考虑晶界效应的多晶体有限变形分析

将晶界及其影响区综合考虑，建立了考虑晶界效应的力学模型，结合晶体塑性理论，利用有限变形有限元对多晶体进行数值模拟，数值结果显示了细观层次下晶粒变形场的特点，理论计算同实验定性一致。     

Flow development of xanthan solutions in capillary rheometers

Flow experiments through capillaries with 0.2% xanthan in aqueous solution and 0.1 N NaCl brine were carried out to study the influence of the molecular conformation on the flow development at relatively low shear rates, from 20s^–1 to 400s^–1. Capillaries with a wide range of length-to-diameter ratios, L/D = 4.5 to 1015 were used.The apparent viscosity as a function of L/D at a constant shear rate shows a continuous decrement of the viscosity as L/D increases, until an asymptotic value is reached. The decrement in the apparent viscosity is partially explained in terms of slip. It was found that slip is a function of L/D as well as shear stress, i.e., slip develops during flow, thus inducing spatial anisotropy in the fluid until a stable state is reached. However, the substantial difference in apparent viscosity between short capillaries and capillaries longer than 300 D may be attributed to dominant elongational flow due to the contraction in the small capillaries and slip in long capillaries.The flow in a sufficiently long capillary can be divided in four regions rather than three, as is usually assumed. In the first region, which corresponds to the entry, elongational and shear flow coexist and elongational flow dominant. In the second region, end effects and slip development are coupled. In the third region the flow is fully developed and end effects are negligible. However, the fluid shows physical characteristics different from those of the fluid at rest, as a consequence of prior slip development. The fourth zone is the exit region in which the velocity rearranges due to the change of boundary conditions. The length of each region depends on the conformation of the macromolecules and shear rate. In addition, it was found that the stiffness of xanthan increases with the increase of the ionic strength.Finally, a performance of Bagley's analysis in the whole range of L/D studied showed that the use of the Bagley correction is not a reliable way to correct for end effects when the flow is not fully developed and/or in the presence of slip.Dedicated to Arthur S. Lodge at the occasion of his 70th birthday and his retirement from the University of Wisconsin.     

Convective Instability in Superposed Fluid and Porous Layers with Vertical Throughflow

A closed form solution to the convective instability in a composite system of fluid and porous layers with vertical throughflow is presented. The boundaries are considered to be rigid-permeable and insulating to temperature perturbations. Flow in the porous layer is governed by Darcy–Forchheimer equation and the Beavers–Joseph condition is applied at the interface between the fluid and the porous layer. In contrast to the single-layer system, it is found that destabilization due to throughflow arises, and the ratio of fluid layer thickness to porous layer thickness, , too, plays a crucial role in deciding the stability of the system depending on the Prandtl number.     

On the relationship between the work of adhesion and the critical shear stress for the onset of flow instabilities

The relationship between the critical shear stress for the onset of flow instabilities and the work of adhesion at the interface has been evaluated experimentally for a series of polyolefins on several steels, brasses, and coated steels. The critical shear stress was considerably affected by the chemical nature of the die. Low-surface-energy materials were found to produce smooth extrudates presumably by inducing slippage at the wall. Steel, tungsten carbide, and brass surfaces promoted sharkskin defect at shear stresses above the first critical shear stress. A linear relationship between the critical shear stress and the work of adhesion was found to be valid for values of work of adhesion smaller than approximately 30 mN/m. This indicates that slippage occurs due to a breakdown of the adhesion at the interface. For values of work of adhesion greater than approximately 30 mN/m a stronger interaction at the interface may induce a cohesive failure at the interface and subsequently, extrudate distortions.     

Estimation of the parameters of Herschel-Bulkley fluid under wall slip using a combination of capillary and squeeze flow viscometers

The determination of the parameters of viscoplastic fluids subject to wall slip is a special challenge and accurate results are generally obtained only when a number of viscometers are utilized concomitantly. Here the characterization of the parameters of the Herschel-Bulkley fluid and its non-linear wall slip behavior is formulated as an inverse problem which utilizes the data emanating from capillary and squeeze flow rheometers. A finite element method of the squeeze flow problem is employed in conjunction with the analytical solution of the capillary data collected following Mooneys procedure, which uses dies with differing surface to volume ratios. The uniqueness of the solution is recognized as a major problem which limits the accuracy of the solution, suggesting that the search methodology should be carefully selected.     

黄河下游堤防地质险段研究

由地质作用影响形成的易出险堤段称为地质险段 ,主要包括活断层作用影响形成的堤基易渗漏段、强地震高发区段和地基稳定性差段等。构造节点是识别地质险段的重要的河流地貌标志之一。根据成因 ,本文将黄河下游的地质险段分为三类 ,即新构造险段、沉降险段、断裂复活险段。针对黄河下游堤防地质特征 ,圈定出东坝头、大刘屯—董口黄河南岸和路那里—十里堡黄河南岸地质险段 ,提出了治理的有关措施     

The effect of slip in the flow of a branched PP melt: experiments and simulations

In this paper visualisation and direct velocity profile measurement experiments for a branched polypropylene melt in a 10:1 axisymmetric contraction demonstrate the onset of wall slip. Video processing of the flow shows the formation of vortices and their diminution with increasing flow rate. Numerical simulations using a multimode K-BKZ viscoelastic and a purely viscous (Cross) model—both of them incorporating a nonlinear slip law—were used to predict the flow kinematics and dynamics as well as to deduce the slip velocity function by performing fitting to the velocity profiles. It was found that the numerical predictions agree well with the experimental results for the velocity profiles, and vortex formation, growth and reduction. It is suggested that such experiments (visualisation of entrance flow and direct velocity profile measurement) can be useful in evaluating the validity of constitutive equations and slip laws in the flow of polymer melts through processing equipment.     

可压缩材料平面应变滑移线场的数值解和边界条件

简要介绍了可压缩材料平面应变滑移线理论。导出了滑移线场应力和速度数值解。处理了应力边界条件，阐明了应力和速度间断规律。举例说明了边界条件处理和数值解步骤。     

抚顺石油一厂地表变形初步探讨

石油一厂地表变形的主要因素是西露天矿露天台阶开采, 引起厂南缘边坡失稳、变形和地面沉陷, 同时促使其它因素活化, 更加剧了地裂缝和变形发展。     

基于在线HHT和SVM的汽油机轻微漏气故障识别方法

针对汽油机轻微漏气故障会被闭环反馈控制所掩盖,提出了一种基于在线希尔伯特变换(Hilbert-Huang Transform,HHT)和支持向量机(Support vector machine,SVM)的两阶段微小故障识别方法(Online HHT-SVM,OHS).第一阶段在嵌入式两滑动时间窗内通过HHT对发动机空燃比数据流进行在线时频分析,以实时获取空燃比发生异常的时刻;第二阶段通过SVM对异常时刻的数据流故障模式进行离线识别.根据氧传感器信号特征,对经验模态分解(Empirical mode decomposition,EMD)算法进行了改进,并从理论上进行了证明.基于两款发动机的实际运行数据验证了该方法的有效性.