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首页> 外文学位 >Developpement d'une methode d'elements finis pour predire l'hemolyse mecanique dans des ecoulements (French text).
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Developpement d'une methode d'elements finis pour predire l'hemolyse mecanique dans des ecoulements (French text).

机译：预测流动中机械性溶血的有限元方法的发展（法文）。

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We developped a finite element method to predict hemolysis in flows. It uses a discontinuous Galerkin formulation to solve the hemolysis prediction model. The latter is a hyperbolic advection-reaction equation. Solving such equations is not a trivial task. The task becomes even more complicated when the reaction term (source term) is complex and discontinuous, and the flow contains recirculation zones. To overcome these difficulties, we developped a solution algorithm that includes adaptive remeshing driven by error estimates for both the velocity and hemolysis fields. To our knowledge we present the first such error estimator for hemolysis. Code verification using the method of manufactured solutions shows that the finite element method delivers the theoretical convergence rate. Lower convergence rates were observed for more complex, realistic flows in cannulae and sudden axisymmetric contractions. Hemolysis predictions in cannulae allowed us to assess the usability of our tool and its capability to produce realistic predictions in this particular case. We then measured in vitro the hemolysis in blood circulating through sudden and gradual contractions. The flow Reynold's number for experiments and simulations was set to 1200, based on contraction's inlet diameter and average velocity, and blood's viscosity at infinite shear rate (mu infinity) for a shear-thinning fluid. Detailed experimental procedures were put together to ensure accurate and consistent hemolysis measurements in the laboratory. In particular, a lot of energy was spent on the precise measurement of blood's muinfinity viscosity. Due to the presence of red cells, detrimental effects such as slip or end effects are often observed when measuring blood viscosity. We finally found out that those effects could be neglected due probably to the low hematocrit levels (28 and 31%) measured in our bovine blood samples. Comparisons between hemolysis predictions and experimental measurements lead us conclude that the threshold value of the mechanical stress to produce hemolysis (set to 250 Pa in the prediction model and based on the literature) is probably too low for this type of flow.
机译：我们开发了一种预测流动中溶血的有限元方法。它使用不连续的Galerkin公式求解溶血预测模型。后者是一个双曲线对流反应方程。解决这样的方程式并非易事。当反应项（源项）复杂且不连续且流程包含再循环区域时，任务将变得更加复杂。为了克服这些困难，我们开发了一种解决方案算法，该算法包括针对速度场和溶血场的误差估计驱动的自适应重划。据我们所知，我们提出了第一个这样的溶血误差估计器。使用制造解决方案的方法进行的代码验证表明，有限元方法可提供理论收敛速度。对于更复杂，更现实的套管流动和突然的轴对称收缩，观察到较低的收敛速度。套管中的溶血预测使我们能够评估工具的可用性及其在这种特殊情况下产生实际预测的能力。然后我们在体外测量了通过突然和逐渐收缩而循环的血液中的溶血现象。基于收缩的入口直径和平均速度以及无限稀疏剪切速率（μ无穷大）的血液稀薄度，用于实验和模拟的雷诺流动数被设置为1200。详细的实验程序组合在一起，以确保在实验室中进行准确而一致的溶血测量。尤其是，大量的能量花费在精确测量血液的多亲和力粘度上。由于存在红细胞，因此在测量血液粘度时通常会观察到有害影响，例如滑倒或末端影响。我们最终发现，这些影响可能被忽略了，可能是由于在我们的牛血样本中测得的血细胞比容水平很低（分别为28％和31％）。溶血预测和实验测量值之间的比较使我们得出结论，对于这种类型的流动，产生溶血的机械应力阈值（在预测模型中并根据文献设置为250 Pa）可能太低。

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