拦截弹道快速设计方法

针对传统优化算法在解决多约束条件下拦截弹道设计问题时迭代计算耗时过长的缺点,提出了一种快速拦截弹道设计方法.该方法基于人工神经网络的非线性拟合技术,先通过普通优化算法进行离线样本计算,对样本中目标位置和优化得到的飞行程序参数进行输入-输出映射拟合训练,从而实现在给定目标位置的情况下对最优飞行程序参数的快速计算,达到提高拦截弹道设计效率的目的.经过数值仿真验证,将该方法应用于拦截弹道设计,在保证良好命中精度的同时,设计所需的计算时间大大减少,从而提高了弹道设计的时效性.      

Analysis of spacecraft motion under constant circumferential propulsive acceleration

This paper reassesses the classical circumferential-thrust problem, in which a spacecraft orbiting around a primary body is subjected to a propulsive acceleration of constant modulus, whose direction is in the plane of the parking orbit and orthogonal to the spacecraft-primary line. In particular, a new formulation is proposed to obtain a reduction in the number of differential equations required for the study of the spacecraft propelled trajectory. The mathematical complexity of the problem may be further reduced assuming that both the propulsive acceleration modulus and the spacecraft distance from the primary body are sufficiently small. In that case, an approximate model is able to accurately describe the characteristics of the propelled trajectory when the parking orbit is circular. Finally, using the data obtained by numerical simulations, the approximate model is extended to generate a set of semi-analytical equations for the analysis of a classical escape mission scenario.     

地月循环轨道动力学建模与计算研究

根据地月循环轨道的概念,按照生成第二类周期轨道的弧段进行分类,并讨论了其共振性与对称性在轨道设计与应用中的作用。然后归纳了三种循环轨道的动力学建模与计算方法及其轨道延拓策略,最后总结了三种方法的利弊和应用轨道类型。对地月系统循环轨道的研究和分析,能够为我国未来载人登月工程提供一种新的思路与理论支持。     

一种改进的UAV三维航迹实时规划算法

航迹规划对于战场环境中无人机完成其作战任务具有非常重要的意义.针对真实战场环境中低空无人机的三维航迹实时规划问题,构建了一个更加真实的战场威胁精简模型;提出遗传个体的基因优劣对比度,改进一种共享小生境遗传算法中编码基因的遗传特性.经过改进,增大优化基因的遗传概率,实现提高小生境遗传算法的全局优化能力和收敛速度,增强航迹规划的实时性.对三维数字地形空间进行定长网格编码,将改进的小生境遗传算法应用于三维虚拟战场环境中的无人机航迹规划,实验验证了改进算法的有效性,并能满足在线航迹规划的实时性要求.     

Simulation study of motion of charged particles trapped in Earth’s magnetosphere

This article aims to understand the motion of the charged particles trapped in the Earth’s inner magnetosphere. The emphasis is on identifying the numerical scheme, which is appropriate to characterize the trajectories of the charged particles of different energies that enter the Earth’s magnetosphere and get trap along the magnetic field lines. These particles perform three different periodic motions, namely: gyration, bounce, and azimuthal drift. However, often, the gyration of the particle is ignored, and only the guiding center of the particle is traced to reduce the computational time. It is because the simulation of all three motions (gyro, bounce, and drift) together needed a robust numerical scheme, which has less numerical dissipation. We have developed a three-dimensional test particle simulation model in which the relativistic equation of motion is solved numerically using the fourth and sixth-order Runge-Kutta methods. The stability of the simulation model is verified by checking the conservation of total kinetic energy and adiabatic invariants linked with each type of motion. We found that the sixth-order Runge-Kutta method is suitable to trace the complete trajectories of both proton and electron of a wide energy range, 5 keV to 250 MeV for L = 2 – 6. We have estimated the bounce and drift periods from the simulations, and they are found to be in good agreement with the theory. The study implies that a simulation model with sixth-order Runge-Kutta method can be applied to the time-vary, non-analytical form of magnetic configuration in future studies to understand the dynamics of charged particles trapped in Earth’s magnetosphere.     

基于模糊理论的跳跃轨迹多目标优化设计

针对探月返回跳跃轨迹的多目标优化设计问题,提出了一种基于模糊理论的优化设计方法,并对非线性隶属度函数对优化结果的影响进行了研究.首先,将连续的无限维优化问题进行离散化,转化为非线性规划问题;其次,用隶属度函数将各个子目标进行模糊化,将多目标优化问题转化为求模糊判决隶属度函数的最大值问题;最后,求解经过模糊化的非线性规划问题.分析了探月返回跳跃轨迹的特性,表明模糊多目标优化更能体现决策者的偏好.构造了具有不同凹凸性、不同形状的非线性隶属度函数,比较了它们对优化结果的影响,结果表明隶属度函数影响多目标模糊优化结果的首要因素是隶属度函数的凹凸性.     

Properties of transit trajectory in the restricted three and four-body problem

In the restricted three-body problem if the Jacobi constant is just below the value corresponding to Lagrangian point only a little neck exists around the equilibrium point and capture trajectories are indicated as low-energy. Capture properties depend on the dynamics around these critical points and qualitative results can be obtained using linearized systems. In this paper, to study transit trajectory properties in the restricted three and four-body problem, the Earth–Moon–Sun–Satellite system is considered as example and studied using different models. In the circular restricted three-body problem (Earth–Moon–Satellite), transit, non transit and asymptotic trajectories, are easily identified by using the principal reference frame. Dynamics around Lagrangian point are then studied introducing the Moon eccentricity into the elliptical restricted three-body model. A preferential region for transit orbit is individuated and studied as a function of eigenvalue properties. To introduce the Sun effect, the bi-circular four-body model is considered and dynamics around Lagrangian points studied as a function of angular distance between Earth–Sun and Earth–Moon line. Finally, results obtained in the elliptical three-body model and bi-circular four-body model, are compared with numerical simulations using real Sun–Moon–Earth ephemeris.     

水滴撞击特性的高效计算方法

针对拉格朗日方法计算水滴撞击特性效率低、通用性差等问题,发展了一种水滴撞击特性的高效计算方法。在求解绕流流场的基础上,结合逐级结构化管理的边界信息存储方式,采用目标扩散追踪方法对水滴所在网格单元进行快速计算,并插值得到该点处的流场信息,逐个求解水滴运动方程得到各水滴的运动轨迹,从而确定水滴撞击极限、收集系数等撞击特性参数。通过对NACA0012翼型、GA-W(1)两段翼型和某三段翼型的计算得到不同状态下的水滴撞击特性,计算结果表明,该方法与传统方法相比具有计算效率高、结果可靠、通用性好等优点。     

发动机进气道水滴撞击特性分析

针对某发动机进气道的防冰系统设计,对进气道的水滴撞击特性进行了研究.在对进气道流场进行计算的基础上,采用差分法对水滴运动方程进行了数值求解,得到了水滴运动轨迹,从而确定了水滴的撞击极限、总收集系数和局部水收集系数等水滴撞击特性参数;此外,还研究了飞行高度、飞行速度及水滴半径对水滴撞击特性的影响;研究发现水滴撞击极限、总收集系数和局部水收集系数随飞行速度的减小、飞行高度的增加或者水滴半径的增加而增大.这些为进气道的防冰系统设计奠定了基础.