Newsvendor problems with sequentially revealed demand information

This article analyzes a capacity/inventory planning problem with a one‐time uncertain demand. There is a long procurement leadtime, but as some partial demand information is revealed, the firm is allowed to cancel some of the original capacity reservation at a certain fee or sell off some inventory at a lower price. The problem can be viewed as a generalization of the classic newsvendor problem and can be found in many applications. One key observation of the analysis is that the dynamic programming formulation of the problem is closely related to a recursion that arises in the study of a far more complex system, a series inventory system with stochastic demand over an infinite horizon. Using this equivalence, we characterize the optimal policy and assess the value of the additional demand information. We also extend the analysis to a richer model of information. Here, demand is driven by an underlying Markov process, representing economic conditions, weather, market competition, and other environmental factors. Interestingly, under this more general model, the connection to the series inventory system is different. © 2012 Wiley Periodicals, Inc. Naval Research Logistics 2012     

火箭发动机应储数量的研究

火箭发动机应储数量的确定是其维修保养工作中的一个重要问题。在满足一定精度的前提下,以可靠性评估为中心研究寿命服从逆威布尔分布的火箭发动机的应储数量问题。在具有二项移走的逐步增加I型区间截尾模型下(被随机移走的产品数目服从二项分布),采取不同方案给出决定火箭发动机寿命的关键性参数的可靠性估计,据此确定其应储数量。最后,通过随机模拟方法给出在一定精度指标下火箭发动机的应储数量。     

Peridynamic modeling and simulation of thermo-mechanical de-icing process with modified ice failure criterion

De-icing technology has become an increasingly important subject in numerous applications in recent years. However, the direct numerical modeling and simulation the physical process of thermo-mechanical deicing is limited. This work is focusing on developing a numerical model and tool to direct simulate the de-icing process in the framework of the coupled thermo-mechanical peridynamics theory. Here, we adopted the fully coupled thermo-mechanical bond-based peridynamics (TM-BB-PD) method for modeling and simulation of de-icing. Within the framework of TM-BB-PD, the ice consti-tutive model is established by considering the influence of the temperature difference between two material points, and a modified failure criteria is proposed, which takes into account temperature effect to predict the damage of quasi-brittle ice material. Moreover, thermal boundary condition is used to simulate the thermal load in the de-icing process. By comparing with the experimental results and the previous reportedfinite element modeling, our numerical model shows good agreement with the pre-vious predictions. Based on the numerical results, we find that the developed method can not only predict crack initiation and propagation in the ice, but also predict the temperature distribution and heat conduction during the de-icing process. Furthermore, the influence of the temperature for the ice crack growth pattern is discussed accordingly. In conclusion, the coupled thermal-mechanical peridynamics formulation with modified failure criterion is capable of providing a modeling tool for engineering ap-plications of de-icing technology.     

Partial penetration of annular grooved projectiles impacting ductile metal targets

Changing and optimizing the projectile nose shape is an important way to achieve specific ballistic performance. One special ballistic performance is the embedding effect, which can achieve a delayed high-explosive reaction on the target surface. This embedding effect includes a rebound phase that is significantly different from the traditional penetration process. To better study embedment behavior, this study proposed a novel nose shape called an annular grooved projectile and defined its interaction process with the ductile metal plate as partial penetration. Specifically, we conducted a series of low-velocity-ballistic tests in which these steel projectiles were used to strike 16-mm-thick target plates made with 2024-O aluminum alloy. We observed the dynamic evolution characteristics of this aluminum alloy near the impact craters and analyzed these characteristics by corresponding cross-sectional views and numerical simulations. The results indicated that the penetration resistance had a brief decrease that was influenced by its groove structure, but then it increased significantly-that is, the fluctuation of penetration resistance was affected by the irregular nose shape. Moreover, we visualized the distribution of the material in the groove and its inflow process through the rheology lines in microscopic tests and the highlighted mesh lines in simulations. The combination of these phenomena revealed the embed-ment mechanism of the annular grooved projectile and optimized the design of the groove shape to achieve a more firm embedment performance. The embedment was achieved primarily by the target material filled in the groove structure. Therefore, preventing the shear failure that occurred on the filling material was key to achieving this embedding effect.     

强化学习在多阶段装备组合规划问题中的应用

针对多阶段武器装备组合规划中的选择难、规划难问题,提出基于多目标优化算法以及强化学习技术的混合优化方法。在各个阶段以装备组合效能最大和成本最小为准则,构建单阶段多目标优化模型,并设计基于非支配排序遗传算法的求解算法以生成各阶段的Pareto解,在此基础上建立多阶段的组合优化模型。通过强化学习的Q-Learning方法,在各阶段的Pareto解中采用探索或者利用两种模式,生成各阶段的装备组合,并指导下一阶段的装备选型,从而生成整个周期内的规划方案。通过对比实验分析,验证了所提模型和算法的有效性,能够为多阶段武器装备组合规划提供辅助决策。     

T300和JC2#纤维增强C/SiC复合材料力学性能对比

以聚碳硅烷(PCS)为先驱体,采用聚合物浸渍裂解法(PIP)分别制备得到T300碳纤维和JC2#碳纤维增强C/SiC复合材料。JC2#C/SiC复合材料具有优异的力学性能,抗弯强度和断裂韧性分别达到662MPa和19.5MPa.m1/2;T300 C/SiC复合材料表现出低强度、高脆性,其抗弯强度和断裂韧性不足前者的四分之一。T300 C/SiC复合材料低性能的根本原因在于T300纤维在PCS裂解过程中性能严重下降,复合材料中纤维与基体间存在强界面结合是另一个影响因素。     

基于Arena仿真的事故网络风险耦合特性分析

风险传递过程中,耦合是导致风险突变的重要原因。为提供风险耦合控制方法,给出风险耦合的形式化描述,采用风险耦合弹性系数对耦合强度进行计算;基于Arena软件对某型非致命武器设计论证阶段的进度风险和费用风险之间的耦合特性进行仿真分析,分别仿真了单指标、多指标在线性和非线性耦合情形下的系统行为,结果表明:全局性的线性耦合和高强度非线性耦合能显著改变系统行为。相关结果为风险耦合控制策略的制定提供了参考。     

非高斯噪声下的滤波方法

干扰条件下的机动目标跟踪在一些文献[1][2]中已有讨论,但利用多传感器,尤其是被动传感器进行非高斯观测噪声条件下的目标跟踪仍需要研究。本文讨论了被动传感器在随机干扰条件下进行机动目标跟踪的方法,其观测量包含非高斯噪声,也可能包含影响观测值的随机干扰。与基于卡尔曼滤波的常见方法不同,采用动态规划算法进行多假设检验,从而估计目标的状态。仿真试验表明,本文方法能有效地处理非高斯噪声情况下的目标跟踪问题,而基于卡尔曼滤波的跟踪方法,比如EKF,则效果较差。     

并联TBCC动力对高超声速飞行器性能的影响

针对马赫数为6的一级高超声速巡航飞行器的动力需求,提出涡轮/亚燃冲压/双模态超燃冲压组合动力（T/RJ/DMSJ）和射流预冷涡轮/亚燃冲压/双模态超燃冲压组合动力(PCT/RJ/DMSJ)两种方案。在给定的飞行任务下,分析起飞推重比分别为0.8和1.0时,飞行器完成任务时的航程和飞行时间,并对比了PCT/RJ/DMSJ在两种工作模态下的性能。研究结果表明：在相同的起飞推重比下,两种组合动力方案的航程和飞行时间相差不大。当起飞推重比为0.8时,采用PCT/RJ/DMSJ组合动力方案比T/RJ/DMSJ组合动力方案的航程高出3.6%,飞行时间高出3.8%;当起飞推重比为1.0时,PCT/RJ/DMSJ的航程和飞行时间比T/RJ/DMSJ的分别高出4.6%和4.8%。在小推重比下,跨声速段的燃料消耗和飞行时间占整个加速爬升段的比例较大,随着推重比的增加,这个比例减小,巡航可用的燃料比例增大,巡航距离增加,提高起飞推重比可以提高超声速飞行器的航程并缩短飞行时间。