本文關(guān)鍵詞： 生物瓣膜 流固耦合 任意拉格朗日歐拉法 有限體積法 脈動流測試　出處：《山東大學》2017年碩士論文　論文類型：學位論文

【摘要】：心臟是人體的重要器官,心臟瓣膜一旦出現(xiàn)病變就會危及人的生命。目前,更換瓣膜仍是心臟瓣膜病的主要治療方法。生物瓣膜因具有良好的力學性能而逐漸成為瓣膜置換手術(shù)的首選,但仍存在著耐久性方面的問題,主要表現(xiàn)在瓣膜材料的疲勞、破壞以及鈣化現(xiàn)象。利用計算流體力學的方法對生物瓣膜與血液的耦合過程進行分析,獲得瓣葉的變形特點及應(yīng)力分布情況,對研究瓣膜損壞及鈣化的原因有重要的理論意義和參考價值。本文根據(jù)原生心臟瓣膜的特點,建立了生物瓣膜瓣葉的彈性結(jié)構(gòu)模型和血液不可壓縮粘性的流體模型。利用有限體積法和任意拉格朗日歐拉法分別推導血液與瓣葉的流固耦合方程。利用單向流固耦合分析軟件FLUENT及雙向流固耦合分析軟件LS-DYNA對瓣葉與血液的耦合過程進行仿真模擬,加入了血管壁對血液與瓣葉流固耦合的影響,得到了瓣葉變形、表面應(yīng)力及開口面積變化情況,分別比較泊松比和彈性模量對兩種流固耦合分析結(jié)果的影響。采用與仿真模型相近的生物瓣膜進行脈動流測試,通過將測試結(jié)果中瓣葉的變形及開口面積變化情況與仿真結(jié)果比較,評價兩種耦合分析方法得到結(jié)果的準確性。對比兩種耦合分析以及脈動流測試的結(jié)果,可以得出:LS-DYNA雙向流固耦合分析的結(jié)果與脈動流測試的結(jié)果更接近,瓣葉在開啟過程中開口面積形狀近似由三角形逐漸變?yōu)閳A形,且開啟速度在前期較快后逐漸變慢,瓣葉在45ms時完全開啟。FLUENT單向流固耦合分析結(jié)果在瓣葉變形較小時,與脈動流測試結(jié)果近似,當瓣葉變形較大時,發(fā)生了一定程度的失真。所以在分析瓣葉與血液耦合這種大變形問題上,采用LS-DYNA雙向流固耦合分析更合適。根據(jù)LS-DYNA雙向流固耦合分析的結(jié)果,瓣葉等效應(yīng)力及剪切應(yīng)力均主要集中在瓣葉縫合邊與自由邊的交界處,而最大主應(yīng)力主要集中在瓣葉的縫合邊。泊松比對瓣葉變形和有效開口面積的影響較小,但瓣葉的表面應(yīng)力會隨著泊松比的增大而減小,泊松比為0.45時,瓣葉的力學性能最好。彈性模量的增加會使瓣葉變形及有效開口面積減小,等效應(yīng)力及最大剪切應(yīng)力也隨著彈性模量的增大而減小,最大主應(yīng)力隨著彈性模量的增大而增大,彈性模量為4Mpa時,瓣葉的力學性能最好。綜合考慮應(yīng)對瓣葉進行處理,以獲得較大的泊松比以及較小的彈性模量。本文通過使用FLUENT及LS-DYNA對生物瓣膜與血液的耦合過程進行單向和雙向流固耦合分析,并對生物瓣膜進行脈動流測試,得到瓣葉變形及表面應(yīng)力分布情況。通過對比,得出任意拉格朗日歐拉法雙向流固耦合分析結(jié)果與測試結(jié)果更接近,其結(jié)果中也更加真實,對評估生物瓣膜的力學性能有重要參考價值,也為生物瓣膜的設(shè)計優(yōu)化提供了依據(jù)。
[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.
【學位授予單位】：山東大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：R318.11

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