arXiv subjects

Mederic Argentina

Publications and source records attributed to Mederic Argentina.

4 recordsLinked to original sources

arXiv2023

Scaling the tail beat frequency and swimming speed in underwater undulatory swimming

Due to its great efficiency and maneuverability, undulatory swimming is the predominant form of locomotion in aquatic vertebrates. A myriad of animals of different species and sizes oscillate their bodies to propel themselves in aquatic environments with swimming speed scaling as the product of the animal length by the oscillation frequency. Although frequency tuning is the primary means by which a swimmer selects its speed, there is no consensus on the mechanisms involved. In this article, we propose scaling laws for undulatory swimmers that relate oscillation frequency to length by taking into account both the biological characteristics of the muscles and the interaction of the moving swimmer with its environment. Results are supported by an extensive literature review including approximately 1200 individuals of different species, sizes and swimming environments. We highlight a crossover in length around 0.5-1 m. Below this value, the frequency can be tuned between 2-20 Hz due to biological constraints and the interplay between slow and fast muscles. Above this value, the fluid-swimmer interaction must be taken into account and the frequency is inversely proportional to the length of the animal. This approach predicts a maximum swimming speed around 5-10 m.s$^{-1}$ for large swimmers, consistent with the threshold to prevent bubble cavitation.

physics.flu-dyn↗

arXiv2016

Shape and coarsening dynamics of strained islands

We investigate the formation and the coarsening dynamics of islands in a strained epitaxial semi-conductor film. These islands are commonly observed in thin films undergoing a morphological instability due to the presence of the elasto capillary effect. We first describe both analytically and numerically the formation of an equilibrium island using a two dimensional continuous model. We have found that these equilibrium island-like solutions have a maximum height $h_0$ and they sit on top of a flat wetting layer with a thickness $h_w$. We then consider two islands and we report that they undergo a non-interrupted coarsening that follows a two stage dynamics. The first stage may be depicted by a quasi-static dynamics, where the mass transfers are proportional to the chemical potential difference of the islands. It is associated with a time scale $t_c$ that is function of the distance $d$ between the islands, and leads to the shrinkage of the smallest island. Once its height becomes smaller than a minimal equilibrium height $h_{0}^{*}$, its mass spreads over the entire system. Our results pave the way for a future analysis of coarsening of an assembly of islands.

cond-mat.mtrl-sci↗

arXiv2010

Wave-train induced unpinning of weakly anchored vortices in excitable media

A free vortex in excitable media can be displaced and removed by a wave-train. However, simple physical arguments suggest that vortices anchored to large inexcitable obstacles cannot be removed similarly. We show that unpinning of vortices attached to obstacles smaller than the core radius of the free vortex is possible through pacing. The wave-train frequency necessary for unpinning increases with the obstacle size and we present a geometric explanation of this dependence. Our model-independent results suggest that decreasing excitability of the medium can facilitate pacing-induced removal of vortices in cardiac tissue.

physics.bio-ph↗

arXiv2004

Flutter of a Flag

We give an explanation for the onset of wind-induced flutter in a flag. Our theory accounts for the various physical mechanisms at work: the finite length and the small but finite bending stiffness of the flag, the unsteadiness of the flow, the added mass effect and vortex shedding from the trailing edge. Our analysis allows us to predict a critical speed for the onset of flapping as well as the frequency of flapping. We find that in a particular limit corresponding to a low density fluid flowing over a soft high density flag, the flapping instability is akin to a resonance between the mode of oscillation of a rigid pivoted airfoil in a flow and a hinged-free elastic filament vibrating in its lowest mode.

physics.flu-dyn↗