基于遗传算法的虚拟物流联合库存控制研究

针对随机需求条件下的虚拟物流库存控制问题进行了深入研究,提出了一种新的联合库存控制策略——（T,S,s）策略,建立了相应的库存成本模型,并构造遗传算法对模型进行求解。结果分析表明,所提出的（T,S,S）联合库存控制策略是有效的。     

What you should know about simulation and derivatives

Derivatives (or gradients) are important for both sensitivity analysis and optimization, and in simulation models, these can often be estimated efficiently using various methods other than brute‐force finite differences. This article briefly summarizes the main approaches and discusses areas in which the approaches can most fruitfully be applied: queueing, inventory, and finance. In finance, the focus is on derivatives of another sort. © 2008 Wiley Periodicals, Inc. Naval Research Logistics, 2008     

Analysis of artillery shoot‐and‐scoot tactics

Firing multiple artillery rounds from the same location has two main benefits: a high rate of fire at the enemy and improved accuracy as the shooter's aim adjusts to previous rounds. However, firing repeatedly from the same location carries significant risk that the enemy will detect the artillery's location. Therefore, the shooter may periodically move locations to avoid counter‐battery fire. This maneuver is known as the shoot‐and‐scoot tactic. This article analyzes the shoot‐and‐scoot tactic for a time‐critical mission using Markov models. We compute optimal move policies and develop heuristics for more complex and realistic settings. Spending a reasonable amount of time firing multiple shots from the same location is often preferable to moving immediately after firing an initial salvo. Moving frequently reduces risk to the artillery, but also limits the artillery's ability to inflict damage on the enemy.     

基于整车虚拟道路行驶试验的车辆零部件疲劳分析

针对现有车辆零部件精确疲劳分析依赖成本高昂的实车试验的问题,提出了一种利用整车虚拟样机仿真分析零部件疲劳寿命的方法。该方法通过在ADAMS/CAR中用整车虚拟样机在虚拟道路模型上进行行驶试验,利用多体系统动力学基于模态坐标的求解特点,使用模态应力恢复技术准确还原出了用于零部件疲劳寿命分析的载荷历程。将该方法应用于某车辆双横臂前悬中的下控制臂,在较短的时间内获得了该零件的预测疲劳寿命、寿命安全系数及危险部位等信息。应用结果表明,该方法可作为汽车设计过程与测试过程中的有效试验手段。     

基于分布式排队网络的防空战术协同模型

分析了多个防空火力单元的作战过程,将战术BM/C3的控制协调决策抽象为决策策略。建立了多个火力单元协同作战的排队网络模型,并运用SPN理论对排队网络的运行机制进行了强有力的描述,有效地体现了防空作战过程中的威胁评估、目标分配等战术决策过程。这将为建立大型复杂排队网络,模拟仿真战役层面防空作战过程奠定基础。     

GSPN的分析方法及其应用

随着计算机和信息技术的发展,广义随机Petri网(G SPN)作为一种图形化的建模工具,不仅可以对系统进行形式化的描述和快速原型开发,而且由于其具有坚实的数学理论基础,可以对系统进行正确性验证和性能评价,因此在系统的设计过程中,得到了广泛的应用。基于结构分析方法、可达图分析和数值分析方法讨论分析了G SPN,并给出了具体的算例,最后讨论了G SPN的应用领域。     

A model of supply-chain decisions for resource sharing with an application to ventilator allocation to combat COVID-19

We present a stochastic optimization model for allocating and sharing a critical resource in the case of a pandemic. The demand for different entities peaks at different times, and an initial inventory for a central agency are to be allocated. The entities (states) may share the critical resource with a different state under a risk-averse condition. The model is applied to study the allocation of ventilator inventory in the COVID-19 pandemic by FEMA to different U.S. states. Findings suggest that if less than 60% of the ventilator inventory is available for non-COVID-19 patients, FEMA's stockpile of 20 000 ventilators (as of March 23, 2020) would be nearly adequate to meet the projected needs in slightly above average demand scenarios. However, when more than 75% of the available ventilator inventory must be reserved for non-COVID-19 patients, various degrees of shortfall are expected. In a severe case, where the demand is concentrated in the top-most quartile of the forecast confidence interval and states are not willing to share their stockpile of ventilators, the total shortfall over the planning horizon (until May 31, 2020) is about 232 000 ventilator days, with a peak shortfall of 17 200 ventilators on April 19, 2020. Results are also reported for a worst-case where the demand is at the upper limit of the 95% confidence interval. An important finding of this study is that a central agency (FEMA) can act as a coordinator for sharing critical resources that are in short supply over time to add efficiency in the system. Moreover, through properly managing risk-aversion of different entities (states) additional efficiency can be gained. An additional implication is that ramping up production early in the planning cycle allows to reduce shortfall significantly. An optimal timing of this production ramp-up consideration can be based on a cost-benefit analysis.     

Pricing and inventory management during new product introduction when shortage creates hype

In this study, we analyze the joint pricing and inventory management during new product introduction when product shortage creates additional demand due to hype. We develop a two‐period model in which a firm launches its product at the beginning of the first period, before it observes sales in the two periods. The product is successful with an exogenous probability, or unsuccessful with the complementary probability. The hype in the second period is observed only when the product is successful. The firm learns the actual status of the product only after observing the first‐period demand. The firm must decide the stocking level and price of the product jointly at the beginning of each of the two periods. In this article, we derive some structural properties of the optimal prices and inventory levels, and show that (i) firms do not always exploit hype, (ii) firms do not always increase the price of a successful product in the second period, (iii) firms may price out an unsuccessful product in the first period if the success probability is above a threshold, and (iv) such a threshold probability is decreasing in the first‐period market potential of the successful product. © 2015 Wiley Periodicals, Inc. Naval Research Logistics 62: 304–320, 2015     

Chance‐constrained multi‐terminal network design problems

We consider a reliable network design problem under uncertain edge failures. Our goal is to select a minimum‐cost subset of edges in the network to connect multiple terminals together with high probability. This problem can be seen as a stochastic variant of the Steiner tree problem. We propose two scenario‐based Steiner cut formulations, study the strength of the proposed valid inequalities, and develop a branch‐and‐cut solution method. We also propose an LP‐based separation for the scenario‐based directed Steiner cut inequalities using Benders feasibility cuts, leveraging the success of the directed Steiner cuts for the deterministic Steiner tree problem. In our computational study, we test our branch‐and‐cut method on instances adapted from graphs in SteinLib Testdata Library with up to 100 nodes, 200 edges, and 17 terminals. The performance of our branch‐and‐cut method demonstrates the strength of the scenario‐based formulations and the benefit from adding the additional valid inequalities that we propose. © 2015 Wiley Periodicals, Inc. Naval Research Logistics 62: 321–334, 2015     

随机布阵条件下同时数字多波束干扰优化设计方法

针对现有方法普遍存在的波束形成算法效率低、难以形成多频点多方向的同时多波束干扰、不适用于随机布阵条件下的波束形成等缺点,提出了一种基于二阶锥规划(SOCP,Second-Order Cone Programming)理论的同时数字多波束干扰形成方法。首先,给出了在随机布阵条件下干扰多波束优化设计问题的数学描述;其次,以范数准则为例,将随机布阵条件下干扰多波束设计问题的解析形式转化为相应的SOCP形式;再次,利用现有的原-对偶内点算法工具箱Se Du Mi或者CVX进行快速求解。最后,仿真结果表明该方法可以较好地解决随机布阵条件下的多频率多方向雷达目标同时多波束干扰优化设计问题。