How does flutter impose a limit on drag reduction by reconfiguration

Trees and plants bend and deform under the wind, we say that they reconfigure. This elastic reconfiguration enables a drag reduction. However, a flag fluttering in the wind is a good example that flexibility can lead to flow-induced vibrations with its accompanying dynamic loads.
In her new paper, Maryam Boukor investigates the ideal flexibility that enables the best compromise between drag reduction and flutter instability. The work is the fruit of collaborative work with Augustin Choimet and my colleague Éric Laurendeau
Watch the 2min summary video below and read the full paper in Physics of Fluids.

Spiderweb-inspired, transparent, impact-absorbing composite!

Shibo Zou’s new paper is out in Cell Reports Physical Science!
Dans cet article, Shibo montre comment une instabilité de mécanique des fluides peut être utilisée pour microstructurer des fibres avec une imprimante 3D, et comment, lorsqu’elles sont imprimées avec du polycarbonate, ces fibres peuvent être intégrées dans un composite transparent absorbant les chocs. Parce que les fibres se bouclent et fusionnent sur elles-mêmes lors de l’impression, elles nécessitent beaucoup d’énergie pour se briser.
Regardez un résumé vidéo d’une minute trente secondes de ce travail ci-dessous.

Lisez l’article complet ici, c’est gratuit ! (open access)

Vibration of a high-head Francis turbine runner

The runner of a high-head Francis hydraulic turbine is flattened and has vibration modes resembling those of a disc. When the runner rotates in water, the vibrating waves propagating in the direction of rotation and against rotation interact differently with water. There is therefore a doubling of natural frequencies. This implies that the turbine designer must work harder to identify these frequencies and ensure that no resonance phenomenon will occur on the turbine in operation.
This task is now (slightly) simplified by the new analytical model developed by Max Louyot as part of his master’s degree in partnership with Andritz Hydro Canada, published in the Journal of Fluids and Structures.

Review paper on FSI in plants

My review paper on the “Mechanics of a plant in fluid flow” is out in the Journal of Experimental Botany. This review covers the statics and dynamics of plant–fluid interactions, e.g., the static reconfiguration of a plant deforming under fluid flow, and also its dynamic swaying and flapping. It covers the mechanics at play in terrestrial plants as well as aquatic plants and seaweeds. Biological implications are highlighted and ideas for future research avenues are suggested.

Preprint is available here on researchgate and arXiv.

Our work highlighted in the Top-10 discoveries of 2018 by Québec Science magazine

Sampada Bodkhe‘s PhD work on 3D printing of piezo-electric sensors has been selected by Quebec Science magazine in its Top-10 Discoveries of the Year 2018! The breakthrough allows 3D printing at room temperature of a deformation sensor and its electrodes in one step. We demonstrate how this can be used to make smart clothes that measure breathing or movement. We also demonstrate how one can print embedded sensors on a miniature drone wing allowing to monitor in real time its vibrations.

Visit the Québec Science website to vote for her invention and make it the Top discovery of 2018 in Quebec!

Des capteurs de mouvement imprimés en 3D

3D Printing a piezoelectric sensor in one go!

Before she finished her PhD and left the Laboratory for Multiscale Mechanics at Polytechnique Montréal, Sampada Bodkhe invented a way to 3D print piezoelectric sensors in one step: she coextrudes the active sensor and the electrodes together in one go, without the need for a subsequent poling or treatment step. Just print your sensor and its ready to use!
You can read a popularized account of her work on Advanced Science News. FYI, we applied for a patent with Gestion Univalor.

Single Step 3D Printing of Piezoelectric Sensors

New publication on the reconfiguration of rods

Trees bend and twist when subjected to wind. This deformation, or reconfiguration, allows the tree to reduce its drag. In our paper published in the Journal of Fluids and Structures we investigate how torsional and bending deformations play different roles in reconfiguration. We investigate this through a combination of wind tunnel experiments on flexible reinforced foam rods and a theoretical Kirchhoff rod model.


Kirchhoff rod bending and twisting with large amplitude under fluid flow