Whether it is to understand the physical behaviour of complex materials, biochemical processes or biology inaccessible to experimentation, multiscale simulation takes researchers into the realm of small structures, allowing them to apprehend, and even anticipate their behaviour, on a large scale.
What common points do the service life of a car, the efficiency of a solar panel and a magnetic resonance imaging (MRI) have? All performance will soon be anticipated using a “multiscale simulation”. It will enable complex biological and physical phenomena to be represented using mathematical equations and experimental data at different scales: the scale at which the object - a solar panel for example - has been examined with the naked eye (macroscopic scale), or the one with the smallest details taken into account in the simulation
within the material (microscopic scale), or the intermediate scales, in between, that can affect the object studied (mesoscopic scale).
In media res
“Our superconducting magnets combine these different scales”, explains Pierre Manil of University Paris-Saclay (CEA, Research Institute on Fundamental Laws of the Universe). “They are metallic reels and are several meters long. They consist in a superconducting
metallic cable that is several kilometres long and about a centimetre wide. This cable itself consists in millimetric strands that encloses precious superconducting filaments with a diameter of a few tens of micrometres”.
The magnetic properties of these magnets enable the observation of the human brain using a MRI scan or particles' guiding within an accelerator. Intense magnetic fields delivered by new alloys such as niobium-tin could increase precision of medical examinations or the energy of the accelerator. “The electromagnetic performance of the magnet and the mechanical strength of the niobium-tin operates at a microscopic scale. We analyse the microstructural behaviour in order to come to conclusions on the performance of the magnet” explains Pierre Manil.
Citius, altius, forties
The CEA teams are constantly trying to improve the magnetic field of superconducting magnets in order to open up new experimental horizons. “Our next challenge? Combining the current ‘multiscale' approach with a ‘multiphysical' modelling and thus assess conjointly the mechanical and electromagnetic performances of the magnet”, adds Pierre Manil.
This research faces two challenges: obtaining useful data for mechanical models and developing microscopic models, the speciality of experts in physics of materials. To develop this, investigators come to theorists' aid. This is where Véronique Aubin and her team at the Laboratory of Soil, Structure and Material Mechanics (MSSMAT) of CentrealeSupélec take action. As part of the Cocascope* project, they use state-of-the-art techniques such as nano-indentation to examine the superconductor. Thanks to a micrometric sensor the researchers are able to access the mechanical properties of very small-scale objects.
Multiscale simulation scatters well beyond physics. “For several decades we have used simulations founded on equations to translate plant growth”, comments Nicolas Guilpart of AgroParisTech. “These models enable us to predict the biomass that is produced according to meteorological parameters such as solar radiation, the temperature of the air and the humidity of the soil”. Researchers gather information on the potential yield of a concerned plot in order to assess agricultural practices in given regions. Food safety of a continent can depend on this. Research, carried out by the Convergence Institute, Climate Change and Land Use (CLAND) involves climatologists, agronomists and economists. They aim to provide direction on agricultural land use. It is then possible to create models predicting optimal conditions for new cultures such as soya, a legume rich in protein and seldom grown in our latitudes, and also to anticipate moving agricultural zones according to climatic evolution.
* Cocascope: modelling the behaviour of superconducting cables at various scales to optimise their electric performances (project financed by ANR).
∙ D. Makowski et al., Global agronomy, a new field of research. A review. Agronomy for sustainable development, vol. 34, 2014.
∙ P. Manil et al. A numerical approach for the mechanical analysis of superconducting Rutherford-type cables using bi-metallic description. IEEE Transactions on Applied Superconductivity, 2017.
"In cooperation with the CERN, I contribute to designing prototypes of superconducting magnets to increase the energy collision of the LHC, the largest particle accelerator in the world which enabled to confirm the existence of the Higgs boson."
Pierre Manil is an engineer-researcher in mechanics. He runs the Mechanical and Thermal studies bureau of the Research Institute on Fundamental Laws of the Universe (CEA), in charge of the architecture of large physical instruments.