反作用轮低速特性观测补偿方法

反作用轮在现代高精度卫星姿态控制中占据着重要的地位。但由于反作用轮工作于低速状态,其转速过零时摩擦力矩的非线性特征将会对姿态控制精度产生较大的影响,并影响卫星运行寿命。基于Dahl摩擦模型建立了直流电机驱动的反作用轮系统数学模型,在此基础上设计了用于改善反作用轮低速性能的补偿观测器,并将其应用于三正交结构姿态控制系统。数字仿真说明此方法可以有效地抑制反作用轮低速摩擦产生的扰动,从而大幅度改善卫星姿态控制精度及其姿态稳定性。最后探讨了该观测器方法同变结构控制方法的综合应用前景。     

支持广义多方案分析仿真的异地克隆研究

仿真克隆可以提高并行离散事件仿真的效率和并行性,方便快捷地对仿真中的多种可能性进行分析、比较和评估.给出广义多方案分析仿真概念,介绍仿真克隆的相关概念,分析当前仿真克隆方法的不足,提出提高广义多方案分析仿真整体运行效率的异地克隆概念.基于检查点与恢复方法,在动态并行仿真引擎中实现了异地克隆.利用Phold测试程序对异地克隆方法的效率进行测试,测试结果表明,异地克隆可以提高多方案分析仿真系统整体运行效率.     

电视制导系统抗干扰性能评估

提出了一种空地电视制导导弹图像传输系统抗干扰评估的总体框架,建立了电磁干扰条件下系统的抗干扰评估的空间模型。而后基于有限状态机理论,建立了电视制导导弹图像识别模态转换模型,详细讨论了典型干扰对电视图像数据链的影响。最后,应用计算机仿真技术,得到制导系统在不同信噪比条件下导弹的最大作用距离和图像干扰效果。     

动基座条件下垂直发射装置状态参数检测方法

针对在海上动基座条件下舰载垂直发射装置的安装精度和发射架导轨状态参数的检测问题,在分析其技术难点的基础上,提出了利用测距仪差分原理实现对水平误差的检测;采用数字激光自准直仪解决发射筒各架体的垂直度测量。并通过对该检测方法进行的不确定度分析与计算,验证了该检测理论的正确性。     

基于磁强计和光纤陀螺的小卫星姿态确定非线性滤波算法

提出了一种小卫星姿态确定的非线性滤波算法,该算法利用三轴磁强计和光纤陀螺作为姿态敏感器。在非线性滤波器的设计中,从两个方面对平方根sigma点卡尔曼滤波方法进行改进。第一,把姿态四元数的矢量部分、光纤陀螺的漂移和噪声组合,得到滤波器的增广状态向量;第二,分别建立向量旋转模型、最优化模型和误差四元数乘法模型来确保非线性滤波过程中四元数的归一化约束。仿真分析结果表明,本文提出的非线性滤波算法能够有效地提高小卫星的定姿性能,与扩展卡尔曼滤波相比,具有较高的精度、稳定性和较快的收敛速度;与无迹卡尔曼滤波相比,收敛性相当,但是精度略优,稳定性和计算效率较高。     

应用于四旋翼无人机角速度估计的几何滑模观测器设计

对四旋翼无人机的角速度进行估计时,传统的基于单位四元数的滑模观测器需要引入强制比例重调,因而影响了跟踪精度。本文提出一种基于数值积分的李群方法的滑模观测器设计框架。该算法基于等变映射思想,在齐性流形空间的等价李代数空间中设计滑模反馈,从而避免了直接在流形空间中设计反馈的复杂性,并消除了传统方法在每个积分步骤中强制加入的比例重调,提高了观测器的跟踪性能。仿真结果表明,几何滑模观测器算法可以有效的对四旋翼无人机的角速度进行估计。     

Using a birth‐and‐death process to estimate the steady‐state distribution of a periodic queue

If the number of customers in a queueing system as a function of time has a proper limiting steady‐state distribution, then that steady‐state distribution can be estimated from system data by fitting a general stationary birth‐and‐death (BD) process model to the data and solving for its steady‐state distribution using the familiar local‐balance steady‐state equation for BD processes, even if the actual process is not a BD process. We show that this indirect way to estimate the steady‐state distribution can be effective for periodic queues, because the fitted birth and death rates often have special structure allowing them to be estimated efficiently by fitting parametric functions with only a few parameters, for example, 2. We focus on the multiserver M_t/GI/s queue with a nonhomogeneous Poisson arrival process having a periodic time‐varying rate function. We establish properties of its steady‐state distribution and fitted BD rates. We also show that the fitted BD rates can be a useful diagnostic tool to see if an M_t/GI/s model is appropriate for a complex queueing system. © 2015 Wiley Periodicals, Inc. Naval Research Logistics 62: 664–685, 2015     

基于无偏GM(1,1)幂模型的意图威胁建模

在态势威胁的基础上,利用无偏GM(1,1)幂模型设计了一种敌机意图威胁的模型。首先,提出了素质因子和探测概率因子,在此基础上,建立了改进的态势威胁模型。然后,将角度作为特征量对敌机机动进行预测,并建立了意图威胁模型。最后,分别对态势威胁和意图威胁模型进行仿真。结果表明,意图威胁模型行之有效。     

State fragility and violent uprisings in Nigeria

Abstract

The emergence of the Islamic sect, Boko Haram, and its transformation into a terrorist organisation has dominated recent discourse in the fields of political science and security studies, both within and without the socio-politico enclave known as Nigeria. Much of the discussion has centred on the extra-judicial execution of its founder, Mohammed Yusuf, which purportedly intensified the radicalisation of the group, and whether or not the sect receives operational and/or financial support from foreign terrorist associations. The interest of others has been to forecast the possibility of the internationalisation of the group's activities. This paper aligns with those whose interest is to identify and proffer ways of resolving factors that predisposed the Nigerian state to the levels of violence perpetrated by Boko Haram, with a view to averting much greater crises in the future. It adopts some historicism in demonstrating that the responsibility for the deepening insecurity in the country resides in the Nigerian state structure, which has often been seen as willing to sacrifice the well-being of the many for the benefit of a few. On the whole, the paper utilises state fragility as the framework of analysis by identifying the incapacity of the state in effective service delivery, which has as a result created a situation of mass unemployment and extreme poverty that has fanned the Boko Haram uprising. It concludes that a sustainable solution to the crisis lies in addressing the root causes of inequality, unemployment and poverty, with which most Nigerians, particularly in the north, subsist.     

罐底渗漏的罐基油气质量分数探测法识别

油罐是油品储运的重要设备,罐底最易出现穿孔渗漏油现象,致使罐基内部油气质量分数高于正常值。以油库中柴油覆土罐群为例,研究并试验了根据罐基油气质量分数识别罐底渗漏的方法：分析罐基探漏孔位置分布并钻孔;多次探测罐基油气质量分数,根据探测数据识别各罐有无底部渗漏;为了便于以后检测油库时识别各罐有无渗漏,为各罐建立状态监测表,并将无渗漏的罐基油气质量分数最高值暂定为该类罐的安全值,低于该安全值的油罐可直接判定为无渗漏。实践结果证明,这种不开罐检测罐底渗漏油的方法可及时发现故障并采取措施,对储油安全具有重要意义。