互层状岩体及节理岩体的粘弹性模型

采用对互层岩体或节理岩体的不同介质进行“分离、集中”的方法得到了互层或节理岩体的二维和三维粘弹性模型。这个模型在互层或节理岩体的数值分析中是较实用的。     

粘弹性基支薄板的准静态弯曲

本文讨论粘弹性基础上的粘弹薄板准静态弯曲的一般解法.文中利用板-地基系统的弹性粘弹性相应原理,以对边简支、另两边自由的粘弹性基支矩形板为例,导出了在拉氏象空间中的有关算式,然后采用数值逆变换的方法,求得板的挠度、基支反力和内力.数值计算中,同时给出了粘弹基支的弹性板、弹性基支的粘弹板和非基支粘弹性薄板的各种解答.     

二维粘弹性问题的边界单元法

本文通过对粘弹性拟静态问题的方程进行Laplace变换,将粘弹性问题变换成在Laplace空间下与弹性静力问题相同的形式,推导出了用边界单元法分析粘弹性问题的基本公式,并用FORTRAN语言编制的计算机程序对粘弹性问题进行了分析计算。     

高聚物PMMA的受力变形行为与粘弹－塑性本构理论模型

对高聚物ＰＭＭＡ实验测定了不同（Ｔ，ε）的单轴加卸载循环的应力－应变曲线。讨论了应力促进热激活塑性变形的活化粘壶理论和塑性变形的发展规律。提出由ＳＬＳ或ＭＳ与活化粘壶作串联耦合的粘弹－塑性本构理论模型，给出了微分和积分形式的本构方程组，用于拟合求解加卸载循环的应力－应变曲线，获得良好吻合的结果。详细讨论了ＰＭＭＡ在加载过程中的受力变形行为，包括起始加载的粘弹性变形，ε＿ｖ和ε＿ｐ的互相挤占，屈服点，以及屈服后应变软化和硬化的抗衡过程。对应变软化－硬化效应提出一种新的起因于粘弹变形内禀滞后效应的理论解释，并定名为粘弹软化－强化效应。对所包含的粘弹变形成分，从Ｅ＿ｖ的移位因子和归一化应力－应变主曲线两方面，讨论了可能存在的率温等效关系。     

Rheological properties of paraffin suspensions of surface-modified alumina powder for low-pressure injection moulding

Due to the hygroscopic nature of fine alumina powders, the presence of water may have a detrimental effect on the rheological properties of a suspension in melted paraffin for low-pressure injection moulding (LPIM). For this reason, a modification of the powder surface from hydrophilic to hydrophobic is essential for the production of high-quality moulded ceramics. In our paper, the efficiency of the application and the chemisorption of protective monomolecular layers of a long-chain carboxylic acid or its salts will be presented. The effect of the powder treatment on the shear viscosity and the viscoelastic properties of the suspensions for LPIM as well as on their stability in terms of the detrimental effect of water will be discussed.This paper was presented at the first Annual European Rheology Conference (AERC) held in Guimarães, Portugal, September 11-13, 2003.     

Realistic rotating convection in a DNA suspension

In this work we report theoretical and numerical results on convection in a viscoelastic binary mixture under rotation for realistic rigid-rigid boundary conditions. We focus our analysis in the DNA aqueous suspensions. Instability thresholds for oscillatory convection are calculated. Finally, we analyze the stabilizing effect for the onset of convection.     

Three-dimensional flow over a stretching surface in a viscoelastic fluid

This article looks at the hydrodynamic elastico-viscous fluid over a stretching surface. The equations governing the flow are reduced to ordinary differential equations, which are analytically solved by applying an efficient technique namely the homotopy analysis method (HAM). The solutions for the velocity components are computed. The numerical values of wall skin friction coefficients are also tabulated. The present HAM solution is compared with the known exact solution for the two-dimensional flow and an excellent agreement is found.     

Analysis of polymer drag reduction mechanisms from energy budgets

The transfer of energy in drag reducing viscoelastic flows is analyzed through a sequence of energetic budgets that include the mean and turbulent kinetic energy, and the mean polymeric energy and mean elastic potential energy. Within the context of single-point statistics, this provides a complete picture of the energy exchange between the mean, turbulent and polymeric fields. The analysis utilizes direct simulation data of a fully developed channel flow at a moderately high friction Reynolds number of 1000 and at medium (30%) and high (58%) drag reduction levels using a FENE-P polymeric model.Results show that the primary effect of the interaction between the turbulent and polymeric fields is to transfer energy from the turbulence to the polymer, and that the magnitude of this transfer does not change between the low and high drag reduction flows. This one-way transfer, with an amplitude independent of the drag reduction regime, comes in contradiction with the purely elastic coupling which is implicit within the elastic theory of the polymer drag reduction phenomenon by Tabor and De Gennes (Europhys. Lett. 2, pp. 519–522, 1986).     

On the lubrication approximation for a class of viscoelastic fluids

We present a rigorous derivation of a dimensionally reduced Reynolds type equation for thin film flow lubrication of a class of viscoelastic fluids by employing a perturbation analysis on the upper-convected Maxwell model in natural orthogonal coordinates. This approximation accounts for the viscoelastic and curvature corrections to the classical Reynolds lubrication approximation. Comparison of our approximation with the classical Reynolds approximation suggests that viscoelasticity can have a significant influence on the lubrication characteristics, at least for certain values of the film thickness and of the eccentricity ratios of the journal bearing.     

A blow-up result in a Cauchy viscoelastic problem

In this work we consider a Cauchy problem for a nonlinear viscoelastic equation. Under suitable conditions on the initial data and the relaxation function, we prove a finite-time blow-up result.