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.
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.
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
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
Plants bend and twist when they are subjected to wind and gravity, even more so when their structure is chiral, i.e., twisted along its axis. In this paper published in Extreme Mechanics Letters, we investigate the effect of chirality on the bending and twisting deformation of a rod and a ribbon in a wind tunnel.
Hydraulic turbines are subjected to various sources of excitation. How are their vibrations damped? It is the added damping due to the water flow on the turbine blades which reduces the vibration amplitude. The paper by Jean-Philippe Gauthier who works in collaboration with Hydro Quebec was just accepted in the Journal of Fluids and Structures. The preprint is available here.
Vibration mode of turbine blades.
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
Our paper on the developpement of an instability-assisted microfabrication technique base on the liquid rope coiling instability was accepted for publication in Advanced Materials.
Back cover of june 24th 2015 issue of Advanced Materials.
In the figure above, featured on the back cover of Advanced Materials, a 30 μm diameter thread of poly(lactic acid) (PLA) dissolved in dichloromethane is deposited on top of the eye of a sewing needle. The deposition robot traces a straight line; the helical shape of the thread is due to the liquid rope coiling instability. This instability is used to fabricate microstructured fibers with tailored mechanical.
Preprint available here: Passieux2015-InstabilityAssistedDirectWrite-AdvMat
Our work on the extrusion of a beam in a viscous fluid was published in Physical Review E. This project was inspired by the emergency swimming gait of unicellular Paramecium which expels Trichocysts to propel itself away from danger.
Time-lapse photography of a piano wire extruded at constant velocity in corn syrup.