平行平板流动腔脉动流切应力的计算

高度远小于横向和纵向几何尺寸的矩形平行平板流动腔是人们用以体外研究细胞在切应力作用下力学行为的主要工具之一。大多数研究者主要对定常层流情进行研究。本文通过对矩形平行平板流动腔内的层流脉动流进行详细分析,给出腔内速和腔室底部切应力的准确计算公式。当Ｗｏｍｅｒｓｌｅｙ数较小时,准确公式简化为准定常公式。数值计算结果表明,在脉动流条件下,对于人们常用的流动腔几何尺寸,准定常公式具有相当高的精度。这为在脉     

含悬浮固粒的旋转射流剪切层稳定性研究

本文在理想不可压旋转圆射流的运动方程中添加了固粒作用项，由此推得了时间增长率的表达式，进而得关于含悬浮固粒放置射流稳定性的修正瑞利稳定性准则，求出了不同固粒质量密度固－气脉动速度比值，固气脉动速度相位差及Ｓｔｏｋｅｓ数情况下旋转射流场的增长率与径向空间波数的关系曲线，在比较这些曲线的基础上，给出了关于固粒属性对旋转射流场稳定性影响的几个重要结论为控制旋转射流场和后续发展提供了依据。     

非线性波在半影区焦散曲线处的会聚

本文考虑一个非线性波的模式，通过研究它在半影区焦散曲线处的会聚，将Ｋｒａｖｔｓｏｖ和Ｏｏｒｌｏｖ及我们先前得到的结果推广到更一般的情形。在线笥的情况下，其渐近开矿可分别由不完全Ａｉｒｙ或Ｐｃａｒｃｅｙ积分所描述，但在非线性的情况下，由渐近展开分析法由带有一个相似变量的多重位相模式所确定。进一步考虑使用多重尺度法及渐近展开匹配法，得到了波在会聚前后位相的一般表达式。结果表明，当波穿越半影区焦散曲线时     

贝雷砂岩射孔孔道流动效应正交计算分析

对射孔孔道流动效应进行了量纲分析,建立了轴向和径向流量与影响流量因素间的工程表达式。综合考虑影响流动效应的主要因素和取值范围,设计了数值模拟计算工况的正交计算方案,并利用ANSYS/FLOTRAN流体程序进行了带损伤区贝雷砂岩流量数值模拟研究,获得了各个计算方案的径向流量和轴向流量,用以确定出流量公式的系数。最终确定的流量公式表明,各要素对流量影响的重要顺序依次为固有渗透率、损害区厚度、孔深、渗透率剩余百分数和孔径。     

动脉狭窄对血液流速的影响

为了定量计算动脉局部狭窄对动脉管中血液流动速度的影响，本文分别对狭窄区域内定常流和非定常流动进行了求解，得出了狭窄区域内定常流和脉动流的速度表达式。本文将均匀段的流速形经Ｆｏｕｒｉｅｒ分解成定常和脉动两部分，然后分别计算出狭窄区域内对应的定常和脉动流速，经Ｆｏｕｒｉｅｒ合成还原成流速时域波形，同时针对各种情况将不同狭窄对不同的流速波形的作了分析比较。     

非轴对称扰动下含悬浮固粒旋转射流场稳定性研究

考虑含有悬浮固粒的理想不可压旋转圆射流的运动方程，借助势流理论推得扰动增长率随径向波数变化的表达式，进而得到含悬浮固粒射流稳定性的修正瑞利稳定性准则，求出了非轴对称扰动下不同扰动阶数、固粒质量密度、固－气脉动速度比值、固－气脉动速度相位差、斯托克斯数时旋转射流的增长率曲线。然后根据修正瑞利稳定性准则分析给出了关于悬浮固粒的属性对旋转射流场稳定性影响的几个重要结论，为控制旋转射流场和后续发展提供了合理的依据。     

液体调谐减振器的分析

本文利用Ｌａｍｂ变换，考虑液体的粘性，略去二维Ｎａｖｉｅｒ－Ｓｔｏｋｅｓ方程中的非线性预后，建立了频域内Ｎａｖｉｅｒ－Ｓｔｏｋｒｅｓ方程的边界积分表达式，完整地处理了边界条件（包括自由面边界条件和固壁边界条件）并且给出了液体随结构振动时的附加质量与阻尼的计算表达式。     

复合材料层合板的动力特性分析

本文采用渐近分析方法,研究了对称角铺设复合材料层合板的动力特性问题,并给出了层合板自振频率关于铺设角的一般渐近表达式。最后,文中对三种常用的纤维增强复合材料板,给出了具体的计算数值结果。本文的所有方法均可推广到各种复合材料层合板的静力和稳定性的问题分析中。     

计算机磁头／磁盘超薄气膜润滑压强的算子分裂算法

以任意拉森数的超薄气体润滑方程为基础，采用算子分裂法和非结构三角网格的有限元法计算Ω型磁头的空气轴承气垫面(ABS)气膜压强分布、气浮力和纵倾力矩；在分析比较流量系数的各种算法的基础上，确定采用多项式拟合数据库计算流量系数．计算结果表明：采用算子分裂法可以有效克服在高轴承数时的数值不稳定性，消除数值振荡；在小轴承数时，气浮力随轴承数增加而增大，当轴承数增大到某一数值后，气浮力趋近某一稳定值，此时气膜压强分布与磁头造型基本一致；气膜的纵倾力矩在轴承数的某一临界值附近出现最大值．     

非线性缓冲包装系统的跌落冲击响应

本文考虑阻尼的影响，研究了三次函数强非线性缓冲包装系统的跌落冲击响应，提出了基于系统无阻尼响应特征的渐近解法，所得阻尼系统冲击响应的渐近表达式对缓冲包装设计和新型缓冲材料的开发具有重要价值。     

Pulsatile flow in arteries with external restraint of visco-elastic tissue

The presence of a longitudinal constraint must be conceived physiologically as due largely to the connective tissue attachments on the outside of the artery. Living tissues are viscoelastic bodies. In order to analyse the effect of external viscoelastic tissue to pulsatile flow in arteries, in this paper the external connective tissue of artery will be considered as a Voigt visco-elastic body, and the expressions of pulse wave velocity and the velocity of pulsatile flow will be found by the velocity of pulsatile flow will be found by the blood motion equations (Navier-Stokes equation) as well as wall motion equations (Lamb equation). The results of free elastic tube^[4] and those of external elastic restraint^[6] by Womersley can be considered as a particular case and can be covered in this paper.     

Study on hemodynamics in patient-specific thoracic aortic aneurysm

The objective of this study is to investigate the hemodynamics in patient-specific thoracic aortic aneurysm and discuss the reason for formation of aortic plaque. A 3-Dimensional pulsatile blood flow in thoracic aorta with a fusiform aneurysm and 3 main branched vessels was studied numerically with the average Reynolds number of 1399 and the Womersley number of 19.2. Based on the clinical 2-Dimensional CT slice data, the patient-specific geometry model was constructed using medical image process software. Unsteady, incompressible, 3-Dimensional Navier-Stokes equations were employed to solve the flow field. The temporal distributions of hemodynamic variables during the cardiac cycle such as streamlines, wall shear stresses in the arteries and aneurysm were analyzed. Growth and rupture mechanisms of thoracic aortic aneurysm in the patient can be analyzed based on patient-specific model and hemodynamics simulation.     

Steady and pulsating flow characteristics in straight tubes with and without a lateral circular protrusion

 Flow characteristics in straight tubes with and without a lateral circular protrusion had been investigated using Particle Image Velocimetry over a range of Reynolds numbers from 400 to 1400, and at Womersley number of 65. The practical interest of the flows considered lies mainly in blood flows through arteries with saccular aneurysm. Both steady and pulsating flow experiments had been conducted. It was found that under the steady flow conditions, a recirculating vortex would be formed inside the circular protrusion. The maximum strength of the vortex would be as low as 10% of the bulk mean velocity in the main tube at the highest Reynolds number tested (i.e. at 1400). Under the pulsating flow conditions, the vortex appeared and disappeared at different phase of a cycle. The sequence was only punctuated by quasi-inviscid flow behavior. The steady flow results only resembled those of the pulsating ones for about 1 10 of the time at each cycle. Received: 13 August 1997/Accepted: 30 June 1998     

Numerical study of physiological turbulent flows through series arterial stenoses

A numerical investigation on the characteristics of transitional turbulent flow over series bell‐shape stenoses for a physiological pulsatile flow is presented in the present study. The flow behaviours for the physiological pulsatile flow are studied by considering the effects of the Reynolds number, Womersley number, constriction ratio and spacing ratio of the stenoses on the pulsatile turbulent flow fields. Especially, the mutual influences between the double stenoses under different flow conditions are considered. The numerical results show that the variation of these flow parameters puts significant impacts on the flow developments in the arteries with series stenoses. The double stenoses lead to the higher peak turbulence disturbance and the greater area with comparatively high turbulence intensity distal to the stenoses in comparison with the single stenosis. The analysis shows that for the physiological pulsatile flow, the downstream stenosis usually does not have perceptible influences on the upstream flow fields. Copyright © 2004 John Wiley & Sons, Ltd.     

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.     

A study on the unsteady flow in a helical pipe

IntroductionRecently ,theresearchofunsteadyflowincurvedpipesmaintainsclosetiewiththatofbloodflowinbio_mechanics.Sothecharacteristicsofbloodflowinvesselscanbestudiedthroughtheresearchofflowincurvedpipesandthelocationthattheatherosclerosistakeplacecanbeprejudged[1].Theessentialcauseofatherosclerosiscanbeprobedinto ,too .In 1 971 ,Lyne[2 ]successfullysolvedtheproblemofflowinacircularcross_sectioncurvedpipeundertheconditionthattheaxialpressuregradientvariedinaccordwiththecosinelawusingthemethodof…     

Migration in an oscillatory flow of a laminar suspension measured by laser anemometry

Oscillatory flow occurs in a wide range of areas of engineering importance. Two-way lateral migration of particles was observed in the flow of a steady, laminar, dilute, neutrally-buoyant suspension of rigid particles in a tube. The equilibrium particle-position was dependent on the dimensionless Womersley parameter. Experiments were performed in which the Womersley parameter was varied between 1.12 and 8.0. For low values of the parameter, two-way radial migration was observed as in steady, laminar flow. For higher values of the parameter, two equilibrium positions were observed, together with three particle free layers across the radius of the tube.     

Performance modeling and analysis of blood flow in elastic arteries

Nomenclature　　τ　　wallshearstressγshearrateτy yieldstressηc Cassonviscosityktheconsistencyindexnnon_Newtonianindexτp shearstressofthepthelementωangularvelocityRvessel’sradiusCwavespeedM　　magneticparameter (Hartmannnumber)u,w　velocitycomponentinther_andz_directions,respectivelyP　　pressureα　　unsteadinessparameter k , R meanparametersTp relaxationtimeofthepthelementρ densityIntroductionTheimportancetoatherogenesisofarterialflowphenomenasuchasflowseparation ,recirculationands…     

Time resolved analysis of steady and oscillating flow in the upper human airways

In this experimental study a thorough analysis of the steady and unsteady flow field in a realistic transparent silicone lung model of the first bifurcation of the upper human airways will be presented. To determine the temporal evolution of the flow time-resolved particle-image velocimetry recordings were performed for a Womersley number range 3.3 ≤ α ≤ 5.8 and Reynolds numbers of Re _D = 1,050, 1,400, and 2,100. The results evidence a highly three-dimensional and asymmetric character of the velocity field in the upper human airways, in which the influence of the asymmetric geometry of the realistic lung model plays a significant role for the development of the flow field in the respiratory system. At steady inspiration, the flow shows independent of the Reynolds number a large zone with embedded counter-rotating vortices in the left bronchia ensuring a continuous streamwise transport into the lung. At unsteady flow the critical Reynolds number, which describes the onset of vortices in the first bifurcation, is increased at higher Womersley number and decreased at higher Reynolds number. At expiration the unsteady and steady flows are almost alike.     

Perpendicular ultrasound velocity measurement by 2D cross correlation of RF data. Part B: volume flow estimation in curved vessels

A novel axial velocity profile integration method, obtained from ultrasonic perpendicular velocimetry, for flow estimation in curved tubes was validated. In an experimental set-up, physiologically relevant curved geometries and flows were considered. Axial velocity profile measurements were taken by applying particle imaging velocimetry-based methods to ultrasound data acquired by means of a linear array transducer positioned perpendicular to the axial velocity component. Comparison of the assessed asymmetric velocity profiles to computational fluid dynamics calculations showed excellent agreement. Subsequently, the recently introduced cos θ-integration method for flow estimation was compared to the presently applied Poiseuille and Womersley models. The average deviation between the cos θ-integration-based unsteady flow estimate and the reference flow was about 5%, compared to an average deviation of 20% for both the Poiseuille and Womersley approximation. Additionally, the effect of off-centre measurement was analysed for the three models. It was found that only for the cos θ-integration method, an accurate flow estimation is feasible, even when it is measured off centre.