固体热容激光器温度场应力场分析

采用有限元分析方法,对Nd:YAG作为激活介质的固体热容激光器的温度场及应力场进行了研究.结果表明固体热容激光器的温度场、应力场与常规的固体激光器有很大的差异,常规的固体激光器激活介质必须在泵浦的同时进行冷却,晶体表面温度比中心温度低,晶体表面受到的是张应力.固体热容激光器发射激光时,激活介质处于绝热状态.激活介质表面的温度要比中心高,激活介质表面出现的是压应力.这种差异是固体热容激光器可以高功率运转的物理机制.     

基于位置预测的靶场图像实时判读方法

在靶场经纬仪对目标实时跟踪测量时,会发生相机随机抖动的情况,引起目标在图像中大幅度运动。应对大幅度运动时,基于搜索窗口的跟踪方法容易丢失目标,而基于全图搜索的跟踪方法时效性差。针对以上问题,提出一种结合核相关滤波算法(Kernelized Correlation Filter, KCF)和目标位置预测的改进的跟踪学习检测算法(Tracking-Learning-Detection, TLD)跟踪框架。利用正交多项式最优线性滤波器及相机角度信息预测目标下一帧位置,在此区域利用KCF进行快速跟踪,可以提高跟踪的成功率和时效性,跟踪失败时再进行检测。仿真实验表明,最优线性滤波器能较准确预测目标位置,给KCF提供较准确的搜索位置,算法每帧耗时仅为1.1 ms,且定位精度优于TLD和KCF,能有效应对相机抖动的问题。靶场实际试验证明该方法可提高靶场自动判读水平,减少人工干预。     

Modeling and simulation of muzzle flow field of railgun with metal vapor and arc

During the electromagnetic railgun launching process, there will be a complex flow field with high temperature in the muzzle area because of the high-speed friction, transition and secondary arc-ignition. This paper models the muzzle area of railgun when the projectile is far away from the muzzle, and the dynamic simulation of the flow field with secondary arc in the muzzle area is carried out based on the magneto hydrodynamic equations. Meanwhile, a multi-component plasma transport model is used to analyze the muzzle arc plasma flow process of the mixed gas of Al vapor and the air. Furthermore, the pressure boundary conditions are fitted by the dynamic mesh simulation results. The current and voltage of the muzzle are obtained through the emission experiment of the railgun experimental prototype. We load the current data into the simulation model and the voltage of experiments and simulations are compared, which proves the accuracy of the simulation. Then the plasma temperature and the composition of Al vapor in the muzzle flow process are analyzed in-depth.     

深度神经网络指导下的无线覆盖预测算法

为保证新一代移动无线网络能够根据实时覆盖情况动态地调节小区天线参数,需要实现高效且准确的无线覆盖预测。传统的求解方法通过精确的场强预测判断天线参数的优劣,虽然精度很高但需要大量的计算资源,无法满足5G和后5G移动网络通过实时覆盖预测进行射频参数动态调整的实际需求。现采用基于深度神经网络的算法对给定天线参数的覆盖效果进行预测,以取代对目标区域的精确场强预测。数值结果表明:该方法能够在保持计算准确性的同时显著减少计算量,为5G动态网络规划提供基础性参考数据。     

提高近场精度的海洋声学快速场改进模型

为了提高海洋声学快速场模型在近场区域的计算精度,分析了影响经典快速场模型精度的因素,主要包括Bessel函数近似、忽略内行波项以及在水平距离最远处波数采样率过低,这些因素导致快速场模型近场误差较大、远场水平距离最远处结果不正确(计算结束后需要去除水平距离后段的声场)。提出能够提高经典快速场模型近场计算精度的改进模型,改进部分主要是采用保留内行波项的近似Bessel函数,再将近场上下两个基于声源点与对称轴的三角形区域用波数积分解(使用精确Bessel函数)覆盖。算例测试结果表明:与经典快速场模型相比,改进模型可在绝对时间增加较少的情况下,显著提高近场计算精度,综合性能更优;与波数积分法相比,改进模型在误差为同量级的情况下,积分时间大幅降低,实际应用价值更高。     

船舶轴频电场跟踪

针对轴频电场包络跟踪中先验信息缺失的问题,研究了船舶轴频电场跟踪对传感器阵列的基本要求,引入了一种基于最大似然选择的多初值渐进更新扩展卡尔曼滤波算法。建立船舶轴频电场包络跟踪的状态空间模型,用水平电偶极子对船舶轴频电场包络进行建模;建立基于最大似然选择的多初值模型;基于轴频包络信号特征,研究了对传感器阵列排布方式的要求。仿真结果表明,利用轴频电场包络对船舶进行跟踪是可行的,要求传感器阵列至少由3个传感器组成,且3个传感器不在一条直线上;在传感器阵列满足要求的情况下,该算法可以有效解决轴频电场包络跟踪中的先验信息缺失问题,具有较高的实用价值。     

Effect of energy content of the nitraminic plastic bonded explosives on their performance and sensitivity characteristics

Information about the forty nine nitraminic plastic bonded explosives (PBXs) and different nitramines were collected. Fillers of these PBXs are nitramines 1,3,5-trinitro-1,3,5-triazinane (RDX) and β-1,3,5,7-tetranitro-1,3,5-tetrazocane (β-HMX), cis-1,3,4,6-tetranitro-octahydroimidazo-[4,5-d]imidazole (bicyclo-HMX, BCHMX) and ε-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (ε-HNIW, CL-20) which are bonded by polyfluoro-elastomers, polydimethyl-siloxane, poly-glycidyl azide, polyisobutylene, polystyrene-butadiene, poly-acrylonitrile-butadiene and hydroxyl-terminated polybutadiene in addition to a melt cast compositions based on 2,4,6-trinitrotoluene. For thirty two of these PBXs the relationships are specified and analyzed between heats of their combustion and relative explosive strengths; by means of these relationships it might be possible to estimate, which groupings in the macromolecule of binder could be liable to their primary fission in the PBXs initiation. Similarly, for forty two of these explosives, the relationships are described and analyzed between their enthalpies of formation and impact sensitivities; here is especially attention paid to PBXs filled by BCHMX. Specific rate constants from Vacuum Stability Test (VST) of four nitramines and twenty PBXs are introduced into relationships with their enthalpies of formation. Regarding to all the mentioned cases, increasing of energy content of the studied explosives leads to increase of the relative explosive strength or initiation reactivity, respectively. Exception with the opposite trend, the outputs of VST are for BCHMX, where in PBXs are matrices with the esteric plasticizers or the energetic poly-glycidyl azide. Admixture of RDX or HMX, respectively, into the BCHX PBXs gives ternary PBXs whose thermal stability, in the sense of applied VST, is higher comparing to the original binary explosives.     

重塑军队作战力量体系的几点思考

作战力量体系是一个国家军事力量体系的核心组成部分。近些年通过深化国防和军队改革,我军军事力量体系宏观上发生了脱胎换骨的变化,接下来到了对作战力量体系进行重塑的攻坚阶段,本文结合当前作战力量体系发展的一些特点和建设存在的短板,提出了重塑我军作战力量体系的决策建议。      

磁梯度张量的旋转计算方法

为了获得磁梯度张量数据,提出旋转计算磁梯度张量的方法。使倾斜放置的磁梯度计绕竖直轴线转动,利用测得的空间磁梯度数据计算得到磁梯度张量。以磁梯度张量的理论值作为参考,选取一组较优的转动角、倾角和基线长度等模型参数,分析磁力仪三轴指向误差对磁梯度张量计算结果的影响。数值仿真结果表明:该旋转合成方法能够有效获取磁张量信息,合成计算值与理论值之间的差别较小。     

二次流引射对保形非对称喷管性能的影响

发动机与飞机后体结构设计合理与否直接影响发动机的部件匹配和性能。利用三维雷诺平均N-S方程和k-ωSST湍流模型对飞翼布局无人机保形非对称喷管在典型飞行状态下开展了内外流流场特性的数值分析,获得了后体尾喷管推力性能和三维流动特征随二次流压力比的变化趋势。结果表明:发动机喷管落压比条件一定的前提下,通过合理优化二次流通道、增大二次流压力比,可以有效改善后体/喷管主流流场特性;当二次流与主流的流量比在0. 2%～1. 86%内时,后体尾喷管轴向推力系数的变化幅度大约为3%,在一定程度上能够减弱发动机主流的过膨胀程度,减小发动机推力损失,无人机后体尾喷管性能得到显著提高。