变形破碎特性对SLD结冰过程影响

基于结冰过程数值模拟,针对过冷大水滴（SLD）条件下的变形破碎特性及其对成冰过程影响进行了研究。利用动态阻力计算模型,分析了水滴变形对水滴运动轨迹影响,采用基于泰勒类比理论的计算模型,研究了水滴破碎过程、子液滴粒径分布特性等。完成了NACA 0012翼型典型SLD结冰算例的数值分析,与参考文献计算结果和实验数据进行对比。结果表明:对于SLD结冰,变形和破碎主要改变了水滴运动轨迹和表面撞击水分布,使水滴撞击极限变小,在加入变形破碎特性的计算模型后,可以较好预测结冰极限位置和冰形轮廓,说明该方法对SLD变形破碎效应及其影响的模拟是可行和正确的。      

基于强化学习的多无人机避碰计算制导方法

针对大量固定翼无人机在有限空域内的协同避碰问题,提出了一种基于多智能体深度强化学习的计算制导方法。首先,将避碰制导过程抽象为序列决策问题,通过马尔可夫博弈理论对其进行数学描述。然后提出了一种基于深度神经网络技术的自主避碰制导决策方法,该网络使用改进的Actor-Critic模型进行训练,设计了实现该方法的机器学习架构,并给出了相关神经网络结构和机间协调机制。最后建立了一个实体数量可变的飞行场景模拟器,在其中进行"集中训练"和"分布执行"。为了验证算法的性能,在高航路密度场景中进行了仿真实验。仿真结果表明,提出的在线计算制导方法能够有效地降低多无人机在飞行过程中的碰撞概率,且对高航路密度场景具有很好的适应性。     

针栓式喷注器无旋锥形液膜线性不稳定分析

将离心式喷嘴锥形液膜破碎模型应用于针栓式喷注器,对无旋锥形液膜进行了线性不稳定分析。求解色散方程获得了色散关系曲线,分析了无旋锥形液膜表面波发展过程。研究了喷注压降、喷注通道长宽比、液膜半锥角以及正弦模式扰动波加权因子等参数对无旋锥形液膜无量纲破碎时间和破碎长度的影响。结果表明:正弦模式扰动波比曲张模式扰动波增长更快,并且更不稳定。正弦模式扰动波在无旋锥形液膜破碎过程中占优,并且喷注压降越大,液膜破碎的越快。喷注通道长宽比的增加会使得无量纲破碎时间和破碎长度近似线性增大。针栓式喷注器设计时,为利于液膜破碎,喷注通道长宽比应取小值,而液膜半锥角应取大值。     

多弹最优协同诱导突防制导律

针对多弹协同突防问题提出了一种最优协同诱导突防制导律，基于诱导碰撞策略实现有效突防。首先构建了多弹协同对抗非线性模型，并基于零控脱靶量和零控碰撞角进行线性化。然后考虑拦截弹和进攻弹均为二阶驾驶仪动力学特性条件下，将各拦截弹碰撞距离和拦截弹碰撞角扩展到状态方程中，并利用状态转移矩阵降低状态方程维度。在此基础上,设计包含碰撞角约束的快收敛扩展性能指标函数，采用碰撞时间匹配策略推导出多弹最优协同诱导解析制导律的一般形式，并给出2枚进攻弹对2枚拦截弹典型场景下的突防制导律。最后通过典型场景仿真验证了最优协同诱导突防制导律的有效性。     

Extended dynamic system modulation for real-time obstacle avoidance

In this paper, a novel real-time obstacle avoidance method based on Dynamic System (DS), is proposed. The proposed method ensures the impenetrability of multiple convex obstacles by online modulating the original velocity field of the DS. It can be applied to perform obstacle avoidance in the state space of the DS with both autonomous and non-autonomous DS-based controllers. While realizing the obstacle avoidance, the equilibrium points of the original DS can be saved. The modulation matrix form is extended based on the earlier dynamic system modulation methods of the literature. The asymmetric modulation provided by this method allows the modulated DS to satisfy the dynamic constraints of a class of DSs. In addition, the proposed method has the inherent ability of multiple-obstacle avoidance and the direction selectivity of avoidance maneuver. Moreover, to solve the simultaneous guidance and obstacle avoidance problem, a guidance law for Unmanned Aerial Vehicles (UAVs) based on the proposed method, is designed. Finally, a numerical simulation is performed to analyze the performance of the proposed method and the obstacle avoidance guidance law.     

Model predictive control for close-proximity maneuvering of spacecraft with adaptive convexification of collision avoidance constraints

This study investigated model predictive control (MPC) for close-proximity maneuvering of spacecraft. It is essential for a designed MPC to effectively handle collision avoidance between the servicer spacecraft and the client spacecraft, especially while the client is rotating. The rotating motion of the client leads to dynamic changes in the collision avoidance constraints, which increases the difficulty of optimizing the control input in the MPC framework. Therefore, this study presents a method to improve the performance and computational efficiency of MPC for rendezvous and docking with a nonrotating or rotating client. An ellipsoid is adopted to model the client’s keep-out zone (KOZ). Given the spherical KOZ of the servicer, an expanded ellipsoid is introduced to describe the KOZ for the center of mass of the servicer and modeled as a nonlinear constraint. The linearization method for reference points located at the expanded ellipsoid is adopted to convexify the nonlinear constraints. The reference points are adaptively determined according to the positions of the servicer, client, and expanded ellipsoidal KOZ. The resulting hyperplanes are then used to describe the collision avoidance constraints. By utilizing the aforementioned strategies, combined with the calculated reference points, an adaptive convex programming algorithm suitable for real-time implementation of MPC is derived. The performance of the proposed method is demonstrated through numerical simulations.     

航天器反应式碎片规避动作规划方法

提出一种航天器反应式碎片规避动作规划方法，首先以扰动流体动态系统(IFDS)算法作为动作规划的基础算法，通过其中的总和扰动矩阵对航天器的轨道速度矢量进行修正，实现轨道机动规避；然后，建立基于双延迟深度确定性策略梯度(TD3)深度强化学习算法的反应式动作规划方法，通过TD3在线优化IFDS规划参数，实现对碎片群的“状态-动作”最优、快速规避决策。在此基础上，将优先级经验回放和渐进式学习策略引入该方法中，提升训练效率。最后，仿真结果表明，所提方法可使航天器安全规避多发、突发、动态且形状各异的空间碎片群，且具有较好的实时性。     

无人机防相撞空中威胁态势的探测与告警研究

空中威胁态势探测与告警是无人机飞行防相撞预警的关键。为此,提出一种基于航迹预测的无人机防相撞空中威胁态势探测与告警方法。在该方法中,先采用滑动窗多项式拟合法对入侵机航迹进行动态预测,然后,在航迹预测基础上,利用无人机与入侵机飞行信息,建立针对入侵机的无人机动态避撞区,最后,结合静态保护区原理,对特定飞行场景下的无人机飞行冲突趋势、空中危险接近趋势和飞行碰撞趋势的探测与告警。仿真实例验证了所提出方法的有效性,也验证了其用于无人机飞行防相撞预警的可行性。     

气液比对气液同轴离心式喷嘴缩进室内流动过程的影响

为了研究气液同轴离心式喷嘴缩进室内部非定常流动过程,采用Level Set和VOF相耦合的方法结合网格自适应技术对缩进长度为8 mm的液体中心式气液同轴离心式喷嘴流动过程进行了数值仿真研究,计算得到了较为精细的液膜一次破碎过程、流场结构和压力振荡特性。结果表明：液膜的破碎模式受气液比的影响较大,随气液比的增加,液膜破碎模式由曲张表面波主导的破碎变为穿孔破碎。此外,清晰获得了自激振荡过程,分析了缩进室内部压力场及速度场分布特征,研究发现随着气体压降增加,气体环缝出口会出现膨胀波和激波,形成一个“扇环形”的超声速流场区域；激波后气流分离,出现旋涡,形成局部高压区,旋涡中心随激波面周期性地上下移动,致使局部压力出现周期性振荡。