Tag Archives: simulation

Reliable predictions of non-Newtonian flows of sludge

Regular readers of this blog will be aware that I have been working for many years on validation processes for computational models of structures employed in a wide range of sectors, including aerospace engineering [see ‘The blind leading the blind’ on May 27th, 2020] and nuclear energy [see ‘Million to one’ on November 21st, 2018].  Validation is determining the extent to which predictions from a model are representative of behaviour in the real-world [see ‘Model validation’ on September 18th, 2012].  More recently, I have been working on model credibility, which is the willingness of people, besides the modeller, to use the predictions from models in decision-making [see, for example, ‘Credible predictions for regulatory decision-making’ on December 9th, 2020].  I have started to consider the complex world of predictive modelling of fluid flow and I am hoping to start a collaboration with a new colleague on the flow of sludges.  Sludges are more common than you might think but we are interested in modelling the flow of waste, both wastewater (sewage) and nuclear wastes.  We have a PhD studentship available sponsored jointly by the GREEN CDT and the National Nuclear Laboratory.  The project is interdisciplinary in two dimensions because it will combine experiments and simulations as well as uniting ideas from solid mechanics and fluid mechanics.  The integration of concepts and technologies across these boundaries brings a level of adventure to the project which will be countered by building on well-established research in solid mechanics on quantitative comparisons of measurements and predictions and by employing current numerical and experimental work on wastewater sludges.  If you are interested or know someone who might want to join our research then you can find out more here.

Image: Sewage sludge disposal in Germany: Andrea Roskosch / UBA

A conversation about a virtual world and global extinction

Photograph of an octopusI went for a haircut a week or so ago and my barber asked me about the books I had been reading recently.  He always has a book on the shelf next to him and sometimes I find him reading when I arrive and the shop is quiet.  So it is not unusual for us to talk about our current books.  I told him about ‘Reality+: virtual worlds and the problems of philosophy’ by David Chalmers which led into a conversation about the possibility that we are in a simulation.  My posts on this topic [see ‘Are we in a simulation’ on September 28th 2022 and ‘Virtual digitalism’ on December 7th, 2022] have provoked a number of negative reactions.  People either think I have written nonsense or would rather not consider the prospect of us being part of a giant simulation.  Fortunately, my barber was happy to accept the possibility that we were part of a simulation which led to a discussion about whether our creator was the equivalent of a teenager playing on a computer in their bedroom or a scientist interested in the evolution of society; and, in either case, why they would have decided to give us hair on our heads that grows steadily throughout our life – perhaps as a personal indication of the passage of time or, simply to provide a living for barbers.  The development of human society and the use of probability to reason that a more advanced society might have created a virtual world in which we are living also led us to talk about the probability that a more advanced society finding us on Earth would annihilate us without pausing to learn about us in the same way that we are destroying all other forms of intelligent life on the planet.  For example, populations of vertebrates living in freshwater ecosystems have declined by 83% on average since 1970 [see World Wide Fund for Nature Living Planet Report 2022].  Maybe it would be preferable for someone to switch off the simulation rather than to suffer the type of invasion mounted by the Martians in the War of the Worlds by HG Wells.

Regular readers with good memories might recall a post entitled ‘Conversations about engineering over dinner and a haircut’ on February 16th, 2022 which featured the same barber who I visit more frequently than these two posts might imply.

The image shows Ollie the Octopus at the Ocean Lab, (Ceridwen CC BY-SA 2.0) for more on the intelligence of an octopus see ‘Intelligent aliens?‘ on January 16th, 2019.

Virtual digitalism

Decorative image of 10 micron spheres in nanoscopeSome months ago I wrote about the likelihood that we are in a simulation [see ‘Are we in a simulation?‘ on September 28th, 2022] and that we cannot be sure whether are or not.  For some people, this will raise the question that if we are in a simulation, then what is real?  In his book, Reality+, David J Chalmers provides a checklist of properties possessed by real things, namely: existence, causal powers, mind-independence, non-illusoriness and genuineness.  The possession of these properties could be established by answering the five questions in the box below and we would expect real objects to possess one or more of these properties.  Objects that are found in a virtual world generated by a simulation are real objects because they have at least one, and often many of these properties, such as causal powers and independence from our minds.  We can consider them to be digital objects, or structures of binary information or bits.  This leads to a form of the ‘It-from-bit’ hypothesis because it implies that molecules are made of atoms, atoms are made of quarks, and quarks are made of bits – unless of course we are not in a simulation but we will probably never know for certain.

Source: David J Chalmers, Reality+: virtual worlds and the problems of philosophy, Penguin, 2022.

Image shows a self-assembly of 10 micron spheres viewed out-of-focus in bright-light optical microscope.

Storm in a computer

Decorative painting of a stormy seascapeAs part of my undergraduate course on thermodynamics [see ‘Change in focus’ on October 5th, 2022) and in my MOOC on Thermodynamics in Everyday Life [See ‘Engaging learners on-line‘ on May 25th, 2016], I used to ask students to read Chapter 1 ‘The Storm in the Computer’ from Philosophy and Simulation: The Emergence of Synthetic Reason by Manuel Delanda.  It is a mind-stretching read and I recommended that students read it at least twice in order to appreciate its messages.  To support their learning, I provided them with a précis of the chapter that is reproduced below in a slightly modified form.

At the start of the chapter, the simplest emergent properties, such as the temperature and pressure of a body of water in a container, are discussed [see ‘Emergent properties’ on September 16th, 2015].  These properties are described as emergent because they are not the property of a single component of the system, that is individual water molecules but are features of the system as a whole.  They arise from an objective averaging process for the billions of molecules of water in the container.  The discussion is extended to two bodies of water, one hot and one cold brought into contact within one another.  An average temperature will emerge with a redistribution of molecules to create a less ordered state.  The spontaneous flow of energy, as temperature differences cancel themselves, is identified as an important driver or capability, especially when the hot body is continually refreshed by a fire, for instance.  Engineers harness energy gradients or differences and the resultant energy flow to do useful work, for instance in turbines.

However, Delanda does not deviate to discuss how engineers exploit energy gradients.  Instead he identifies the spontaneous flow of molecules, as they self-organise across an energy gradient, as the driver of circulatory flows in the oceans and atmosphere, known as convection cells.  Five to eight convections cells can merge in the atmosphere to form a thunderstorm.  In thunderstorms, when the rising water vapour becomes rain, the phase transition from vapour to liquid releases latent heat or energy that helps sustain the storm system.  At the same time, gradients in electrical charge between the upper and lower sections of the storm generate lightening.

Delanda highlights that emergent properties can be established by elucidating the mechanisms that produce them at one scale and these emergent properties can become the components of a phenomenon at a much larger scale.  This allows scientists and engineers to construct models that take for granted the existence of emergent properties at one scale to explain behaviour at another, which is called ‘mechanism-independence’.  For example, it is unnecessary to model molecular movement to predict heat transfer.  These ideas allow simulations to replicate behaviour at the system level without the need for high-fidelity representations at all scales.  The art of modelling is the ability to decide what changes do, and what changes do not, make a difference, i.e., what to include and exclude.


Manuel Delanda Philosophy and Simulation: The Emergence of Synthetic Reason, Continuum, London, 2011.

Image: Painting by Sarah Evans owned by the author.