机体/推进一体化飞行器动导数频域计算方法

运用Etkin非定常气动力模型,将谐波平衡法应用于复杂外形动导数辨识。计算结果表明:谐波平衡法和时域方法的动导数辨识结果一致,与实验值吻合,验证了程序的正确性和谐波平衡法的可靠性。采用谐波平衡法对类X-51高超声速机体/推进一体化飞行器WR-A进行动导数辨识,并与时域方法的计算结果比较,考察了该方法在复杂外形下数值模拟非定常流动和动导数辨识的能力。实验结果表明:对于WR-A这种复杂外形飞行器,谐波平衡法也能在保证精度的同时具有较高的计算效率。     

箭(弹)级间螺栓法兰连接结构冲击失效实验与数值仿真

基于火箭(导弹)级间螺栓法兰连接结构,简化设计并制作了一组原理性实验件,利用ABAQUS软件建立有限元模型,设计并进行了多次落锤冲击失效实验,其中包括轴向和横向两种工况,考虑了螺栓均布与非均布、螺栓直径和螺栓-栓孔间隙等不同结构特点。实验过程中采集了螺栓力时程响应数据、柱段关键点应变时程响应数据、锤头冲击力和冲击速度及连接界面开缝位移等多组数据。根据实验效果和实测数据,分析了连接结构冲击失效机理,并对比验证发现有限元模型数值模拟效果和精度与实验结果吻合较好。研究结论可为箭(弹)级间连接结构抗冲击设计提供参考。     

A computationally efficient approach for determining inventory levels in a capacitated multiechelon production‐distribution system

The system under study is a single item, two‐echelon production‐inventory system consisting of a capacitated production facility, a central warehouse, and M regional distribution centers that satisfy stochastic demand. Our objective is to determine a system base‐stock level which minimizes the long run average system cost per period. Central to the approach are (1) an inventory allocation model and associated convex cost function designed to allocate a given amount of system inventory across locations, and (2) a characterization of the amount of available system inventory using the inventory shortfall random variable. An exact model must consider the possibility that inventories may be imbalanced in a given period. By assuming inventory imbalances cannot occur, we develop an approximation model from which we obtain a lower bound on the per period expected cost. Through an extensive simulation study, we analyze the quality of our approximation, which on average performed within 0.50% of the lower bound. © 2000 John Wiley & Sons, Inc. Naval Research Logistics 47: 377–398, 2000     

Impacts of logistics information on sales: Evidence from Alibaba

Facing fierce competition from rivals, sellers in online marketplaces are eager to improve their sales by delivering items faster and more reliably. Because logistics quality can be known only after a transaction, sellers must identify effective ways to communicate logistics information to consumers. Drawing on the accessibility-diagnosticity framework, we theorize that the sales impacts of logistics information depend on its relative diagnostic value. Using data on 1493 items with 505,785 consumer reviews from an online marketplace, we examine how sales are affected by three information sources for logistics services: online word of mouth (WOM) about logistics, self-reported logistics services, and expected delivery time. We use an instrumental variable method to address the endogeneity issue between sales and WOM. We find that, ceteris paribus, consumers give more weight to WOM about logistics and delivery time when they make purchase decisions but less weight to self-reported logistics service. The effects of logistics information on sales are asymmetric for large and small sellers.     

ASLR机制脆弱性自动分析方法

地址随机化是一种针对控制流劫持漏洞的防御机制。已有的漏洞自动分析与利用技术缺少对地址随机化机制影响的分析,导致生成的测试用例在实际环境中的运行效果受到极大限制。针对地址随机化的缺陷及其绕过技术的特点,提出了一种地址随机化脆弱性分析方法。该方法使用有限状态机描述程序运行路径中各关键节点的状态;针对常见的内存泄漏与控制流劫持场景建立约束条件;通过求解内存泄漏状态约束与控制流劫持状态约束的兼容性,分析地址随机化机制在特定场景下的脆弱性。实验结果表明,该方法可有效检测通过内存泄漏导致的地址随机化绕过及控制流劫持攻击,实现自动化的地址随机化脆弱性分析,提高针对软件安全性分析的效率。     

Analysis of a finite‐buffer bulk‐service queue with discrete‐Markovian arrival process: D‐MAP/Ga,b/1/N

Discrete‐time queues with D‐MAP arrival process are more useful in modeling and performance analysis of telecommunication networks based on the ATM environment. This paper analyzes a finite‐buffer discrete‐time queue with general bulk‐service rule, wherein the arrival process is D‐MAP and service times are arbitrarily and independently distributed. The distributions of buffer contents at various epochs (departure, random, and prearrival) have been obtained using imbedded Markov chain and supplementary variable methods. Finally, some performance measures such as loss probability and average delay are discussed. Numerical results are also presented in some cases. © 2003 Wiley Periodicals, Inc. Naval Research Logistics 50: 345–363, 2003.     

Scheduling jobs with piecewise linear decreasing processing times

We study the problems of scheduling a set of nonpreemptive jobs on a single or multiple machines without idle times where the processing time of a job is a piecewise linear nonincreasing function of its start time. The objectives are the minimization of makespan and minimization of total job completion time. The single machine problems are proved to be NP‐hard, and some properties of their optimal solutions are established. A pseudopolynomial time algorithm is constructed for makespan minimization. Several heuristics are derived for both total completion time and makespan minimization. Computational experiments are conducted to evaluate their efficiency. NP‐hardness proofs and polynomial time algorithms are presented for some special cases of the parallel machine problems. © 2003 Wiley Periodicals, Inc. Naval Research Logistics 50: 531–554, 2003     

舰炮火控系统反应时间与精度关系的仿真

对舰炮火控系统中反应时间和系统精度之间的关系做了简要的介绍,并论述了舰炮火控系统中时间和精度之间复杂的关系,通过分析采样点数和误差之间的关系,结合采样点数和系统反应时间之间的联系以及误差与系统精度之间的联系,引出反应时间与精度之间的某种关系,最后对从接收目标指示到给出射击诸元这个过程的各个时间段与其相对应的精度之间的关系进行计算机仿真。     

数字化部队指挥网络系统效能评价模型

以结构熵理论为基础,分析数字化部队作战指挥信息网络系统组织结构对系统内信息流的影响,从信息的角度对系统组织结构的有序度进行评价,引入信息流的时效和质量的概念,建立定量评价系统结构有序度计算的时效质量模型,结合系统数据传输业务效能的评价方法,形成作战指挥信息网络系统整体综合效能的评价模型。最后辅以实例。     

基于分布式信息融合的多舰纯方位跟踪

提出一种基于信息融合的分布式多舰纯方位跟踪算法 ,该算法采用时变采样间隔的修正增益推广卡尔曼滤波器 ,用多条舰艇的舰载电子侦察设备对海上多个运动辐射源目标进行分布式纯方位跟踪融合。计算机模拟结果表明 ,该算法能满足工程应用的要求