访问多个特定相对位置的航天器轨道设计

在航天器轨道设计问题中,将惯性空间中经典的吉布斯三矢量定轨方法拓展到相对运动空间中,给出了一种相对运动条件下的三矢量定轨方法。针对已知轨道的目标航天器,以及二个或三个给定的空间相对位置,基于相对运动方程,提出了设计跟随航天器飞行轨道的数值方法。以轨道面共面或异面,以及目标航天器轨道形状为椭圆或圆,将问题分为四种情况进行约束条件和自由变量个数的分析讨论。对于自由变量个数多于约束方程的情况,额外给定周期重访约束,将各种情况下的特定相对位置访问问题转化为一至二维的非线性方程(组)求解问题。对一维方程求解采用分段黄金分割+割线法进行快速求解;对二维方程组通过网格法搜索迭代初值并通过牛顿迭代快速求解。进一步基于线性模型的解,采用微分修正方法求解了各情况下J2摄动模型下的结果。数值算例验证了提出方法的正确性及有效性。     

Coning motion instability of spinning missiles induced by the delay of strap-down seeker

The strap-down seeker, which combines the seeker’s and the onboard gyro’s measurements to obtain the target information, has been extensively applied by spinning missiles. The response delay of the strap-down seeker, a novel factor that could result in crosscoupling between the acceleration commands in the pitch and yaw channels and subsequently cause the significant deterioration in dynamic stability of the spinning missile equipped with a rate loop, is noted in this paper. The sufficient and necessary stability conditions are also analytically established based on the system equation with complex coefficient, which are further verified by numerical simulations. It could be indicated that the response delay of the strap-down seeker will greatly deteriorate the dynamic stability of the whole guidance system designed by the conventional method. It is also noticed from analysis that the stable region of the combined guidance coefficient is shrunken significantly with the increase of the spinning rate.     

Precessing motion in stratified radial swirl flow

Vortex/flame interaction is an important mechanism for unsteady combustion in a swirl combustion system. Technology of low emission stirred swirl(Te LESS), which is characterized with stratified swirl flow, has been developed in Beihang University to reduce NOXemission. However,large-scale flow structure would be induced in strong swirl flow. Experiments and computational fluid dynamics(CFD) simulation were carried out to investigate the unsteady flow feature and its mechanism in Te LESS combustor. Hotwire was firstly applied to testing the unsteady flow feature and a distinct mode with 2244 Hz oscillation frequency occurred at the pilot swirl outlet.The flow mode amplitude decayed convectively. Large eddy simulation(LES) was then applied to predicting this flow mode and know about its mechanism. The deviation of mode prediction compared with hotwire test was 0.8%. The spiral isobaric structure in pilot flow passage indicates that precessing vortex core(PVC) existed. The velocity spectrum and phase lag analysis suggest that the periodic movement at the pilot outlet was dominated by precessing movement. Negative tangential momentum gradient reflects that the swirl flow was unstable. Another phenomenon was found out that the PVC movement was intermittently rotated along the symmetric axis.     

Structural Design and Control Strategy Analysis of Micro/Nano Transmission Platform

A fully flexure micro/nano transmission platform(MNTP)which has five degrees of freedom is designed on the basis of bridge type amplification mechanism.According to the kinematic theory and the elastic beam theory,the theoretical output displacement equation of the platform is derived,and then piezoelectric actuator(PZT)is calibrated.Meanwhile,a full closed-loop control strategy of the platform is established using the feedforward proportional-integral-derivative(PID)compound control algorithm based on the Preisach model.Moreover,the total transfer function of the micro positioning system is derived,and the calculation method of output signal is acquired.Finally,the theoretical output displacement is verified by finite element analysis(FEA)and positioning experiments.     

基于倒谱的运动模糊图像参数估计方法

通过分析运动模糊图像点扩展函数的倒谱特性,提出了基于倒谱特性的运动模糊参数估计方法。仿真实验结果与理论分析一致,验证了理论分析的正确性。数值实验表明,该方法具有较高的准确性,且具有较强的鲁棒性。     

双曲面自动铺带机床的构型改进

结合预浸带在铺叠过程中的特点,分析了铺带成型压力对铺带工艺过程和最终成型构件的影响.对双曲面的特点进行了研究,阐述了通用5轴铺带机在铺放此类曲面时所遇问题及对策.为了更好地解决传统铺带机由于缺少俯仰自由度所造成的铺带头压力方向与模具表面不能垂直的问题,提出了6轴自动铺带机构型,并分析了改进机构在铺放双曲面时的可行性以及...     

大载荷摆动情况下飞行器姿态控制研究(英文)

天文观测卫星的主敏感器安装在一个具有二自由度、并直接与卫星平台相连的万向支架上。因敏感器的质量和长度不能忽略,故卫星姿态及其质心位置、转动惯量等结构参数将因敏感器与卫星间的角运动而发生改变,因此大载荷摆动情况下的飞行器姿态控制是本文研究的重点。本文根据动量矩定理推导出了存在内部相对运动的二刚体动力学模型,卫星系统的转动惯量将由该模型确定。由卫星的当前及其期望姿态四元数,构建出描述卫星姿态偏差的拟欧拉角;对拟欧拉角进行规范化处理,以保证三通道所对应的拟欧拉角分量分别由控制力矩的3个分量所控制。之后,提出了基于拟欧拉角的姿态开关控制律,该控制律可保证三通道所对应的相轨迹可沿开关线滑向坐标原点(其期望状态)。仿真结果表明,即使是在结构不对称和三通道严重耦合的情况下,该控制律也能保证卫星姿态可以得到较好的控制。     

空间近程高速相对运动方程的状态转移矩阵

分析了空间近程高速相对运动的特点,建立了描述近程高速相对运动的线性微分方程组,并给出了状态转移矩阵与解析解。仿真结果表明:对于HEO-GEO近程高速相对运动,所建方程的相对距离计算误差仅为16 cm,不足Hill方程计算误差的15%。所给出的状态转移矩阵对于实现空间目标拦截等任务的实时高精度相对导航和制导算法具有一定的应用价值。     

考虑刚体/弹性耦合的飞机动稳定性研究

以大展弦比无人机为例,研究刚体运动对飞机纵向气动伺服弹性(ASE)稳定性以及弹性运动对飞机纵向飞行力学稳定性的影响。针对带有反馈控制的飞机,建立了时域的刚体/弹性耦合运动方程;以刚体运动频率与一阶弹性频率的比值为参数,分别研究有无刚体模态时的ASE系统稳定裕度和有无弹性模态时的飞行力学稳定裕度。数值仿真表明,当飞机刚体运动频率与一阶弹性频率的比值大于0.01时,飞机刚体运动对ASE稳定裕度的影响逐渐显现;当该频率比值大于0.03时,飞机弹性运动对飞行力学稳定裕度的影响开始突现;当该频率比大于1时,刚体弹性耦合效应不可忽略。     

威海天文台1米望远镜天体测量试验

利用威海天文台1米望远镜观测了2009年10月7日晚的疏散星团M39.观测过程中使用了I滤光片,并将CCD绕光轴旋转90°分别成像.使用最新的UCAC3星表和Platais的自行星表归算表明,该望远镜具有良好的天体测量性能,最好的单次位置测量精度达到了4～5 milli-arcsec.此外,观测资料还发现UCAC3星表具有明显的自行不准确性,证实了文献[14]的最新发现.