Inventory cost impact of order processing priorities based on demand uncertainty

We evaluate an approach to decrease inventory costs at retail inventory locations that share a production facility. The retail locations sell the same product but differ in the variance of retail demand. Inventory policies at retail locations generate replenishment orders for the production facility. The production facility carries no finished goods inventory. Thus, production lead time for an order is the sojourn time in a single server queueing system. This lead time affects inventory costs at retail locations. We examine the impact of moving from a First Come First Served (FCFS) production rule for orders arriving at the production facility to a rule in which we provide non‐preemptive priority (PR) to orders from retail locations with higher demand uncertainty. We provide three approximations for the ratio of inventory costs under PR and FCFS and use them to identify conditions under which PR decreases retail inventory costs over FCFS. We then use a Direct Approach to establish conditions when PR decreases retail inventory costs over FCFS. We extend the results to orders from locations that differ in the mean and variance of demand uncertainty. The analysis suggests that tailoring lead times to product demand characteristics may decrease system inventory costs. © 2002 Wiley Periodicals, Inc. Naval Research Logistics 49: 376–390, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/nav.10016     

任务空间概念模型VV&A研究

任务空间概念模型是现实世界军事知识的第一层抽象,是仿真系统开发的业务基础。所以任务空间概念模型的质量直接影响到仿真系统的质量,任务空间概念模型自身的VV&A是一个非常值得关注的问题。任务空间概念建模本质上看是军事领域的知识表示或者需求描述,定性描述占主要,定量成分非常少。因此,传统的通过分析输出数据的方法不能适应任务空间概念模型的特点。概要介绍了任务空间概念模型建模,并且提出了从专家法、静态校核机制、概念执行机制三个角度来考察模型质量的思路。     

云模型及其在指挥控制系统可靠性分析中的应用

根据指挥控制系统的特点及作战应用的具体情况,从指挥控制系统的可靠性出发,提出了适合指控系统可靠性分析的云模型。通过拟定性能评价指标,导出各指标的云模型及其多维加权综合云的重心,应用云重心评价方法进行分析;并通过案例,运用基于PC-L INM AP的云重心评价方法,以影响指挥控制系统可靠性的两个重要性能指标为依据,分析了未来联合作战中指挥控制系统的可靠性,比较贴近作战实际,可信度较高。     

Optimal pricing and inventory control policy in periodic‐review systems with fixed ordering cost and lost sales

This paper studies a periodic‐review pricing and inventory control problem for a retailer, which faces stochastic price‐sensitive demand, under quite general modeling assumptions. Any unsatisfied demand is lost, and any leftover inventory at the end of the finite selling horizon has a salvage value. The cost component for the retailer includes holding, shortage, and both variable and fixed ordering costs. The retailer's objective is to maximize its discounted expected profit over the selling horizon by dynamically deciding on the optimal pricing and replenishment policy for each period. We show that, under a mild assumption on the additive demand function, at the beginning of each period an (s,S) policy is optimal for replenishment, and the value of the optimal price depends on the inventory level after the replenishment decision has been done. Our numerical study also suggests that for a sufficiently long selling horizon, the optimal policy is almost stationary. Furthermore, the fixed ordering cost (K) plays a significant role in our modeling framework. Specifically, any increase in K results in lower s and higher S. On the other hand, the profit impact of dynamically changing the retail price, contrasted with a single fixed price throughout the selling horizon, also increases with K. We demonstrate that using the optimal policy values from a model with backordering of unmet demands as approximations in our model might result in significant profit penalty. © 2005 Wiley Periodicals, Inc. Naval Research Logistics, 2006     

Priority and dynamic scheduling in a make‐to‐stock queue with hyperexponential demand

We consider the scheduling problem in a make‐to‐stock queue with two demand classes that can be differentiated based on their variability. One class experiences Poisson arrivals and the other class experiences hyperexponential renewal arrivals. We provide an exact analysis of the case where the demand class with higher variability is given non‐preemptive priority. The results are then used to compare the inventory cost performance of three scheduling disciplines, first‐come first‐serve and priority to either class. We then build on an existing dynamic scheduling heuristic to propose a modification that works well for our system. Extensions of the heuristic to more than two classes and to the case where demand state is known are also discussed. © 2006 Wiley Periodicals, Inc. Naval Research Logistics, 2006.     

地空导弹群火力优化分配模型

地空导弹群火力优化分配是对多批空中目标分别选择最有效的地空导弹火力单元进行拦截,形成最佳兵力、兵器使用方案,它是地空导弹武器指控系统的一项重要功能。从研究地空导弹群火力优化分配过程出发,建立了地空导弹拦截适宜性检查模型、射击优先度指标计算模型和火力分配方案优化模型,为仿真地空导弹群火力优化分配过程提供了模型依据。     

应用于飞控系统评估的风洞虚拟飞行试验系统与关键技术分析

基于传统意义上的飞控系统评估方法的不足,分析了风洞虚拟飞行试验应用于飞控系统评估的优势;按飞控系统常用的姿态控制回路及制导控制回路的组成形式,介绍了风洞虚拟飞行试验系统方案与工作原理,详细分析了它与半实物仿真系统的差异;分析了风洞虚拟飞行试验应用于飞控系统评估需解决的关键技术问题,包括风洞虚拟飞行试验评估方法、飞行器模型设计技术、飞控系统改进技术及模型支撑技术。     

利用OH发射谱进行的高温低浓度甲烷着火研究

采用激波管进行低浓度甲烷和空气混合气的着火实验,通过测量压力和OH发射光谱,得到不同工况下的着火延迟,并与甲烷的详细反应机理计算结果作比较。结果表明:不同浓度下甲烷着火延迟的对数与温度倒数呈线性关系,着火延迟随甲烷浓度的降低而减少;贫燃条件下,采用详细动力学机理计算的表观活化能与实验数据拟合较好。     

基于输出饱和条件下磁浮列车悬浮控制参数优化

低速磁浮列车利用电磁吸力支撑车体,相比轮轨列车具有噪音小、转弯半径小、爬坡能力强等优点。研究控制器输出饱和条件下悬浮系统的稳定性问题,可以避免由于电网电压约束而可能出现的失稳现象,提高了系统运行的可靠性。基于磁浮列车单点悬浮模型,使用电流-位置双环设计方法设计得到可稳定悬浮的控制算法。由于磁浮列车悬浮控制器的输出饱和环节,进一步提出了一种基于搜索极大椭球的控制参数优化方法,在不改变控制算法设计的前提下实现了参数优化。通过仿真和试验均验证了优化后的控制效果,有效指导了实际系统的工程调试。     

基于共进化的多任务分配与调度

在考虑多种约束关系基础上 ,提出一种并行与分布式系统中多约束关系的任务分配与调度的共同进化遗传算法。仿真试验结果表明所给算法比传统单种遗传算法更能有效地进行多任务分配与调度 ,具有一定的工程价值