Morphing surfaces leading to aerodynamic drag control
Smart Morphable Surfaces enable switchable and tunable aerodynamic drag reduction of bluff bodies. Their topography, resembling the morphology of golf balls, can be custom-generated through a wrinkling instability on a curved surface. Pneumatic actuation of these patterns results in the control of the drag coefficient of spherical samples by up to a factor of two, over a range of flow conditions.
More press coverage : NewScientist,
Wrinkling crystallography on spherical surfaces
Curved crystals cannot comprise hexagons alone; additional defects are required by both topology and energetics that depend on the system size. Treating dimples, generated through curved wrinkling, as point-like packing units, we show that our system can be mapped into and described within the framework of curved crystallography, albeit with some important differences attributed to the far-from-equilibrium nature of our patterns.
Curvature-induced symmetry breaking determines the wrinkling pattern
The wrinkling morphologies of our curved elastic bilayer materials are further analyzed in collaboration with a team from the Math department of MIT. The pattern formation is described here by deriving a generalized Swift-Hohenberg theory. This theory, universally applicable to macroscopic and microscopic systems, can be extend to arbitrarily shaped surfaces, thereby solving a longstanding problem in elasticity theory.
N. Stoop, R. Lagrange, D. Terwagne, P. M. Reis and J. Dunkel, “Curvature-induced symmetry breaking determines elastic surface patterns“, Nat. Mat. 14, 337, 2015. [html]
See also Nature Materials News & Views
Planar vs. non-planar buckling
Inspired by the morphology of growing plant roots and compressed microtubules in cells, our team from MIT devised a model experiment to study, in collaboration with a team of Harvard University, the multi-dimensional buckling of fibers in an elastic matrix. This latter research could open opportunities for functionality by generating complex 3D shapes, reversibly and on-demand.
S. Tianxiang, J. Liu, D. Terwagne, P. M. Reis and K. Bertoldi, “Buckling of an elastic rod embedded on an elastomeric matrix: planar vs. non-planar configurations”, Soft Matter, 10, 6294, 2014. [html, pdf]
Bouncing droplets resonant modes
To enhance the bouncing droplet deformation we consider a low viscosity droplet on a high viscosity bath. Depending of the excitation frequency, different deformation modes appear. Theoretically, these modes correspond to spherical harmonics Y(l,m).
The singing bowl
The Tibetan singing bowl is a type of standing bell originating from Himalaya. A singing bowl is played by striking or rubbing its rim with a wooden or leather-wrapped mallet. The sides and rim of the bowl then vibrate to produce a rich sound. When the bowl is filled with water, this excitation can cause crispation of the water surface that can be followed by more complicated surface wave patterns and ultimately the creation of droplets. We present here an extensive investigation of the acoustics and the fluid dynamics of the bowl.
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Microfluidic on a wire
Using simple fiber networks, elementary microfluidic operations with droplets are performed, such as coalescence, division, encapsulation and chemical reactions by adjusting gravity and capillary forces.
Summary on a poster presented at the American Physical Society, Division of Fluid Dynamics at Mineapolis in November 2009.
When a droplet impacts a dry granular bed, it creates all sorts of dry and stable structures after impact that looks like donuts, pancakes or complex blobs. These are frozen “splashes”. Depending on the impact speed, the droplets wet the sand and shape it before being sucked by the granular bed underneath.