Orthogonal crack approaching an interface

We consider the problem of a tensile crack approaching a sliding interface in the direction normal to it in an attempt to find the mechanisms that control the crack offset. The crack in a plane free of loading is driven by uniform load applied to its faces. The interface is assumed to have no resistance to opening. The common conception is that as the crack approaches the interface it creates a zone of opening. When the crack touches the interface this opening zone eventually arrests the crack such that the continuation of the crack growth through the interface is only possible from an offset position. Our computer simulations conducted for frictionless interface and supported by a simple analytical model show that the situation is more complex. As the crack tip gets close, the zone of opening shrinks and the opening displacement increases. After the crack tip touches the interface, the opening zone disappears. Frictionless interface produces concentration of this stress only at the ends of the interface which physically corresponds to the points where sliding is artificially arrested.     

一种新型的加工中心背镗刀具设计

本文着重介绍了一种新型的加工中心用背镗刀具的结构组成及工作原理,这种刀具非常适合CNC机床,能很好解决封闭空间的通孔内台阶面的背镗加工问题.     

Optimization models for operative planning in drinking water networks

The topic of this paper is minimum cost operative planning of pressurized water supply networks over a finite horizon and under reliable demand forecast. Since this is a very hard problem, it is desirable to employ sophisticated mathematical algorithms, which in turn calls for carefully designed models with suitable properties. The paper develops a nonlinear mixed integer model and a nonlinear programming model with favorable properties for gradient-based optimization methods, based on smooth component models for the network elements. In combination with further nonlinear programming techniques (Burgschweiger et al. in ZIB Report ZR-05-31, Zuse Institute Berlin, 2005), practically satisfactory near-optimum solutions even for large networks can be generated in acceptable time using standard optimization software on a PC workstation. Such an optimization system is in operation at Berliner Wasserbetriebe.     

梯级水电投资的动态规划模型

针对梯级水电开发的多阶段、多因素和不确定的属性,结合动态规划的多阶段寻优特点,构建了梯级水电投资决策的动态优化模型.同时,探索了用蒙特卡罗模拟技术对电站未来的发电收益进行模拟的可行途径;构建算例检验了梯级水电投资动态优化模型的有效性.计算和分析的结果表明,基于动态规划的梯级水电投资优化模型能够合理反应梯级水电投资的动态特征,显著地提高了梯级水电投资决策的可靠性.研究结论可为扩展利用动态规划理论分析解决梯级水电投资决策问题提供理论支撑.     

Polygonal Model Fitting

The celebrated minimum inertia line problem is reconsidered: a line is to be fitted to a planar cloud of points so that the sum of squared distances of all points to the line becomes minimal. The classical algebraic solution based on the tensor of inertia is complemented by a closed form trigonometric solution allowing various generalizations including the fit of elastic polygons. Proper polygons will be fitted numerically with non-closed partial solutions being reduced to the lowest dimension possible. This is complemented by segmentation heuristics for the measurement cloud.The approach allows to solve the robot localization problem with high accuracy for position and orientation to be inferred from distance measurements in a known polygonal environment. The essential feature of the current approach is to fit the polygonal geometry as a whole.     

冷冲模具材料数据库及其应用

根据我国冷冲模具的研制和使用现状，通过调研和实测性能，建立了冷冲模具材料的数据库，用作指导模具生产企业的合理选材和工艺调整。     

基于ODBC的控制网络与管理系统的接口方法

本介绍了一个基于ＯＤＢＣ的控制与管理系统的接口方法，与其它方法相比，具有费用少，不需要专门的编程技术，实现方例等特点是一个比较有价值的方法。     

Application of evolutionary programming for economic dispatch of cogeneration systems under emission constraints

This paper studies the economical operation of cogeneration systems under emission control with NO_x and SO_x from fossil-fueled thermal generation. The emission model is formulated as a function of fuel enthalpy dependent on the emission factor. The objective function includes fuel cost, emission cost, and tie-line energy cost, subject to the use of mixed fuels, operational limits, and emission constraints. An evolutionary programming was adopted to solve this problem. The steams, fuel mix, and generations will be found by considering the time-of-use dispatch between cogeneration systems and utility companies. A real cogeneration system is given to illustrate the proposed method.     

Studies on the development of aluminium alloy–mild steel reinforced composite

With a view to developing a new metal–metal cast composite material as a possible substitute for ferrous materials in wear resistant applications, Al alloy (LM11) is reinforced with mild steel (ms) wires and it is heat treated to get ‘reaction interface’ (RI). Microhardness, tensile properties and wear characteristics of the matrix, as-cast and heat treated composites have been determined. While microhardness of the composite showed variation from 150 to 45 VHN across the interface in the as-cast composite, annealed (500–525°C) composite showed a microhardness of 350–420 VHN at the interface indicating the effectiveness of the heat treatment. It is seen that the % improvement in wear resistance increased with increase in number of wires when embedded in the aluminium alloy matrix. Further imrpovement of about 30% was observed when heat treated at 500°C for 15 h. These results have been discussed in terms of wetting between ms wires and the matrix, particularly the increase of hardness and tensile strength to the formation of ‘reaction interface’ due to annealing. The width of the interface increased with annealing time and temperature and the kinetics of reaction followed logarithmic and parabolic growth rate. The activation energy for the formation of intermetallics constituting the reaction interface is found to be 20.7 KJ mol⁻¹. From the measured hardness and ultimate tensile strength of the constituents and composites an empirical relation was deduced.     

光纤综合宽带接入网技术

阐述了光纤综合宽带接入网的特点和构成，研究了系统结构、业务类型、主要接口以及光纤分配网的结构，比较了光纤综合宽带接入网与光纤数字网的系统性能，举例说明了光纤综合宽带接入网在电力系统的应用情况。