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L'HYDROPTERE: HOW MULTIDISCIPLINARY SCIENTIFIC RESEARCH MAY HELP BREAK THE SAILING SPEED RECORD

Pascal Fua, Véronique Michaud, Mohamed Farhat, Mark Sawley, Michel Deville, Robin Amacher, Joël Cugnoni, Guillaume Bonnier, Luc Blecha, Olivier Braun, Antoine Sigg, Marc Oggier, Daniel Schmäh, Martin Calmon, Stéphane Dyen, Davy Moyon

In 2009, l’Hydroptère broke the symbolic barrier of 50 knots and became the world fastest sailing boat over both 500 meters and 1 nautical mile. This major achievement relied on the high skills of the sailing team but also on technical advances of the boat, resulting from the scientific collaboration between the Hydroptère Design Team and the Ecole Polytechnique Fédérale de Lausanne (EPFL). In the present article, we highlight the multidisciplinary research activity performed within EPFL in the course of this collaboration involving aero- and hydrodynamics, materials and structure as well as computer vision. Various foils were tested at reduced scale in a high speed water tunnel, and the results used to validate the numerical simulations. Composite materials, their processing parameters and assembly components were tested. The structural behaviour was also investigated to determine strains and stresses in normal and extreme sailing conditions, taking waves into account, and a combined model was derived for dynamic simulation. Finally, advanced computer vision methods were developed and implemented on the boat to monitor foil immersion and cross beams deformations.

RINA2010

L'Hydroptère: A story of a dream

2010

Mechanical interaction between cells and fluid for bone tissue engineering scaffold: modulation of the interfacial shear stress

Dominique Pioletti, Alexandre Terrier, Lalaonirina Rakotomanana Ravelonarivo, Luc Blecha

An analytical model of the fluid/cell mechanical interaction was developed. The interfacial shear stress, due to the coupling between the fluid and the cell deformation, was characterized by a new dimensionless number . For above a critical value, the fluid/cell interaction had a damping effect on the interfacial shear stress. Conversely, for below this critical value, interfacial shear stress was amplified. As illustration, the role of the dynamic fluid/cell mechanical coupling was studied in a specific biological situation involving cells seeded in a bone scaffold. For the particular bone scaffold chosen, the dimensionless number Nfs was higher than the critical value. In this case, the dynamic shear stress at the fluid/cell interface is damped for increasing excitation frequency. Interestingly, this damping effect is correlated to the pore diameter of the scaffold, furnishing thus target values in the design of the scaffold. Correspondingly, an efficient cell stimulation might be achieved with a scaffold of pore size larger than 300 μm as no dynamic damping effect is likely to take place. The analytical model proposed in this study, while being a simplification of a fluid/cell mechanical interaction, brings complementary insights to numerical studies by analyzing the effect of different physical parameters.

2010