Analysis of a production system in a general configuration

We consider a production system comprising multiple stations (or workshops) such as an entry station, a set of work stations, a central station, and an exit station, which are arranged in a general configuration. A worker (or a vehicle tool) is assigned to each station, who sends a part from the station to the destination station according to the required process path of the part. Any part is allowed to visit a work station more than once if its process path requires. We propose a new control strategy with the push policy for instructing each worker to send a part and the kanban mechanism for controlling the work‐in‐process (WIP) in each work station. As all work stations have limited local buffers, the central station is used for storing blocked parts temporarily. Such a production system is modeled as an open queueing network in a general configuration with a Markovian part sending policy and a machine no blocking mechanism. The queueing network is analytically characterized. Some important performance measures are compared with other control strategies. A semi‐open decomposition approach is applied to the queueing network for computing the blocking probabilities when parts arrive at the work stations. An algorithm is developed based on the semi‐open decomposition approach. Numerical experiments show the quality of the solutions obtained by the algorithm as well as a property of a performance measure. © 2001 John Wiley & Sons, Inc. Naval Research Logistics 48: 128–143, 2001     

基于Petri网的C2S性能分析方法研究

给出了用时间连续随机Petri网和时间离散随机Petri网计算系统稳态概率的方法,并将其应用于指挥控制系统(C2S)的性能分析中,分析结果表明这种计算方法是可行的。     

采用M阶正交信号的DS-CDMA系统性能分析

随着移动通信的迅速发展 ,码分多址技术受到越来越多的关注。为了提高系统的抗干扰性能 ,在CDMA系统中采用了M阶正交信号。通过分析采用M阶正交信号的DS CDMA系统基带接收信号的统计性能 ,文中得出了多址、多径干扰下系统的误码率计算公式 ,并详细分析了系统的抗干扰性能。     

Economic design of a two-stage control chart based on both performance and surrogate variables

The traditional approach to economic design of control charts is based on the assumption that a process is monitored using only a performance variable. If, however, the performance variable is costly to measure and a less expensive surrogate variable is available, the process may be more efficiently controlled by using both performance and surrogate variables. In this article we propose a model for economic design of a two-stage control chart which uses a highly correlated surrogate variable together with a performance variable. The process is assumed to be monitored by the surrogate variable until it signals out-of-control behavior, then by the performance variable until it signals out-of-control behavior or maintains in-control signals for a prespecified amount of time, and the two variables are used in alternating fashion. An algorithm based on the direct search method of Hooke and Jeeves [6] is used to find the optimum values of design parameters. The proposed model is applied to the end-closure welding process for nuclear fuel to compute the amount of reduction in cost compared with the current control procedure. © 1999 John Wiley & Sons, Inc. Naval Research Logistics 46: 958–977, 1999     

A nonparametric approach to accelerated life testing under multiple stresses

Accelerated life testing (ALT) is concerned with subjecting items to a series of stresses at several levels higher than those experienced under normal conditions so as to obtain the lifetime distribution of items under normal levels. A parametric approach to this problem requires two assumptions. First, the lifetime of an item is assumed to have the same distribution under all stress levels, that is, a change of stress level does not change the shape of the life distribution but changes only its scale. Second, a functional relationship is assumed between the parameters of the life distribution and the accelerating stresses. A nonparametric approach, on the other hand, assumes a functional relationship between the life distribution functions at the accelerated and nonaccelerated stress levels without making any assumptions on the forms of the distribution functions. In this paper, we treat the problem nonparametrically. In particular, we extend the methods of Shaked, Zimmer, and Ball [7] and Strelec and Viertl [8] and develop a nonparametric estimation procedure for a version of the generalized Arrhenius model with two stress variables assuming a linear acceleration function. We obtain consistent estimates as well as confidence intervals of the parameters of the life distribution under normal stress level and compare our nonparametric method with parametric methods assuming exponential, Weibull and lognormal life distributions using both real life and simulated data. © 1998 John Wiley & Sons, Inc. Naval Research Logistics 45: 629–644, 1998     

支持高效组播的高性能路由器QoS机制研究与实现

研究并提出一种有效支持组播的高性能路由器QoS机制QoS RESM,该机制以多阈值机制为基础,考虑远程转发引擎的拥塞状态信息,引入全局控制反馈机制,有效完成了高性能路由器上支持组播的流量控制。最后描述QoS RESM在基于网络处理器的核心路由器上的实现方法。     

三维石英纤维增强氮化物基复合材料的烧蚀性能及显微结构

采用先驱体转化法制备了三维石英纤维增强氮化物基复合材料(3D SiO2f/Si3N4-BN),用等离子射流烧蚀方法研究了复合材料的烧蚀性能,运用扫描电镜及能谱仪对烧蚀表面微观形貌进行了观察和分析。结果表明氮化物基复合材料在高压高热流等离子体烧蚀下线烧蚀率为0.91mm/s,石英纤维熔融并被吹除带走了大量的热量,熔融层抑制了基体的机械剥蚀。基体由于强度高、升华温度高,延缓了熔融层的吹除,表明氮化物基复合材料是一种良好的耐高温烧蚀透波材料。     

高超声速飞行器保预设性能的反演控制方法

为了解决高超声速飞行器纵向运动模型的稳定轨迹控制问题,设计了一种在非仿射模型基础上保证预设性能的反演控制方法。对于速度子系统,直接设计非仿射控制律,保证预设性能,通过合理的变换将高度子系统转化为严格的反馈形式,便于反演控制步骤的设计。基于动态性能和稳态精度,设计了预设性能函数,将跟踪误差的稳定性限制在预设范围内,引入指令滤波器,有效克服了传统反演控制中虚拟信号重复推导的问题。控制器的设计不依赖于精确的模型。引入径向基函数来逼近过程中的未知函数,使得控制律具有令人满意的鲁棒性和实用性。基于李雅普诺夫稳定性理论,证明了所有闭环系统的稳定性。仿真结果表明,该控制器能够稳定地跟踪参考信号。     

空气深度预冷组合循环发动机吸气式模态建模及性能分析

针对空气深度预冷组合循环发动机——协同吸气式火箭发动机(Synergistic Air-Breathing Rocket Engine,SABRE),采用部件法对其进行建模,匹配计算得到吸气式模态下飞行走廊内其性能参数变化规律,并研究其高度速度特性。计算模型可信度较高,推力误差小于6%,能够较为准确地模拟SABRE吸气式模态的性能参数。结果表明:SABRE兼具火箭发动机大推力和航空发动机高比冲的特点,吸气式模态下比冲介于21 300~27 380 m/s,随着高度速度的增大,其推力比冲先增大后减小;SABRE利用预冷器将入口空气温度降低,可使其空域速域拓宽至25 km、5Ma,满足高超声速飞行的动力需求;发动机速度下限由压气机最大流量决定,速度上限则由氦气回路减压器工作限制条件决定。     

蓄电池在线检测方法研究

在对阀控铅酸蓄电池的性能指标、失效机理、检测方法研究的基础上,通过比较各种检测方法,提出了一种新的蓄电池内阻在线检测方法——四线两端法,阐述了四线两端法的测试原理,给出了该方法在蓄电池在线检测中的检测步骤,同时分析了影响测量精度的主要因素,提出了提高测量精度所采取的措施,并给出系统测量误差。