Tag Archives: research

Diving into three-dimensional fluids

My research group has been working for some years on methods that allow straightforward comparison of large datasets [see ‘Recognizing strain’ on October 28th 2015].  Our original motivation was to compare maps of predicted strain over the surface of engineering structures with maps of measurements.  We have used these comparison methods to validate predictions produced by computational models [see ‘Million to one’ on November 21st 2018] and to identify and track changes in the condition of engineering structures [see ‘Out of the valley of death into a hype cycle’ on February 24th 2021].  Recently, we have extended this second application to tracking changes in the environment including the occurance of El Niño events [see ‘From strain measurements to assessing El Niño events’ on March 17th, 2021].  Now, we are hoping to extend this research into fluid mechanics by using our techniques to compare flow patterns.  We have had some success in exploring the use of methods to optimise the design of the mesh of elements used in computational fluid dynamics to model some simple flow regimes.  We are looking for a PhD student to work on extending our model validation techniques into fluid mechanics using volumes of data from measurement and predictions rather than fields, i.e., moving from two-dimensional to three-dimensional datasets.  If you are interested or know someone who might be interested then please get in touch.

There is more information on the PhD project here.

Fancy a pint of science?

In September I am planning to initiate a new research project on the interaction of bacteria with cellular and hard surfaces.  It is in collaboration with Jude Curran and is co-funded by Unilever and the Biotechnology and Biological Sciences Research Council.  We have already used the optical method of caustics in a microscope to track and characterise the movement of synthetic nanoparticles as small as 3 nm in an array of biologically-relevant solutions [see ‘Nano biomechanical engineering of agent delivery to cells’ on December 15th, 2021].  We have also used the same technique to characterise and quantify the motion and growth of bacteria in solutions.  Now, we plan to use caustic signatures as a label-free tracking technology for pre-clinical testing of antimicrobial solutions and coatings.  We plan to start by considering binding and removal of viral particles and bacterial spores from hard and soft laundry surfaces using various bacterial species, including Staph aureus which is responsible for laundry malodour; before progressing to the interaction of bacteria with human oral and skin cell cultures.  We are in the process of recruiting a suitable PhD student so if you are interested or know someone who might be suitable then get in touch.  If you want to learn more about our tracking technology and fancy a pint of science, then join us in Liverpool in May for part of the world’s largest festival of public science.  I will be talking about ‘Revealing the invisible: real-time motion of virus particles’  on May 10th at 7.30pm on Leaf of Bold Street.

Liverpool Pint of Science programme

UK Pint of Science programme

 

On flatness and roughness

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/

Ice bores and what they can tell us

Map of Greenland sheet showing depth of iceAbout forty years ago, I was lucky enough to be involved in organising a scientific expedition to North-East Greenland.  Our basecamp was on the Bersaerkerbrae Glacier in Scoresby Land, which at 72 degrees North is well within the Arctic Circle and forty years ago was only accessible in summer when the snow receded.  We measured ablation rates on the glacier [1], counted muskoxen in the surrounding landscape [2] [see ‘Reasons for publishing scientific papers‘ on April 21st 2021] and drilled boreholes in the ice of the glacier.  We performed mechanical tests on the ice cores obtained from different depths in the glacier and in various locations in order to assess the spatial distribution of the material properties of the ice in the glacier. This is important information for producing accurate simulations of the flow of the glacier, although our research did not extend to modelling the glacier.  We could also have used our ice cores to investigate the climatic history of the region.  The Greenland ice sheet contains an archive record of the climate on Earth for about the last half million years, stored in the snow and trapped air bubbles accumulated over that time period.  If the ice sheet melts then that unique record will be lost forever.

The thumbnail image is a map of the depth of ice in the Greenland ice sheet.  The map is about five years old and has a wide green fringe along the east coast.  Scoresby Land is the penisula to the north of the large fiord in the middle of the east coast.  In 1982, the edge of the ice sheet was about 80 miles from the Bersaerkerbrae Glacier, whereas today it is at least twice that distance because the ice sheet is receding.

References:

[1] Patterson EA, 1984, A mathematical model for perched block formation. Journal of Glaciology. 30(106):296-301.

[2] Patterson EA, 1984, ‘Sightings of Muskoxen in Northern Scoresby Land, Greenland’, Arctic, 37(1): 61-63.

Image: https://upload.wikimedia.org/wikipedia/commons/thumb/b/b5/Greenland_ice_sheet_AMSL_thickness_map-en.svg/2000px-Greenland_ice_sheet_AMSL_thickness_map-en.svg.png