关于流体力学教学内容改革的探讨

就流体力学系列课程中适当增加非牛顿流内容的必要性及具体措施进行阐述.     

国内非牛顿流体力学进展

非牛顿流体;;本构方程;;流变测量;;流动稳定性;;收缩流动;;聚合物加工;;石油工业;;生物流体力学     

固体还是流体？

当有人问,刷墙的涂料是固体还是流体时？需要仔细想想才能给出一个正确的回答. 日常的生活经验告诉我们,液体涂料似乎是一种流体. 但是,在粉刷墙壁的时候,涂料薄层的流动需要用刷子来帮助. 也就是说,只有在一定大小力的作用下,涂料才能流动. 从这个角度看,涂料在不同的外力条件下,可能呈现固体或流体两种不同的特性. 在流变学和非牛顿流体力学中,涂料被称为屈服应力流体. 当作用力小于屈服应力时,屈服应力流体呈现固体的特性;当作用力大于屈服应力时,屈服应力流体就开始流动.     

非牛顿流体力学研究的若干进展

简要介绍微极性流体,应力偶流体,非整数阶Maxwell流体和智能流体的基本概念,通过简单的例子阐述它们与牛顿流体的本质差别,并介绍非牛顿流体在以上热点研究领域的若干进展．     

关于流体力学方法论问题

 力学是以实验为基础的科学. 流体力学中绝大多数重要的概念和原理都源于实验. 对 于流体力学问题，数值模拟与物理实验的本质区别并未消失；数值模拟不能代替物理实验， 大规模数值模拟的结果仍需由巧妙设计的物理实验来检验其正确性.     

液压技术中的流体力学

介绍了流体静力学和流体动力学在液压工程技术中的应用,说明了流体力学理论在液压工程中所起到的非常重要的作用. 用流体力学的原理来解释液压技术中出现的问题,而这些问题的解决都离不开流体力学的发展.     

流体力学大师Batchelor的几件史事

Batchelor是湍流剑桥学派的领军人物,国际流体力学大师. 本文分析影响他成长的人和事,有助于理解湍流研究的历史兴衰.     

电磁功能材料的多场耦合实验研究进展

将对电磁功能材料多物理场耦合性能检测技术和设备做一综述介绍,介绍如何在多物理场耦合条件下测试电磁滞回线、蝶形曲线、电磁致伸缩、应力应变曲线和磁电效应等物理力学性能,并介绍电磁功能材料在多物理耦合场作用下的新的实验现象,包括铁电材料在多轴电场和双轴力载荷作用下的电滞回线、裂纹尖端的畴变规律、磁致伪弹性、磁致伸缩的"回落"等现象.这对于理解电磁功能材料和结构在耦合场下的变形与断裂机制有重要的意义.     

流体力学在选矿中的应用

分析了一些典型的选矿设备中流体的运动,阐述了流体力学对选矿发展的重要性,说明了选矿中流体力学的特点及选矿中面临的流体力学问题.     

牛顿流变转变为非牛顿流变行为的教学方法

牛顿流变与非牛顿流变是流体力学的重要分支。本文从基本的流变模式出发,介绍了非牛顿流变的特性与分类,引入并推导非晶合金牛顿流变转变为非牛顿流变行为的力学机制。最后介绍了假塑性流体在工程实际中的应用。本文综合作者近年来对于无序固体高温流变力学行为的研究结果和非牛顿流变力学的教学实践,结合了学生的学习效果,从教学内容和思路逻辑方面进行讨论。文中教学方法可为讲授非牛顿流变力学课程的教师提供借鉴。

     

An objective rotation tensor applied to non-Newtonian fluid mechanics

To develop objective constitutive equations, local frames which translate and rotate with the fluid particle can be used. For example, the corotating frame rotates such that the curl of the velocity calculated in this frame vanishes. From the corotating frame, the Jaumann derivative can be derived. In this paper, a new local frame is developed which causes the cross product of the velocity and acceleration to vanish and is designated as the rigid-rotating frame. The corotating and rigid-rotating frames rotate identically for a rigid-body rotation of the fluid, but rotate differently in flows that contain shearing. This difference in rotation can be used to develop an objective rotation tensor that can be applied to constitutive equations for viscoelastic liquids. The rigid-rotating frame can also be used to develop a rheological time derivative which has been designated the rigid-rotating derivative. These new quantities expand the traditional set of kinematical variables and invariants available for use in constitutive equations. Use of this expanded set of kinematic variables is demonstrated in limiting constitutive equations. Received: 1 March 1999 Accepted: 5 March 1999     

Infinite interval problems arising in non-linear mechanics and non-Newtonian fluid flows

Existence results are presented for second-order boundary value problems on the infinite interval modelling phenomena which arise in non-Newtonian fluid theory and in circular membranes.     

D'Alembert motions for non-Newtonian second grade fluid

Solutions to the unsteady flow of a viscoelastic second grade fluid are found under the assumption that the streamfunction is a product of functions of space and time. Flows with this property are called D'Alembert motions. It is also shown that the streamlines are independent of time.     

Similarity solutions for non-Newtonian power-law fluid flow

The problem of the boundary layer flow of power law non-Newtonian fluids with a novel boundary condition is studied.The existence and uniqueness of the solutions are examined,which are found to depend on the curvature of the solutions for different values of the power law index n.It is established with the aid of the Picard-Lindel¨of theorem that the nonlinear boundary value problem has a unique solution in the global domain for all values of the power law index n but with certain conditions on the curvature of the solutions.This is done after a suitable transformation of the dependent and independent variables.For 0 n 1,the solution has a positive curvature,while for n 1,the solution has a negative or zero curvature on some part of the global domain.Some solutions are presented graphically to illustrate the results and the behaviors of the solutions.     

Weakly-imposed Dirichlet boundary conditions for non-Newtonian fluid flow

We propose a new formulation for weakly imposing Dirichlet boundary conditions in non-Newtonian fluid flow. It is based on the Gerstenberger–Wall formulation for Newtonian fluids [1], but extended to non-Newtonian fluids. It uses a stabilization term in the weak form that is independent from the actual fluid model used, except for an adjustable parameter κ, having the physical dimension of a viscosity. The new formulation is tested, combined with an extended finite element method, for the flow past a cylinder between two walls using both a generalized Newtonian and a viscoelastic fluid. It is shown that the convergence is optimal for the generalized Newtonian fluid by comparing with a converged boundary-fitted solution using traditional strong boundary conditions. Also the solution of the viscoelastic fluid compares very well with a traditional solution using a boundary-fitted mesh and strong Dirichlet boundary conditions. For both fluid models we also test various values of the κ parameter and it turns out that a value equal to the zero-shear-viscosity gives good results. But, it is also shown that a wide range of κ values can be chosen without sacrificing accuracy.     

Analytical solutions for non-Newtonian fluid flows in pipe-like domains

This paper deals with some unsteady unidirectional transient flows of an Oldroyd-B fluid in unbounded domains which geometrically are axisymmetric pipe-like. An expansion theorem of Steklov is used to obtain exact solutions for flows satisfying no-slip boundary conditions. The well known solutions for a Navier-Stokes fluid, as well as those corresponding to a Maxwell fluid and a second grade one, appear as limiting cases of our solutions. The steady state solutions are also obtained for t→∞.     

Simplified lattice Boltzmann method for non-Newtonian power-law fluid flows

In this paper, we present a simplified lattice Boltzmann method for non-Newtonian power-law fluid flows. The new method adopts the predictor-corrector scheme and reconstructs solutions to the macroscopic equations recovered from the lattice Boltzmann equation through Chapman-Enskog expansion analysis. The truncated power-law model is incorporated into this method to locally adjust the physical viscosity and the associated relaxation parameter, which recovers the non-Newtonian behaviors. Compared with existing non-Newtonian lattice Boltzmann models, the proposed method directly evolves the macroscopic variables instead of the distribution functions, which eliminates the intrinsic drawbacks like high cost in virtual memory and inconvenient implementation of physical boundary conditions. The validity of the method is demonstrated by benchmark tests and comparisons with analytical solution or numerical results in the literature. Benchmark solutions to the three-dimensional lid-driven cavity flow of non-Newtonian power-law fluid are also provided for future reference.     

Extended thermodynamics of a non-Newtonian fluid

Thermodynamics restrictions are calculated upon the constitutive equations of a non-Newtonian fluid. The fluid is of the rate type and the proper thermodynamic theory for such materials is seen to be extended thermodynamics. Thermodynamic stability conditions lead to the proper sign of the normal-stress coefficient, i.e. the sign that is compatible with experiment. Wave speeds for shear waves are calculated and the treatment of incompressible fluids is discussed.