临近空间大气压力传感器现场校准装置研究

本文针对临近空间大气压力传感器现场校准需求,介绍了临近空间大气压力传感器现场校准装置工作原理, 进行理论分析与仿真,提出需突破的关键技术,给出了不确定度预估。     

有翼再入飞行器的超/高超声速气动力工程方法

有翼再入飞行器气动力的工程计算方法尚有待进一步完善,计算精度有待进一步提高。文章根据有翼再入飞行器的气动布局特点,改进和发展了一套适于其气动布局的部件划分策略和压强计算选取准则。以此对航天飞机轨道器和类X-34飞行器的纵向气动力特性进行工程计算,并与其风洞试验和数值模拟结果进行对比分析。结果表明,文中的工程计算方法在马赫数3以上的超/高超声速范围内可准确预测有翼再入飞行器的升阻特性,其中升力系数和阻力系数误差小于10%;并可准确预测俯仰力矩特性随迎角改变的变化规律。与现有方法相比,文中的部件划分策略和压强计算选取准则在升阻特性精度相当情况下,可明显提高俯仰力矩的预测精度,并反映飞行器表面的压强分布特征。     

新能源汽车电机发展趋势及测试评价研究

为缓解能源短缺与环境污染问题,新能源汽车得到了迅速发展、推广,并成为当今汽车产业的重要研究方向。以新能源汽车电机的种类及国内外新能源汽车电机选型应用情况出发,对新能源汽车电机的发展趋势和对评价有关的测试项目作了分析研究。     

航行体出水过程头部流场载荷特性分析

航行体高速出水过程中流场变化剧烈且复杂,为研究其水动力载荷变化,采用均质多相流模型及空化模型,开展了出水过程的数值模拟研究.通过数值模拟分析了不同头部形状及出水攻角对航行体出水过程流场的影响.分析结果表明:空化性能较强的头形能产生头部空泡,并在穿越水面时溃灭,引起较为强烈的流场变化并产生较高压强作用于航行体壁面.而空泡溃灭过程也会因头形的不同而略有差别.有攻角出水时空泡溃灭呈现非对称性,因此形成了较大的力矩.而力矩的变化情况也受攻角影响较大.      

Prospects of sea launches for Chinese cryogenic liquid-fueled medium-lift launch vehicles

This paper introduces the sea-launch technology of a cryogenic liquid-fueled medium-lift rocket. It first reviews the current state of sea launch technology, and then gives a brief introduction of China’s New Generation Medium-lift Launch Vehicle (NGMLV). The innovations in the NGMVL, such as responsive test and launch control, a H³ launch model, and unmanned operations, provide convenience for sea launches. Based on these innovations, this paper proposes a sea launch scheme, including the system configuration, test and launch processes, and an improved adaptive design for the rocket. Then, the launch platform is discussed in detail, which integrates the functions of sea transportation, assembly and test, as well as technical and launch areas. The layout and function divisions, fluid filling, gas supply and distribution systems, and lossless storage technology of LH2 are described in order. This breakthrough in sea launch technology will enable China to launch medium and large satellites and constellations ‘both on land and sea’, especially into low-inclination Low-Earth Orbits (LEOs), and it allows China to remain competitive in the fast-paced space industry.     

应用保护映射理论的高超声速飞行器自适应控制律设计

针对高超声速飞行器包线范围广、参数变化大的控制需求,应用保护映射理论提出一种高超声速飞行器的自适应控制律设计方法。首先建立整个飞行包线内的线性变参数(LPV)模型,在参数变化边界点设计一个初始的控制结构和参数,然后基于保护映射理论分析初始控制结构使闭环系统稳定的参数范围,通过迭代自动获取整个包线内满足性能指标的控制参数,进而通过多项式拟合设计出高超声速飞行器自适应控制律。所提出的方法能够根据初始控制结构自动寻找一系列满足性能要求的控制器参数,并确定这些控制参数满足闭环系统稳定的设计范围。仿真结果表明,所设计的自适应控制律能够确保高超声速飞行器大包线的设计要求,实现闭环系统的鲁棒稳定。     

高性能飞机发展对控制理论的挑战

根据笔者30余年来飞行试验研究的实践,从实际飞行的角度简要综述了影响飞行安全的大迎角过失速机动、超低空重载空投、飞行器突发故障和无人机控制方法研究。描述了操纵稳定性飞行试验获取飞机模型的手段和通常飞行控制器设计对模型的近似,给出了8个飞行鲁棒控制的研究问题;对超低空重载空投控制方法进行了描述,并给出了飞行器出现故障时突变模型和容错控制方法;同时,描述了测量对飞行控制特别是对保障无人机飞行安全的重要性,指出了飞行控制方法研究存在的部分问题,并建议有关高校研究单位从稳定性很好的四旋翼转向固定翼或单旋翼战术无人机等高层次研究。     

高超声速飞行器推进系统建模

为在高超声速飞行器设计初期快速地获得推力和推力矩,以满足控制相关分析和建模需要.提出一种推进系统建模方法,基于激波/膨胀波相交理论来建模与机身耦合的进气道模型;用有摩擦变截面加热管来描述双模态燃烧室;将内喷管建模成一维变截面摩擦管,采用动量定理估算推力,并通过曲线拟合得到推力的解析表达式.与CFD计算结果相比,该模型计算得到双模态冲压发动机入口气流马赫数和温度误差小于5%,压强误差小于10%;计算得到的推力随马赫数、燃油当量比和迎角的增大而增加,随高度增加而减小,单个状态平均计算时间小于0.5s.计算结果表明:该建模方法满足面向控制建模的效率和精度需求,有助于此类飞行器设计初期的动力学和控制相关的分析和设计.      

UAV navigation in high dynamic environments: A deep reinforcement learning approach

Unmanned Aerial Vehicle (UAV) navigation is aimed at guiding a UAV to the desired destinations along a collision-free and efficient path without human interventions, and it plays a crucial role in autonomous missions in harsh environments. The recently emerging Deep Reinforcement Learning (DRL) methods have shown promise for addressing the UAV navigation problem, but most of these methods cannot converge due to the massive amounts of interactive data when a UAV is navigating in high dynamic environments, where there are numerous obstacles moving fast. In this work, we propose an improved DRL-based method to tackle these fundamental limitations. To be specific, we develop a distributed DRL framework to decompose the UAV navigation task into two simpler sub-tasks, each of which is solved through the designed Long Short-Term Memory (LSTM) based DRL network by using only part of the interactive data. Furthermore, a clipped DRL loss function is proposed to closely stack the two sub-solutions into one integral for the UAV navigation problem. Extensive simulation results are provided to corroborate the superiority of the proposed method in terms of the convergence and effectiveness compared with those of the state-of-the-art DRL methods.     

Aerodynamic performance of owl-like airfoil undergoing bio-inspired flapping kinematics

Natural flyers have extraordinary flight skills and their prominent aerodynamic performance has attracted a lot of attention. However, the aerodynamic mechanism of birds' flapping wing kinematics still lacks in-depth understanding. In this paper, the aerodynamic performance of owl-like airfoil undergoing bio-inspired flapping kinematics extracted from a free-flying owl wing has been numerically investigated. The overset mesh technique is used to deal with the large range movements of flapping airfoils. The bio-inspired kinematics consist of plunging and pitching movement. A pure sinusoidal motion and a defined motion composed of plunging of sinusoidal motion and pitching of the bio-inspired kinematics are selected for comparison. The other two NACA airfoils are also selected to figure out the advantages of the owl-like airfoil. It is found that the cambered owl-like airfoil can enhance lift during the downstroke. The bio-inspired kinematics have an obvious advantage in lift generation with a presence of higher peak lift and positive lift over a wider proportion of the flapping cycle. Meanwhile, the bio-inspired motion is more economical for a lower power consumption compared with the sinusoidal motion. The sinusoidal flapping motion is better for thrust generation for a higher peak thrust value in both upstroke and downstroke, while the bio-inspired kinematics mainly generate thrust during the downstroke but produce more drag during the upstroke. The defined motion has similar lift performance with the bio-inspired kinematics, while it consumes more energy and generates less thrust. The unsteady flow field around airfoils is also analyzed to explain the corresponding phenomenon. The research in this paper is helpful to understand the flight mechanism of birds and to design a micro air vehicle with higher performance.