This work package aims to improve the understanding and modelling of systems involving strong interactions between solid and liquid phases: geomaterials (soils, rocks, concrete, snow, clays, etc.), complex industrial media (pastes, fibre suspensions, porous media, metallic alloys, etc.), dense multiphase flows (avalanches, mudflows, multiphase reactors, etc.), biological and bio-inspired matter (wood, etc.). These systems are generally characterised by strong heterogeneities, anisotropy, and/or polydispersity, which can be pre-existing, induced by processes such as biocementation, suffusion, solidification, etc., or dynamically created by deformation and flow through feedback mechanisms such as migration, segregation, aggregation, fragmentation, etc. Progress is expected from the use and development of advanced characterization techniques such as multiresolution and phase-contrast X-ray tomography and coupled Neutron and X-ray imaging. Proper consideration of micro-macro couplings also requires the development of enriched multi-scale theoretical and numerical modelling approaches based on generalized continua, numerical homogenization, out-of equilibrium statistical physics, etc. Extension of models and characterization techniques to nano-scales is also needed to better account for interactions between objects, boundary and interfacial conditions, etc.

Five research axes are put forward: solid in fluids (suspension…), fluid in solids (porous media…), solid-fluid transition and associated instabilities (shear-banding, diffuse instabilities, liquefaction, etc.), fracture and rupture (fracture propagation and fragmentation, statistical and mechanical characterization of (micro-)damage), flow-structure interactions…

The goal of the WP2 is to understand, predict and control complex flows, especially those involving mass, momentum and energy transfers and those coupled with chemical reactions, biochemical transformations or other physical fields such as electromagnetism and acoustics. This implies a better understanding of turbulence, mixing, multiphase flows with fluid-fluid and/or fluid-solid interfaces including heat and mass transfer (as implied in phase change), as well as complex couplings between flow and phenomena arising at a very small scale, down to the nanometre scale, and being both physical (e.g., adsorption on interfaces in flotation), chemical (e.g., reactions that arise at the molecular level and micro-mixing issues) or biochemical (e.g., biomass-flow couplings in bioreactor). This relates to industrial processes (including oil, nuclear, chemical, propulsion engineering, food processing industry...), to eco-technologies (recycling and durability issues, remediation, water resources...) and clean technologies (intensified industrial processes, from heat exchangers to chemical reactors... as well as new biorefinery processes for vegetal biomass), with important societal issues related to the development of a sustainable and environmentally friendly economy.

Four research axes are put forward: advanced fluid mechanics, interfacial dynamics and transfers, flow of active micronic objects, development and understanding of new processes linked to sustainable development and based on fluid mechanics and interfacial phenomena.

The objective of this work package is to improve the understanding and control of mechanical processes in living organisms from the cell to the macroscopic tissue scale. Recent developments in biology and life sciences reveal the relevance of multi-scale approaches to tackle these problems and that the combination of multidisciplinary approaches mixing mechanics, physics, biology and medicine is necessary to produce significant advances. Two research axes are put forward: (i) mechanics of the living matter which concerns a wide range of issues such as the understanding of cell deformation under flow, the analysis of cell motility, mechanotransduction. At the scale of tissues or organs, an emerging issue is the complexity of the mechanical behaviour which is often non-linear, dependent on the speed of solicitation, non-homogeneous and anisotropic. One of the issues is therefore the determination of rheological laws for systems capable of mimicking the deformations of living tissues. Moreover, when these tissues are active it is necessary to develop adapted models. In particular, characterising and mechanically modelling the appearance of spatial structures during growth (organoid, embryo) or biological fluid flows (organization of red blood cells in complex networks, clot formation in the bloodstream, transport of intestinal mucus) is essential to elucidate the mechanisms of tissue organization.; (ii) mechanics for the living matter which includes scientific issues associated with the mechanics of biomaterials for the living, particularly prostheses, considering the specific anatomy of patients (posture, movement, pathology) and their interactions with biological tissues. The conditions at the interfaces between these different elements are often ignored and need to be addressed precisely. In addition, this theme also includes questions related to the mechanics of organoids (organs on a chip) and the design of new matrices/substrates for cell growth and the development of fibrous substitutes (laryngeal, vessels), using modern methods (electro-spinning, additive printing, etc.). Assisted drug delivery via active artificial microcapsules (in connection with WP2) is also a subject of study, which could be based on recent concepts based on controlled changes in the shape of capsules leading to effective displacement (microrobots).

This work package is devoted to transverse methodological developments needed to address the scientific challenges targeted in WP 1, 2, 3. This includes advances in modelling concepts, numerical methods, simulations, measuring techniques, signal processing, data analysis, etc. Whenever possible, the goal is to promote original methods and tools that are sufficiently versatile to be used in, or adapted to, a wide range of situations (materials, scales, etc.)

Three research axes are put forward: (i) Advanced modelling and simulations. Efforts will be put into developing original numerical methods and improving computational performances for the modelling of diverse multi-scale and multi-physical processes: coupled fluid-solid simulations in the presence of complex flows and/or deformable objects, coupling of numerical methods (continuous and discrete, etc.), interface tracking in presence of phase changes. Among future challenges, specific attention will be devoted to micro-macro homogenization approaches based on statistical physics, numerical homogenization (hierarchical methods), generalized continua, etc. (ii) Multiscale characterisation and field measurements. This theme concerns the development of original experimental methods to obtain highly-resolved 2D-3D field measurements covering large dynamics as well as sophisticated conditional measurements (coupled Eulerian/Lagrangian measurements). Enormous challenges remain to be tackled to extend the dynamical range and the space/time resolution of measuring techniques, to simultaneously explore 2D-3D fields of two or more variables and to adapt these techniques to largescale systems. The development of nano-scale observations and measurements (radiation scattering WAXS/SAXS/USAXS…) will be pursued together with specific devices for the identification of local stresses and constitutive parameters of complex, active or biological media. (iii). Coupling with AI. Methods and tools coming from Artificial Intelligence (machine learning, deep learning, etc.) are quickly becoming staples for handling big data, improving data processing, and interpretation, and simulating complex systems. An important objective in future years will be to further support efforts and promote fruitful synergies between AI and traditional mechanical approaches through the development of specific, physically-constrained AI methods (physics-informed neural networks, etc.). Foreseen applications concern, e.g., the control of experimental setups, the multi-resolution characterisation of materials, the simultaneous processing of heterogeneous data, or the simulation and control of multiscale flows and deformation processes (turbulence, geomaterials, etc.).

IN BRIEF

With 250 permanent scientists specialised in fluid and solid mechanics, soft matter physics and process engineering, we develop experimental and numerical tools to contribute to technological innovation in the fields of energy management and conservation, propulsion and aerospace, process engineering, civil engineering, natural risks assessment, biorefinery, and health.