Tag Archives: power stations

Can you trust your digital twin?

Author's digital twin?

Author’s digital twin?

There is about a 3% probability that you have a twin. About 32 in 1000 people are one of a pair of twins.  At the moment an even smaller number of us have a digital twin but this is the direction in which computational biomedicine is moving along with other fields.  For instance, soon all aircraft will have digital twins and most new nuclear power plants.  Digital twins are computational representations of individual members of a population, or fleet, in the case of aircraft and power plants.  For an engineering system, its computer-aided design (CAD) is the beginning of its twin, to which information is added from the quality assurance inspections before it leaves the factory and from non-destructive inspections during routine maintenance, as well as data acquired during service operations from health monitoring.  The result is an integrated model and database, which describes the condition and history of the system from conception to the present, that can be used to predict its response to anticipated changes in its environment, its remaining useful life or the impact of proposed modifications to its form and function. It is more challenging to create digital twins of ourselves because we don’t have original design drawings or direct access to the onboard health monitoring system but this is being worked on. However, digital twins are only useful if people believe in the behaviour or performance that they predict and are prepared to make decisions based on the predictions, in other words if the digital twins possess credibility.  Credibility appears to be like beauty because it is in eye of the beholder.  Most modellers believe that their models are both beautiful and credible, after all they are their ‘babies’, but unfortunately modellers are not usually the decision-makers who often have a different frame of reference and set of values.  In my group, one current line of research is to provide metrics and language that will assist in conveying confidence in the reliability of a digital twin to non-expert decision-makers and another is to create methodologies for evaluating the evidence prior to making a decision.  The approach is different depending on the extent to which the underlying models are principled, i.e. based on the laws of science, and can be tested using observations from the real world.  In practice, even with principled, testable models, a digital twin will never be an identical twin and hence there will always be some uncertainty so that decisions remain a matter of judgement based on a sound understanding of the best available evidence – so you are always likely to need advice from a friendly engineer   🙂

Sources:

De Lange, C., 2014, Meet your unborn child – before it’s conceived, New Scientist, 12 April 2014, p.8.

Glaessgen, E.H., & Stargel, D.S., 2012, The digital twin paradigm for future NASA and US Air Force vehicles, Proc 53rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, AIAA paper 2012-2018, NF1676L-13293.

Patterson E.A., Feligiotti, M. & Hack, E., 2013, On the integration of validation, quality assurance and non-destructive evaluation, J. Strain Analysis, 48(1):48-59.

Patterson, E.A., Taylor, R.J. & Bankhead, M., 2016, A framework for an integrated nuclear digital environment, Progress in Nuclear Energy, 87:97-103.

Patterson EA & Whelan MP, 2016, A framework to establish credibility of computational models in biology, Progress in Biophysics & Molecular Biology, doi: 10.1016/j.pbiomolbio.2016.08.007.

Tuegel, E.J., 2012, The airframe digital twin: some challenges to realization, Proc 53rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference.

Happenstance, not engineering?

okemos-art-2extract

A few weeks ago I wrote that ‘engineering is all about ingenuity‘ [post on September 14th, 2016] and pointed out that while some engineers are involved in designing, manufacturing and maintaining engines, most of us are not.  So, besides being ingenious, what do the rest of us do?  Well, most of us contribute in some way to the conception, building and sustaining of networks.  Communication networks, food supply networks, power networks, transport networks, networks of coastal defences, networks of oil rigs, refineries and service stations, or networks of mines, smelting works and factories that make everything from bicycles to xylophones.  The list is endless in our highly networked society.  A network is a group of interconnected things or people.  And, engineers are responsible for all of the nodes in our networks of things and for just about all the connections in our networks of both things and people.

Engineers have been constructing networks by building nodes and connecting them for thousands of years, for instance the ancient Mesopotamians were building aqueducts to connect their towns with distance water supplies more than four millenia ago.

Engineered networks are so ubiquitous that no one notices them until something goes wrong, which means engineers tend to get blamed more than praised.  But apparently that is the fault of the ultimate network: the human brain.  Recent research has shown that blame and praise are assigned by different mechanisms in the brain and that blame can be assigned by every location in the brain responsible for emotion whereas praise comes only from a single location responsible for logical thought.  So, we blame more frequently than we praise and we tend to assume that bad things are deliberate while good things are happenstance.  So reliable networks are happenstance rather than good engineering in the eyes of most people!

Sources:

Ngo L, Kelly M, Coutlee CG, Carter RM , Sinnott-Armstrong W & Huettel SA, Two distinct moral mechanisms for ascribing and denying intentionality, Scientific Reports, 5:17390, 2015.

Bruek H, Human brains are wired to blame rather than to praise, Fortune, December 4th 2015.

 

More uncertainty about matter and energy

woodlandvalley

When I wrote about wave-particle duality and an electron possessing the characteristics of both matter and energy [see my post entitled ‘Electron uncertainty’ on July 27th, 2016], I dodged the issue of what are matter and energy.  As an engineer, I think of matter as being the solids, liquids and gases that are both manufactured and occur in nature.  We should probably add plasmas to this list, as they are created in an increasing number of engineering processes, including power generation using nuclear fission.  But maybe plasmas should be classified as energy, since they are clouds of unbounded charged particles, often electrons.   Matter is constructed from atoms and atoms from sub-atomic particles, such as electrons that can behave as particles or waves of energy.  So clearly, the boundary between matter and energy is blurred or fuzzy.  And, Einstein’s famous equation describes how energy and matter can be equated, i.e. energy is equal to mass times the speed of light squared.

Engineers tend to define energy as the capacity to do work, which is fine for manufactured or generated energy, but is inadequate when thinking about the energy of sub-atomic particles, which probably is why Feynman said we don’t really know what energy is.  Most of us think about energy as the stuff that comes down an electricity cable or that we get from eating a banana.  However, Evelyn Pielou points out in her book, The Nature of Energy, that energy in nature surrounds us all of the time, not just in the atmosphere or water flowing in rivers and oceans but locked into the structure of plants and rocks.

Matter and energy are human constructs and nature does not do rigid classifications, so perhaps we should think about a plant as a highly-organised localised zone of high density energy [see my post entitled ‘Fields of flowers‘ on July 8th, 2015].  We will always be uncertain about some things and as our ability to probe the world around us improves we will find that we are no longer certain about things we thought we understood.  For instance, research has shown that Bucky balls, which are spherical fullerene molecules containing sixty carbon atoms with a mass of 720 atomic mass units, and so seem to be quite substantial bits of matter, exhibit wave-particle duality in certain conditions.

We need to learn to accept uncertainty and appreciate the opportunities it presents to us rather than seek unattainable certainty.

Note: an atomic mass unit is also known as a Dalton and is equivalent to 1.66×10-27kg

Sources:

Pielou EC, The Energy of Nature, Chicago: The University of Chicago Press, 2001.

Arndt M, Nairz O, Vos-Andreae J, Keller C, van der Zouw G & Zeilinger A, Wave-particle duality of C60 molecules, Nature 401, 680-682 (14 October 1999).

 

Subtle balance of sustainable orderliness

129-2910_IMGI wrote this short essay a couple of weeks for another purpose and then changed my mind about using it.  So I thought I would share it on this blog.

Whenever we do something, some of our useful resource gets converted into productive activity but some is always lost in useless waste.  In other words, 100% efficiency is impossible – we can’t convert all of our resource into productive activity.  Engineers call this the second law of thermodynamics.  Thermodynamics is about energy transitions, for instance converting chemical energy in fossil fuels into electrical energy in a power station, and in these circumstances, the useless waste is called entropy.  At the time of the industrial revolution, Rudolf Clausius recognised that entropy can be related to the heat losses which occur whenever we do something useful, such as generating electricity in a power station, cleaning the house with an electric vacuum cleaner or running to catch the bus.

Clausius’s definition of entropy was really useful for designers of 19th century steam engines but it is difficult to use in other walks of life.  Fortunately Ludwig Boltzmann gave us a more valuable description.  He equated entropy to the number of states in which something could be arranged, or its lack of orderliness.  In other words, the more ways you can arrange something, the less ordered it is likely to be and the higher its entropy.  So a box of children’s building blocks has a low entropy when the blocks are packed in their box because there is a relatively small number of ways of arranging them to fit in the box.  When the box is emptied onto your living room floor, there are very many more possible arrangements and so the blocks have a high entropy.  The chance of knowing the whereabouts of a particular block is small. Whoops!  Now we’ve wondered into information theory.

Let’s get back to the second law, which using Boltzmann’s description of entropy, we can express as the level of orderliness should always decrease.  Stephen Hawking describes this as the arrow of time.  Because, if someone shows you a video clip in which steam gathers itself together and returns into a cup of coffee, or that box of children’s blocks repacks itself, then we know the video is being run backwards because these processes involve decreasing entropy and this can only happen spontaneously if we reverse the direction of time.  If this is true then why do we exist as highly ordered structures?

Erwin Schrödinger in his book, ‘What is Life’ says that organisms suck orderliness out of the environment in order to exist, so that the orderliness of the universe, that’s the organism and its environment, decreases.  Humans digest highly-ordered food to sustain life and food, in the form of plants, is brought into existence by metabolising energy from the sun and releasing entropy in the form of heat.  When we die these processes cease and the orderliness is sucked out of us to sustain insects, maggots and bacteria.

We are organisms, known as Sapiens, that organise ourselves into cultures and societies.  Organisation implies an increase in the level of orderliness in apparent contradiction of the second law.  So, we would expect to find a corresponding increase in disorder somewhere to counterbalance the order in society.  The more regimented society becomes the greater the requirement for counterbalancing disorder to occur somewhere in order to satisfy the second law, which might happen unexpectedly and explosively if the level of constraint or regulation is too great.  This is not an argument for anarchy or total deregulation, the financial sector has already demonstrated the risks associated with this path, but for an optimum and sustainable level of orderliness.  This requires subtle judgment just like in elegant engineering design and living a healthy life, both physically and psychologically.