基于圆型限制性三体问题模型的行星卫星逃逸能量研究

 基于由飞行器、行星及其卫星组成圆型限制性三体问题模型,通过庞加莱映射的方法,研究了飞行器从行星卫星附近逃逸的问题。在Jacobi常数确定的前提下,通过逆向积分,飞行器从L1或L2点附近返回近月点,得到近月点速度出发速度。研究结果表明绕飞L1点和L2点逃逸行星卫星需要的最低能量是不同的,从月球表面逃逸所需的速度脉冲分别比开普勒算法节省46.5m/s和42.3m/s,且均小于Villac等人在Hill模型下得到38.9m/s,从而改进了Villac等人的相关工作,同时也给出了从太阳系主要行星卫星表面逃逸所需的最小能量。     

The Effects of Transverse Magnetic Field and Density Variations on the Particle Energy Spectra in a Reconnecting 3D Current Sheet

Electron and proton acceleration by a super-Dreicer electric field is further investigated in a non-neutral reconnecting current sheet (RCS) with a variable plasma density. The tangential B _z and transverse magnetic field components B _x are assumed to vary with the distances x and z from the X nullpoint linearly and exponentially, respectively; the longitudinal component (a ‘guiding field’) is accepted constant. Particles are found to gain a bulk of their energy in a thin region close to the X nullpoint where the RCS density increases with z exponentially with the index λ and the tangential magnetic field B _x also increases with z exponentially with the index α. For the RCS with a constant density (λ = 0), the variations of the tangential magnetic field lead to particle power-law energy spectra with the spectral indices γ₁ being dependent on the exponent α as: for protons and for electrons in a strong guiding field (β > 10⁻²) and for electrons in a moderate or weak guiding field (β > 10⁻⁴). For the RCS with an exponential density increase in the vicinity of the X nullpoint (λ≥ 0) there is a further increase of the resulting spectral indices γ that depends on the density exponent index λ as for protons and for electrons in weaker guiding fields and as for electrons in stronger guiding fields. These dependencies can explain a wide variety (1.5–10) of particle spectral indices observed in solar flares by the variations of a magnetic field topology and physical conditions in a reconnecting region. This can be used as a diagnostic tool for the investigation of the RCS dynamics from the accelerated particle spectra found from hard X-ray and microwave emission.     

系统科学与民航安全文化建设

用现代系统理论观战,审视了中国民航安全文化建设的历史经验,得出了有益于安全文化建设的指导思想。首先,通过对安全文化与民航系统的协同问题的分析,探讨了对”安全第一“原则的深层次理解及在实际工作中的把握;其次,研究了系统的运动与安全文化发展的内在关系,提出了保证安全文化建设健康发展的思路。     

蒙皮拉形加载轨迹优化

对双曲度飞机蒙皮拉伸成形问题,探讨了加载轨迹对成形质量的影响,提出了采 用最优化理论与算法和有限元数值模拟相结合,确定最优拉形加载轨迹的原理与方法.分析 了单凸双曲度蒙皮拉伸成形常用加载轨迹的成形特点和不足,采用有限元数值模拟和序列二 次规划相结合的方法,通过正交试验设计建立近似响应模型和设计变量的取值范围,以减小 卸载回弹提高贴模度为研究目标、最大主应变为约束条件建立最优化数学模型,确定最合理 的拉形加载轨迹.优化结果表明成形零件贴模度和应变分布与厚度的均匀程度均有明显提高 .      

基于改进粒子群算法辨识Volterra级数的目标机动轨迹预测

目标机动轨迹预测是空战态势感知和目标威胁评估的重要前提。针对传统目标机动轨迹预测模型复杂度大、预测精度低等问题，结合目标机动轨迹时间序列的混沌特性，提出一种基于相空间重构理论和Volterra泛函级数的目标机动轨迹预测模型。该模型首先采用0-1检测法验证了目标机动轨迹时间序列具有混沌特性；其次，利用C-C法确定嵌入维数和时间延迟，对目标机动轨迹时间序列进行了相空间重构；然后，引入Volterra泛函级数预测模型，为了克服高阶Volterra核函数求解复杂的难题，提出一种混沌变异自适应粒子群算法，构建一种基于改进粒子群算法辨识的Volterra级数预测模型，并将其应用于目标机动轨迹预测；最后，将所提算法与卡尔曼滤波算法以及机器学习算法进行单步和多步预测对比，同时将改进粒子群算法与其他智能算法进行性能比较。仿真结果表明：所提预测模型具有良好的单步和多步预测性能，改进的粒子群算法具有参数辨识精度高、收敛速度快的优点。     

集群无人机队形重构及虚拟仿真验证

队形重构是集群无人机（UAV）控制的重要问题，指无人机按照要求安全、无碰撞地从一个队形变换到另一个队形，其难点在于快速规划最优安全轨迹并控制无人机进行轨迹姿态的高精度跟踪。针对集群无人机队形重构的上述问题，首先，基于CAPT（Concurrent Assignment and Planning of Trajectories）算法，解决了多无人机的目标分配和轨迹生成的实时性问题，实现了集群无人机的最优安全路径规划；其次，提出一种有限时间多变量积分滑模连续控制算法，解决了无人机轨迹姿态的高精度跟踪问题，并通过MATLAB仿真验证了该控制算法的有效性；最后，为了更加真实直观地演示无人机三维仿真效果，建立了基于Gazebo-ROS的无人机仿真平台，实现了12架四旋翼无人机队形重构"建模-仿真-可视化"的一体化仿真演示，验证了上述路径规划算法和轨迹姿态控制算法的有效性。     

具有时间约束的无人机遗传算法航迹规划

为无人机进行航迹规划不仅要满足路径的有效性,还需要考虑无人机的到达时间约束.将遗传算法应用于动态环境中无人机的航迹规划,通过编码生成初始航迹,确定合理的适应度函数和进化操作,同时根据要求到达时间约束为每个航迹加入过点速度和到达时间信息,最终搜索规划出可飞且满足时间约束的航迹.在仿真实验中实现了针对移动目标的规划和突然出现威胁的局部重规划.     

Analysis of precipitable water vapour characteristics from GNSS measurements during the snow season in Liaoning Province,China

Global Navigation Satellite System (GNSS) remote sensing precipitable water vapour (PWV) data from November 2015 to March 2019 were combined with snowfall observation data and used to analyse PWV characteristics in Liaoning Province during the snow season (from November to March the following year) and their relationship with snowfall. The potential of using GNSS for PWV measurements was demonstrated using sounding data with a correlation coefficient higher than 0.9 and a mean bias error lower than 0.5 mm. According to the GNSS PWV data gathered at 30-min intervals from 68 GNSS stations in Liaoning during the snow season, the monthly PWV average was highest in November and lowest in January. Negative correlations were found between PWV and altitude. Most of the water vapour was concentrated in the low layer of the atmosphere, and the contribution of this vapour to the PWV was higher during the snow season than in summer. A total of 43 snow cases were identified using the snowfall records from 53 GNSS stations, and the characteristics of PWV during these snowfalls were analysed. An increase in PWV was observed before snowfall events. Moreover, the influence of synoptic systems and air mass origins on PWV was analysed based on National Centers for Environmental Prediction (NCEP) reanalysis data and the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model. The results show that the water vapour condition was better when the synoptic systems or air masses came from areas south of Liaoning.     

弹道跟踪数据融合处理的快速算法

针对弹道跟踪数据融合处理中的大计算量环节研究了快速算法。用样条函数表示弹道参数,建立了多测元的联合观测模型和弹道参数的非线性融合计算模型,给出了弹道参数的求解算法,分析了弹道参数融合计算中的大型矩阵运算问题,利用基础线性代数函数库提高了大型矩阵的运算速度。建立了样条模型计算的非线性约束优化模型,给出了确定样条节点位置的优化算法,通过分析样条模型的计算原理设计了并行算法,实现了样条模型的并行化计算。仿真结果表明,弹道参数融合计算和样条模型计算的效率都得到了显著提高,计算时间减少了65.47%,对缩短数据处理周期有重要意义。