Ces travaux visent à améliorer la biofidélité des modèles virtuels de l’être Humain. Les statistiques montrent que la tête humaine est fréquemment sujette à des traumatismes cérébraux, des lésions et autres blessures. Une attention particulière sera donc donnée à la modélisation de la tête. Afin de mieux prédire les mécanismes lésionnels de la tête, la biofidélite des modèles doit être améliorée, pour cela les effets du fluide situé à l’intérieur de la tête doivent être pris en compte. Cependant, la modélisation des interactions entre un fluide corporel visqueux et un matériau mou comme le cerveau reste un verrou scientifique. Il est proposé d’étudier en détail la modélisation des interactions fluide-structure entre un fluide et un corps mou. Premièrement, une étude bibliographique détaillée sur les méthodes numériques de modélisation des interactions fluides-structure a permis d’évaluer chacune d’elles et de juger de celle qui est la mieux adaptée pour la résolution de la problématique. Deuxièmement, lors de travaux de thèse précédents, une expérience a été réalisée montrant l’influence du liquide cérébrospinal sur la cinématique du cerveau lors d’un chargement dynamique. Cette expérience est utilisée dans un premier temps pour caractériser numériquement le gel silicone Sylgard 527 utilisé comme substitut de cerveau. Dans un second temps des méthodes de couplage partitionné disponible dans le code commercial LS-Dyna ICFD sont utilisées pour modéliser l’expérience. Bien que les modèles de gel précédemment caractérisés ont été utilisés, la version avec fluide n’a pas pu être modélisée avec succès. Troisièmement, un code de couplage partitionné est donc développé. Il consiste en un middleware écrit en C++ couplant deux codes éprouvés, OpenFOAM et LS-Dyna pour la modélisation du fluide et du solide respectivement. De plus, parce que très peu d’essais expérimentaux utilisables pour la validation de code d’interaction fluide-structure sont disponibles dans la littérature, une expérience permettant cela a été réalisée dans une soufflerie. La comparaison des prédictions numériques avec les résultats expérimentaux est prometteuse et donne des résultats globaux satisfaisants. Les points qui ne peuvent pas être validés nécessitent de plus amples investigations et permettront d’améliorer les techniques de modélisations et le développement du code. / The purpose of this work is to improve the biofidelity of the human body models. The work is focused on the human head as it is one of the most injured part. In order to improve the traumatic brain injury onset and mechanism, the biofidelity of the head models has to be increased, thus, the fluids embedded inside the head has to be taken into account. Nevertheless, the modelling of the interactions occurring between the viscous corporal fluids and the soft matter as the brain remains a challenge. This study intends to investigate the fluid-structure interactions between a soft structure and a fluid. Firstly, in order to found the most relevant methods to solve the problem, a deep literature survey has pointed-out all the numerical methods available nowadays. Secondly, in a previous PhD work an experimental test has been carried-out to demonstrate the influence of the cerebrospinal fluid on the brain kinematics under dynamical load case. On one hand, the Silicon Sylgard 527 gel used as brain substitut has been characterized . Subsequently the partitioned coupling methods available in LS-Dyna ICFD have been assessed to model the experiment. Although, the previous characterized gel model has been used, the experiment has been unsuccessfully completed. Accordingly, it has been decided to develop an in-house coupling code. Thirdly, a partitioned coupling code has been developed. It is a middleware in C++ between two well establishing solvers OpenFOAM and LS-Dyna respectively for the fluid and the solid. Because there is very few experimental tests for the coupling code validation, it has been carried-out in this work a fluid-structure interaction experiment involving a soft plate in a wind channel. This appealing experiment allows the scientific community to validate easily their coupling algorithms. Subsequently, the developed coupling code is used to model the wind channel. The results depict a good overall agreement between the experiment and the simulation. Nonetheless, in order to get validated results further investigation are required mainly about the flow modelling.

Ice buildup on structures leads to problems that include reduced performance, structural damage and power outages. It is therefore important to limit the energy required for removal of ice from substrates to minimize buildup. Understanding the mechanism of ice adhesion and its dependence on variables like coating thickness, stiffness, surface free energy and morphology is critical for minimizing adhesion. Despite several developments in “icephobic” coatings, which are those that have low ice adhesion, it is important to understand adhesion on the fundamental level to make way for advanced coatings. To do so, a study has been carried out that explores key variables affecting ice adhesion using a commercially available silicone, Sylgard 184®. Sylgard 184 is a two-part, platinum cured silicone elastomer available from Dow Corning with good physical and chemical stability and is used in widely diverse research studies. The thermodynamic work of ice adhesion is related to the receding contact angle θ_r of water by Equation 1. wa≈ γ_w (1+cos⁡ θ_r) Eq 1. where γ_w is the surface tension of water. Considering an elastomeric substrate and ice as a rigid cylindrical adherent, the Kendall modelcan be adapted to relate peak removal force (Pc) with work of adhesion (wa), modulus (K), thickness (t), and radius (a) according to Equation 2. Pc ∝ πa^2 ((2wa K)/t)^(1⁄2) Eq. 2 Considering these relationships, hydrophobic materials with low surface energies and high receding contact angles are generally predicted to show low adhesion. To begin to understand details, the force required to remove an ice cylinder from the silicone elastomer Sylgard 184 was investigated by focusing on three variables: coating thickness, modulus and cure temperature. “Cure” refers to the network formation or crosslinking within the material. The Wynne research group has previously established a surprising dependence of qR on Sylgard 184 cure temperature.In this thesis, the relationship among variables noted above was examined by measuring Pc for Sylgard coatings. Additionally, effects of test temperature on ice adhesion strength was studied. Surface characterization methods including ATR-IR (attenuated total reflectance infrared spectroscopy), DCA (Wilhelmy plate dynamic contact angles) and AFM (atomic force microscopy) were employed. In summary, defined processing conditions were found optimum for minimizing ice adhesion to Sylgard coatings.

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