Age replacement policies in two time scales

We develop and estimate optimal age replacement policies for devices whose age is measured in two time scales. For example, the age of a jet engine can be measured in the number of flight hours and the number of landings. Under a single‐scale age replacement policy, a device is replaced at age τ or upon failure, whichever occurs first. We show that a natural generalization to two scales is to replace nonfailed devices when their usage path crosses the boundary of a two‐dimensional region M, where M is a lower set with respect to the matrix partial order. For lifetimes measured in two scales, we consider devices that age along linear usage paths. We generalize the single‐scale long‐run average cost, estimate optimal two‐scale policies, and give an example. We note that these policies are strongly consistent estimators of the true optimal policies under mild conditions, and study small‐sample behavior using simulation. © 2003 Wiley Periodicals, Inc. Naval Research Logistics 50: 592–613, 2003.     

接近速度和放电电压对空气式静电放电参数的影响

对影响空气式静电放电的一个重要因素——电弧结构进行了理论分析。在此基础上,利用新研制成功的静电放电模拟测试系统,分析了接近速度和放电电压对静电放电电流峰值、上升时间以及感应电压峰-峰值的影响。试验得出,在放电电压一定的情况下,放电电流峰值和感应电压峰-峰值随接近速度的增大而增大;上升时间随接近速度的增大而减小。这些试验结果为建立静电放电抗扰度试验新方法提供了依据。     

考虑资源约束的复杂维修任务时间预计模型

在分析装备维修过程时间影响因素的基础上,研究了维修过程时间模型的建模要素关系。采用Petri网技术建立了反映子任务基本关系、资源约束和调度策略的典型维修过程模型,并对典型子任务执行过程进行了细化建模,研究了模型冲突和资源调度策略。针对典型实例进行了维修时间预计和资源利用率分析。     

库存照明弹药照明炬照明时间研究

照明弹药经过长期贮存后,照明炬中照明剂的理化性能可能已发生变化从而影响其照明效应。通过抽取库存照明弹药样品,分解出弹丸中的照明炬进行静态燃烧试验,测定其光学性能。由测得的数据可以绘制出照明炬发光强度和时间的曲线,分析得出照明弹药经过长期贮存后其照明时间仍符合设计要求。     

具有时滞的比率型Chemostat模型的全局稳定性

研究一类具有时滞的比率型功能性反应的Chemostat模型。研究了模型的边界平衡点和正平衡点的局部稳定性以及Hopf分支的存在性;利用比较定理证明了边界平衡点的全局稳定性;通过构造Liapunov泛函给出了保证系统正平衡点全局稳定的充分条件;并通过数值模拟验证了理论结果。     

Competition under time‐varying demands and dynamic lot sizing costs

We develop a competitive pricing model which combines the complexity of time‐varying demand and cost functions and that of scale economies arising from dynamic lot sizing costs. Each firm can replenish inventory in each of the T periods into which the planning horizon is partitioned. Fixed as well as variable procurement costs are incurred for each procurement order, along with inventory carrying costs. Each firm adopts, at the beginning of the planning horizon, a (single) price to be employed throughout the horizon. On the basis of each period's system of demand equations, these prices determine a time series of demands for each firm, which needs to service them with an optimal corresponding dynamic lot sizing plan. We establish the existence of a price equilibrium and associated optimal dynamic lotsizing plans, under mild conditions. We also design efficient procedures to compute the equilibrium prices and dynamic lotsizing plans.© 2008 Wiley Periodicals, Inc. Naval Research Logistics 2009     

A two‐echelon inventory‐location problem with service considerations

We study the problem of designing a two‐echelon spare parts inventory system consisting of a central plant and a number of service centers each serving a set of customers with stochastic demand. Processing and storage capacities at both levels of facilities are limited. The manufacturing process is modeled as a queuing system at the plant. The goal is to optimize the base‐stock levels at both echelons, the location of service centers, and the allocation of customers to centers simultaneously, subject to service constraints. A mixed integer nonlinear programming model (MINLP) is formulated to minimize the total expected cost of the system. The problem is NP‐hard and a Lagrangian heuristic is proposed. We present computational results and discuss the trade‐off between cost and service. © 2009 Wiley Periodicals, Inc. Naval Research Logistics 2009     

To wait or not to wait: Optimal ordering under lead time uncertainty and forecast updating

There has been a dramatic increase over the past decade in the number of firms that source finished product from overseas. Although this has reduced procurement costs, it has increased supply risk; procurement lead times are longer and are often unreliable. In deciding when and how much to order, firms must consider the lead time risk and the demand risk, i.e., the accuracy of their demand forecast. To improve the accuracy of its demand forecast, a firm may update its forecast as the selling season approaches. In this article we consider both forecast updating and lead time uncertainty. We characterize the firm's optimal procurement policy, and we prove that, with multiplicative forecast revisions, the firm's optimal procurement time is independent of the demand forecast evolution but that the optimal procurement quantity is not. This leads to a number of important managerial insights into the firm's planning process. We show that the firm becomes less sensitive to lead time variability as the forecast updating process becomes more efficient. Interestingly, a forecast‐updating firm might procure earlier than a firm with no forecast updating. © 2009 Wiley Periodicals, Inc. Naval Research Logistics, 2009     

C~4ISR系统任务实时性的评价方法

提出一种定量评价C4ISR(Command Control Communication Computer Intelligence Surveillance and Reconnaissance)系统任务实时性方法--时序着色模糊时间Petri网(TCFTPN)方法.用时序逻辑公式来限制着色Petri网的变迁引发行为,用模糊时间来表示各工作过程的时延特性和降级工作问题.通过估计在规定的时间内标识从任务开始状态到达任务完成状态的概率来确定C4ISR系统的任务实时性.     

战术数据链网络设计优化方法

网络设计优化问题直接关系到战术数据链系统效能的发挥。在分析数据链系统中不同消息类别有不同系统响应时间要求的基础上,提出了一种新的网络设计优化方法。通过建立模型讨论了单个数据链轮询网络的轮询周期、网络成员容量、每个轮询周期内各成员的点名次数等因素间的数学关系。并以Link-11为例进行分析计算。结果表明,该分析方法有效可行,为解决战术数据链网络设计及优化问题提供了一种思路。