advocated by Kofi Annan and reported in my post entitled ‘New Year Resolution’ on December 31st, 2014.

By the way, look out for the announcement of the $2M Wendy Schmidt Ocean Health XPrize on July 20th to one of five teams of scientists for the best sensor for making real-time measurements of ocean acidity.

Sources:

Bell R, The removal of a service we can’t do without’, The Observer, 25.01.15.

Schmidt D, Some don’t like it hot, Geology, 42(9):831-832, 2014.

Brodie et al, The future of the northeast Atlantic benthic flora in a high CO2 world, Ecology and Evolution, 4(13):2787-2798, 2014.

Cotton DWK, Whitehead CL, Vyas S, Cooper C & Patterson EA, Are hip fractures caused by falling and breaking or breaking and falling? Photoelastic stress analysis, Forensic Science Int. 65: 105-112, 1994.