Category Archives: mechanics

All arms and legs

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Imagine building a humanoid robot with head, arms and legs from different organisations that will not share the technical details of the products, probably because they are worried about their intellectual property being stolen.  The likely result would be a robot that moves in slow uncoordinated jerky steps, unlike those seen at the recent World Humanoid Robot Games in China where a humanoid robot beat Usain Bolt’s 100m record.  We have encountered this problem in attempting to build an industrial metaverse consisting of a connected series of digital twins [see ‘Digital twins that thrive in the real-world’ on June 9th, 2021] that represent different parts of a complex engineering system, e.g., a power station.  The organisations that have developed the digital twins or computer simulations are reluctant to share technical information because they want to protect their intellectual property.  Our solution has been to develop an apex software architecture that seamlessly and securely connects computer models of all of the parts of the system with high-speed two-way exchange of information – the equivalent of the central nervous system in the humanoid robot.  Our architecture reduced the processing times for simulations of a nuclear reactor sixteen-fold compared to current approaches and required one-third of the number of analysts to perform the simulations.  The architecture is readily adaptable too; you can plug n’ play with different computational models – the equivalent to changing a leg on a humanoid robot using a snap-fit connector.  Read our 2022 paper if you would like to know more or get in touch if you would like to use our apex architecture.

Image: Figure 9b from Bowman et al, 2022, showing simulated power distribution and control rod position overlayed on a model of a PWR reactor.

Reference: Bowman D, Dwyer L, Levers A, Patterson EA, Purdie S, Vikhorev K. A unified approach to digital twin architecture—proof-of-concept activity in the nuclear sector. IEEE Access, 10:44691-709, 2022

Mapping the road between digital twins and NDE

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RoadmapMichael Grieves, who probably first formulated the concept of digital twins in 2002, stated that all information about a physical entity should be present in its cyber or digital twin with data flow from the physical entity to the digital twin, and information flow from the digital twin to the physical entity throughout its lifecycle [1] [see ‘Digital twins that thrive in the real-world’ on June 9th, 2021].  The realisation of data flows between cyber-physical twins has been slow and there are relatively few cases where this definition has been fully implemented.  Non-destructive evaluation (NDE) is a well-established set of techniques used to assess the properties, integrity and condition of engineering components and structures that could play a significant role in supplying data to digital twins.  At the moment NDE is commonly used in quality control to check for manufacturing defects, in integrity assessments to investigate damage in safety critical components during maintenance inspections, and for determining the remaining life expectancy of engineering parts.  The integration of NDE in digital engineering has been slow; so, in a recent study, involving representatives from a wide range of industries, we have defined in a roadmap [2] the potential opportunity and the route to its realisation.  This work represents a different approach to research for my group in that we have explored the need or the ‘pull’ from industry rather than delivering innovative technology which can result in a ‘push’ to industry [see for example, ‘Our last DIMES’ on September 22nd, 2021].  My regular readers might also detect the influence of social science, which also surfaced in our recent work on knowledge management [see ‘Opportunities lost in knowledge management using digital technology’ on October 25th, 2023 and ‘Evolutionary model of knowledge management’ on March 6th 2024].  We have used the same methods, based on semi-structured interviews and thematic analysis, across all of these studies.

Image: roadmap [© University of Liverpool] which should be read in conjunction with [2].

References:

  1. Grieves, M., Vickers, J. (2017). Digital Twin: Mitigating Unpredictable, Undesirable Emergent Behavior in Complex Systems. In: Kahlen, J., Flumerfelt, S., Alves, A. (eds) Transdisciplinary Perspectives on Complex Systems. Springer, Cham.
  2. Middleton CA, Nguyen T & Patterson EA, NDE4.0 and digital twins in industry: current user experiences and future development, J. Nondestructive Evaluation, 45:107, 2026.

Iron Nanochains

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Caustics formed from iron nanoparticles coalescing into chains aligned with the lines of the magnetic field from an adjacent magnet

Many people will be familiar with an iron filings and magnet experiment often performed in high school physics classes.  Iron filings on a sheet of paper with a magnet underneath, when the paper is gently tapped, align with the lines of the magnetic field sometimes forming ‘chains’.  In our research group, we have performed a version of this experiment at the nanoscale using iron nanoparticles smaller than 200nm in diameter floating in deionised water on a microscope slide.  We brought a magnet into close proximity with the slide and the nanoparticles formed chains aligned along the lines of magnetic field which we visualised using caustics [see ‘Holes in fluids’ on October 22, 2014].  When we removed the magnet, the nanoparticles resumed their Brownian motion.  Not a ground-breaking experiment but it’s exciting to be able to demonstrate that the phenomenon occurs at the nanoscale and that we can observe it.

Passive nanorheology measurements

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What do marshmallows, jelly (or Jell-O), cream cheese and Chinese soup dumplings have in common?  They are often made with gelatin.  Gelatin is derived from the skin and bones of cattle and pigs through the partial hydrolysis of collagen.  Gelatin is a physical hydrogel meaning that it consists of a three-dimensional network of polymer molecules in which a large amount of water is absorbed, as much as 90% in gelatin.  These polymer molecules are cross-linked by hydrogen bonds, hydrophobic interactions and chain entanglements.  External stimuli, such as temperature, can change the level of cross-linking causing the material to transition between its solid, liquid and gel states.  This is why jelly sets in the fridge and melts when it’s heated up – the cross-links holding the molecules together break down.  This type of responsive behaviour allows the properties of hydrogels to be controlled at the micro and sub-micron scale for a host of applications including tissue engineering, drug delivery, water treatment, wearable technologies, and supercapacitors.  However, the design and manufacture of soft hydrogels can be challenging due to the lack of technology for measuring the local properties.  Current quantitative techniques for measuring the properties of hydrogels usually focus on bulk properties and provide little data about local variations or real-time responses to external stimuli.  My colleagues and I have used gold nanoparticles as probes in hydrogels to map the properties at the microscale of thermosensitive hydrogels undergoing real-time transition from the solid to gel phases [see ‘Passive nanorheological tool to characterise hydrogels’].  This is an extension, or perhaps more accurately an application, of our earlier work on tracking nanoparticles through the vitreous humour of the eye [see ‘Nanoparticle motion-through heterogeneous hydrogels’ on November 6th, 2024].  The novel technique, which yields passive nanorheological measurements, allows us to evaluate local viscosity, identify time-varying heterogeniety and monitor dynamic phase transitions at the micro through to nano scale.  The significant challenges of other techniques, such as weak signals due to high water content and the dynamism of hydrogels, are overcome with a fast, inexpensive and user-friendly technology.  Although, even with these advantages, you are unlikely to use it when you are making jelly or roasting marshmallows over the campfire; however, it is really useful for understanding the transport of drugs through biological hydrogels or designing manufacturing processes for artificial tissue.

Reference

Moira Lorenzo Lopez, Victoria R. Kearns, Eann A. Patterson & Judith M. Curran, Passive nanorheological tool to characterise hydrogels, Nanoscale, 2025,17, 15338-15347.

Image: Figure 5 from the above reference showing a hydrogel transitioning to a gel phase as result of an increase in temperature with 100 nm diameter gold nanoparticles with some particles (yellow arrows) at the interface between phases.  The image was taken in an inverted optical microscope set up for tracking the nanoparticles.