A reduced mechanism for ethylene/methane mixtures with excessive NO enrichment

A detailed mechanism for methane–ethylene mixtures enriched with excessive amount of NO was systematically reduced for efficient numerical simulations of flames in arc-heated co-flowing air. Methane and ethylene were selected as the surrogate fuel in the present study due to their drastically different features of ignition and extinction properties and flame propagation speeds, such that the mixtures of them may be utilized to mimic practical hydrocarbon fuels with various kinetic properties in experiments. The recently released USC Mech-II for C1–C4 was grafted with the NO_x sub-mechanism in GRI-Mech 3.0 with updated reaction parameters for prompt NO formation. The resulting detailed mechanism with 129 species and 900 reactions was first validated against experiments involving NO_x enrichment and reasonably good agreements were observed. The detailed mechanism was then employed as the starting mechanism for the reduction. A skeletal mechanism with 44 species and 269 reactions was derived using the methods of directed relation graph (DRG) and DRG-aided sensitivity analysis (DRGASA); a 39-species reduced mechanism with 35 semi-global reaction steps was further obtained using the linearized quasi steady state approximations (LQSSA). Five species related to prompt NO were retained in the reduced mechanism because of their significant impacts on the fuel oxidation. The reduced mechanism closely agrees with the detailed mechanism for ignition and extinction of homogenous mixtures, as well as selected 1-D flames over a wide range of parameters with NO concentrations between 0% and 3%. The observed worst-case relative error of the reduction is approximately 20%. The reduced mechanism was further validated with experiments involving excessive NO_x enrichment.     

The stability graph after three decades in use: Experiences and the way forward

The stability graph was introduced approximately three decades ago for open stope design. Since then, it has gained wide recognition in open stope design around the world in hard rock metalliferous mining. Several developments have taken place following its initial inception aimed at improving its reliability in predicting the stability state of open stopes. These developments include redefinition of the stability graph number factors, the transition zones and addition of new factors. Various types of stability graphs have also emerged over the years for other purposes such as cablebolt layout design. The original database has also been significantly expanded from the 26 cases in 1981 to 483 cases to date. This article critically reviews the developments of the stability graph to date with the objective of: (1) Synthesising the scattered knowledge of these developments in the literature to a single source. (2) Creating awareness among potential users of the method, of the problems and risks arising from the uncoordinated developments in the method and the consequences of the lack of consensus in the choice of stability number factors. (3) Identifying areas for further research to improve the reliability of the method. (4) Finally, providing guidelines to inexperienced users and practitioners unaware of the various developments on the stability graph on when to use any one of the several stability graph types currently available. The article stresses that as an empirical method, the reliability of the stability graph method is largely dependent on the size, quality and consistency of the database. Hence, there must be consistency in the determination of the stability graph factors and accepted stope stability state transition zones. The present tendency for authors to arbitrarily choose between the original and modified stability number factors result in incomparable data that cannot be combined, while the different transition zones result in different interpretations of the stability state of stopes. The review also shows that there is need for factors that account for stope stand-up time, blast damage and gravity factor that is stress factor dependent. There is also a need to develop procedures for determining stability of open stope surfaces that are made of backfill. The inexperienced user and practitioner unaware of the various versions of the stability graph should be conscious of the different versions and types of stability graphs to make the appropriate choice for his/her design. The stability graph should also be used with caution, when applied to narrow vein orebodies because no version of the graphs accounts for orebody thickness in the definitions of the stability states.     

Minimizing the makespan in the non-preemptive job-shop scheduling with limited machine availability

This paper addresses the makespan minimization in a job-shop environment where the machines are not available during the whole planning horizon. The disjunctive graph model is used to represent the schedules and the concept of blocks is generalized to include the unavailability periods of machines. To solve the problem, we develop a taboo thresholding heuristic that uses a new block-based neighborhood function. Some sufficient conditions to eliminate the evaluation of non-improving moves are proposed. Experiments performed on existing problem instances of the literature show the efficiency of the proposed heuristic.     

基于分层图的动态RWA算法的仿真与实现

RWA问题是光网络中的一个核心问题。随着RWA优化算法求解方式的简化,算法的运算效率得到了提高,但却牺牲了解的优化性能。如何使优化效率和时间效率协调统一是当前光网络中RWA优化算法设计的难点。对光网络中动态RWA问题进行了阐述,对基于分层图的动态RWA算法进行了仿真与分析,仿真证明,该算法可以大幅降低网络的阻塞性能,且算法稳定性更好、资源利用率较高。     

Automatic Generation of Persistent Formations for Multi-agent Networks Under Range Constraints

In this paper we present a collection of graph-based methods for determining if a team of mobile robots, subjected to sensor and communication range constraints, can persistently achieve a specified formation. What we mean by this is that the formation, once achieved, will be preserved by the direct maintenance of the smallest subset of all possible pairwise inter-agent distances. In this context, formations are defined by sets of points separated by distances corresponding to desired inter-agent distances. Further, we provide graph operations to describe agent interactions that implement a given formation, as well as an algorithm that, given a persistent formation, automatically generates a sequence of such operations. Experimental results are presented that illustrate the operation of the proposed methods on real robot platforms.     

并行设计耦合任务集的识别方法

并行设计中强调多种知识的有效集成，耦合任务是一组具有相互依赖关系的任务的集合，它正反映了这种知识集成的要求，它对设计时间和质量均有着关键的影响。通过对耦合任务集的识别可以为合理分配设计资源、在效规划设计过程、科学组建集成开发队伍提供参考。本文在建立设计过程图的基础上提出了识别耦合任务集的有效方法。     

试井解释图版拟合分析的神经网络方法

图版拟合是现代试井分析的主要方法,由于图版上典型曲线分辨率的限制,使得典型曲线图版拟合分析不可避免地存在误差。除此之外,复杂试井问题的图版分析常常同时需要多幅图版,因而限制了典型曲线图版拟合分析方法的应用。利用前馈神经网络的函数逼近性质,建立了神经网络典型曲线图版,并给出了相应的解释方法。所建立的神经网络图版包含了全部理论曲线的信息,克服了传统典型曲线图版的不足,使得任意的实测曲线都能在神经网络典型曲线图版上直接得到精确拟合。同时,该图版大大简化了传统图版的拟合分析过程,使图版拟合分析更易实现。神经网络图版的研制成功,使实现图版拟合分析的智能化成为可能;另外,利用神经网络的函数映射能力,建立的神经网络图版可以包含更多信息,从而可以解释出更多的参数值。图3参4(邓远忠摘)     

条干图谱在涤纶长丝生产中的应用

主要讨论了条干图谱在涤纶丝生产中的应用及其对长丝生产的指导作用。     

两种斯坦纳问题的近似算法

本文对图的斯坦纳问题和直角斯坦纳问题各设计了一个近似算法。     

加工曲轴用车拉刀的设计

介绍了加工曲轴用车拉刀的结构原理和设计、加工要点。