ANALYSIS OF PULSATILE BLOOD FLOW IN AXIALLY MOVING ARTERIES

1.　 INTRODUCTIONCoronary arteries are the arterial system that supplies the heart with blood to maintaincardiac normal functions.The disease of coronary arteries is one of primary diseases thatendanger human being′s health severely.By the particular physiological functions andanatomical positions of this system,every coronary artery is destined to take a large extentof overall to-and-fro movement with the heart beat during which the contraction and therelaxation of the heart occur altern…     

血浆层对小血管中脉动流的影响

本文研究了血浆层的存在对小血管中脉动流的影响。分析表明,在小血管中血浆层的存在可以明显改变脉动血流量的峰值,但几乎不改变血流量的相位。也就是说,在一定的压力梯度下,由于血浆层的存在,血管中血流量的脉动幅度可大大增加,这对人体血液循环有特殊的生理意义。     

半无限饱和土内部作用集中力的初值解

应用 Mc Namee和 Schiffman位移函数把轴对称和非轴对称的 Biot固结方程解耦为一组偏微分方程 .利用半无限饱和土受集中力作用、体积应变为零的起始条件 ,得出了起始时刻的控制方程 .对该方程进行 Hankel变换 ,并利用半无限饱和土表面的边界条件以及集中力作用面处的连续性条件 ,可得出变换域内的位移、应力和孔隙水压力的解 .进行相应的逆变换后 ,可得集中力作用下饱和土起始时刻的位移、应力和孔隙水压力的封闭形式解     

ANALYSIS OF PULSATILE FLOW IN THE PARALLEL-PLATE FLOW CHAMBER WITH SPATIAL SHEAR STRESS GRADIENT

The Parallel-Plate Flow Chamber (PPFC), of which the height is far smaller than its own length and width, is one of the main apparatus for the in-vitro study of the mechanical behavior of cultured vascular Endothelical Cells (ECs) exposed to fluid shear stress. The steady flow in different kinds of PPFC has been extensively investigated, whereas, the pulsatile flow in the PPFC has received little attention. In consideration of the characteristics of geometrical size and pulsatile flow in the PPFC, the 3-D pulsatile flow was decomposed into a 2-D pulsatile flow in the vertical plane, and an incompressible plane potential flow in the horizontal plane. A simple method was then proposed to analyze the pulsatile flow in the PPFC with spatial shear stress gradient. On the basis of the method, the pulsatile fluid shear stresses in several reported PPFCs with spatial shear stress gradients were calculated. The results were theoretically meaningful for applying the PPFCs in-vitro, to simulate the pulsatile fluid shear stress environment, to which cultured ECs were exposed.     

变速运动锥体超空泡形状分析与预测

研究了锥体空化器变速运动时非定常自然超空化流问题。基于势流理论,通过在对称轴上分布奇点(源和汇)的方法,建立了变速运动超空泡的积分方程。应用时间有限差分离散化方法,对问题进行了数值求解。分析了锥体空化器在做变速运动时(如速度脉冲变化、加速或减速等),超空泡长度和形状的非定常变化规律。同时,对基于本文方法得到的结果与已有理论的计算结果作了定性比较。本文的分析和预测结果可望为水下航行体空化器的分析与设计起到指导和数据参考作用。     

LAMINAR FLUID FLOW IN HELICAL ELLIPTICAL PIPE

1.　INTRODUCTIONHelicalductsappearinvariousindustrialapplictionsandadetailedknowledgeofthefluidflowbehaviorisimportantforpredictingthepressuredropandheatandmasstransfercharacteristics.Experimentalandtheoreticalanalysishaveattestedthatthesecondaryflowappearsthenormalcross-sectionbecauseofthecurvature.Thissecondaryflowisveryfaintcomparedwiththeaxialflow,butitcausestheincreaseofheattransfer.Thestudyonthisflowbeganin1927withthepaperofDean[1],inwhichtheflowintoroidalsystemwasstudied.Sincethen…     

APPLICATIONS OF CFD TECHNIQUE IN THE DESIGN AND FLOW ANALYSIS OF IMPLANTABLE AXIAL FLOW BLOOD PUMP

Based on established numerical methods and hydrodynamic performance testing facilities, CFD technique are applied to improve the design of the implantable axial flow blood pump and the flow analysis. (1) Applying brushless machine magnet steel, reducing its thickness while increasing the length, the flow channel's cross-section is increased, with no space connection between the large and the small rotators, and with a cone transition segment from the bearing to the principal axis, the flow is made smoother. The rotating speed is lowered by 1000 rpm – 1200 rpm under the same flow rate and pressure head, and thus the hemolysis can be avoided. (2) Different outlet stator guiding vanes are selected for the same blood pump for analyses of hydrodynamic performances and flow fields. An excellent design not only can regulate the rotating flow field into an axial one, reduce the circulation loss and improve the pump efficiency, but also can avoid backflow, vortex and secondary flow at the pump outlet, and thus the thrombus can be prevented. (3) The calf live tests show that some residual clots exist at the inner wall of the outlet connection bends, which are analyzed and explained by CFD techniques and the corresponding improvements are proposed. All results are verified by hydrodynamic performance tests and PIV flow field tests, and consistent conclusions are obtained.     

Comparison of blood rheological models in patient specific cardiovascular system simulations

Newtonian, Quemada and Casson blood viscosity models are implemented in order to simulate the rheological behavior of blood under pulsating flow conditions in a patient specific iliac bifurcation. The influence of the applied blood constitutive equations is monitored via the wall shear stress(WSS) distribution, magnitude and oscillations, non-Newtonian importance factors, and viscosity values according to the shear rate. The distribution of WSS on the vascular wall follows a pattern which is independent of the rheological model chosen. On the other hand, the WSS magnitude and oscillations are directly related to the blood constitutive equations applied and the shear rate. It is concluded that the Newtonian approximation is satisfactory only in high shear and flow rates. Moreover, the Newtonian model seems to overestimate the possibility for the formation of atherosclerotic lesions or aneurysms at sites of the vascular wall where the WSS are oscillating.     

考虑连接管的调压室水头损失系数回归分析

为研究调压室结构参数与流态工况对局部水头损失系数的影响,在物理模型实测数据的基础上建立多元线性回归模型。得到了用于计算带连接管的尾水调压室水头损失系数的回归方程,并将回归分析结果与水工模型试验结果进行比较分析。研究表明：回归分析结果与水工模型试验结果吻合度高,相应回归方程能够在分流比、管径比及水流流态的交互作用下较好地反映出局部水头损失系数的变化规律,具有很强的工程适用性,可应用于调压室水力设计中水头损失系数的取值计算。     

弹性直圆管局部狭窄对脉动流影响的数值模拟

动脉中脉搏波的分析和中医脉象研究早为人们注目,并越来越受到重视。中医切脉或利用脉象仪测脉,均沿腕部桡动脉处取得信息,由于手指和探头作用,桡动脉形成狭窄从而影响脉动流。本文建立局部狭窄直圆管内脉动流模型,来研究狭窄对脉动流的影响。根据流动的一维非线性方程导出特征方程,采用特征差分方法数值求解。结果表明:(1)随狭窄度增加(相当压迫加重),压力和速度波形变陡,峰值开始时提高,随后下降,和脉象仪取脉情况吻合;(2)血液粘度增加时,速度减慢,压力波形平坦,反映了血流阻力的增大;(3)狭窄宽度的变化对脉搏波影响不大;(4)根据中医脉图若干指标计算得到的数据,随狭窄和血液粘度的变化,和临床结果一致,说明这几个指标是符合血流动力学规律的。     

血管局部扩张对血液流动的影响

本文利用Fung的应力－生长定律，导得血管局部扩张发展规律的基本关系。接着，通过求解局部扩张血管段内的血液流动方程；导得血液流速、压力和血管壁切应力的分析表达式。详细讨论局部扩张对流速、压力和切应力的可能影响。指出局部扩张将引起局部扩张段内管壁切应力的非均匀分布，并可能因此促使血管壁的进一步扩张。本文结果对于分析血管局部扩张与所处的血液动力学环境之间的定量关系有重要的帮助。     

含裂隙类岩试样破坏行为的宏细观数值分析

为了获得单轴荷载下裂隙岩体的裂纹扩展过程及接触力变化的规律,以石膏为相似材料制作含有2种倾角组合的裂隙试样,在刚性试验机上进行单轴条件下的破坏试验,记录裂隙试样的破裂过程。采用离散元软件PFC^2D建立数值分析模型,通过校核试验数据确定细观参数值,从宏观和细观两方面分析裂隙试样在压缩过程中微裂隙增长与轴向应力关系、接触力变化与裂纹的产生和扩展的关系,进行裂纹扩展的数值模拟和室内试验对比。结果表明颗粒间接触力分布随压缩而变得不均匀,主要集中在裂隙的端部,进而产生微裂隙,微裂隙聚集形成宏观裂纹;微裂隙数量在峰值轴向应力之前增加较缓慢,在峰值轴向应力之后迅速增加,微裂隙的增长与应力增长有一定关系;峰值轴向应力之前,观察到轴向应力暂停增加或略微下降,但微裂隙数量持续增加现象,该现象与裂纹扩展有关;用颗粒流程序能较好地分析加载过程试样内细观变化和裂纹的扩展,与试验现象吻合较好。     

地震动参数对锚固岩质边坡地震响应影响权重研究

借助FLAC3D软件建立了含软弱层的锚固岩质边坡数值模型,并利用正交设计方法,以波形、时间压缩比、幅值和持时为分析因素,设计多组具有不同地震动峰值加速度(PGA)、峰值速度(PGV)、阿里亚斯强度(AI)、绝对累积速度(CAV)、持时和特征周期的地震动,分析了地震动各参数对锚固岩质边坡位移和锚杆轴力的影响,得到了地震动各参数的影响权重。结果表明,地震作用下,坡顶处位移最大,自坡顶至坡脚位移逐渐减小;锚杆轴力沿杆长表现为中间大两头小的“人”字形分布;地震动各参数对边坡位移的影响权重由高到低依次为AI、CAV、PGA、PGV、持时和特征周期;对锚杆轴力的影响权重由高到低依次为AI、PGA、PGV、CAV、持时和特征周期。     

ANALYSIS OF OSCILLATORY BLOOD FLOW IN VARYING-AREA ELASTIC VESSEL

In this paper, by solving the fundamental e-quations of periodically oscillatory blood flow, the distributions of pressure gradient and blood velocity in varying-area e-lastic vessel were obtained, and then the wall shear stress and its gradient were calculated. As an example, the pulsatile blood flow in human carotid was analyzed and the effects of vessel taper angle on the distribution of wall shear stress and its gradient were discussed in detail. Numercial results show that the wall shear stress will enlarge when the taper angle increases. Meantime, no matter whether the vessel is converging or diverging, with the increase of the absolute value of taper angle, the amplitude of wall shear stress gradient will enlarge significantly.     

EXPERIMENTAL RESEARCH OF FLOW STRUCTURE IN A GAS-SOLID CIRCULATING FLUIDIZED BED RISER BY PIV

Particle Imaging Velocimetry (PIV) techniques were applied to investigate the particle motion and cluster properties in a gas-solid two-phase flow in a circulating fluidized bed riser. Visual images and micro-structure of various clusters were captured. After the boundary of clusters was determined by the gray level threshold method, clusters were classified by the distance between particles and the shape and position of clusters. In addition, the process of clusters forming and breaking up was described, and the sizes of clusters were also obtained. With the Minimum Quadric Difference (MQD) cross-correlation algorithm suitable for high-density particles, the axial velocities of the particles were obtained in the dilute phase section. The features of particle motion were revealed by investigating statistically the magnitude and distribution of particle axial velocity in the radial direction. At most radial cross-sections, there exists a parabola-shaped distribution of upward axial velocity of particles, namely, the magnitude of axial velocity in the core region is higher than that near the wall region of the riser.     

圆柱容器内流经环形填充层流动的研究

本文对圆柱容器内流经环形填充层的流动进行了分析,导得了基本运动方程,并进行了实验研究。计算结果与实验结果符合得比较好。研究表明,结构型式、中心通道与环形通道面积比、填充层自身的阻力系数以及圆柱容器的长径比,对于流经填充层的径向流速沿轴向的分布都有影响。     

分级加载条件下深部灰岩蠕应变特性研究

为研究深部灰岩蠕应变特性,采用GDS-VIS三轴流变仪对不同深度试样做分级加载单轴蠕变试验。基于试验结果,计算出灰岩长期强度与瞬时强度之比的均值为0.758,且深度越深比值越小;分析不同深度灰岩在各分级应力水平下轴向蠕应变增量与加载级数的变化规律,并将蠕应变增量进行一次累加,得到轴向蠕应变。结果表明:蠕应变增量随级数的增加呈现先减小后剧增的变化规律,且随深度增加,蠕应变增量达到谷底所对应的应力百分比有明显增大趋势;在分级加载过程中,随级数增加,轴向蠕应变先后呈现减速增加、等速增加和加速增加3个发展阶段;当恒载应力百分比为60%~70%时,蠕应变趋于稳定,当超过该范围后,蠕应变加速增加直至发生蠕变破坏。研究得到的这一应力百分比范围可以为识别深部灰岩是否会发生蠕变破坏提供依据。     

流道宽度及来流速度对鲫鱼运动模式的影响

为考察鲫鱼在不同流道宽度和来流速度下的运动模式,在自循环型水槽中进行了鱼游运动观测实验。实验用鱼体长18~20 cm,体重180~200 g,流道宽度为7~60 cm,来流速度0.1~0.6 m/s。利用高速摄影对不同条件下的鲫鱼游泳运动过程进行了记录,使用image Pro等图像数据分析软件对鱼游运动的摆尾频率、振幅、体波数等参数进行了定量分析,并拟合得到了鱼游运动方程,归纳了各运动参数随来流速度和流道宽度的变化规律。分析结果表明:鲫鱼的摆动频率、摆动幅度及体波数随来流速度变化有明显的改变,而流道宽度对鱼游泳运动模式的影响有限;来流速度增大,鱼的运动频率、运动幅度、体波数均有所增加。目前与鱼游运动相关的研究多集中于流速对其摆尾频率和振幅的影响,少有探讨鱼体摆动的体波数这一参数,更少有探究流道宽度对鱼运动的影响。研究成果积累了相关实验数据,可增加对鱼游运动机理的认识,为鱼类洄游通道恢复措施的制定提供理论支撑。     

FLOW OF OLDROYD-B FLUID IN ROTATING CURVED SQUARE DUCTS

The fully developed Oldroyd-B fluid flow through rotating square ducts was numerically studied. The effects of the rotation on secondary flow, axial velocity, and axial normal stress were examined in detail. The results indicated that all of the secondary flow, the axial flow, and the axial normal stress were evidently affected by the rotation. The Taylor–Proudman phenomenon could be observed in the flow. For the secondary flow, the four vortices structure and the six vortices structure were described. Recent studies also showed the effects of rotation on the axial normal stress.     

A COUPLED THERMO-HYDRAULIC MODEL FOR STEAM FLOW IN PIPE NETWORKS

This article aims to establish a coupled thermo-hydraulic mathematical model for steam network by adopting a set of equations, i.e., the continuity equation, motion equation, energy equation, state equation and enthalpy equation and considering the interaction of hydraulic and thermal working conditions. The model is simplified according to steam flow features in pipe networks. The unsteady flow model is simplified to a steady one with considering engineering practice and the solution to the governing equations are obtained by using the standard fourth-order Runge-Kutta method. Many factors of steam flow are generally considered, such as condensability, change of state, friction and heat transfer in the model. It is concluded that coupled iteration can be employed in steam network thermo-hydraulic computation. The numerical results with the model are basically in accordance with practical operation data.