Macrokinetic model of the trapping process in two-phase fluid displacement in a porous medium

A microinhomogeneity-averaged model of the kinetics of the trapping process is proposed for a porous medium in which two fluids are mutually displaced. The traps are treated as a new hydrodynamic phase, and the trapping process as a phase transition. Kinetic relations for the average trapping process are obtained. The structure and quantitative values of the kinetic coefficients are obtained for a model of a porous medium in the form of a system of doublets. The dependence of the characteristic time of the process on the degree of inhomogeneity of the medium is investigated. A variant of the macroscopic model of the process of two-phase flow, in which the kinetic relations obtained are used as the closing relations, is proposed.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 3, pp. 92–101, May–June, 1995.     

Influence of diffusion and kinetic characteristics on the combustion of a carbon particle

The spherically symmetric steady-state problem of heterogeneous combustion for a carbon particle is discussed. The exact solution of this problem is obtained. The dimensionless mass flux through the particle surface is graphically represented as a function of oxygen concentration in the external domain. The rate ratio for the diffusion process and the kinetic process is introduced as a dimensionless characteristic of the combustion process. The dimensionless mass fluxes through the particle surface are graphically represented as functions of external constitutive parameters. The resulting solution is approximated. The diffusion and kinetic modes of combustion are considered as limiting cases.     

Parametric study of macrosegregation in the horizontal strip casting process for different cooling rates and different casting speeds

The objective of this paper is to investigate sensitivity of the macrosegregation profiles in steel strips produced by the horizontal strip casting process to the major technological parameters controlling this process, such as the cooling rate and the casting speed. To perform this investigation, a mathematical model which accounts for fluid flow as well as for heat and solute transport is suggested. Extensive numerical simulations of the horizontal strip casting process for different cooling rates and different casting speeds are carried out. Received on 17 September 1998     

Challenges in process rheometry

Process rheometers are useful as process sensors for on-line quality control as well as for process control. Unlike passive sensors for equilibrium properties, such as temperature and pressure, a rheometer must subject the material of interest to a controlled deformation while monitoring the resulting stress. To accomplish this in a compact, robust device suitable for use in a manufacturing environment is not straightforward. Problems that arise in processing applications include the need for frequent sample renewal without interference from the measurement or the process itself and the fact that the process stream is usually under pressure. Considerable ingenuity has been applied to developing rheometers to meet these requirements.However, there remain many potential applications for which presently available units are not suitable. In particular, special problems arise when a very fast response is required, when the fluid being processed is non-Newtonian or has a very high viscosity, and when it is a multiphase system, as for example in the case of mineral slurries. In addition, in food processing and fermentation applications, all the exposed surfaces of the rheometer must be sterilizable. Possible solutions to these problems are described.Delivered as a Keynote Lecture at the Golden Jubilee Conference of the British Society of Rheology and Third European Rheology Conference, Edinburgh, 3–7 September, 1990.     

Modeling and simulation of the viscoelastic fluid mold filling process by level set method

A model for unifying a viscoelastic fluid and a Newtonian fluid is established, in which the governing equations for the viscoelastic fluid and the Newtonian fluid are successfully united into a system of generalized Navier–Stokes equations. A level set method is set up to solve the model for capturing the moving interface in the mold filling process. The physical governing equations are solved by the finite volume method on a non-staggered grid and the interpolation technique on the collocated grid is used for the pressure-velocity and the stress-velocity decoupling problems. The level set and its reinitialization equation are solved by the finite difference method, in which the spatial derivatives are discretized by the 5th-order Weighted Essentially Non-Oscillatory (WENO) scheme, and the temporal derivatives are discretized by the 3rd-order Total Variation Diminishing Runge–Kutta (TVD-R–K) scheme. The validity of the method is verified by some benchmark problems. Then a simulation of viscoelastic fluid mold filling process is pursued with the method. The moving interface and all the information of the physical quantities during the injection process are captured. The die swelling phenomenon is found in the simulation. The influences of elasticity and viscosity on the physical quantities such as stresses etc. in the mold filling process are analyzed. Numerical results show that elastic characteristics such as the stretch and die swelling etc. reinforce accordingly as Weissenberg number increases. Pressures increase continuously in the mold filling process and the pressure maintains the maximum value at the inlet. Injection velocity is proportional to injection pressure. A higher viscosity leads to a higher pressure distribution, that is, the pressure decreases as Reynolds number increases.     

Stochastic stability of a rotating shaft

The stochastic stability problem of an elastic, balanced rotating shaft subjected to action of axial forces at the ends is studied. The shaft is of circular cross-section, it rotates at a constant rate about its longitudinal axis of symmetry. The effect of rotatory inertia of the shaft cross-section is included in the present formulation. Each force consists of a constant part and a time-dependent stochastic function. Closed form analytical solutions are obtained for simply supported boundary conditions. By using the direct Liapunov method almost sure asymptotic stability conditions are obtained as the function of stochastic process variance, damping coefficient, damping ratio, angular velocity, mode number and geometric and physical parameters of the shaft. Numerical calculations are performed for the Gaussian process with a zero mean and as well as an harmonic process with random phase.     

The maximal Lyapunov exponent of a co-dimension two-bifurcation system excited by a bounded noise

In the present paper,the maximal Lyapunov exponent is investigated for a co-dimension two bifurcation system that is on a three-dimensional central manifold and subjected to parametric excitation by a bounded noise.By using a perturbation method,the expressions of the invariant measure of a one-dimensional phase diffusion process are obtained for three cases,in which different forms of the matrix B,that is included in the noise excitation term,are assumed and then,as a result,all the three kinds of singular boundaries for one-dimensional phase diffusion process are analyzed.Via Monte-Carlo simulation,we find that the analytical expressions of the invariant measures meet well the numerical ones.And furthermore,the P-bifurcation behaviors are investigated for the one-dimensional phase diffusion process.Finally,for the three cases of singular boundaries for one-dimensional phase diffusion process,analytical expressions of the maximal Lyapunov exponent are presented for the stochastic bifurcation system.     

花键轴冷挤压成形后的三维光塑性模拟研究

本文利用光塑性方法,以聚碳酸酯（Ｐｏｌｙｃａｒｂｏｎａｔｅ）为材料研究了矩形花键轴冷挤压成形过程,获得了花键挤压成形的三维塑性应变场分布,提出其变形的应变分布特征,并对典型截面的应变进行了计算分析;文中还通过对聚碳酸酯材料的实验,得到了使花键齿形充满的最佳坯料尺寸,为实际工艺生产优选出合理的工艺参数。     

有限宽板中心裂纹断裂过程区的长度和位移公式

对岩石、混凝土和陶瓷等准脆性材料进行断裂分析,有必要研究裂纹前端的断裂过程区所起的作用以及各种因素对它的影响。本文提出分析有限宽中心裂纹板剪切断裂过程区的方法,此方法基于D－B模型的叠加原理,考虑了压剪断裂的摩擦阻力,并将有限板宽影响简化为载荷的修正,以非常简便的方法推导出计算断裂过程区长度和位移的公式,这些公式补充了现有文献只有“无限大”板的解的不足。利用这些公式,分析各种参数对断裂过程区长度和位移的影响变得非常方便。     

On the role of the process zone in dynamic fracture

The evolution of the fracture process zone and its influence on dynamic crack propagation are investigated using a simple constitutive assumption to model the material in the fracture process zone. The mode III problem of anti-plane shear is examined using a finite difference scheme to obtain the full field solution. Unlike the classical approach of determining the steady state solutions for imposed constant speed of crack propagation, here the fracture criterion is imposed along with the formulation of the boundary-initial value problem and the coupled equations are solved numerically to determine the generation and growth of the fracture process zone as well as the crack tip. The results of the simulation indicate that the constitutive behavior of the process zone material (or equivalently the evolution of the process zone itself) plays a key role in determining the dynamics of fast fracture.     

The challenge of validating genetic testing

Validation of genetic testing is a multidisciplinary task that involves medical/clinical geneticists, other medical specialists, legislative authorities and the public. It is an area in which many issues are unresolved. Validation should not focus on the laboratory process alone, but should also include the prerequisites for service delivery, such as education and staffing, data collection and banking and information transfer, as well as pre- and post-test genetic counselling in a cost-effective perspective. It must thus be seen as an ongoing process at laboratory, familial and societal levels which involves many different actors. The challenges for the near future are to continue to develop technical standards for the laboratory and counselling procedures, and, in collaboration among professionals, lay persons and state authorities, to define a legal framework for the actions of the various players. This chapter discusses some problems related to the validation process for genetic testing, broadly defined.     

Utilization of chemical looping strategy in coal gasification processes

Three chemical looping gasification processes, i. e. Syngas Chemical Looping (SCL) process, Coal Direct Chemical Looping (CDCL) process, and Calcium Looping process (CLP), are being developed at the Ohio State University (OSU). These processes utilize simple reaction schemes to convert carbonaceous fuels into products such as hydrogen, electricity, and synthetic fuels through the transformation of a highly reactive, highly recyclable chemical intermediate. In this paper, these novel chemical looping gasification processes are described and their advantages and potential challenges for commercialization are discussed.     

Modeling and correction of peak-locking in digital PIV

The systematic tendency of PIV evaluations to bias towards integral pixel values is known as peak-locking. These errors, although small, significantly affect the statistics extracted from such measurements. In this paper, the process by which such errors accrue is modeled, and a scheme for the removal of the same is suggested. Specifically, the modeling process considers FFT PIV with discrete window offset. The results are applied to actual situations and the results are found to be encouraging. The process is computationally inexpensive, and can be applied as a post processing technique to existing data to correct peak-locking.     

Prismatic tensegrity structures with additional cables: Integral symmetric states of self-stress and cable-controlled reconfiguration procedure

A simple energy method is put forward to determine the prestress distribution for symmetric tensegrity structures with multiple states of self-stress and a class of prismatic tensegrities with additional cables are introduced to show the accuracy of presented method. For the purpose of modifying structural shape as well as mechanical properties, a cable-controlled reconfiguration procedure is subsequently proposed for these structures. By defining the length adjustments as the control parameters, the reconfiguration procedure is regarded as a quasi-static process, consisting of a sequence of equilibrium configurations with varying control parameters. Then the nonlinear iterative algorithm based on the tangent stiffness of the structure is presented to simulate and follow this reconfiguration process. By way of example, a particular class of reconfigurations coined symmetrical reconfigurations are investigated carefully and the key features as well as the potential applications are given.     

复合材料缠绕壳体结构成型和使用过程多场分析的研究进展

综述了复合材料缠绕壳体结构成型和使用过程的多场分析的国内外近代研究进展, 其中包括:缠绕成型工艺,固化工艺,超压工艺,使用过程中的应力分析,低速冲击损伤等相关问题. 在此基础上, 着重介绍了倍受航天界所关注的含薄壁金属内衬的复合材料缠绕容器的成型工艺和低速冲击损伤一体化研究工作, 并提出了该领域今后还需进一步研究的内容.      

并行冲击/侵彻有限元数值模拟技术

探讨了冲击/侵彻问题涉及到的非线性材料模型、接触搜索算法、接触力计算公式、破坏模式等理论和算法,介绍了基于集群并行计算机的有限元法并行化基本思路和方法。应用实例表明本文中提出的有限元计算格式和并行化方法能够有效求解冲击/侵彻问题。     

Non-isothermal analysis of extrusion film casting using multi-mode Phan-Thien Tanner constitutive equation and comparison with experiments

Extrusion film casting (EFC) is an industrially important process which produces thousands of tons of polymer films, sheets, and coating used for various industrial as well as household applications. In this paper, we focus on an instability which occurs during certain polymer processing operations operating under predominantly elongational flow, such as extrusion film casting and fiber spinning. This instability, called the draw resonance, occurs in the form of sustained periodic fluctuations in the film dimensions. It appears when the process goes beyond the critical line speed of the EFC process. In this work, a conventional linear stability analysis is carried out for nonisothermal EFC process to determine the onset of the draw resonance. The polymer rheology is modeled by the Phan-Thien Tanner (PTT) multi-mode constitutive equation. For the implementation, a conventional shooting method approach is used. Extrusion film casting experiments were also carried out using a conventional linear low-density polyethylene (LLDPE) by varying process parameters such as draw ratio and aspect ratio, to observe the effect on the stability of the process. Linear stability analysis results under non-isothermal conditions are compared and validated with existing results from literature and with our own experimental data. This work displays the effect of multiple relaxation modes as well as the temperature influence on the stability of EFC process. Finally, results also indicate that the temperature highly affects the stability of the EFC process and cannot be ignored from modeling of EFC process.     

Control of the Duffing oscillator under non-Gaussian external excitation

The problem of suboptimal linear feedback control laws with mean-square criteria for the linear oscillator and the Duffing oscillator under external non-Gaussian excitations is considered. The input process is modeled as a polynomial of a Gaussian process or as a renewal driven impulse process. To determine the suboptimal control, a modified iterative procedure is proposed, where four criteria of statistical linearization are combined with an optimal control strategy. The results indicate that the obtained minima do not depend on the linearization criterion. The nonlinearity tends to reduce this minimum.     

高层建筑风荷载反演研究

本文研究了结构参数未知条件下的高层建筑风荷载反演问题,通过将平均风速的实测特性作为识别计算中的辅助条件,文中提出了一类荷载归一化统计平均方法,结合工程实例,进行了高层建筑风荷载反演分析,结果表明,本文建议方法可以在幅值、时程等方面均给出良好的风荷载反演结果,同时识别得到的结构参数具有良好的精度。从而为高层建筑风荷载研究提供了一条可行途径。     

转子轴承系统振动响应谱的仿真研究

在转子轴承系统振动信号处理中,针对平稳信号的传统傅里叶变换精度较低、快变启动过程的非平稳信号频谱分析方法较复杂的问题,本文仿真构造了两类响应信号。通过对比给定信号参数与信号识别参数的误差研究了几种谱分析方法或过程的简便性和准确性。对转子系统振动平稳信号离散频谱分析时存在的误差进行了定量分析,利用比例插值法对误差进行校正,开发了高精度谱分析测试软件;分析了转子轴承系统快变过程非平稳振动信号的特征,探索了一种将t时空域非平稳信号转变为tn时空间域平稳信号的办法或过程,然后结合比例插值校正法对其进行频谱分析,再返回到t时空域获得某时刻的谱特征参数;构造了转子系统振动仿真信号检验了上述过程的准确性。研究结果表明:比例插值法提取的谱特征数据近乎与仿真信号设定值相等;针对本文构造的快变过程非平稳仿真信号,利用本文给出的谱分析过程产生的频率误差最大值为0.47%,幅值误差最大值为0.2%。本文的仿真研究为提出和考证新的谱分析方法提供了手段。