Kinetic friction characterizations of the tubular rubber seals

In this paper, both the kinetic friction characterizations and the stick–slip motion phenomena for the tubular rubber seals are studied. First, the kinetic friction model of the rubber seal is established to explain the kinetic friction mechanism of the tubular rubber seals. Second, both the measurement principle and the test instrument for the kinetic friction properties of the tubular rubber seals are developed, and then both the normal force curve and the friction force curve are obtained. Finally, the influences of the sliding velocity and the compressive displacement on the kinetic friction properties and the stick–slip motion of the tubular rubber seals are analyzed. The results will play an important role for designing and evaluating advanced rubber seal components.     

Two-dimensionally quantized friction observed with two-dimensional frictional force microscope

Using a two-dimensional frictional force microscope, we studied the two-dimensional nature of the atomic scale friction between a Si₃N₄ sharp tip and a cleaved graphite surface, which is composed of only C atoms and is a good conductor. As a result, we observed the two-dimensionally quantized friction with the lattice periodicity of the graphite surface, similarly to mica, MoS₂ and NaF surfaces. Thus quantized friction occurs at material surfaces which are composed of not only some elements but also of a single element, and the quantized friction does not depend on the conductivity of the surface.     

2D rolling contact problem involving frictional heating

Rolling of an elastic thermoinsulated cylinder on a thermoelastic half-space is investigated. The frictional heating due to the slipping in the contact area is involved. The problem is reduced to a nonlinear system of integral equations which is solved iteratively. The effects of the heat generated on the rolling contact are explored.     

金属成形数值模拟中的接触单元法

给出了一种基于罚函数方法及库仑摩擦规律的点一面接触形式的接触单元法,根据等向滑动函数的概念,推导了粘着接触与滑动接触的接触单元刚度阵,由于这种方法在单元积分点引入接触约束,扩大了接触搜索面积,因而接计算更加稳定。数值计算表明该方法能得到较好的结果。     

Experimental verification of rate-dependent elastoplastic analogy friction model and its application to FE analysis

When two solid bodies in contact slide slowly past each other without lubrication, an intermittent vibration phenomenon might be observed. Such rate-dependent frictional behaviors are referred to as stick–slip motions, and such motions can impair the stability of machines and structures. The aim of this study is to propose a numerical approach for analyzing stick–slip motion; the approach is based on the finite element method implemented using a rate-dependent friction model. First, we demonstrate the capability of the rate-dependent friction model by comparing its results with experimental results obtained under various material and dynamic conditions. Then, a simple finite element analysis of rate-dependent frictional sliding behavior, including stick–slip motion, is carried out to examine the effect of the material and geometric properties and boundary conditions on the numerical results. The present numerical approach can consider not only the properties of friction and materials but also variations in boundary conditions.     

Limit analysis of frames involving unilateral supports with frictional contact

We consider the classical limit analysis problem of frame structures made up of rigid perfectly plastic members and involving some supports in unilateral frictional contact with the ground. A direct formulation as a mixed complementarity problem (MCP) is used. For the Coulomb case, which forms the focus of this paper, the corresponding MCP may admit multiple upper bound collapse load solutions. In order to identify the least upper bound solution, we propose two algorithms. The first one attempts to enumerate the possible multiple solutions, or at least map the solution space if the solutions are connected. The second scheme tries to find the least upper bound by directly formulating and solving a single nonconvex optimization problem, known in the literature as a mathematical program with equilibrium constraints (MPEC). Two simple examples are provided to illustrate application of these approaches. They also serve to highlight some key features of such structures.     

封隔器胶筒大变形的粘-滑摩擦接触分析

采用罚函数方法,结合橡胶大变形问题的增量分析过程,考虑封隔器胶筒与套管之间的粘-滑摩擦接触问题,研究摩擦因数变化对接触压力的影响规律。给出解决封隔器胶筒摩擦接触问题的数值方法,并在此基础上对胶筒与套管之间的摩擦接触进行有限元分析,分析得到采用大变形非线性粘弹性理论和接触摩擦描述的有限元模型,可以比较准确模拟封隔器在坐封和工作过程中胶筒接触压力和变彤的情况,结果表明,摩擦因数变化对封隔器胶筒的接触压力有着较明显的影响。     

Solution of dynamic frictional contact problems using nondifferentiable optimization

This article is devoted to the development, implementation and application of variational inequalities (VI) to treat the general elastodynamic contact problem. Unlike existing VI algorithms, which rely on the decomposition of the physical problem into two sub-problems, the current study treats the general VI expressions using one-step approach to identify the candidate contact surface and contact stresses. This is accomplished using nondifferentiable optimization algorithm, through a sequence of mathematical programming problems. The dynamic VI formulations are solved using generalized-α time integration scheme. The selected time integration parameters reduce significantly the spurious high-frequency modes, which persist in the traditional Newmark method. In order to demonstrate the versatility and accuracy of the proposed VI and nondifferentiable optimization algorithm, a number of numerical examples are examined. The results show a significant improvement compared with the existing solution techniques.     

Analysis of static and dynamic frictional contact of deformable bodies including large rotations of the contact surfaces

The numerical techniques are presented to solve the static and dynamic contact problems of deformable bodies having large rotations of the contact surfaces. The contact conditions on the possible contact surfaces are enforced by using the contact error vector, and an iterative scheme similar to augmented Lagrange multiplier method is employed to reduce the contact error vector monotonically. For dynamic contact problems using implicit time integration, a contact error vector is also defined by combining the displacement, velocity, and acceleration on the contact surface. The suggested iterative technique is implemented toABAQUS by using theUEL subroutineUEL. In this work, after the computing procedures to solve the frictional contact problems are explained, the numerical examples are presented to compare the present solutions with those obtained byABAQUS.     

基于混合遗传算法的混合装配线排序问题研究

为使混合装配线有效运作,研究了混合装配线的生产排序问题。以装配线上各种零部件消耗速率均匀化和最小生产循环周期最短为优化目标,描述了多目标排序问题,并建立了优化模型。针对基本遗传算法在求解排序问题时的早熟收敛问题,提出一种改进混合遗传算法。该算法借助模拟退火算法思想对适应度尺度进行调整,使遗传进化初期削弱种群中个体适应度差异,而在遗传进化后期强化种群中个体适应度差异,以提高对最优解的搜索能力。同时,根据个体适应度自动调整遗传操作参数,既保存了种群中的优良个体,又不失个体的多样性。最后通过案例分析验证了算法的有效性。     

Using genetic algorithms on facilities layout problems

This article utilises a scheme to solve both equal and unequal area department problems in facilities layout by using genetic algorithms (GAs) for achieving the minimal total layout cost (TLC). With regards the equal area department problems, the objective function is mainly developed according to the measurement of the material flow factor cost (MFFC). However, the objective function for unequal area department problems in this study is a multiple objective function involving MFFC, shape ratio factor, and area utilisation factor to reach minimal TLC. In addition, a rule-based expert system is implemented to create space-filling curves for connecting each unequal area department to be continuously placed without discontinuity (partition). There is no gap between each unequal area department. The experimental results show that the proposed approach achieves lower TLC compared with existing algorithms. Under the practical limitations, the proposed approach in this study is much more feasible for dealing with the facilities layout problems in the real world.     

Job shop调度文化进化算法研究

作业车间调度优化问题属典型的NP-hard问题,其求解通常采用智能启发式算法,文化进化算法基于文化算法及文化进化思想,通过上层文化空间的经验知识指导下层个体进化搜索的方向及步长,通过模拟人类社会文化进化的机制实现文化空间的进化与更新,最后将算法应用到Jobshop问题的求解,用matlab编程仿真测试,结果表明此算法解决车间调度优化问题是可行的,而且其搜索性能优于一般GA算法及一种改进的微粒群算法。     

Improved frictional modeling for the pressure-time method

The pressure-time method is classified as a primary method for measuring discharge in hydraulic machinery. The uncertainty in the discharge determined using the pressure-time method is typically around $\pm 1.5$ %; however, despite dating back almost one hundred years in time, there still exists potential to reduce this uncertainty. In this paper, an improvement of the pressure-time method is suggested by implementing a novel formulation to model the frictional losses arising in the evaluation procedure. By analyzing previously obtained data from CFD, laboratory and full-scale pressure-time measurements it is shown that the new friction model improves the accuracy of the flow rate calculation by approximately 0.1–0.2% points, compared to currently utilized friction models. Despite being a small absolute improvement, the new friction model presents an important development of the pressure-time method because the relative improvement is significant.     

Test procedure for rapid assessment of frictional properties of engine oils at elevated temperatures

A fifteen-minute test sequence has been developed for screening and ranking base oils and friction modifiers. The tests are run on a high-frequency friction machine developed at the authors' company and based on the Mills-Cameron design. The procedure can distinguish clearly and repeatably between the behaviour of different friction modifiers and with a degree of discrimination which is better than has been achieved in engine mechanical loss tests     

利用GASA混合算法对离散生产系统车间设施布置优化研究

这里通过分析模拟退火算法和遗传算法的特性,将两种算法去粕取精,引出GASA混合算法。建立以生产车间布置为研究对象的数学模型,应用GASA混合算法对模型进行优化,并采用VB语言编写车间布置优化程序。通过实例分析表明,利用GASA混合算法对离散生产系统车间进行优化布置,可以最大程度降低企业搬运成本。     

Periodical contact problems for a half-space involving frictional heating

A periodical system of rigid parabolic punches moving steadily over the surface of a half-space is considered. Frictional shear tractions are developed with the heat generation along the interface. It is assumed that the surfaces of the punches are insulated and that the half-space is a thermal conductor. The problem is formulated in terms of two governing integral equations with unknown pressure and temperature at the interface. These equations are solved numerically. The effect of thermal distortion on the temperature profile under the punches and size of the contact region is investigated.     

Plane contact problems involving frictional heating for wavy half-space

Contact problems of a rigid punch sliding over the wavy thermoelastic half-space are studied. The punch geometry is considered to be parabolic or flat-ended. It is assumed that the contact between bodies occurs within a finite number of separated contour areas. The frictional heating in these regions is involved. The problem is reduced to the non-linear system of algebraic equations, which is solved iteratively. The effects of the boundary waviness on the heat generation are studied and presented in diagrams.     

二维一刀切装箱问题的两阶段启发式算法

对用于二维带排样问题的Heuristic Recursive算法进行了调整,给出同一层中两个相邻浪费区域在满足一刀切约束下是否可合并的判定定理。构造了二维带排样问题的多递归层算法,并将它与一维装箱问题的最优匹配递减算法相结合,提出适应二维一刀切非旋转装箱问题的两阶段算法。在500组标准测试案例的基础上,与多种算法进行了比较。实验结果表明,所提算法在绝大多数测试案例上能够获得更好的排样布局。     

Projection-variance algorithms for constructing directional fields

A method for constructing fast projection-variance algorithms based on convolution algorithms for calculating variances of Radon projections is proposed. It is shown that the use of bilinear interpolation of the convolution kernel and parabolic interpolation of quantized estimates of directional fields increases the accuracy of the algorithms by more than a factor of 2. Two methods for constructing directional fields on the basis of Radon projections are considered and compared. Examples are given showing the computational efficiency, accuracy, and noise resistance of the proposed algorithms.     

Using genetic algorithms for the optimization of mechanisms

This work examines the possibility of using genetic algorithms for the optimization of the loads transmitted in mechanisms. The variables of design are the relative positions of the various connections, considered in a comparative manner. The minimization of the loads transmitted in the connections is achieved by optimizing the respective positions of those lead to less expensive solutions for bearings and sections of beams. The examples show that using this stochastic method is an efficient way to minimize loads in mechanisms.