基于FLUENT及LS-DYNA的生物瓣膜流固耦合分析

发布时间：2018-02-02 18:08

本文关键词： 生物瓣膜流固耦合任意拉格朗日欧拉法有限体积法脉动流测试　出处：《山东大学》2017年硕士论文　论文类型：学位论文

【摘要】：心脏是人体的重要器官,心脏瓣膜一旦出现病变就会危及人的生命。目前,更换瓣膜仍是心脏瓣膜病的主要治疗方法。生物瓣膜因具有良好的力学性能而逐渐成为瓣膜置换手术的首选,但仍存在着耐久性方面的问题,主要表现在瓣膜材料的疲劳、破坏以及钙化现象。利用计算流体力学的方法对生物瓣膜与血液的耦合过程进行分析,获得瓣叶的变形特点及应力分布情况,对研究瓣膜损坏及钙化的原因有重要的理论意义和参考价值。本文根据原生心脏瓣膜的特点,建立了生物瓣膜瓣叶的弹性结构模型和血液不可压缩粘性的流体模型。利用有限体积法和任意拉格朗日欧拉法分别推导血液与瓣叶的流固耦合方程。利用单向流固耦合分析软件FLUENT及双向流固耦合分析软件LS-DYNA对瓣叶与血液的耦合过程进行仿真模拟,加入了血管壁对血液与瓣叶流固耦合的影响,得到了瓣叶变形、表面应力及开口面积变化情况,分别比较泊松比和弹性模量对两种流固耦合分析结果的影响。采用与仿真模型相近的生物瓣膜进行脉动流测试,通过将测试结果中瓣叶的变形及开口面积变化情况与仿真结果比较,评价两种耦合分析方法得到结果的准确性。对比两种耦合分析以及脉动流测试的结果,可以得出:LS-DYNA双向流固耦合分析的结果与脉动流测试的结果更接近,瓣叶在开启过程中开口面积形状近似由三角形逐渐变为圆形,且开启速度在前期较快后逐渐变慢,瓣叶在45ms时完全开启。FLUENT单向流固耦合分析结果在瓣叶变形较小时,与脉动流测试结果近似,当瓣叶变形较大时,发生了一定程度的失真。所以在分析瓣叶与血液耦合这种大变形问题上,采用LS-DYNA双向流固耦合分析更合适。根据LS-DYNA双向流固耦合分析的结果,瓣叶等效应力及剪切应力均主要集中在瓣叶缝合边与自由边的交界处,而最大主应力主要集中在瓣叶的缝合边。泊松比对瓣叶变形和有效开口面积的影响较小,但瓣叶的表面应力会随着泊松比的增大而减小,泊松比为0.45时,瓣叶的力学性能最好。弹性模量的增加会使瓣叶变形及有效开口面积减小,等效应力及最大剪切应力也随着弹性模量的增大而减小,最大主应力随着弹性模量的增大而增大,弹性模量为4Mpa时,瓣叶的力学性能最好。综合考虑应对瓣叶进行处理,以获得较大的泊松比以及较小的弹性模量。本文通过使用FLUENT及LS-DYNA对生物瓣膜与血液的耦合过程进行单向和双向流固耦合分析,并对生物瓣膜进行脉动流测试,得到瓣叶变形及表面应力分布情况。通过对比,得出任意拉格朗日欧拉法双向流固耦合分析结果与测试结果更接近,其结果中也更加真实,对评估生物瓣膜的力学性能有重要参考价值,也为生物瓣膜的设计优化提供了依据。
[Abstract]:Heart is an important organ of the human body, once the heart valve disease will endanger people's lives. At present. Replacement of valve is still the main treatment for valvular disease. Biological valve has become the first choice for valve replacement because of its good mechanical properties, but there are still problems in durability. The coupling process of biological valve and blood was analyzed by computational fluid dynamics (CFD), and the deformation characteristics and stress distribution of valve were obtained. It has important theoretical significance and reference value to study the causes of valve damage and calcification. The elastic structure model and the incompressible viscous fluid model of the biological valve leaf were established. The fluid-solid coupling equations of the blood and the valve leaf were derived by the finite volume method and the arbitrary Lagrangian Euler method, respectively, and the unidirectional flow was used. The coupling process between lobe and blood was simulated by FLUENT and LS-DYNA. The effect of vascular wall on the fluid-solid coupling of blood and flap was added to obtain the changes of valve deformation, surface stress and opening area. The effects of Poisson's ratio and elastic modulus on the results of fluid-solid coupling analysis were compared, and the pulsating flow was measured with biological valves similar to the simulation model. The accuracy of the two coupling analysis methods is evaluated by comparing the variation of the lobe deformation and the opening area between the measured results and the simulation results, and the results of the two coupling analysis and the pulsation flow test are compared. It can be concluded that the results of the two-way fluid-solid coupling analysis of the two-way LS-DYNA are closer to those of the pulsating flow test, and the shape of the opening area of the lobe changes from triangle to circle in the process of opening. And the opening speed becomes slower gradually after the earlier period, and the result of unidirectional fluid-solid coupling analysis of completely open. Fluent at 45ms is similar to the result of pulsating flow measurement. A certain degree of distortion occurs when the lobe deformation is large, so the large deformation problem of the leaf and blood coupling is analyzed. It is more suitable to adopt LS-DYNA bidirectional fluid-solid coupling analysis. According to the results of LS-DYNA bidirectional fluid-solid coupling analysis. The equivalent stress and shear stress of the leaf are mainly concentrated at the junction between the suture edge and the free edge, while the maximum principal stress is concentrated on the suture edge of the leaf. Poisson's ratio has little effect on the deformation and effective opening area of the leaf. However, the surface stress of the leaf decreases with the increase of Poisson's ratio. When the Poisson's ratio is 0.45, the mechanical properties of the leaf are the best, and the increase of elastic modulus will reduce the leaf deformation and effective opening area. The equivalent stress and the maximum shear stress also decrease with the increase of the elastic modulus, and the maximum principal stress increases with the increase of the elastic modulus, when the elastic modulus is 4Mpa. The mechanical properties of the leaf are the best. Comprehensive consideration should be given to the treatment of the leaf. In order to obtain higher Poisson's ratio and smaller elastic modulus, unidirectional and bidirectional fluid-solid coupling analysis of biological valve and blood was carried out by using FLUENT and LS-DYNA. The valve deformation and surface stress distribution are obtained by pulsating flow test. By comparison, the results of two-way fluid-solid coupling analysis of arbitrary Lagrangian Euler method are closer to the test results. The results are also more realistic, which have important reference value for evaluating the mechanical properties of biological valves, and also provide a basis for the optimization of the design of biological valves.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：R318.11

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