Category Archives: Uncategorized

We inhabit time as fish live in water

A couple of weeks ago (‘Only the name of the airport changes’ on June 12th, 2019) I wrote about the stretching and compression of time while I waited for my much delayed flight to Reno. I mentioned Aristotle’s view of time as the measurement of change; however, Newton believed that time passes even when nothing changes. Einstein resolved the conundrum, represented by these different views, using the concept of a space-time domain forming a gravitational field containing waves. My title is a quote from Carlo Rovelli’s book, ‘The Order of Time‘. And, according to Rovelli, ‘mass slows down time around itself’, which I think will cause waves in the space-time domain .  Conservation of energy implies that the movement of an object will tend towards space where time passes more slowly, i.e. in the vicinity of large masses. Hence, things fall downwards because time runs more slowly close to the Earth. This implies that time passes more slowly at the airport than on the plane in flight; but, of course, the differences are too small for us to measure or perceive.

Image: Art work ‘Gaia’ by Luke Jerram in Liverpool Cathedral

Source:

Carlo Rovelli, The Order of Time, Penguin, 2019.

Relieving stress

I am relieving my ‘gadget stress‘ by ‘reading offline‘ and allowing some ‘mind wandering‘ to stimulate an increase in my intellectual productivity and creativity with the aid of some walks across green fields and cliff tops.  In other words, I have ‘gone walking‘ on a ‘deep vacation‘.  If you don’t have the opportunity for a vacation, then at least ‘Slow down, breathe your own air‘.

Joining the dots

Six months ago, I wrote about ‘Finding DIMES’ as we kicked off a new EU-funded project to develop an integrated measurement system for identifying and tracking damage in aircraft structures.  We are already a quarter of the way through the project and we have a concept design for a modular measurement system based on commercial off-the-shelf components.  We started from the position of wanting our system to provide answers to four of the five questions that Farrar & Worden [1] posed for structural health monitoring systems in 2007; and, in addition to provide information to answer the fifth question.  The five questions are: Is there damage? Where is the damage? What kind of damage is present? How severe is the damage?  And, how much useful life remains?

During the last six months our problem definition has evolved through discussions with our EU Topic Manager, Airbus, to four objectives, namely: to quantify applied loads; to provide condition-led/predictive maintenance; to find indications of damage in composites of 6mm diameter or greater and in metal to detect cracks longer than 1mm; and to provide a digital solution.  At first glance there may not appear to be much connection between the initial problem definition and the current version; but actually, they are not very far apart although the current version is more specific.  This evolution from the idealised vision to the practical goal is normal in engineering projects.

We plan to use point sensors, such as resistance strain gauges or fibre Bragg gratings, to quantify applied loads and track usage history; while imaging sensors will allow us to measure strain fields that will provide information about the changing condition of the structure using the image decomposition techniques developed in previous EU-funded projects: ADVISE, VANESSA (see ‘Setting standards‘ on January 29th, 2014) and INSTRUCTIVE.  We will use these techniques to identify and track cracks in metals [2]; while for composites, we will apply a technique developed through an EPSRC iCASE award from 2012-16 on ‘Full-field strain-based methods for NDT & structural integrity measurement’ [3].

I gave a short briefing on DIMES to a group of Airbus engineers last month and it was good see some excitement in the room about the direction of the project.  And, it felt good to be highlighting how we are building on earlier investments in research by joining the dots to create a deployable measurement system and delivering the complete picture in terms of information about the condition of the structure.

Image: Infra red photograph of DIMES meeting in Ulm.

References

  1. Farrar & Worden, An introduction to structural health monitoring, Phil. Trans. R Soc A, 365:303-315, 2007
  2. Middleton, C.A., Gaio, A., Greene, R.J. & Patterson, E.A., Towards automated tracking of initiation and propagation of cracks in aluminium alloy coupons using thermoelastic stress analysis, Nondestructive Evaluation, 38:18, 2019.
  3. Christian, W.J.R., DiazDelaO, F.A. & Patterson, E.A., Strain-based damage assessment of accurate residual strength prediction of impacted composite laminates, Composites Structures, 184:1215-1223, 2018.

The INSTRUCTIVE and DIMES projects have received funding from the Clean Sky 2 Joint Undertaking under the European Union’s Horizon 2020 research and innovation programme under grant agreements No. 685777 and No. 820951 respectively.

The opinions expressed in this blog post reflect only the author’s view and the Clean Sky 2 Joint Undertaking is not responsible for any use that may be made of the information it contains.

Stopped in Lime Street

It is a late, slightly muggy, summer afternoon and I am sitting at the window in the last carriage of a train waiting for it to leave Liverpool for London.  So far, it has been a busy day with meetings in the morning at the University’s facility at Daresbury followed by a couple on the main campus before I walked down to Lime Street station.  I stopped for a bite to eat as I travelled from Daresbury to Liverpool; but I am hungry again, so I have a sandwich that I bought in the station.  However, I don’t like to unpack and start eating until the train starts moving, just in case I am on the wrong train or we have to change trains.  Finally, the train starts to move and as it builds up speed I reach for my sandwich.  Suddenly it stops.  My carriage has not even reached the end of the platform.  Station staff appear outside my window talking into their radios.  What’s happened?  Did the train hit someone?  I thought there was a small thud just before we stopped.  But the station staff seem unflustered.  Wouldn’t there be more urgency about their movements if there was a casualty?  We sit in silence for ten minutes before the train starts to move again and the train manager announces that someone pulled the emergency handle because they decided that wanted to get off the train. Why did they want to get off the train?  Did they realise they were trapped on the train to London with someone who was pursuing them?  Was it a police officer who realised that their quarry had jumped off the train just before it set off?  Or, have I been reading too many Eric Ambler stories (see ‘The Mask of Dimitrios‘ or ‘Journey into Fear‘) involving train journeys across Europe?  Maybe it was someone who just decided that they didn’t want to go London after all and didn’t care about inconveniencing several hundred people or paying the fine for improper use of the emergency handle.  But that seems unlikely too or perhaps not…  I contemplate these options as the train accelerates towards London and I munch my sandwich.  It reminds me of a quote from Gillian Tett (in the FT Weekend on June 17/18, 2017) about people believing they have a ‘God-given right that they should be able to organise the world around their personal views and needs instead of quietly accepting pre-packaged options’.