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Engineering

An Institute that Matters

From the subtle intricacies of a piano's melody to the deafening sound of supersonic planes– researchers at the recently created Jean le Rond d'Alembert Institute are exploring the extremely varied landscape of mechanical engineering.

At a recent conference, I was introduced to a fellow member of my institute by an American colleague!” This anecdote, told by CNRS Senior Researcher Danièle Dubois, is not surprising. The Institut Jean le Rond d’Alembert,1 co-founded in January 2007 by the Université Pierre et Marie Curie and CNRS, includes today nearly 190 people spread in five teams at three different sites. Theoreticians and specialists of numerical computations are at Jussieu university, most of the experimentalists are at Saint-Cyr-l’École, on the outskirts of Paris, while musical acoustic specialists work in temporary offices in the 15th arrondissement of Paris. Research at the Institute is extremely varied: what material best prevents leaks in nuclear reactors? Why does a spaghetti break into three pieces when twisted at both ends? How to build and fine-tune tomorrow’s biofuel engine? Can we make supersonic planes quieter? Could string instruments be made from composites instead of wood?
If at first these subjects seem to belong to very different fields, they do have one common denominator: mechanical engineering. As the institute’s director Gérard Maugin points out, “our field of research is broad but consistent: from the mechanics of pure solids to that of the simplest liquids, it includes all the intermediate– and often complex–nuances between these two states.”

mpia

© F. Vrignaud/CNRS Photothèque

Preparation of an experiment to study acoustic radiation of a metallic plate (MPIA).



Acoustic challenges
As a result, it is not surprising within the Institute to find combustion engine specialists rubbing elbows with stringed-instrument makers keen on synthetic materials. In her office in the 15th arrondissement, Danièle Dubois’ work in the LAM2 team demonstrates the institute’s eclectic style. She focuses on the perception of auditory phenomena as seen in human sciences. Her research is based on the initialobsebvátion that music or a simple sound is more than a mere acoustic phenomenon, it has a lot to do with how sounds are perceived by a listener.
As she explains, “a sound is perceived differently when it is heard for the first or the second time, although its physical characteristics may be perfectly identical. So we are attempting to understand how people identify sounds and perceive them as music, words, or noise.” While Dubois’ work has its roots in complex psychological and linguistic concepts, it has very concrete applications: “For example, Myriam Zali and I have worked for the SNCF (the French national railway company) on the acoustic quality in its high-speed TGV trains,” she says.
In an office nearby, Jean-Marc Fontaine, also on the LAM team, has been working for several years–well before the institute’s creation–on preserving audio recordings, particularly for the French Ministry of Culture: “No matter the medium used (hard disk, magnetic tape, compact disc, etc.), recorded information deteriorates over time. We are trying to identify the ageing processes in order to prevent them and to define optimal safeguarding strategies. For instance, we are looking for the best support and most suitable format for storing digital archives. Furthermore, we are working on the restoration of deteriorated analog recordings: Is it better to eliminate the scratching sounds of an old 78 RPM record, or to leave the information untouched to transmit it in its entirety to future generations? One thing is for sure: if nothing is done, we might lose vast amounts of information.”
Different site, different projects. François Coulouvrat is part of the MPIA3 team at Jussieu: “I have been working for a few years now with experimentalists at the INSP,4 on modeling the sonic boom of supersonic planes. This audio shock is created in the wake of an aircraft when it breaks through the sound barrier, and its properties are directly dependent on the plane’s speed or acceleration. Our work led us to develop software that anticipates the optimal flight configurations for supersonic aircraft to reduce noise. Airbus has purchased a license for the software.” One year after the creation of the institute, the research scientists are quite pleased. After all, many of them were already working together before its creation, like Joël Frelat from the MPIA team and Charles Besnainou from LAM. As Besnainou explains, “I am interested in how the history of the mechanical materials used for making a piano affects its tone. To better understand the phenomenon of the instrument’s acoustic radiation, Joël and I developed digital models for testing a piano’s tone for tuning (string tension, mechanical history of the wooden parts, etc.). This area has rarely been explored.”

Clean engines
We should not forget recent or planned collaboration, as illustrated by the FRT5 team at the institute’s third site in the Parisian suburb of Saint-Cyr-l’École. For site manager Philippe Guibert, “one of our activities is to design and offer new strategies for engine injection, combustion, and the reduction of pollution levels in alternative fuels such as biofuel. In order to improve our increasingly thorough understanding of these phenomena, we need to combine the efforts of experimentalists, specialists of computational mechanics, and theoreticians in both physics and chemistry. The institute will greatly facilitate this scientific alliance.” Another example concerns the research scientists in the FCIH group6 currently developing something called a “virtual atomizer.” “The phenomenon of atomization– like the one we observe coming out of an aerosol spray can–is extremely complex, involving both gaseous and liquid phases. In the liquid phase, the spray fragments into droplets whose sizes depend on the shape of the atomizer,” says Stéphane Zaleski, the team’s manager. “In order to study the phenomenon, we worked with specialists of computational mechanics on an open-source numerical software which we should eventually be able to apply to any concrete situation.” One, of course, would be the injection of fuel into the combustion chamber of an engine.

institute that matters

© F. Vrignaud/CNRS Photothèque

In order to analyze the dynamics of hydrocarbon combustion in an engine, scientists sample the intermediate chemical substances created between two strokes of the piston (FRT).



Breaking down materials
Theoreticians have similar prospects. For Pierre Sagaut, a specialist in hydrodynamic turbulence and manager of the FRT team, “some of our research involves simulating the turbulent flow around the wing of an aircraft. New collaborations will let us compare different numerical strategies in real time.” But there is also Dominique Leguillon of the MISES7 team: “While I am interested in the issue of rupture–the violent phenomenon that occurs when an object breaks– some of my new colleagues are specializing in fatigue and damage, both of which can also lead to the deterioration of a material. The complementary nature of our work is obvious. And looking ahead, why not consider a link between the study of rupture and that of droplet breakup? But we’re not there yet...”
“The obvious danger is too much dispersion,” says Gérard Maugin. “But it is also part of the richness of the Institut d’Alembert.” Most research scientists are convinced this richness will open new perspectives as required by the increasingly multidisciplinary nature of science. For LAM’s Hugues Genevois, whose team is working on new musical instruments at the crossroads of musical computing, acoustics, artistic creation, and the man-machine dialog, “what really matters is interaction.”

Mathieu Grousson

Notes :

1. The institute brings together five laboratories: Laboratoire de modélisation en mécanique, Laboratoire d'acoustique musicale, Laboratoire de mécanique physique, Laboratoire d'énergétique et mécanique des fluides internes, Laboratoire de mécanique, matériaux et structures.
2. Lutherie, acoustique et musique.
3. Modélisation, propagation et imagerie acoustique.
4. Institut des nanosciences de Paris (www.insp.upmc.fr).
5. Fluides réactifs et turbulence.
6. Fluides complexes et instabilités hydrodynamiques.
7. Mécanique et ingénierie des solides et des structures.

Contacts :

Institut Jean le Rond d'Alembert.
Danièle Dubois,
ddubois@ccr.jussieu.fr
Gérard Maugin,
gam@ccr.jussieu.fr
Jean-Marc Fontaine ,
jmfontai@ccr.jussieu.fr
François Coulouvrat,
coulouvr@lmm.jussieu.fr
Charles Besnainou,
chbesnai@ccr.jussieu.fr
Philippe Guibert,
philippe.guibert@upmc.fr
Stéphane Zaleski,
zaleski@lmm.jussieu.fr
Pierre Sagaut,
sagaut@lmm.jussieu.fr
Dominique Leguillon,
dol@ccr.jussieu.fr


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