局部狭窄股动脉中脉动流的流动特性数值模拟及试验研究

发布时间：2018-09-10 19:54

【摘要】：随着社会生活水平的提高以及人口老龄化问题日趋严峻,各种诱发因素,比如高血脂、高血压、肥胖等,都会引起血管发生硬化,导致血管狭窄,由此引发的各类心血管疾病威胁着人们的生命健康。开展病灶部位血流动力学的研究,对于研究其发病机理及临床医生手术方案的确定具有重要的实际意义。本文搭建了可模拟生理条件下的动脉血流动力学环境、参数可控的体外试验台,利用高精度的压力传感器监测正常股动脉及病变股动脉内的血液压力。作为试验研究的补充,以股动脉血管为原型,建立血管壁/血液耦合模型,对正常血管、孤立性、节段性和弥漫性病变血管四种情况进行数值模拟,分析血管壁的壁面剪切力分布和变形情况,以及管壁对内部血液流场的影响。具体展开以下工作:(1)研究并确定了血液非定常流动的双向流固耦合分析方法。血液在流动过程中,由于黏性的影响,会对血管壁产生较大的切应力,可将血液视为黏性流体。在血流动力学研究中,牛顿流体与非牛顿流体对所得结果影响并不大,误差不到2%,故本文数值模拟所用的流体为牛顿流体,试验流体用水和甘油的混合溶液(牛顿流体)代替血液。试验是在压强和温度变化较小的情况下进行的,所以可将流体视为不可压缩流体。运用雷诺数公式,计算得出在体股动脉的最大雷诺数约为1474~1942,均小于2300,故本文选用Laminar模型。血管为薄壁、各向同性、无渗透、无滑移(no slip)的线弹性直圆管。(2)搭建了管内脉动压力测量试验台,该试验台由电脑、电源、伺服电机、驱动器、PLC控制器、滚珠丝杆、注射器、微型压力传感器和数据采集器组成。PLC和驱动器通过上机程序控制伺服电机的运行。注射器固定安装在滚珠丝杆滑块上,伺服电机连接滚珠丝杆,从而控制注射器杆的进给速度。利用综合精度为±0.2%的微型压力传感器测量血管内脉动压力值,并用数据采集器获取数据。基于狭窄股动脉简化模型参数要求,将人体真实血管模型几何尺寸放大3.2倍,制备了血管试验样件。通过血管狭窄率公式,制作出孤立性、节段性、弥漫性血管和狭窄率为40%、60%、80%的病变血管模型。采用拉伸试验机测量血管的弹性模量,其值为1.62×106Pa。通过试验对比分析正常及病变股动脉两监测点处的压力差可以看出,股动脉的压力随时间的变化范围和趋势与入口速度变化趋势存在紧密的联系。随着速度的增大,脉冲压力达到峰值的数值变小。狭窄段区域越长,狭窄段前后的压力差幅值变化越大。狭窄度不同,病变血管压力差达到的幅值也不同,狭窄度为80%的血管脉动压力幅值最大。狭窄区域后端压力差的增大,导致血管内壁损伤,易引起其它未发病部位的病变。(3)应用Solidworks软件构建血管的三维CAD模型,采用ICEM对固体和流体域划分网格。应用ANSYS软件,模拟分析了人工血管监测点处压力差的大小,并与试验结果做了对比,发现狭窄段前后端的试验结果幅值比模拟结果稍大且达到峰值的时刻稍微滞后,但基本变化一致,确定了数值模拟计算方法的可行性。因此,本文所采取的流固耦合数值模拟方法可用来模拟分析人体正常股动脉和病变股动脉内的血流动力学特性。(4)对比分析正常及病变股动脉压力、速度、壁面切应力、血管形变、速度流线等参数可以看出,正常血管的压力和速度呈均匀性变化,股动脉狭窄造成狭窄处速度增大。狭窄后区域有涡流形成,对管壁造成损伤,加速了其它未发病部位的病变。在整个心动周期内,病变血管的狭窄处壁面切应力值较大,剥离内皮细胞,导致脂质等大分子物质沉附、累积在细胞损伤处。血管狭窄后区域管壁变形最大,管壁出现疲劳效应,易导致血管破裂。
[Abstract]:With the improvement of social living standards and the increasing severity of population aging problem, all kinds of inducing factors, such as hyperlipidemia, hypertension, obesity, will cause vascular sclerosis, resulting in vascular stenosis, resulting in a variety of cardiovascular diseases threatening people's lives and health. It is of great practical significance to study the pathogenesis and determine the operation plan of clinicians.In this paper, an in vitro test-bed with controllable parameters and simulated hemodynamic environment of arteries under physiological conditions was set up to monitor the blood pressure in normal femoral artery and diseased femoral artery with high precision pressure sensor. In order to analyze the distribution and deformation of wall shear force and the influence of wall on the internal blood flow field, the following work was carried out: (1) To study and determine the effect of wall on the internal blood flow field. A bi-directional fluid-solid coupling method for the analysis of unsteady blood flow is presented.During the process of blood flow, due to the influence of viscosity, a large shear stress will occur on the wall of the blood vessel and the blood can be regarded as a viscous fluid.In the study of hemodynamics, Newtonian and non-Newtonian fluids have little influence on the results, and the error is less than 2%. The fluid to be used is a Newtonian fluid. The mixed solution of water and glycerol (Newtonian fluid) is used to replace the blood. The experiment is carried out under the condition of small pressure and temperature change, so the fluid can be regarded as incompressible fluid. The maximum Reynolds number of the femoral artery in vivo is calculated by using Reynolds number formula, which is about 1474-1942, and is less than that of the femoral artery in vivo. In this paper, the Laminar model is used. The blood vessels are thin-walled, isotropic, impermeable and no-slip linear elastic straight circular tubes. (2) A test-bed for measuring the fluctuating pressure in tubes is built. The test-bed consists of a computer, a power supply, a servo motor, a driver, a PLC controller, a ball screw, a syringe, a micro-pressure sensor and a data collector. The actuator controls the operation of the servo motor by a program on the computer.The syringe is fixed on the ball screw slider and the servo motor is connected to the ball screw to control the feed speed of the syringe rod.The pulsating pressure in the blood vessel is measured by a micro-pressure sensor with a comprehensive accuracy of (+0.2%) and the data is obtained by a data collector. The parameters of the simplified model of narrow femoral artery were enlarged by 3.2 times the geometric size of the real blood vessel model, and the vascular test sample was prepared. The pressure difference between normal and diseased femoral arteries was compared and analyzed. It was found that the range and trend of femoral arterial pressure with time were closely related to the trend of inlet velocity. The greater the amplitude of pressure difference is, the different the degree of stenosis is, the greater the amplitude of pressure difference is. The amplitude of pressure difference is 80% of the stenosis. ICEM was used to mesh the solid and fluid domains. ANSYS software was used to simulate and analyze the pressure difference at the monitoring point of artificial blood vessel. The results were compared with the experimental results. It was found that the amplitude of the experimental results at the front and back of the narrow segment was slightly larger than that of the simulation results and the time lagged slightly when the peak value was reached, but the basic changes were consistent. Therefore, the fluid-solid coupling numerical simulation method adopted in this paper can be used to simulate and analyze the hemodynamic characteristics of normal and diseased femoral arteries. (4) Comparing and analyzing the normal and diseased femoral arteries pressure, velocity, wall shear stress, vascular deformation, velocity streamline and other parameters can be seen, normal blood vessels. The stenosis of the femoral artery results in an increase in the velocity of the stenosis. Eddies form in the stenosis area, causing damage to the wall of the vessel and accelerating the pathological changes of other non-pathogenic sites. After vascular stenosis, the wall deformation is the greatest, and fatigue effect appears on the wall, which is easy to lead to vascular rupture.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：R54

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