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MEchanics GAthering -MEGA- Seminar: Talk1 - Interplay between geometry and growth generates bending cracks in the African bush elephant’s skin; Talk2 - High fidelity and fast simulations of deformable red blood cells using a combined finite elements immersed boundary lattice Boltzmann method

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Event details

Date and time 29.11.2018 16:1517:30  
Place and room
Speaker Antonio MartinsLANEUniversity of Geneva and Christos Kotsalos, SPC, University of Geneva
Category Conferences - Seminars
Interplay between geometry and growth generates bending cracks in the African bush elephant’s skin by Antonio MartinsLANEUniversity of Geneva
Abstract An intricate network of crevices adorns the skin surface of the African bush elephant, Loxodonta africana. These micrometer-wide channels enhance the effectiveness of thermal regulation (by water retention) and provide protection against parasites and intense solar radiation (by mud adherence). However, while the adaptive value of these structures was well established , their morphological characterization and generative mechanism remained unknown. Using microscopy, computed tomography and numerical simulations, we show that the African elephant’s skin channels are cracks in the animal’s brittle outermost skin layer, the stratum corneum. Our results reveal that the latter lies on top of an intricately curved lattice of millimetric skin elevations (papillae), and we propose that the continuous growth of the underlying skin layers forces the stratum corneum to bend inside the troughs between papillae, eventually causing it to crack. Therefore, the network of skin crevices emerges from the bending-dominated cracking of the animal’s stratum corneum.

High fidelity and fast simulations of deformable red blood cells using a combined finite elements immersed boundary lattice Boltzmann method by Christos Kotsalos, SPCUniversity of Geneva
Abstract We present a computational framework for the simulation of blood flows at the microscopic level using a modular approach that consists of a lattice Boltzmann solver for the blood plasma, a finite element solver for the deformable bodies and an immersed boundary method for the fluid-solid interactions. The novelty of our approach comes from the fact that our suggested FEM solver with its unconditional stability and versatile material expressivity, is almost as fast as mass-spring systems. For a known material, our solver has only one free parameter that demands tuning, which is related to the membrane viscoelasticity. In contrast, state-of-the-art solvers for deformable bodies have more free parameters (typically 4), while the calibration of the models demand special assumptions on mesh topology which restricts their generality. We suggest as well a correction on the energy proposed by Skalak et al. for the red blood cell membrane enhancing the strain hardening behavior at higher deformations. Our viscoelasticity model for the red blood cells, while simple enough and applicable to any kind of solver as a post-processing step, can capture accurately the characteristic recovery time and tank-treading frequencies. The framework is validated using experimental data, e.g., optical tweezers, low viscosity ektacytometry, while its scaling capability for multiple deformable bodies is proved.

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  • General public
  • Free

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  • MEGA.Seminar Organizing Committee

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Solids Structures Fluids

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