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Control Prediction and LeaRning in Mixing processes

Periodic Reporting for period 2 - CoPerMix (Control Prediction and LeaRning in Mixing processes)

Periodo di rendicontazione: 2023-01-01 al 2024-12-31

The CoPerMix ITN program was intended to make fundamental progress in the field of mixing, the science describing the route to uniformity in stirred systems. This goal was achieved in several respects:

On the heuristic side, we have developed and promoted a novel and unified lamellar description of mixing processes, in its `quantum’ representation (identifying the elementary bricks and their interaction in a mixture). This approach has generated new results in e.g. mixing in porous media (soils), mixing in stratified flows (ocean) of very viscous substances (pastes), for example.

We has from the start payed on purpose attention at identifying all sub-area of science and technology where these new concepts can find relevance and/or usefulness, hence the broad range and diversity of topics of our 15 PhD students (Early Scientific Researchers, ESRs). Their work goes from cloud physics (mixing of droplets in a varying field of water vapor), chemotaxis (the locomotion of animals in stirred nutriment fields), safety (dispersion of pollutants), landscape formation (mixing in soils and porous media), thermo-aline convection (mixing of salinity in the ocean), or to the developments of news bioreactors, for example. In all these sectors, our impact has contributed to a better understanding, and therefore to improved practices and policies, the prerequisite for solid and informed decisions concerning societal changes.

Our faith was that pushing further the boundaries of knowledge is the best way to contribute to applications, of whatever nature they may be. Given the success of our two thematic workshops, and notably of our Cargèse School devoted to all the facets of the discipline (which has gathered the nec-plus-ultra of the fluid mechanics community), and of our Solvay Workshop on the same theme, and given the enthusiasm of our ESRs, we are confident that it was worth pursuing our efforts following this virtuous track.
A number of very original observations have been made in various sub-aspects of the project, for instance regarding mixing in stratified media (like the ocean), and mixing of fluids with very different viscosities (like in several industrial applications involving pastes), including some of them beyond our initial expectations (the `diffuselet’, or `quantum' concept for mixing), a major conceptual advance for the modeling of mixing. All these advances have been published in the leading journals of the field (Journal of Fluid Mechanics, Physical Review Letters, Physical Review Fluids etc...). A few examples among other achievements are:
 
ESR 1 and 6 (Aix-Marseille and CNRS) have finalized groundbreaking experiments: they consists in rotating Taylor-Couette devices to study mixing in rotating/stratified/viscous flows with applications to geophysics, the industry of pastes and stirring of fragile objects like algae in bioreactors. The secondment of ESR2 (Cambridge) has been the opportunity to finally understand what a mixing efficiency is in stratified environments.

ESR 10 At TUIL work on simulation on the theoretical foundations of turbulence, turbulent mixing in relation to cloud microphysics. He implemented a Lagrangian module which tracks the individual water droplets in the cloud to compute various statistical properties of the swarm of droplets necessary to elaborate a physical understanding of the processes involved in storms, in particular. A collaboration with ESR6 dueling his secondment has culminated in a very original application of the `diffuselet' concept.

ESR 13 at UNESCO studies chemotactic strategies in stirred environments and have developed a new finite-state-controller algorithm that is competitive with previous approaches. A public repository has been created which allows to compute the optimal policy and evaluate its performance in user-defined environments. Demos for a selected choice of environments are given.

ESR 15 at EAWAG in Zürich has setup a microfluidic platform for the study of chemotaxis experiments for unique in-situ measurments and works in parallel on numerical and the theoretical modeling of his configuration.
 
Several ESRs have attended several top level conferences to disseminate their results. The Copermix Project has been represented at: the GRC - Oscillations and Dynamic Instabilities in Chemical Systems (USA), COST Chemobionics Pisa Annual Meeting (IT), GRC on Flow and Transport in Permeable Media (SZ), EGU (AT), GRS/GRC Ocean Mixing (USA),EFMC14 (GR), Spain InterPore Chapter (SP), APS Division of Fluid Dynamics (USA) etc... in addition to the two scientific workshops in Marseille and Trieste organized within the ITN frame, and a school devoted to mixing in Cargèse (Corsica) as well as a closing Solvay Workshop (Bruxelles).
Our faith was that pushing further the boundaries of knowledge is the best way to contribute to applications: Concerning heuristics progresses on the lamellar representation of mixing, the concept of `diffuselet’, and the ongoing `quantum’ theory of mixing, which consists in representing a mixture as the sum of its fundamental constituents (the diffuselets which we call quanta) and their interaction rule, is with no doubt way beyond the state of the art of the discipline. It provides very precise predictions and is easily adapted to numerical computations. It is undoubtedly one of the highlights of this program and has found many applications in seals ESRs work.

Other advances have occurred in the field of mixing in stratified flows, a longstanding question, which has received recently, within this program (with ESR2) decisive elements of answers. The -practically not investigated before- mixing of fluids with very different viscosities has progressed fundamentally. More generally, our ESRs, working at the forefront of their respective disciplines, contribute to a better understanding of the fundamentals, and therefore foster improved methods when these need to be improved, may they concern the search for better productivity, design policies, or safety practices.

In sum, the goal of CoPerMix was to train a new generation of scientists via research on these scientific objectives to revolutionize the approach to mixing across different fields ranging from blending/stirring protocols, chemistry, biology, and physics to environmental sciences using a multidisciplinary approach which integrates leading academic and industrial partners. This endeavor has involved original experiments, refined theories, modeling, intellectual rethinking, and the enrollment of students in fertilizing exchanges between various research communities to open their minds to unexpected aspects, consequences, or applications of their work. 

It has been a great privilege of this interdisciplinary program (and a real pleasure for its coordinator) to raise a generation of young researchers for addressing these outstanding issues in the future.
The transition diagram associated to the algorithm (UNESCO)
1.scalar supersaturation field, 2.turbulent velocity field mag 3.the kinetic energy dissipation rate
A trajectory obtained by our search algorithm (UNESCO)
Background flow is imposed from left to right.The white pillar corresponds to the source of nutrient
Mixture of miscible fluids with different viscosities (Aix-Marseille)
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