存在滑移时两圆球间的幂律流体挤压流动

基于Reynolds润滑理论分析了壁面滑移对任意圆球颗粒间幂律流体的挤压流动的影响。研究表明有壁面滑移时挤压流动的粘性力可通过引进本文定义的滑移修正系数分离出无滑移解。推导出的挤压力滑移修正系数是一积分表达式，依赖于滑移参数、幂律指数、球间隙和积分上限。一般地壁面滑移导致粘性力减小，粘性力的减小量随幂律指数的增大而增大，表明壁面滑移对剪切增稠流变材料有更大的影响；粘性力的减小量还随着滑移参数的增大而增加，而这恰与假设相符合；粘性力的减小量又随球间隙减小或积分上限的增大（从液桥情况到完全浸渍）而减小直到趋于常数，这一特性在离散元模拟时可以有效地减少计算量。     

微通道周期流动电位势及电粘性效应

求解了双电层的Poisson-Boltzmann方程和流体运动的Navier-Stokes方程,得到在周期压差作用下,二维微通道的周期流动电位势,流动诱导电场和液体流动速度的解析解．量纲分析表明,流体电粘性力与以下3个参数有关:1) 电粘性数,它表示定常流动时,通道最大电粘性力与压力梯度的比;2) 形状函数,它表示电粘性力在通道横截面的分布形态; 3) 耦合系数,它表示电粘性力的振幅衰减特征和相位差．分析结果表明,微通道周期流动诱导电场、流动速度与频率Reynolds数有关．在频率Reynolds数小于1时,流动诱导电场随频率Reynolds数变化很慢．在频率Reynolds数大于1时,流动诱导电场随频率Reynolds数的增加快速衰减．在通道宽度与双电层厚度比值较小情况下,电粘性效应对周期流动速度和流动诱导电场有重要影响．     

宾汉流体稠密两相湍流流动中的二阶矩模型

建立的Bingham流体稠密两相流动的二阶矩-颗粒动力论湍流模型（USM-theta模型）既体现了两相的作用,又体现了屈服应力所引起的附加项,并提出了USM-theta模型下考虑浓度修正值影响的两相湍流流动的算法．利用该模型对圆管内Bingham流体的单相湍流流动、稠密液固两相的湍流流动进行了计算,并和五方程湍流模型进行了比较,结果表明该模型的预测效果更好．利用USM-theta模型对含颗粒的Bingham流体的两相湍流流动进行了模拟,随着屈服应力的增加,Bingham流体相与颗粒相在管道中心附近的主流速度减小．液固两相湍流和Bingham流体两相湍流的计算结果表明屈服应力引起的附加项对流动有很重要的影响．     

蠕动流中圆球阻力系数的入口效应

本文研究了圆球在半无穷长圆管入口处的蠕动流。得到了速度分布,压力分布和流函数的无穷级数形式的分析解.采用配置法将无穷级数截断并确定出级数中各项系数.求出了均匀入口流绕静止圆球以及圆球以瞬时速度在管内静止流体中运动这两种情形下圆球的阻力系数以及圆球表面上的应力分布.结果表明,当圆球在入口处运动时会遭受到较无穷圆管内为大的阻力.本文还对配置法的收敛性进行了数值实验.试验证明,该法具有好的收敛性.     

Oldroyd-B流体在孔隙壁面残余油上的作用力分析

为了分析计算粘弹性流体驱替残余油的微尺度力,从水动力学角度探索非牛顿流体的流变特性,选取Oldroyd-B本构方程来模拟粘弹性流体,并结合连续性方程和运动方程得到了粘弹性流体在微孔道中的流动方程,利用边界条件计算得到流动的流场,结合应力张量理论,计算出粘弹性流体作用在残余油上的法向偏应力和水平应力差,计算结果表明:沿流动方向,粘弹性流体的弹性越大,法向偏应力越大;垂直于流动方向,法向偏应力近似对称分布;随着粘弹性流体的弹性变化,水平应力差的变化趋势发生了变化,威森伯格数We越大,残余油所受的水平应力差先逐渐增加,达到峰值后降低,这种趋势更有利于残余油的变形,为下一步分析残余油的变形,并从主体上分离奠定了基础.     

流体动力学的客观性要求

从流体动力学的客观性要求导出了新的流动理论.流动运动的不均匀性产生粘性力,不同观察者的选取会影响这种不均匀分布特征.将粘性力看作一种与观察者的选取无关的客观存在时,粘性力和动量方程在局域旋转变换下的形式不变性要求引入一种新的动力学场——涡旋场,通过构造流体系统的拉朗日密度并利用能量变分方法得到了所有场量的动力学方程.     

环空管内粘弹性流体不定常旋转流的解及流动特性分析

本文用Hankel积分变换法分别求得二阶流体和Maxwell流体在环管内不定常旋转流运动方程的解析解,据此可以分析环管内旋转速度和切应力的分布与变化特征;流体物性参数、管道环隙大小等参量在解析公式中有明确反映,便于定性分析和讨论,本解可以为钻探工程和高分子加工工艺的设计提供理论依据,另外还可用来分析双筒粘度计的流动状态和应力特征,拟合曲线,确定材料的粘弹性参数,在对这种流体进行特性分析时,我们发现,Maxwell流体的旋转流动在起动初期表现为方波振荡,振动的幅度和周期随Ha(物质常数)的增大而增大,此种现象还是首次发现,可能对实际应用有一定的意义。     

基于第二粘性用局部微分求积法计算激波

考虑第二粘性效应,采用局部微分求积法数值求解激波问题．首先解释了在激波计算时,有必要考虑第二粘性,然后基于粘性模型,对一维和二维激波进行了数值模拟,还分别考察了剪切粘性力和第二粘性力对数值结果的影响．结果表明,采用粘性模型加上局部微分求积法能够模拟出激波特征,具有客观、简单的优点．     

二阶非牛顿流体环管流动解析解

本文采用积分变换的方法,找到了一类非牛顿流体在环形管道中不定常流动的解析解,并进行了数值计算,详尽分析了非牛顿性系数和其他各参数对二阶流体不定常流动的影响.指出当二阶流体非牛顿系数相同时,环管流与一般管流相比达到稳定的特征时间较短,并且相应的速度分布、平均速度分布的数值均较小,在外半径相同时,环管流内壁的剪应力较之一般管流,其大小随内半径的大小而变,环管流的外壁剪应力总相应地小于内壁剪应力.     

双筒流变仪中广义二阶流体运动分析

将分数阶导数运算引入二阶流体本构方程,研究双筒流交仪中的流动特征.先求山了1/2阶导数情况下的解析解.用以验证Laplace数值反演的Crump方法的有效性,然后用Crump方法分析这种环管旋转流动 结果表明粘弹性特征越明显的流体,其速度与应力对分数导数的阶数越具有敏感性.另外,引入Crump数值反演法,成功地分析了所提出的问题.给二阶流体的实验测试工作提供了解析模型和分析手段.     

非线性边界滑移挤压膜流动

用一种包含初始滑移长度和临界剪切率的非线性边界滑移模型研究了两个球体间的挤压流体膜问题．研究发现初始滑移长度对低剪切率下的滑移行为起主要作用,而临界剪切率决定了高剪切率下的边界滑移程度．球体表面挤压流体膜的边界滑移量是与半径坐标相关的高度非线性函数．在挤压膜的中心点和远离中心点处由于低剪切率滑移量等于初始滑移长度,然而在高剪切率区域滑移长度迅速增加．球体挤压膜的流体动压力随着初始滑移长度的增加和临界剪切率的减小而减小,并且临界剪切率对流体动力的影响要比初始滑移长度大的多,当临界剪切率很小的情况下,流体动压随着最小膜厚的减小几乎不再增加．所用模型给出的理论预报和实验非常吻合．     

Boundary element method for simulating the coupled motion of a fluid and a three-dimensional body

A boundary element method for potential flow problem coupled with the dynamics of rigid body was developed to determine numerically the resultant force and moment of force acting on an arbitrarily three-dimensional solid body and its motion in a current of an infinite fluid. An accurate integration method for singular integrands occurring in the boundary integral equations, a computational method for the tangential gradient of a velocity potential on a surface, and a method to properly treat the singularities appearing in the system of the dynamic equations of a rigid body, were proposed to complete the numerical solution of the problem. Several numerical examples were given to show the validity of the method.     

Incipient sediment transport for non-cohesive landforms by the discrete element method (DEM)

We introduce a numerical method for incipient sediment transport past bedforms. The approach is based on the discrete element method (DEM) [1], simulating the micro-mechanics of the landform as an aggregate of rigid spheres interacting by contact and friction. A continuous finite element approximation [2] predicts the boundary shear stress field due to the fluid flow, resulting in drag and lift forces acting over the particles. Numerical experiments verify the method by reproducing results by Shields [3] and other authors for the initiation of motion of a single grain. A series of experiments for sediments with varying compacity and constituting piles yields enhanced relationships between threshold shear stress and friction Reynolds number, to define incipient sediment transport criterion for flows over small-scale bed morphologies.     

两种人工机械心瓣启闭过程的ALE有限元分析*

本文采用任意拉格朗日-欧拉(ALE)有限单元法,将血液视为不可压缩粘性流体,同时将人工机械瓣简化为定轴转动刚体,建立了机械心瓣/血液耦合运动的二维计算模型。在此基础上。计算了顺向人工机械瓣(DDM)的开闭过程,并与St.Jude瓣(SJM)进行了对比。由本文研究可得以下主要结论:1.DDM瓣与SJM相比,开启较为迅速,关闭则较为柔和。2.DDM瓣的峰值回流量较之SJM瓣小。本文研究表明DDM瓣由于更好利用了天然心瓣的关闭机理,而具有较高的耐久性潜力。     

Inertia effects in circular squeeze film bearing using Herschel–Bulkley lubricants

Recent engineering trends in lubrication emphasize that in order to analyze the performance of bearings adequately, it is necessary to take into account the combined effects of fluid inertia forces and non-Newtonian characteristics of lubricants. In the present work, the effects of fluid inertia forces in the circular squeeze film bearing lubricated with Herschel–Bulkley fluids with constant squeeze motion have been investigated. Herschel–Bulkley fluids are characterized by an yield value which leads to the formation of a rigid core in the flow region. The shape and extent of the core formation along the radial direction is determined numerically for various values of Herschel–Bulkley number and power-law index. The bearing performances such as pressure distribution and load capacity for different values of Herschel–Bulkley number, Reynolds number, power-law index have been computed. The effects of fluid inertia and non-Newtonian characteristics on the bearing performances have been discussed.     

Slow motion of a sphere moving normal to two infinite parallel plane walls in a micropolar fluid

In the present work, we consider the slow steady motion of a rigid sphere moving normal to two parallel plane walls in a micropolar fluid. Non-dimensional variables are introduced. A combined analytical-numerical technique based on the superposition principle and a numerical method, namely the collocation method, is used. The drag force and the wall correction factor are evaluated. Numerical results are obtained and represented graphically.     

Acoustic radiation force of attraction,cancellation and repulsion on a circular cylinder near a rigid corner space

The purpose of this study is to derive exact partial wave series expansions for the longitudinal and transverse radiation force components, for a circular cylinder in the proximity of a rigid corner space, and illuminated by incident plane waves with arbitrary orientation in the polar plane. Based on the multipole expansion method in cylindrical coordinates, the method of images as well as the translational addition theorem, an effective incident field (resulting from the primary waves as well as the multiple scattered fields from the image sources) is determined first, and used subsequently with the scattered field to derive the mathematical expressions for the radiation force components, stemming from the integration of the radiation stress in a non-viscous fluid. Numerical computations illustrate the analysis for rigid and soft cylinders with particular emphasis on the distances from the particle edges to the neighbouring walls, the size of the cylinder and the angle of incidence. Depending on the choice of these parameters, the radiation force components can vanish, rendering complete “invisibility”; i.e., the cylinder becomes unresponsive to the transfer of linear momentum carried by the incident effective field. Moreover, the radiation force components alternate between positive and negative values, suggesting a force of repulsion or attraction. The results find potential applications in acoustofluidics design and optimization as they shed light on the anechoic radiation force effect on a particle nearby a rigid corner. Other applications in noise and vibration control could also benefit from the results of the present investigation along with further related topics.     

含界面电极压电介质的Green函数

研究了由两个不同压电材料和一半无限长电极组成的复合材料系统的广义二维问题·　基于Stroh公式,提供了当一个线力、线电荷和一个线电偶极子施加在电极端附近时,精确的Green函数解·　进一步地,获得了相应的场强度系数·　这些结果可作为边界元的基本解,以分析更加复杂的压电复合材料断裂问题·     

圆形界面刚性线夹杂的平面问题

研究了圆弧形界面刚性线夹杂的平面弹性问题．集中力作用于夹杂或基体中的任意点,并且无穷远处受均匀载荷作用．利用复变函数方法,得到了该问题的一般解答．当只含一条界面刚性线夹杂时,获得了分区复势函数和应力场的封闭形式解答,并给出刚性线端部奇异应力场的解析表达式．结果表明,在平面荷载下界面圆弧形刚性线夹杂尖端应力场和裂纹尖端相似具有奇异应力振荡性．对无穷远加载的情况,讨论了刚性线几何条件、加载条件和材料失配对端部场的影响．