圆孔外Stokes流中球形粒子的运动*

在研究悬浮液入孔问题时,粒子在孔外任意位置所受的力和力矩是所需的最基本数据.本文在严宗毅等(1987)算出的有限个离散数据的基础上.首次给出了球在圆孔外的全部十二个力和力矩系数的近似解析表达式.我们应用这些系数计算零雷诺数下球形粒子入孔时的轨道和旋转角速度,结果与现有实验数据完全一致.分析不同系数的相对重要性表明,在孔口和孔壁附近不能忽略旋转效应.在靠近孔口边缘的局部区域必须计及侧向力效应.以往的理论结果在孔口附近与实验不符,正是由于忽略了这些因素.本文还详细讨论了粒子和孔口尺寸的相对大小以及重力和浮力对于粒子运动轨道、速度分布和旋转的影响,指出用大粒子做中性悬浮实验时,对其密度的要求特别严格.本文所提供的力和力矩系数,考虑因素全面、比较准确,便于计算,为进一步研究各种涉及粒子入口的问题提供了良好的前提.     

固壁近旁Stokes流中粘性液滴的运动和变形

发展了一种模拟固壁近旁轴对称Stokes流中粘性液滴的运动和变形及直接计算固壁上应力的边界积分方法．用此方法对不同的液滴-固壁初始相对间距、粘度比、表面张力和浮力联合参数以及环境流动参数情况进行了数值实验．数值结果显示,由于环境流动和浮力的作用,随着时间的推进,液滴在轴向压缩,在径向拉伸．当环境流动的作用弱于浮力作用时,随着时间的推移,液滴上升并向上弯,固壁上由液滴运动所引起的应力不断减小．当环境流动的作用强于浮力作用时,随着时间的推移,液滴变得越来越扁．在这种情形,当大初始间距时,壁面上的应力随液滴的演变而增大;当小初始间距时,由环境流动、浮力及壁面对流动的较强作用的联合影响,此应力随液滴的演变而减小．由于液滴运动所引起的壁面应力的有效作用仅限于对称轴附近的一个小范围内,且此范围随液滴与固壁的初始间距增大而增大．应力的大小随初始间距增大而大为减小．表面张力对液滴变形有阻止作用．液滴粘性会减小液滴的变形和位置迁移．     

任意流场中颗粒运动方程的通解(英)

给出了任意流场中颗粒运动方程的无因次和线性微分方程形式．估计了颗粒运动方程中的一些相关项．借助于一些数学推导和处理，求得了比线性颗粒运动方程的通解．     

Stokes Flow in Cylindrical Containers With Rotating Ends北大核心CSCD

该文以端部旋转的圆柱形容器内的Stokes流为研究对象,根据流动的特点,将轴向坐标模拟为时间,则问题归结为Hamilton对偶方程的本征值和本征解问题.利用本征解空间的完备性和本征解之间的共轭辛正交关系,给出了问题解的展开形式,并建立了展开系数的数值求解方法.采用该方法研究了单端旋转、两端以相同或相反角速度旋转时不同外形比(容器的高度与半径之比)时圆柱形容器内流动速度和应力的分布情况,展示了不同边界条件下流场的一些特点.     

平面Stokes流动中改良的空间衰减限

研究半无限通道中,时变粘性流体Stokes流动时的空间衰减限和衰减率.得到了一个近乎最优的衰减率,且与Reynolds数无关.修正了Lin和Song的分析,选用更佳的任意常数得到衰减率为1.328,明显地改进了Lin得到结果0.91.     

Drag minimization for Navier–Stokes Flow

This paper investigates the drag minimization in a two‐dimensional flow which is governed by a nonhomogeneous Navier–Stokes equations. Two approaches are utilized to derive shape gradient of the cost functional. The first one is to use the shape derivative of the fluid state and its associated adjoint state; the second one is to utilize the differentiability of a minimax formulation involving a Lagrange functional with a function space parametrization technique. Finally, a gradient type algorithm is effectively formulated and implemented for the mentioned drag minimization problem. © 2008 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2009     

Stokes流动的罚-杂交有限元分析*

本文建议了一种用于分析Stokes流动的罚-杂交变分原理,其中,偏应力张量和静水压力事先满足线动量平衡.建立了相应的有限元模型.由此,压力可在列式过程中消去,使得有限元矩阵方程仅以节点速度作为唯一的求解未知量.推导了几种4-节点和8-节点四边形单元.通过数值算例,显示了单元性能.     

A Boundary Integral Method for Compressible Stokes Flow

A recently developed type of biochip employs ultrasonic surface acoustic waves (SAWs) as a microscale pumping and mixing mechanism for fluids. The driving force for fluid flow is an effect of nonlinear acoustics known as acoustic streaming. We recently studied a two–scale numerical model to describe this effect, which was discretized using classical finite element methods. The micro–scale part of the model describes the propagation of damped acoustic waves. Since the used equations are linear and homogeneous, it is natural to look toward a boundary integral method and attempt a coupling with the FEM scheme still employed in the macro–scale model part. One main ingredient for this approach, namely explicit formulas for free–space Green's functions describing damped acoustics, appear to be novel. We will describe some details of the new scheme, which shows a promising gain of efficiency compared to using FEM for damped acoustics. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Infinite Element Approximation to Axial Symmetric Stokes Flow

We considered in [1] the finite element approximation to axial symmetric Stokes flow in a bounded domain. The problem for the flow passing an obstacle in an unbounded domain is also frequently encountered. In this paper, we are going to give approximate solutions for this problem by an approach stated in [2]. An iterative method is used to calculate the combined stiffness matrix.     

Optical Stokes Flow Estimation: An Imaging-Based Control Approach

We present an approach to particle image velocimetry based on optical flow estimation subject to physical constraints. Admissible flow fields are restricted to vector fields satifying the Stokes equation. The latter equation includes control variables that allow to control the optical flow so as to fit to the apparent velocities of particles in a given image pair. We show that when the real unknown flow observed through image measurements conforms to the physical assumption underlying the Stokes equation, the control variables allow for a physical interpretation in terms of pressure distribution and forces acting on the fluid. Although this physical interpretation is lost if the assumptions do not hold, our approach still allows for reliably estimating more general and highly non-rigid flows from image pairs and is able to outperform cross-correlation based techniques. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

半无穷平面到半无穷长圆管的低雷诺数流动

本文利用匹配法和配置法求出了粘性流体从半无穷平面到半无穷长圆管的Stokes流动的无穷级数形式的解.结果表明,经过圆柱半径的一半路程之后,速度剖面和Poiseuille剖面只差1%.初始段长度比Dagan的有限长圆管情形显著缩短,在孔口外的半无穷空间内,孔口右边的边界只对孔口附近一倍管径的区域有强烈影响.在此以外的区域内几乎没有影响.此外,本文还对压力和流量的关系进行了研究.     

Rapid Solution of Stokes Flow using Multiscale Galerkin BEM

Two issues that arise when solving Stokes flow problems with the hydrodynamical single‐layer potential are addressed. First, the resulting boundary integral equation is singular, and second, discretizations lead to dense matrices. We discuss a well‐posed modified equation which is equivalent for zero net‐flux. Furthermore, we describe a multiscale basis that lead to sparse stiffness matrices. This approach is suitable for complicated geometries and is an extension of our previous work for the Laplace equation.     

Wavelets and Optical Flow Motion Estimation

This article describes the implementation of a simple wavelet-based optical-flow motion estimator dedicated to continuous motions such as fluid flows. The wavelet representation of the unknown velocity field is considered. This scale-space representation, associated to a simple gradient-based optimization algorithm, sets up a well-defined multiresolution framework for the optical flow estimation. Moreover, a very simple closure mechanism, approaching locally the solution by high-order polynomials is provided by truncating the wavelet basis at fine scales. Accuracy and efficiency of the proposed method are evaluated on image sequences of turbulent fluid flows.     

三维Stokes绕流问题的无限元逼近(英文)

设计了一种最少自由度的无限元方法来实现三维Stokes绕流问题的求解.通过验证强制性和inf-sup条件,我们证明了相应的离散混合变分问题解的适定性,并在加权Sobolev空间中得到了误差的先验估计.数值实验结果验证了解的收敛性.     

Singular Matched Eigenfunction Expansions for Stokes Flow around a Corner

A singular matched eigenfunction expansion method is describedfor solving Stokes flow around a corner. The flow region isdecomposed into a number of simpler rectangular subregions;this enables the stream function to be represented by meansof an expansion of Papkovich-Fadle eigenfunctions in each ofthese subregions. The coefficients in these expansions are obtainedby matching them across common interfaces in a weak sense. Theresulting solution is used in a post-processing technique todetermine the coefficients in the known locally convergent expansionof the stream function at reentrant and salient corners. A smallnumber of terms in this expansion is necessary to produce accurateapproximations.     

平面边界前Stokes流动基本的奇异性

利用双调和函数A和调和函数B，给出了三维Stokes流动速度场和压力场的描述．由此建立了计算区域边界为固定无滑移平面边界Stokes流动基本奇异性的一般定理．刚性平面前轴对称Stokes流动的Collins定理成为本定理的特例．给出的几个例证说明了方法的有效性．     

半无限长圆管内Stokes流的入口流

本文研究了半无限长圆管内Stokes流的入口流问题.我们导出了一种新的级数解,它与文献[1,2]的解有一个明显的区别就是该解中不包含无穷积分,因此有利于计算.本文利用配点法进行了计算,得到了满意的结果.