基于符号树信息熵的机械振动瞬态信号特征提取

用简单的二进制划分简要说明了信号符号化问题,给出了二进制划分下符号树结构及其Shannon熵计算方法,叙述了符号序列编码方法和符号序列直方图的作用,提交了符号时间序列分析的计算机流程图,对内燃机机身振动信号和转轴振动信号用符号树信息熵进行了特征提取。     

美国SpaceX公司技术创新的启示

文章研究信息化时代陆军作战领域、作战形式、力量融合方式和打击手段的不断更新,对陆军主要作战行动样式发生的深刻变化进行了分析。     

导弹撞击角度与飞行时间两阶段控制制导律

为了实施饱和攻击,需要对撞击角度与飞行时间同时进行控制。通过一种导弹撞击角度与飞行时间两阶段控制制导策略实现导弹撞击角度与飞行时间控制。第一阶段:基于切换滑模思想在纵向通道内对导弹飞行时间进行精确控制,侧向通道制导指令采用传统的纯比例导引律。第二阶段:切换到含重力补偿轨迹调节最优制导律对撞击角度进行精确控制,与显式制导不同,该制导律显式包含重力补偿项。设计数值仿真验证撞击角度与飞行时间两阶段控制制导方法的有效性,仿真结果表明,所给出的撞击角度与飞行时间两阶段控制制导方法能够实现撞击角度与飞行时间的同时控制。     

Evasion policies for a vessel being chased by pirate skiffs

Piracy attack is a serious safety problem for maritime transport worldwide. Whilst various strategic actions can be taken, such as rerouting vessels and strengthening navy patrols, this still cannot completely eliminate the possibility of a piracy attack. It is therefore important for a commercial vessel to be equipped with operational solutions in case of piracy attacks. In particular, the choice of a direction for rapidly fleeing is a critical decision for the vessel. In this article, we formulate such a problem as a nonlinear optimal control problem. We consider various policies, such as maintaining a straight direction or making turns, develop algorithms to optimize the policies, and derive conditions under which these policies are effective and safe. Our work can be used as a real‐time decision making tool that enables a vessel master to evaluate different scenarios and quickly make decisions.     

Comparison of rank aggregation methods based on inherent ability

Ranking is a common task for selecting and evaluating alternatives. In the past few decades, combining rankings results from various sources into a consensus ranking has become an increasingly active research topic. In this study, we focus on the evaluation of rank aggregation methods. We first develop an experimental data generation method, which can provide ground truth ranking for alternatives based on their “inherent ability.” This experimental data generation method can generate the required individual synthetic rankings with adjustable accuracy and length. We propose characterizing the effectiveness of rank aggregation methods by calculating the Kendall tau distance between the aggregated ranking and the ground truth ranking. We then compare four classical rank aggregation methods and present some useful findings on the relative performances of the four methods. The results reveal that both the accuracy and length of individual rankings have a remarkable effect on the comparison results between rank aggregation methods. Our methods and results may be helpful to both researchers and decision‐makers.     

Allocation with demand competition: Uniform,proportional, and lexicographic mechanisms

We examine capacity allocation mechanisms in a supply chain comprising a monopolistic supplier and two competing retailers with asymmetric market powers. The supplier allocates limited capacity to retailers according to uniform, proportional, or lexicographic mechanism. We study the impact of these allocation mechanisms on supplier pricing decisions and retailer ordering behavior. With individual order size no greater than supplier capacity, we show that all three mechanisms guarantee equilibrium ordering. We provide precise structures of retailer ordering decisions in Nash and dominant equilibria. Further, we compare the mechanisms from the perspective of the supplier, the retailers, and the supply chain. We show that regardless of whether retailer market powers are symmetric, lexicographic allocation with any priority sequence of retailers is better than the other two mechanisms for the supplier. Further, under lexicographic allocation, the supplier gains more profit by granting higher priority to the retailer with greater market power. We also extend our study to the case with multiple retailers. © 2017 Wiley Periodicals, Inc. Naval Research Logistics 64: 85–107, 2017     

无人机电磁弹射器效能分析

无人机电磁弹射器是一个由多子系统构成的装备,且各部分之间联系紧密,并不同程度的影响着整体效能。为了确定各组成部分与电磁弹射器效能的影响关系,对其进行系统评价,将系统的整体效能分解为几种典型的效能指标,并采用关联矩阵法(RMA)对由弹射器子系统和效能指标构成的评价体系进行分析。明确了电磁弹射器各部分对系统效能的影响程度,并给出了提高电磁弹射器效能指标的几点建议。     

光纤通道调度算法研究

针对光纤通道协议中没有规定数据调度算法的问题,在满足系统实时性的情况下,经过对FC-AE-ASM协议的深入分析,提出一种基于令牌桶的优先级和加权轮转相结合的调度算法,同时给出了权值分配和轮转周期的确定方法。在以消息的延迟率作为算法性能的评价指标的基础上,经过仿真,对调度算法的性能进行了验证,结果显示出该算法可以很好地满足航空电子系统实时性要求。     

直觉层次模糊评价法的航材逆向物流效益评估

在分析影响航材逆向物流效益因素的基础上,构建了航材逆向物流效益指标体系,提出了一种新的效益评估方法,这种方法将直觉模糊熵权法与层次分析法有效地结合起来,共同确定指标权重,再通过模糊综合评价法对航材逆向物流效益进行评估,提高了评估的科学性和准确性,为航材部门完善物流环节、提高物流效益提供了一定的参考。     

平方根无迹卡尔曼滤波仅测角导航的空间交会闭环协方差分析方法

针对基于仅测角导航的空间交会问题,开展了采用线性协方差进行闭环控制误差快速分析方法的研究。建立了基于平方根无迹卡尔曼滤波(Square Root Unscented Kalman Filter,SRUKF)的仅测角导航算法并推导了观测敏感矩阵,构建了基于多脉冲Hill制导的闭环控制线性协方差分析模型。算例验证结果表明:提出的闭环控制协方差分析结果与Monte Carlo打靶结果能够很好地吻合;该方法适用于采用传统扩展卡尔曼滤波(Extended Kalman Filter,EKF)的仅测角导航问题,但其迹向位置的估计存在一个与该方向控制误差方差相当的偏心,其误差椭圆的长轴和短轴分别比基于SRUKF的估计结果大24.68%和20.56%。此外,由于采用了QR分解和Cholesky因子更新两种高效的代数运算,基于SRUKF的协方差分析模型的计算速度要比基于EKF的协方差分析模型的大10%。