The effect of dissolved polymers on the rheological properties of coating colours

Coating colours used for the coating of paper and board consist mainly of a mineral pigment, which is very often clay, a synthetic binder such as a styrenebutadiene latex, dispersion agents and water retention aids. The latter are often water soluble polymers. These polymers have a very strong influence on the rheological properties of the coating colours, both on the strain rate dependence of the apparent viscosity and on the viscoelasticity. The effects of two different grades of carboxymethylcellulose (CMC) and one grade of hydroxyethylcellulose (HEC), on the rheological properties at room temperature of a clay-based coating colour at pH 8, have been investigated. It is concluded that the high values of the dynamic modulus of the colours are due to interactions between the cellulose derivatives and the solid particles, i.e. mainly the clay particles. For HEC this interaction is associated with adsorption of the polymeric molecules on the clay particles. In the case of CMC, the adsorption is strongly retarded by the presence of the dispersant (a polyacrylate salt). It is suggested that the marked elasticity of the CMC-containing colour in addition to a possible polymer adsorption may be due to charge interactions and/or depletion flocculation. The effect of CMC and HEC on the water-retention properties of the colour is also discussed.     

Effect of Elevated Velocity of Particles in Groundwater Flow and Its Role in Colloid-facilitated Transport of Radionuclides in Underground Medium

Colloid-facilitated transport of radionuclides by groundwater can increase the level of ecological hazard from radioactive contaminant migration in geological medium. The reason for this is that the migration velocity of a radioactive colloid can be higher than that of radionuclides carried by the groundwater as a solute. On the basis of their field and laboratory studies, a few researchers have concluded that the velocity of the colloid can even exceed the interstitial velocity of the groundwater by a few times. A theoretical analysis of this effect is carried out in this article. The analysis is based on the assumption that the only mechanism responsible for the effect is caused by a redistribution of the colloid in a cross section of the groundwater flow in a representative volume to such domains of the cross section where the local velocity of the flow is higher than the average velocity over the whole cross section. This redistribution can be caused by drift forces arising as a result of the Magnus effect. The influence of these drift forces on a particle’s movement is considered in two extreme cases; that of relatively large and relatively small colloid particles. Particles are considered relatively small if the thermal motion of water molecules exerts a decisive influence on the particles’ movement. Otherwise the particles are considered as being relatively large. It is shown that in the case of relatively large particles this redistribution can be caused by the instability of their movement. The redistribution in the case of relatively small particles can be caused by an influence of the drift forces on characteristics of Brownian motion. It follows from the results of the theoretical analysis that an influence of the drift forces in both cases does not lead to an increase in the particles’ migration velocity at near-horizontal direction of the groundwater flow. Data from experimental studies of the elevated velocity of colloids in porous medium are analyzed. It is shown that some findings of colloidal migration velocity exceeding the interstitial velocity of the groundwater are a result of misinterpretation of experimental results.     

Large Scale Experiment on Transport of Trichloroethylene in a Controlled Aquifer

Pollution by dense non-aqueous phase liquids (DNAPLs) represents a major threat to groundwater resources. In a real case of site contamination, the efficiency of remediation techniques is often limited by a lack of knowledge of both the extent of the pollution and the behavior of the different phases of the pollutant in the subsurface. An experiment simulating pollution of an aquifer by a chlorinated solvent (Trichloroethylene: TCE) was conducted on a large controlled experimental site called SCERES. The experiment consisted of an injection of 8.9 liters of TCE under controlled conditions at 35cm below the soil surface with an appropriate set up. The goal was to study the behavior of the three phases of the pollutant (trapped TCE phase forming the impregnation body, vapors in the vadose zone, and dissolved traces in the aquifer) in order to better comprehend the mechanisms which govern the propagation and the transfer of this type of pollution underground. The SCERES experimental data indicate that mass transfer from the saturated zone to the vadose zone is important, affecting the repartition of the vapor plume and causing a significant decrease of dissolved TCE concentrations in the groundwater. Furthermore, vertical leaching of TCE vapors due to rainfall strongly influences the degree of groundwater pollution and its lateral extent. The transient mass balance of the experiment is very satisfactory and shows that the main part of the spilled quantity is lost to the atmosphere.     

含气泡油滴撞击油膜壁面时气泡的变形与破裂

油--气润滑过程中润滑油液滴受高速气流扰动易形成含气泡油滴,微气泡将对油滴撞击壁面时的运动过程以及壁面油膜 层的形成质量产生重要影响. 基于耦合的水平集--体积分数 方法,对含气泡油滴撞击油膜壁面行为进行数值模拟研究, 考察含气泡油滴撞击油膜壁面时气泡的变形运动过程,探讨气泡破裂的动力学机制,分析气泡大小、碰撞速度和液体黏度等因素对含气 泡油滴撞壁过程中气泡变形特征参数的影响规律. 研究表明:含气泡油滴撞击油膜壁面后气泡会发生变形,并破裂形成膜液滴;气泡随同 液滴运动过程中,气泡内外压力和速度梯度变化是使气泡发生破裂的主要诱因. 气泡大小对气泡破裂方式影响较大,气泡较小时发生单 点破裂,而气泡较大时更容易发生多处破裂. 不同大小气泡受力差异较大,气泡大小与破裂发生时刻没有明显相关性. 碰撞速度和液体 黏度对气泡的变形、破裂和破裂发生时刻都具有一定的影响. 碰撞速度越大,油滴动能越大,更容易产生气泡变形和破裂现象. 液体黏 度增大,在油滴撞壁运动前期促进气泡变形,而在运动后期可以阻延气泡破裂行为发生.      

Non-linear in-plane buckling of rotationally restrained shallow arches under a central concentrated load

This paper investigates the non-linear in-plane buckling of pin-ended shallow circular arches with elastic end rotational restraints under a central concentrated load. A virtual work method is used to establish both the non-linear equilibrium equations and the buckling equilibrium equations. Analytical solutions for the non-linear in-plane symmetric snap-through and antisymmetric bifurcation buckling loads are obtained. It is found that the effects of the stiffness of the end rotational restraints on the buckling loads, and on the buckling and postbuckling behaviour of arches, are significant. The buckling loads increase with an increase of the stiffness of the rotational restraints. The values of the arch slenderness that delineate its snap-through and bifurcation buckling modes, and that define the conditions of buckling and of no buckling for the arch, increase with an increase of the stiffness of the rotational end restraints.     

Microstructural Changes in Surface Layers of Metal During Running-in Friction Processes

Studies of the dislocation structure of surface layers of some FCC and BCC metals, such as copper and steel, after sliding-friction tests for various lengths of time are reported. The results of the transmission electron microscopy and X-ray investigations show that each material is characterized by its own definite state of surface layer structure, which corresponds to the conditions of the friction, such as load, materials of counterbody and others. A sequence of microstructural changes for increasing test time consists of an increase in dislocation density and formation of dislocation pileups and a fragmented structure. It is established that under constant conditions of friction, the characteristics of the microstructure only vary in the running-in period. The kinetics of microstructure formation in the surface layers during friction predetermine the hardening and negative hardening processes and the wear of material. Comparison of the results of investigation of the structure with wear data and the data on roughness changes, shows that the time of transition to stable wear and equilibrium roughness of the surface coincides with the time of stabilization of the structure. The changes of the surface roughness in the running-in period occur simultaneously with those of the microstructure. These two processes are interrelated. First, when the equilibrium roughness is reached, the pressure on the contact spots decreases. Second, the fragmented structure, formed during the running-in period, strengthens the surface layers. Both these phenomena lead to a reduction in the wear rate. The results of this investigation can be used for development of structural methods of tribosystem diagnostics. They show that the running-in period is characterized by the change of microstructural state of surface layers. Consequently, the parameters of the microstructure can be used to determine this period.     

Un modèle discret du couplage entre les fils dans une structure tisséeA discrete model for the coupling between the yarns in a woven fabric

The coupling between yarns in a piece of fabric has been analysed at the mesoscopic scale, in terms of its impact on the macroscopic unidirectional behaviour. Starting from a discrete model of a woven structure associated to a variational formulation of the equilibrium of the structure, the coupling between both yarns is introduced, the potential energy of which is calculated. The initial shape of the yarn, represented by a planar undulated beam supposed to be periodic, is described by a Fourier series. The coefficients of the series are expressed vs. the contact force exerted at the top of the undulations, and vs. the mechanical properties of the solicited yarn. The contact force is then expressed vs. the mechanical properties of the transverse yarn and vs. the vertical displacement of the contact point. The potential energy of the coupling is then built, assuming the continuity of the displacement at the contact points. The equilibrium shape of the yarn submitted to unidirectional traction is obtained numerically as the minimum of the total potential energy. The simulated traction curve reproduces in a satisfactorily manner the observed behaviour. The respective contributions of the flexional and extensional effects of the yarn are analysed. The consideration of the coupling enhances the rigidity of the response of the yarn; one demonstrates the effect of the geometrical and mechanical parameters of the transverse yarn. To cite this article: B. Ben Boubaker et al., C. R. Mecanique 331 (2003).     

骨陷窝-骨细胞形状和方向对骨单元内液体流动行为的影响

骨组织内的流体流动不仅为骨细胞的生存提供了充足营养供应及代谢物排放途径,也在骨重建过程中起到关键作用. 为了更精确地阐明骨内液体流动的具体形式,这项研究利用骨陷窝-骨细胞的密度,形态和方向等参数来计算骨单元内液体的流动行为. 首先,计算出不同形状和方向的骨陷窝周围骨小管的数量及分布情况,其次利用算出的参数以及骨组织其他微结构数据来估计骨组织的渗透率和孔隙率等参数,最后根据计算所得的参数建立骨单元的多孔弹性力学有限元模型,并分析了在轴向位移载荷作用下骨陷窝形状和方向对骨单元内液体渗流行为的影响. 结果表明,在所研究的参数范围内不同骨单元模型的相同区域上,骨陷窝形状影响下的骨单元最大压力和流速比最小的分别增加了86%和18%;骨陷窝方向影响下的最大压力和流速比最小的分别增加了125%和56%. 伸长形骨陷窝对单个骨单元局部压力的影响远大于扁平形和圆形骨陷窝. 骨陷窝从0°绕$x$轴旋转到90°过程中压力是逐渐降低的,且30°,45°和60°的模型对骨单元内局部流速有显著影响. 该模型表示骨陷窝的形状和方向以及骨小管的三维分布对骨单元内液体压力和流速幅值及沿不同方向的流动差异有显著的影响. 这项研究将有助于精确量化描述骨内液体的流体行为.      

Response of blood flow through an artery under stenotic conditions

This paper presents an analytical study on the behavoiur of blood flow in an artery having a stenosis. This is basically formulated through the use of a suitable mathematical model. The arterial segment under consideration is simulated by an anisotropically elastic cylindrical tube filled with a viscous incompressible fluid representing blood. The analysis is carried out for an artery with mild local narrowing in its lumen forming a stenosis. Particular emphasis has been paid to the effect of the surrounding connective tissues on the motion of the arterial wall. Blood is treated as a Newtonian fluid. The analysis is restricted to propagation of small amplitude harmonic waves, generated due to the flow of blood whose wave length is large compared to the radius of the arterial segment. The effect of the shape of stenosis on the resistance to blood flow has been well illustrated quantitatively through numerical computations of the resulting expressions. A quantitative analysis is also made for the variation of the phase velocity, as well as the velocity of wave propagation and the flow rate, in order to illustrate the applicability of the model.     

NON-CONSERVATIVE NONLINEAR RIGID-ELASTIC-LIQUID- CONTROL COUPLING ANALYTICAL DYNAMICS AND ITS APPLICATIONS$^{\bf 1)}$

非保守非线性刚-弹-液-控耦合分析动力学是与航天动力学和多体动力学相关的重要研究课题之一, 研究这一理论和应用课题具有重要理论意义和实际应用价值. 本研究建立了非保守非线性两类变量的刚-弹-液-控耦合分析动力学的Hamilton型拟变分原理, 并以该Hamilton型拟变分原理的泛函为依据, 分析了刚-弹-液-控耦合中的刚-弹耦合、刚-液耦合与弹-液耦合、控-刚耦合的特点. 借助于Lagrange-Hamilton体系, 从Hamilton型拟变分原理出发推导出非保守非线性刚-弹-液-控耦合系统的Lagrange方程, 并应用该Lagrange方程推导出系统的控制方程. 进一步以该控制方程为依据, 分析了刚-弹-液-控耦合中的刚-弹耦合、刚-液耦合与弹-液耦合、控-刚耦合的机理. 从两个方面概要地研究了非保守非线性刚-弹-液-控耦合系统的Lagrange方程的应用: 一方面, 应用该Lagrange方程建立了相应的有限元计算模型, 分析了这类计算模型的优越性; 另一方面, 应用系统的控制方程对实际问题进行解析的分析讨论, 说明了应用解析的分析讨论来研究问题与应用数值的、定量的分析方法来研究问题的互补特性. 最后, 讨论了几个相关的问题.     

考虑可控性的压电作动器拓扑优化设计

压电作动器可以把电能转换成机械能,在结构主动振动控制中具有应用背景. 由于压电作动器的布局对振动控制效果影响很大,因此作动器布局优化一直是结构控制研究的关键之一. 为了提高压电结构控制能量的利用效率,本文提出了以提高结构可控性为目标的压电作动器的拓扑优化方法. 基于经典层合板理论对压电结构进行了有限元建模,并采用模态叠加法将动力控制方程映射到模态空间,推导了基于控制矩阵奇异值的可控性指标. 优化模型中,选取可控性指标指数形式为目标函数,将设计变量定义为作动器单元的相对密度,并基于人工密度惩罚模型构造了压电系数惩罚模型,给出了基于控制矩阵奇异值的可控性指标关于设计变量的灵敏度分析方法. 优化问题采用基于梯度的数学规划法求解. 数值算例验证了灵敏度分析方法和优化模型的有效性,并讨论了主要因素对优化结果的影响.      

摩擦作用下直杆在对称斜面间的稳定平衡分析

摩擦提供的约束反力在由正应力所确定的范围之内．对称平板支承下的直杆在水平状态时平衡,但重心最高,因而没有摩擦时不能稳定平衡;摩擦作用下直杆平衡的倾角范围与平板坡度相关,可依据摩擦力达到极限值确定;若直杆与平板夹角小于90o,则平衡是稳定的,否则将跳跃到一侧平板,且摩擦角小于板面倾角时下滑到底部．支承板倾角变化时,处于稳定平衡状态的直杆将在一端发生滑移：倾角增大则高端向上、减小则低端向下,以使直杆重心位置较低．若支承板倾角作周期性变化,则直杆将逐渐倾斜而失稳：下滑到底部或跳跃到一侧平板．摩擦使力学系统具有非线性特征,其平衡位置可以在状态参数连续变化时发生跳跃．     

Maximal speed of particles in super-Lévy process

We introduce a super-Lévy process and study maximal speed of all particles in the range and the support of the super-Lévy process. The state of historical super-Lévy process is a measure on the set of paths. We study the maximal speed of all particles during a given time period, which turns out to be a function of the packing dimension of the time period. We calculate the Hausdorff dimension of the set of a-fast paths in the support and the range of the historical super-Lévy process.     

Surface finish of open holes on fatigue life

In this paper, the effect of surface finish of open holes on the fatigue life has been studied. Four defects of the surface finish are simulated. They are scratch, void, inclusion and roundness. Firstly, the effect of the four defects on the stress distributions around the holes has been studied by the finite element method (FEM). The fatigue lives are determined based on the stress distributions by the method of nominal stress approach. The results show that the fatigue lives are dependent on the quantity of the surface finished. There are the critical defect values of scratch, void and inclusion, smaller than which there is no effect of the surface finish on the fatigue life. For these three defects, the fatigue lives decrease with the increasing of the values of the defects. It is the same to the defect of roundness, e.g. the bigger roundness tolerance is, the shorter the life is. Further, an approximate quadratic curve has been found for the relationship between the roundness tolerances and their logarithmic fatigue lives.     

Experimental and numerical investigation of a viscoplastic Carbopol gel injected into a prototype 3D mold cavity

A numerical model for free-surface flow of a viscoplastic liquid into a cavity is presented. This flow is regarded as a basic model of injection molding, which is a widely used processing technology. Model experiments of the injection process are performed with a water-based gel with shear-thinning behavior. The filling process is visualized by tracing the free surface of the gel within the cavity. Filling times of the cavity are deduced from the experimental observations. The filling process is also analyzed by means of numerical simulation.The flow equations are integrated according to the finite-volume method. The volume-of-fluid method is employed in order to describe the flow of two incompressible, immiscible phases, the phase interface is resolved by the method of geometric reconstruction or alternatively by the method of surface compression. The Herschel–Bulkley model is used in order to describe the shear-thinning behavior of the gel and the effects of a yielding point. The governing equations of the flow are solved by means of the commercial code Fluent as well as the Open Source code OpenFOAM.The results of the numerical simulations are analyzed in detail. They are compared with the experimental findings. Cavity filling times in the experiments and the simulations are in good agreement. Different patterns of the filling flow depending on the injection parameters are evident in the experiments and the simulations. They are characterized and arranged with respect to the similarity parameters of the flow configuration. Again, the results of the simulation are found to agree well with the experimental observations.     

The motion equations of rotors,gyrostats and gyrodesics: application to powertrain-vehicle mechanical systems

The kinematics of wheels and rotors is described using a new auxiliary frame called gyrodesic frame or simply gyrodesic. By this, the absolute motion of the wheel becomes a serial composite of two motions: (1) the gyrodesic motion and (2) the wheels eigenmotion (or spin), i.e., the motion relative to the gyrodesic. The eigenmotion is described by an equation called rotor-equation. Gyrodesic coordinates turn out to be a particular useful tool in powertrain- and vehicle-dynamics as well as for general multibody systems. They allow a proper separation of the rotor- from the vehicle-equations and provide a rigorous method of coupling the powertrain-model into full spatial multibody-systems vehicle model. Some common misconceptions regarding this subject are identified and dispelled. The method is generalized to be applicable to the study of motion of general systems of rigid bodies with gyrostats or rotors as subsystems. The usefulness of the formalism is demonstrated by means of an illustrative example of non-trivial nature: the gyrostatic chain. Gyrodesic coordinates lead to a better grasp and deeper understanding of the structure of the dynamic equations of spatial vehicles in particular and of the motion of multibody-systems with rotors in general. The investigation reveals an interesting analogy to concept of parallel transport of vector fields in the sense of Levi-Civita. Dedicated to Prof. J. Wittenburg at the occasion of his 70th birthday.     

风力机叶片翼型动态试验技术研究

风力机叶片动态振荡过程往往伴随着俯仰和横摆同时进行, 以前对许多动态问题不清楚的阶段, 工程上不惜以增加叶片重量为代价而采用偏安全的设计, 通常忽略横摆振荡的影响; 大型风力机设计对获取翼型更加全面、准确的动态载荷提出了更高要求, 研究横摆振荡对翼型动态气动特性的影响规律具有重要意义. 本文首次开展翼型横摆振荡动态风洞试验研究, 采用“电子凸轮”技术代替机械凸轮实现了振荡频率和振荡角度的无级变化, 基于设计的电子外触发装置实现了对动态流场的实时测量, 实现了风洞来流、模型角位移和动态压力数据的同步采集, 分别开展了翼型静态测压、俯仰/横摆动态测压、粒子图像测速和荧光丝线等试验研究, 试验结果准度较高、规律合理; 分析了动态试验洞壁干扰影响机制. 研究表明, 横摆振荡翼型的气动曲线也存在明显迟滞效应; 随着振荡频率升高, 翼型俯仰和横摆振荡下的气动迟滞性均增强; 翼型俯仰振荡正行程的动态失速涡破裂有所延迟; 洞壁与模型端部交界处的强三维效应对翼型压力分布影响较大; 建立的横摆振荡试验技术可为风力机动态掠效应的研究提供技术支撑.      

Bimodal model of slurry viscosity with application to coal-slurries. Part 1. Theory and experiment

The rheological behavior of stable slurries is shown to be characterized by a bimodal model that represents a slurry as made up of a coarse fraction and a colloidal size fine fraction. According to the model, the two fractions behave independently of each other, and the non-Newtonian behavior of the viscosity is solely caused by the colloidal fraction, while the coarse fraction increases the viscosity level through hydrodynamic interactions. Data from experiments run with colloidal coal particles of about 2–3 µm average size dispersed in water show the viscosity of these colloidal suspensions to exhibit a highly shearrate-dependent behavior and, in the high shear limit, to match very closely the viscosity of suspensions of uniform size rigid spheres although the coal volume fraction must be determined semi-empirically. Different amounts of coarse coal particles are added to the colloidal suspension and the viscosity of the truly bimodal slurries measured as a function of shear rate. In agreement with the bimodal model, the measured shear viscosities show the coarse fraction to behave independently of the colloidal fraction and its contribution to the viscosity rise to be independent of the shear rate. It is shown that the shear rate exerted on the colloidal fraction is higher than that applied by the viscometer as a result of hydrodynamic interactions between the coarse particles, and that it is this effective higher shear rate which is necessary to apply in the correlations. For determining the coal volume fraction a relatively simple and quite accurate measurement technique is developed for determining the density and void fraction of coarse porous particles; the technique directly relates volume fraction to mass fraction.