Stagnation‐point flow of Maxwell fluid with magnetic field and radiation effects

The effect of heat transfer on the steady two‐dimensional stagnation point flow of a Maxwell fluid over a stretching sheet is discussed. The fluid is electrically conducting in the presence of a uniform applied magnetic field. The radiation effect in the energy equation is taken into account. The arising nonlinear problem is solved by a homotopy analysis method (HAM). Convergence of the series solutions is checked. The values of skin friction coefficient and local Nusselt number have been computed and discussed. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20385     

三角形河床形态对潜流交换作用的影响

为揭示交错三角形河床影响下的潜流交换机理,利用Fluent和COMSOL软件构建了三角形河床地形影响下的地表水-地下水流动的数学模型,并采用试验数据对模型模拟的地表水流速进行了验证,分析了水沙交界面的流速与压力分布和潜流交换区与缓流区的流速分布等。结果表明,河床几何形态促使水沙交界面形成了高低压交错分布的情况,强烈影响着水沙交界面和潜流带的流速分布及大小。波峰上游侧为下降流区域,波峰下游侧为上升流区域。潜流交换区的横向流速与纵向流速分量分别形成了一条"缓流带",其相交区域为潜流交换区的缓流区,缓流区的位置随着三角形河床波峰的位置而变化。研究成果可为三角形河床地带的工程建设提供参考。     

邻域函数在蚂蚁算法中的研究与应用

邻域函数是优化计算中的一个重要概念，其作用就是指导如何由1个(组)解来产生1个(组)新的解。鉴于蚂蚁算法容易陷入局部最优的缺陷，利用邻域函数对蚂蚁算法进行优化，以减小蚂蚁算法陷入局部最优的概率。仿真实验表明，所采用的方法简单易行，能够有效地防止蚂蚁算法陷入局部最优。     

Fluid-Like Properties of Chip Flow in High-Speed Metal Cutting Process

Strain rate in high-speed metal cutting is high, and properties of chip flow under high strain rate conditions are different under low cutting speed conditions. Shear stress and shear strain rate have a linear relationship; hence, the behavior of chip flow during high-speed metal cutting is more similar to fluid than to solid. Therefore, metal cutting should be analyzed by using fluid analytical method. This article investigated the fluid-like properties of chip flow during high-speed metal cutting and determined velocity, pressure, and strain rate distributions on rake face and shear plane. A speed stagnation point is located some distance from the tool tip on the rake face. The location of this point influences the life of the cutting tool and the quality of the finished surface. The pressure peaks, decreases along the rake face, and then reaches zero at some point away from the tool tip. This point represents the separation of the chip from the tool. The total stress on the shear plane is the sum of tensile stress, pressure stress, and shear stress. The strain rate is related to velocity; its value rapidly increases at the tool tip and the free surface corner and then decreases.     

Mechanical fault diagnosis of outdoor high‐voltage disconnector

A series of experiments are conducted on a 252‐kV pantograph disconnector offline to monitor its mechanical condition. Three parameters, namely the dynamic strain of the post insulator, the rotation angle of the operating shaft, and the stator current of the driving motor, are measured by resistance strain gauges, magnetic‐sensing angle transducer, and Hall current sensor, respectively. Measurement results of the three parameters under mechanical fault conditions including clamping stagnation of the conduct tube knuckle, failure of the balance spring, and uncompleted closing operation are compared with those in normal operating condition of the disconnector. The results indicate that the dynamic strain waveform, the rotation angle curve, and the motor current envelope waveform may get distorted with increased peak value and offset peak time when mechanical faults happen to the transmission or rotating mechanism of the disconnector, and more component of the side frequency will appear in the spectrum of the motor current waveform. The proposed methods are validated to be effective for mechanical fault diagnosis and condition assessment of pantograph disconnector, and are also of reference significance for other types of disconnectors. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

On three new approaches to handle constraints within evolution strategies

Evolutionary algorithms with a self-adaptive step control mechanism like evolution strategies (ES) often suffer from premature fitness stagnation on constrained numerical optimization problems. When the optimum lies on the constraint boundary or even in a vertex of the feasible search space, a disadvantageous success probability results in premature step size reduction. We introduce three new constraint-handling methods for ES on constrained continuous search spaces. The death penalty step control evolution strategy (DSES) is based on the controlled reduction of a minimum step size depending on the distance to the infeasible search space. The two sexes evolution strategy (TSES) is inspired by the biological concept of sexual selection and pairing. At last, the nested angle evolution strategy (NAES) is an approach in which the angles of the correlated mutation of the inner ES are adapted by the outer ES. All methods are experimentally evaluated on four selected test problems and compared with existing penalty-based constraint-handling methods.     

Computerization and employment Annotations with regard to the relationship between technology,productivity and employment

This paper deals with the impact of computerization on employment on the macro level, that is total employment, and on the micro level, that is the specific jobs. On the macro level the problem is mainly the quantitative aspect of the impact of computerization, which is difficult to distinguish from other tendencies in the process of economic development. On the micro level the problem is mainly the qualitative aspect.The author's main argument is, that job degradation is expanding and especially - as something new - introduced in intellectual work. The result is, that for small elitist groups, work will be more challenging and inspiring and give more autonomy to these groups, while the big majority of semi-skilled workers will get more boring routine jobs with less autonomy and less demands for qualifications.The point is, that if future development will not be changed, the qualification gap between the elite and the mass will grow. Thus we need better work planning under democratic control. But first of all the computerized systems must be designed for more human modes of production and more human use of human capabilities. The future perspective should be a true “humanization of work” by the workers themselves.     

Single wafer processing in stagnation point flow CVD reactor: Prospects,constraints and reactor design

A stagnation point chemical vapor deposition (CVD) reactor that obviates substrate rotation can deposit a uniform, thin layer by developing a uniform boundary layer adjacent to the surface of deposition in an axially uniform flow. Such a geometry is highly desirable for high throughput, reproducible single wafer processing in electronic industry. It can also operate effectively at atmospheric pressure if its geometrical and operational parameters are optimized. It is shown here that the nature of the gas distributor, optimized diffuser shape inlet with respect to its angle of divergence, diffuser height and its inverted geometry are the key design parameters. The pressure drop across the gas distributor, inlet gas velocity, gas viscosity, width of hydrodynamic boundary layer on the inner walls of the diffuser that limits the available area for uniform deposition and thermal convection are its important operational parameters. The inverted reactor geometry minimizes the convection related instabilities and helps stabilize the gas flow in the reactor. Analytical expressions are developed to correlate these functional parameters of a stagnation point CVD reactor to its performance in order to develop the reactor design. Finally, the practical aspects including the experimental results of operation of such a CVD reactor design are discussed.