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1.
血流动力学数值模拟与动脉粥样硬化研究进展   总被引:4,自引:0,他引:4  
血流动力学因素被认为与动脉粥样硬化等病理改变密切相关。目前血流动力学数值模拟的对象,主要集中于分支动脉、弯曲动脉以及因血管内膜增生而导致的局部狭窄动脉,这些都是动脉粥样硬化多发的病灶部位。精确的血流动力学数值模拟,必须依赖于解剖精确的血管几何模型和生理真实的血流与管壁有限变形的非线性瞬态流-固耦合。只有在“虚拟血液流动”的基础上,综合考虑血管内的壁面剪应力、粒子滞留时间和氧气的跨血管壁传输等多种因素,血流动力学的数值模拟才能真正有助于人们理解动脉粥样硬化的血流动力学机理,才有可能应用于有关动脉疾病的外科手术规划中。  相似文献   

2.
郭子漪  赵建福  李凯  胡文瑞 《力学学报》2022,54(5):1186-1198
作为流动与传热相互耦合的非线性过程, 热毛细对流有着复杂的转捩过程, 探究流场和温度场随参数变化而发生的分岔现象, 是热毛细对流研究的一个重要课题. 基于本征正交分解的POD-Galerkin降维方法可以通过提取特征模态, 构建低维模型, 实现流场的快速计算. 数值分岔方法可以通过求解含参数动力系统的分岔方程, 直接计算稳定解和分岔点. 探究了将直接数值模拟方法、POD-Galerkin降维方法、数值分岔方法的优势结合, 以提高热毛细对流转捩过程分析效率的可行性. 利用直接数值模拟得到的流场和温度场数据, 构建了不同体积比下, 二维有限长液层热毛细对流的POD-Galerkin低维模型, 在低维模型上采用数值积分及数值分岔方法计算了分岔点, 得到了低维方程的分岔图. 在一定参数范围内, 在低维模型上模拟热毛细对流, 对雷诺数和体积比进行参数外推, 通过与直接数值模拟的结果对比, 验证了低维模型的准确性与鲁棒性. 说明了低维方程可以定性反映原高维系统的流动特性, 而定量方面, 由低维模型和直接数值模拟计算得到的周期解频率的相对误差大约为5%. 验证了利用POD-Galerkin降维方法研究热毛细对流的可行性.   相似文献   

3.
冠状动脉旁路移植管搭桥术后,常会产生血管再狭窄,导致手术失败,。这与移植管的几何结构及血流动力学是密切相关的。作为改进措施,作者提出了采用对称双路搭桥的设想。本文利用有限元分析方法,对冠状动脉搭桥术中对称双路移植管内的生理流动进行了数值仿真。计算了缝合区附近的流场、壁面切应力、压力等血流动力学因素在心动周期内的时空分布情况。计算结果表明,对称双路搭桥具有较好的血流动力学,可以改善血管流场状况和减轻再狭窄发生。这对临床手术计划是很有帮助和指导意义的。  相似文献   

4.
具有切应力梯度的平行平板流动腔的构造   总被引:2,自引:0,他引:2  
覃开蓉  柳兆荣  徐刚 《力学季刊》2001,22(3):281-288
在近年来关于流体切应力与细胞力学行为之间关系的研究中,流体切应力梯度被认为是诱发动脉粥样硬化和内膜增生的重要因素之一.本文探讨如何利用常用的离体细胞力学实验工具--平行平板流动腔模拟具有梯度的定常流切应力环境.结果表明,根据Hele-Shaw流的原理和常用复势W(Z)=AZn(n>1)的特性,可构造出具有各种切应力梯度分布的流动腔.与其它模拟切应力梯度的方法比较,本文的方法更加简洁、可行.  相似文献   

5.
杨烁  丁祖荣  孙刚  王勇 《力学季刊》2005,26(4):604-608
在定常流不对称人口速度剖面条件下,对健康型和致病型颈动脉分叉TF-AHCB模型进行实验和数值模拟研究,发现不对称人口速度剖面的形状对模型外侧壁的低切应力和切应力速度分布有明显影响。在50°模型窦前部的壁面切应力梯度比20°模型高出数倍,当人口速度剖面向颈内动脉偏斜时更可高出10倍以上。这些结果对认识导致动脉粥样硬化斑块的血流动力学因子的影响因素有重要参考价值。  相似文献   

6.
Taylor补丁对新型动脉旁路移植流场影响的数值分析   总被引:1,自引:0,他引:1  
为了研究Taylor补丁对新型(S型)动脉旁路移植术中吻合口处流场的影响,使用数值方法研 究了采用Taylor补丁和未采用该补丁的两个S型旁路移植模型内流场的血流动力学差异. 对 流速、壁面切应力和切应力梯度等参数进行了比较分析. 结果表明,Taylor补丁对吻合口的 流场有显著影响. 采用Taylor补丁的模型其下游吻合口处的流场分布较未采用补丁的模型更 均匀,二次流平均流速减小约34.48%,壁面切应力梯度减小约52.22%,从壁面切应力 梯度方面分析,这将有助于改善血流动力学分布,抑制动脉粥样硬化. 但从壁面切应力值分 析,其动脉底部的壁面低切应力区明显增大,平均壁面切应力值减小30.33%,这又将促 使动脉粥样硬化. 因此,Taylor补丁是否对S型搭桥术具有治疗优越性,仅从血流动力学分 析尚不能定论,配合数值计算结果进行动物和临床实验研究是十分必要的.  相似文献   

7.
申涛  罗宁  向俊庠  高祥涛 《爆炸与冲击》2018,38(5):1172-1180
为研究切缝药包定向控制爆炸机理,基于双缝/耦合切缝药包爆轰行为高速纹影实验,建立"炸药-切缝管-空气"模型,采用数值模拟方法研究切缝药包爆炸过程中冲击波相互作用、爆炸流场压力时空分布和切缝管形态变化。研究结果表明:切缝药包爆炸过程中切缝管能够有效控制爆炸能量释放和爆生气体动力学行为;切缝方向压力超前且高于非切缝方向;在爆炸冲击波及爆生气体共同作用下,切缝管曲率不断变小且从起爆点处以相同的变形特征沿切缝管轴向发展;数值模拟结果与实验结果吻合。  相似文献   

8.
为了探索热刺激下微循环变化的机理,建立了鼠背部皮肤加热实验台,获得了加热过程中的血流量。在热刺激作用下,血流量呈现出两阶段变化,分别受到神经调节和内皮调节作用。根据内皮调节模型,模拟不同温度刺激下血流变化引起的血管径振荡过程,获得了内皮舒张因子NO在血管壁中的分布和不同温度下的血管舒张度。结果表明:加热温度越高,血管舒张程度越剧烈;采用318K加热时,血管增大了0.26倍;通过力学分析,证明了血管舒张可使血管壁所承受壁面切应力保持恒定,同时证实了热刺激促使的二次血流升高是内皮调节作用的结果。  相似文献   

9.
本文求解局部缓慢扩张动脉管中血液振荡流的基本方程,得到血管内血液的流速与压力梯度的关系。通过导出压力梯度沿局部扩张管轴向的变化特性。建立利用扩张段上游血管均匀段中心流速波形确定局部扩张管中血液流的速度和切应力分布的方法,文章以人体颈动脉余弦扩张为例进行分析。详细讨论了局部扩张对血管壁切应力及其梯度分布的影响。数值结果表明,在与刚性均匀管中管壁切应力沿轴向保持不变不同,在局部扩张段,管壁切应力将随着血管半径的增大而减小,因而管壁切应力梯度一般不为零,甚至在某些位置达到相当大的数值。另外,随着血管扩张程度的增加,管壁切应力还将进一步减小,而且管壁切应力梯度也将进一步增大,血管扩张导致管壁切应力的这些变化将直接影响血管壁的结构和功能,使其产生适应性的变化。  相似文献   

10.
采用浸入式边界法,模拟了多个红细胞和血小板在毛细血管内流动过程中的相互影响。通过改变红细胞体积比和红细胞的力学特性,分析了红细胞力学特性对血小板在与内皮细胞发生粘附前的动力学行为的影响机理,包括:红细胞对血小板趋壁效应的影响,血小板在流动过程中的变形情况,并从血小板所受垂直壁向合力的角度深入研究了红细胞和血小板之间的相互作用。数值模拟的结果表明,增加血流中的红细胞体积比,减小了血小板和血管壁之间的距离,增大了血小板的变形,血小板所受垂直壁向合力呈现剧烈波动,两者之间的挤压显著加强;而增大红细胞硬度,使得血小板的离壁距离增大。  相似文献   

11.
窦部对称狭窄对颈动脉内流场影响的数值研究   总被引:1,自引:1,他引:0  
以颈动脉分岔血管为例,采用数值方法研究了窦部环缩狭窄之后的流场分布情况,并和正 常血管情况下的流场分布进行了比较. 结果表明,采用环缩方式给颈动脉分岔血管施加对称 的狭窄改变了颈动脉窦内流场,特别是壁面剪应力的分布规律. 低剪应力区出现在狭窄段之 后的窦内,并且沿整个周向均匀分布. 根据低剪应力和动脉粥样硬化的关系,指出: 若人为地给颈动脉窦内施加对称狭窄,则脂质沉积将在狭窄下游的窦内沿周向轴对称 发展. 为了更真实地反映颈动脉窦内的狭窄,建议根据动脉血管中的实际狭窄情况,采用非 对称的狭窄分布模式.  相似文献   

12.
颈动脉分支的血流动力学数值模拟   总被引:7,自引:0,他引:7  
采用有限元法数值模拟颈动脉分支的血流动力学。根据在体测量的实际尺寸来构造颈动脉分支的几何模型,以保持模型的解剖精确度;利用在体测量的颈内动脉和颈外动脉流量波形以及主颈动脉的压力波形来确定数值计算的边界条件,以保持数值计算的生理真实性。关注的重点是颈动脉窦内的局部血流形态、二次流和壁面剪应力。在心脏收缩的减速期和舒张期的某些时刻,颈动脉窦中部外侧壁面附近产生了流动分离,形成了一个低速回流区。该流动分离是瞬态的,导致了壁面剪应力的振荡,其振荡范围在-2~6dyn/cm^2之间。同时,颈动脉窦中部横截面内的二次流存在于整个心动周期,最大的二次流速度为同时刻轴向速度平均值的1/3左右。  相似文献   

13.
The rheological characterisation of concentrated shear thickening materials suspensions is challenging, as complicated and occasionally discontinuous rheograms are produced. Wall slip is often apparent and when combined with a shear thickening fluid the usual means of calculating rim shear stress in torsional flow is inaccurate due to a more complex flow field. As the flow is no longer “controlled”, a rheological model must be assumed and the wall boundary conditions are redefined to allow for slip. A technique is described where, by examining the angular velocity response in very low torque experiments, it is possible to indirectly measure the wall slip velocity. The suspension is then tested at higher applied torques and different rheometer gaps. The results are integrated numerically to produce shear stress and shear rate values. This enables the measurement of true suspension bulk flow properties and wall slip velocity, with simple rheological models describing the observed complex rheograms.  相似文献   

14.
用电化学方法测试动脉模型壁面剪应力   总被引:3,自引:0,他引:3  
应用电化学方法,对动脉模型T型分叉部位流场壁面剪应力进行测试研究。测试了对于现有理论分析和数值计算都比较困难的高雷诺数(RE=1000-2000)流动流场的壁面剪应力,并且对苦干不同雷诺数及不同支管分流情况进行了系列测试。通过实验发现,此部痊同时存在高剪应力区和低剪应力区,确定了它们的位置和剪应力的大上。系列测试还显示:随着雷诺数的变化,无量纲管应力有一定的变化;而当支管分流变化时,无量纲剪应力的  相似文献   

15.
Both clinical and post mortem studies indicate that, in humans, the carotid sinus of the carotid artery bifurcation is one of the favored sites for the genesis and development of atherosclerotic lesions. Hemodynamic factors have been suggested to be important in atherogenesis. To understand the correlation between atherogenesis and fluid dynamics in the carotid sinus, the blood flow in artery was simulated numerically. In those studies, the property of blood was treated as an incompressible, Newtonian fluid. In fact, however, the blood is a complicated non-Newtonian fluid with shear thinning and viscoelastic properties, especially when the shear rate is low. A variety of non-Newtonian models have been applied in the numerical studies. Among them, the Casson equation was widely used. However, the Casson equation agrees well only when the shear rate is less than 10 s-1. The flow field of the carotid bifurcation usually covers a wide range of shear rate. We therefore believe that it may not be sufficient to describe the property of blood only using the Casson equation in the whole flow field of the carotid bifurcation. In the present study, three different blood constitutive models, namely, the Newtonian, the Casson and the hybrid fluid constitutive models were used in the flow simulation of the human carotid bifurcation. The results were compared among the three models. The results showed that the Newtonian model and the hybrid model had verysimilar distributions of the axial velocity, secondary flow and wall shear stress, but the Casson model resulted in significant differences in these distributions from the other two models. This study suggests that it is not appropriate to only use the Casson equation to simulate the whole flow field of the carotid bifurcation, and on the other hand, Newtonian fluid is a good approximation to blood for flow simulations in the carotid artery bifurcation.  相似文献   

16.
The thickening properties of many commercial thickeners are difficult to measure because of wall slip artefacts. Here we report a series of experiments on a typical thickener where these artefacts have been successfully eliminated. As a result, complete, steady-state flow-curves of aqueous Carbopol 980 (the toxicologically preferred version of the older and more well-known Carbopol 940) dispersions are reported for a range of concentrations of 0.045–1.0 wt%. The vane-and-basket flow geometry was used to avoid slip problems at low shear stress, with the geometry housed in a TA AR1000-N controlled-stress rheometer, whilst a Haake RV2 viscometer with an SV2P and MV2P concentric-cylinder geometries were used at higher shear rates. The flow-curves obtained show a smooth but steep transition from a very high Newtonian viscosity at low shear stress to a much lower viscosity at high shear stress. No real yield stresses were detected, but the higher shear rate results can be fitted to the Herschel-Bulkley model, which assumes an apparent yield stress. The various model parameters are displayed as a function of Carbopol concentration. Received: 29 November 2000/Accepted: 26 February 2001  相似文献   

17.
We investigate the rheology of dilute dispersions of fumed colloidal particles with attractive interactions in hydrocarbon liquids. Surprisingly, these systems display shear thickening due to the breakdown of densified flocs and a concomitant increase in the effective volume fraction of the fractal particles in the fluid. We show that this shear thickening is controlled by a critical stress and accompanied by a positive increase in the first normal stress difference, N 1, at the shear thickening transition. This is in contrast to the well-known hydrocluster mechanism of shear thickening in concentrated hard-sphere and repulsive systems. Gel elasticity depends strongly on the stress applied to suspensions in preshear, scaling roughly as \(G'\sim\sigma_{\text{preshear}}^{2}\). We propose a simple model to account for these results in terms of the cluster number density determined by the preshear stress. At low shear rates, vorticity-aligned aggregates are present at \(\dot\gamma\approx 10^0 {\rm{s}}^{-1}\) . In this regime, the system displays a small but noticeable increase in viscosity on increasing shear rate. We investigate the effect of tool roughness and find that wall slip is not responsible for the observed phenomena. Instead, the increase in the apparent viscosity results from increased flow resistance due to the presence of gap-spanning log-like flocs in rolling flow.  相似文献   

18.
Numerical Simulation of the Flow in the Carotid Bifurcation   总被引:3,自引:0,他引:3  
Pulsatile flow through the three-dimensional carotid artery bifurcation has been studied using the artificial-compressibility method. The part of the flow with large inertia bifurcates and creates a very steep velocity gradient on the divider walls. The flow near the nondivider walls slows down because of dilation of the cross section and strong adverse pressure gradient. The secondary flow in the bifurcation region, which is similar to the Dean vortex in a curved pipe, is strong and very complex. The region of separation is not closed for the cases of steady and pulsatile flow. The extent of this region is small and the streamlines are smooth except in the decelerating phase of systole. The change of common-internal bifurcation angle (25°± 15°) for fixed internal–external bifurcation angle of 50° has more effect on the shear on the bifurcation-internal carotid wall and less effect on the shear on the common-internal carotid wall. The mean wall shears are not sensitive to the input flow-rate waveform for constant mean flow, but the maximum wall shears are. Received 3 January 1997 and accepted 11 April 1997  相似文献   

19.
Considering representative asymmetric aneurysms in the abdominal aorta, the transient 3-D blood flow and pressure distributions as well as aneurysm wall stresses were numerically analyzed. To obtain more realistic and accurate results for blood flow fields and wall stress distributions, a coupled fluid-flow and solid–structure solver was employed. Geometric abdominal aortic aneurysm (AAA) variations studied included the degree of asymmetry, neck angle and bifurcation angle, and hence their impacts on the hemodynamics and biomechanics. The simulation results indicated that the assumption of symmetric AAA geometry may underestimate AAA-wall stress considerably. The neck angle influences the blood flow field substantially. A large neck angle, resulting in strong wall curvatures near the proximal neck, can produce aggravating blood flow patterns and elevated wall stresses (Von Mises). The iliac bifurcation angle affects blood flow patterns insignificantly but plays an important role in wall-stress concentrations. The wall stress of lateral asymmetric AAAs is higher than for the anterior-posterior asymmetric types. The maximum wall stress-site is located near the anterior distal side for the anterior-posterior asymmetric AAA and the distal side towards the asymmetric bulge in the lateral asymmetric AAA.  相似文献   

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