EXACT SOLUTIONS OF A DIPOLAR FLUID FLOW

Exact solutions for three canonical flow problems of a dipolar fluid are obtained: (i) The flow of a dipolar fluid due to a suddenly accelerated plate, (ii) The flow generated by periodic oscillation of a plate, (iii) The flow due to plate oscillation in the presence of a transverse magnetic field. The solutions of some interesting flows caused by an arbitrary velocity of the plate and of certain special oscillations are also obtained.

Simulation of Variable Viscosity and Jeffrey Fluid Model for Blood Flow Through a Tapered Artery with a Stenosis

Non-Newtonian fluid model for blood flow through a tapered artery with a stenosis and variable viscosity by modeling blood as Jeffrey fluid has been studied in this paper. The Jeffrey fluid has two parameters, the relaxation time A1 and retardation time A2. The governing equations are simplified using the case of mild stenosis. Perturbation method is used to solve the resulting equations. The effects of non-Newtonian nature of blood on velocity profile, temperature profile, wall shear stress, shearing stress at the stenotsis throat and impedance of the artery are discussed. The results for Newtonian fluid are obtained as special case from this model.

The Effects of Post-Stenotic Dilatations on the Flow of Couple Stress Fluid through Stenosed Arteries

The flow of incompressible couple stress fluid in a circular tube with stenosis and dilatations has been investigated. The stenosis was assumed to be axially symmetric and mild. The flow equations have been linearized and the expressions for the resistance to the flow, velocity, pressure drop, wall shear stress have been derived. The effects of various parameters on these flow variables have been investigated. It is found that the resistance to the flow and pressure drop increase with height of the stenosis and decrease with post stenotic dilatation. Pressure drop decreases with couple stress fluid parameter for both stenosis and post stenotic dilatation. Further, the wall shear stress increases with height of the stenosis and couple stress parameter but decreases with post stenotic dilatation and couple stress fluid parameter.

Magnetohydrodynamic approach of non-Newtonian blood flow with magnetic particles in stenosed artery

The non-Newtonian blood flow, together with magnetic particles in a stenosed artery, is studied using a magneto-hydrodynamic approach. The wall slip condition is also considered. Approximate solutions are obtained in series forms under the assumption that the Womersley frequency parameter has small values. Using an integral transform method, analytical solutions for any values of the Womersley parameter are obtained.Numerical simulations are performed using MATHCAD to study the influence of stenosis and magnetic field on the flow parameters. When entering the stenosed area, blood velocity increases slightly, but increases considerably and reaches its maximum value in the stenosis throat. It is concluded that the magnitude of axial velocity varies considerably when the applied magnetic field is strong. The magnitude of maximum fluid velocity is high in the case of weak magnetic fields. This is due to the Lorentz's force that opposes motion of an electrically conducting fluid. The effect of externally transverse magnetic field is to decelerate the flow of blood. The shear stress consistently decreases in the presence of a magnetic field with increasing intensity.

Mathematical Analysis on Pulsatile Flow through a Catheterized Stenosed Artery

In this paper, the pulsatile flow of blood through an inclined catheterized stenosed artery is analyzed. Perturbation method is used to solve the implicit system of partial differential equations with suitable boundary conditions. Various analytical expressions axial velocity, flow rate, wall shear stress and effective viscosity have been derived with the help of MATLAB for understanding the fluid flow phenomena. The combined effect of catheterization, body acceleration, slip and inclination has been seen by plotting the graph and observed that axial velocity and flow rate increases with the increase in body acceleration, inclination angle and slip velocity while axial velocity diminishes on increasing the catheter radius. Wall shear stress increases with the increase in catheter radius and body acceleration but presence of slip velocity reduces the wall shear stress. Effective viscosity diminishes on increasing body acceleration and inclination angle, whereas slightly augmented in non-inclined stenosed artery.

A Casson Fluid Model for Multiple Stenosed Artery in the Presence of Magnetic Field

The flow of blood through a multistenosed artery under the influence of external applied magnetic field is studied. The artery is modeled as a circular tube. The effect of non-Newtonian nature of blood in small blood vessels has been taken into account by modeling blood as a Casson fluid. The effect of magnetic field, height of stenosis, parameter determin- ing the shape of the stenosis on velocity field, volumetric flow rate in stenotic region and wall shear stress at surface of stenosis are obtained and shown graphically. Some important observations regarding the flow of blood in multi stenosed artery are obtained leading to medical interest.

冠状动脉树重建扩大到较小动脉提高FFRCT准确性的研究

目的本研究旨在通过在计算流体动力学(CFD)领域扩展冠脉树来提高基于冠状动脉CT血管成像(coronary CT angiography,CCTA)的血流储备分数(FFR)的准确性。进行了一项观察性研究,以评估将冠状动脉树分析从最小直径1.2mm扩展到0.8 mm的效果。方法对接受CCTA和介入性FFR治疗的患者进行回顾性研究。76名患者符合纳入标准。重建三维冠状动脉树,生成具有不同管腔直径下限(1.2 mm和0.8 mm)的有限元网格。根据Murray定律定义了出口边界条件。应用NKS方法求解CFD控制方程,得到FFRCT。结果在个体患者水平上,将冠状动脉树的最小直径从1.2mm扩大到0.8mm,FFRCT的灵敏度提高了16.7%(P=0.022),这导致四个假阴性病例转变为真阳性病例。ROC曲线的AUC值由0.74增至0.83。此外,NKS方法可以解决在2160个处理器核的情况下,在10.5分钟内将冠状动脉树扩展到0.8 mm管腔直径的计算问题。结论将重建的冠脉扩大到较小的管腔直径可以显著提高FFRCT的敏感性,NKS方法可以为未来的临床应用提供良好的计算时间。

颈内动脉狭窄血流动力学数值模拟

目的:基于血流动力学数值模拟条件,探究对颈内动脉进行不同程度人工干预狭窄的颈动脉模型的血流动力学特性,并从血流动力学角度分析颈内动脉位置处产生狭窄及由于其狭窄导致脑部供血疾病的原因。方法:采集内蒙古民族大学附属医院提供的健康个体二维CT数据,应用医学建模软件MIMICS20.0将二维的颈动脉CT数据进行三维模型重建,然后借助3-Matic Medical软件,对颈动脉模型中的颈内动脉同一位置进行不同程度的人为干预狭窄,得到颈内动脉25%、50%、75%狭窄程度的颈动脉模型。经格式转化、边界条件设置、网格划分等操作后,导入计算流体力学软件FLUENT14.5进行颈动脉血管及血液两相流血流动力学数值模拟与分析。结果:比较颈内动脉同一位置3种不同狭窄程度下的血液流线及速度矢量图可知,随着狭窄程度的增大,颈动脉窦处血液的涡旋流动现象迅速减弱,而颈内动脉狭窄处上方和下方血液出现明显的涡旋流动,并且血液流动出现选择性偏流。颈内动脉狭窄程度从25%到50%再到75%的过程中,狭窄处的血管壁面压力始终较低,狭窄下方的血管壁面压力逐渐增大,为高压力区域。狭窄处为高切应力区域,并且狭窄位置上方和下方的低切应力范围明显变大。结论:利用计算机软件进行人为干预狭窄获取模型的技术进行实验研究具有方便、快捷的特点。颈内动脉狭窄从25%到50%再到75%时,颈动脉的血液流场发生明显改变,颈内动脉出现明显的涡旋流动现象,血管壁面的力学性质也发生一定变化。

HEAT AND MASS TRANSFER EFFECTS ON CARREAU FLUID MODEL FOR BLOOD FLOW THROUGH A TAPERED ARTERY WITH A STENOSIS

In the current critique, we deliberate the blood flow through narrowing vein with a steno- sis in the manifestation of heat and mass transmission. The non-Newtonian flora of blood in small veins are examined mathematically by demonstrating the blood as Carreau fluid. The illustration for the blood flow is debated through an axially irregular but outward regular stenosis. Regularity in the dissemination of the fortification clipping stress and resistive impedance and their evolution with the emerging stenosis is a new significant feature of our investigation. Analytical solutions have been appraised for ＂velocity, tem- perature, concentration, resistance impedance, wall shear stress and shearing stress at the stenosis throat＂. The graphical consequences of different types of tapering arteries （i.e. ＂converging tapering, diverging tapering, non-tapered artery＂） have been studied for dissimilar constraints of attention. Rivulet shapes have been strategized for different parameters at the culmination of the article.

双向流固耦合作用下狭窄左冠状动脉内两相血流分析

基于血流与血管壁间双向流固耦合作用,将血液设为两相流体,运用计算流体力学方法对左冠状动脉内血流进行瞬态数值模拟.研究了一个心动周期内典型时刻下左冠状动脉内血流分布特性,并与Newton(牛顿)血液和两相血液模型对比,分析了两相血液和流固耦合作用对血流特性的影响.结果表明,左冠状动脉左回旋支远段和钝缘支近心端外侧分布了低速涡流区,该区域内壁面切应力和红细胞体积分数均较小,为动脉粥样硬化的形成与发展提供了合适的生理环境.左冠状动脉分叉处管壁形变量较大,引起管壁内膜功能发生紊乱,促进了粥样硬化斑块的形成.3种血液模型对比可知,红细胞的流动特性对血流速度及壁面切应力等血流动力学特性影响较大,双向流固耦合模型更符合真实的血液流动情况.

基于人工智能优化与计算流体力学的无创血流储备分数对冠状动脉狭窄缺血的诊断价值

目的:对比基于冠状动脉CTA获得的无创血流储备分数(FFRCT)和有创血流储备分数(FFR)心肌缺血的诊断效能。方法:本研究共纳入61例稳定性心绞痛患者,采用深圳睿心智能医疗开发的基于人工智能计算的专利系统(Ruixin-FFR)计算狭窄处的FFRCT值,并与冠状动脉造影术中测量的FFR值进行比较,以FFR≤0.8为具有血流动力学意义。通过准确性、敏感性、特异性、阳性预测值(PPV)和阴性预测值(NPV)并计算受试者工作特征(ROC)曲线下的面积(AUC)来评价FFRCT的诊断效能。结果:对每个患者的FFRCT与有创FFR相比的准确率为91.8%,敏感性为97.6%,特异性为73.7%,PPV为89.1%,NPV为93.3%。计算获得AUC值为0.890(P<0.0001)。FFRCT和有创FFR间相关系数r:0.652(P<0.0001),一致性检验较好(Kappa=0.757,组内相关系数r=0.770,P值均<0.001),Bland-Altman图显示两者具有良好的一致性。结论:FFRCT对比有创FFR具有良好的一致性及诊断效能,作为评估心肌缺血的一种高效、无创、准确的功能性参数。

应用计算机流体力学技术评估症状性颅内动脉狭窄患者卒中复发风险的研究

目的评估基于计算机流体力学(computational fluid dynamics,CFD)技术的无创血流动力学参数与缺血性卒中复发之间的关系。方法连续入组2018年6月-2019年6月在首都医科大学附属北京天坛医院脑血管病中心住院治疗的急性缺血性卒中且经头颅MRI和MRA证实为症状性颅内动脉狭窄的患者。收集患者的临床及影像学检查信息。对患者的MRA原始图像进行后处理分析,建立CFD模型,并通过计算获得责任血管的血流分数、血流速度比和血管壁剪切力比。所有入组患者完成12个月随访,根据随访期内是否有缺血性卒中或TIA复发分为卒中复发组和无卒中复发组,分析各血流动力学参数与12个月内缺血性卒中复发的相关性。结果共入组48例患者,中位年龄58(52~68)岁,其中男性患者36例(75.0%)。责任血管中位狭窄率为60.3%(53.2%~82.0%),狭窄长度为3.3(2.6~4.9)mm。12个月随访缺血性卒中复发10例(20.8%)。卒中复发组责任血管的血流分数低于无卒中复发组[0.74(0.69~0.81)vs.0.90(0.82~0.97),P=0.01]。ROC曲线显示,血流分数预测缺血性卒中复发AUC为0.796(0.669~0.923),截点值为0.815,敏感度为76.3%,特异度为80.0%。结论通过CFD技术模拟计算的血流分数可能是症状性颅内大动脉狭窄患者缺血性卒中复发的预测因子之一。

人体肺动脉狭窄血流动力学数值分析(英文)

采用计算流体动力学方法,探讨针对同一模型不同主肺动脉狭窄率(0,25%和50%)的血流动力学变化情况。通过对患者CT数据处理,完成了三组肺动脉狭窄几何的全三维数字化重构,结合主肺动脉血流量等临床数据,模拟了伴有不同狭窄程度的肺动脉模型内血流细节。仿真结果得到了连接段内血液流动速度场、压力、壁面剪切应力等分布特性,这对于评判不同肺动脉狭窄程度的影响和相关手术治疗方案的选择有着参考作用。

声门下喉气管狭窄分度的数值模拟分析

根据真实人体喉气管CT影像数据构建了声门下喉气管狭窄的气道模型,并对这些模型进行了吸气条件下的计算流体力学仿真。分析比较了不同狭窄分度模型内的流场特征、不同喉气管部段的阻力特性以及喉气管壁面的压力与切应力分布,并对这些特性与临床病患表象的关联性进行了讨论。分析表明声门下喉气管狭窄分度与狭窄导致的呼吸道阻力变化具有良好的关联性,此外,喉气管狭窄处压力及剪应力效应对病程的影响也需要关注。

双极流体在狭窄管道内的流动

本文研究了双极流体通过带有轴对称柔和狭窄的刚圆管时的流动特性。运用Bleustein和Green的双极流体理论,导出了速度剖面、流量、阻抗和壁面最大剪应力的公式,并做了数值计算,分析了狭窄度与双极参数对上述有关量的影响。

流固耦合分析血液黏滞系数对重度狭窄颈动脉的影响

目的基于流固耦合(FSI)力学的方式,分析不同血液黏滞系数对重度狭窄颈动脉的血液流速及壁面剪切力(WSS)的影响。方法选取2015年8月于天津市第四中心医院经CT血管成像(CTA)检查诊断为颈内动脉重度狭窄(狭窄程度为75%)的1例62岁男性病人,将其CTA影像数据制作模型,导入FSI分析软件中,分别设定血液黏滞系数为1、3.5、6、8.5、11 c P并进行运算。在运算结果中测量并分析颈总动脉末端(A1)、颈动脉窦水平(A2)、颈内动脉狭窄处(A3)、颈内动脉狭窄处远端(A4)截面的血液流速和WSS值。结果随着血液黏滞系数的升高,A1、A2、A3、A4的血流速度均值降低,WSS均值增大;A4的中心血液流速降低,A1、A2和A3的中心血流速度升高。结论随着颈动脉重度狭窄病人的血液黏滞系数升高,其脑部供血不足趋于严重化,从而导致急性脑卒中的发生,而且造成狭窄位置斑块的破损概率和面积进一步增大,因此应引起临床的高度重视并及时干预。

血管壁弹性模量对颈动脉狭窄血流储备分数的影响

目的探索将血流储备分数(fractional flow reserve,FFR)引入颈动脉狭窄评估的可行性,并且分析血管壁弹性模量对颈动脉狭窄中血液动力学参数和FFR计算结果的影响。方法利用计算机辅助设计软件建立颈动脉分叉标准模型并获得不同狭窄率的模型。假设血管壁为线弹性材料,血液为不可压缩牛顿流体,在脉动流条件下,利用有限元分析软件进行颈动脉狭窄模型中血液流动的流固耦数值模拟,获得各种血液动力学参数,并计算相应的FFR值。结果当弹性模量固定时,随着狭窄率增加,模型中狭窄部位的FFR逐渐减小,且此时其弹性壁与刚性壁的FFR相对差异随着狭窄率的增加而增加;当狭窄率固定为70%时,随着弹性模量增加,FFR会逐渐减小。结论采用FFR对颈动脉狭窄程度进行功能性评估需要考虑血管壁弹性的影响;狭窄率越大,血管壁弹性模量对FFR的影响越大。

颅内Willis环二维血液动力学计算分析

采用颅内二维Willis环模型,对血管在不同程度狭窄情况下的血液流动进行稳态计算与分析,计算中采用了进出口处的压力边界条件和无滑移固壁条件。计算得到完整环和交通动脉缺失情况下各进出口血管流量变化曲线。所获结果表明,完整Willis环中,前交通动脉的代偿能力在左颈内动脉狭窄率达到25%以后才能得到比较明显的体现;后交通动脉缺失情况下前交通动脉的代偿能力变弱;Willis环的前部和后部有相对独立性,只有在主要进口动脉严重阻塞的时候,单侧的独立性才丧失。

颈总动脉狭窄两相流数值模拟分析

目的探讨颈总动脉位置处不同狭窄程度对颈动脉内血液流速、血管壁面压力、剪切应力的影响,分析颈总动脉位置处狭窄对脑部供血影响的血流动力学方面原因。方法采用内蒙古民族大学附属医院提供的1例53岁男性健康颈动脉二维CT数据,应用医学建模软件MIMICS20.0将二维CT数据进行三维医学重建,然后利用3-Matic Medical软件,在颈总动脉位置处进行25%、50%、75%狭窄程度的人为干预,得到颈总动脉位置处3种不同程度狭窄的颈动脉模型。在GEOMAGIC中进行模型的光滑处理,经过网格划分及边界条件设置后导入计算流体力学软件FLUENT14.5中,进行液(血浆)—固(红细胞)两相流血流动力学数值模拟。通过观察不同狭窄程度下速度流线图及矢量图(分别截取狭窄处、分叉处上游、分叉处下游及分叉末端处的a、b、c、d 4个不同的横断面)中的血液流速及血液的涡旋流动现象、血管壁面压力及剪切应力的数值变化,为颈动脉狭窄疾病提供血流动力学支持。结果观察速度流线图及速度矢量图可知,从颈动脉入口处流入血液保持狭窄处血管中间流速大、边缘流速小的特点,颈动脉窦处易存在血液的涡旋流动,且随着狭窄程度的增加,涡旋的面积及程度增大。在所取的4个横断面上,随着狭窄程度的增大,涡旋现象持续时间更长。颈总动脉狭窄自25%到50%过程中,血液流速、血管壁面压力及剪切应力扩大至近2倍;当狭窄程度由50%至75%过程中,血液流速扩大至3倍,血管壁面压力扩大至近10倍,剪切应力扩大至近4倍。结论人为狭窄干预技术可以方便、快捷地获取目标模型,并可以在此基础上任意修改,可以为血流动力学研究及临床诊断提供良好的模型基础。颈总动脉狭窄程度由25%到50%时,血管壁面的力学性质发生一定变化;而从狭窄50%到狭窄75%时,血管壁面的力学性质呈指数形式上升。

轴对称有狭窄弹性管流固耦合模型及数值模拟

建立了求解厚壁、有狭窄、大管壁变形的血管及管内血液流动的流固耦合问题的数值计算模型 .血管的几何形状、物质特性及模型的有关物理参数由模拟颈动脉血流及血管壁塌陷的实验获得 .流体采用Navier Stokes方程 ,用广义有限差分方法求解 .基于实验数据建立的固体模型用有限元方法求解 .流体与固体通过边界的耦合由交替迭代技术实现 .结果表明 ,严重的血管狭窄使管壁受压 ,流体出现负压力及高剪切应力 ,这些正是导致血管塌陷、血管瘤破裂 ,从而引发中风及其他心脏疾患的重要原因 .计算结果与实验结果吻合 .