平衡空间到模态空间的反映射模型降阶方法

针对内平衡降阶方法物理意义不清晰,平衡坐标无法由传感器直接测量的问题,文章基于柔性航天器动力学模型,提出了通过反映射实现平衡空间到模态空间的模型降阶方法。利用状态空间线性变换传递函数和特征值的不变性,通过平衡降阶模型零极点传递函数获得了与原系统相对应的特征频率,给出了平衡降阶模型与原模态子空间的映射关系,成功构造了反映射矩阵。频率响应及可控可观性分析结果显示,模态子空间降阶模型能够准确找到与原模型相匹配的状态变量,物理意义清楚,便于控制系统使用。     

带有偏心轮的锁钩式结构锁运动性能和力分析

锁钩式结构锁因动作速度快和误差补偿能力好而广泛应用于空间对接装置中。文章对两航天器空间对接正常拉紧过程中带有偏心轮的锁钩式结构锁进行了受力分析 :分析了对接框下端面粗糙度对结构锁拉紧力的影响 ;针对“仅一组钢索传动”的故障情况 ,进行了结构锁的力学计算 ;提出了改善结构锁啮合性能的方法———增大主动钩特征点的 y坐标值 ,尽可能减小偏心轮偏心距。导出了主动钩啮合面法线与对接框平面法线的夹角计算公式以及结构锁法向载荷在啮合间隙误差影响下的计算公式 ,为设计提供依据     

软隔板双脉冲发动机二级点火延迟试验分析

在进行软隔板双脉冲发动机的试验研究时发现,二级脉冲出现远远超过指标要求的点火延迟.为了改进这种状况,从点火药量和隔板厚度两方面进行试验研究.结果表明单纯增加点火药量使得隔板破裂太快,能量过早地释放;而单纯增加隔板厚度使得隔板不能按预定位置和方式破裂,影响工作性能.最终结合软隔板双脉冲发动机的工作特点,从两方面同时改进,达到了比较合理的点火延迟.     

任意形状目标的多分辨时域(MRTD)散射特性分析

应用三维多分辨时域(Three-dimensionalmu ltiresolution time-dom ain,3D-M RTD)方法研究一些具有任意形状目标的雷达散射截面(R adar cross-section,RCS),其中M RTD中的电磁场量用小波函数Battle-Lemarié的三次样条尺度函数展开。推导出了严格的M RTD方法的场的时空迭代关系式及M RTD方法的三维散射模型,其中包括基于最近邻网格近似的表面等价电流的计算、散射场的近-远场变换和基于离散的傅里叶(Fourier)变换的RCS计算式。采用M RTD方法(并采用其适用的近似网格剖分方法)研究了从低频(瑞利和谐振模式)到高频(准光学模式)的几种结构的双-站(Bi-static)RCS模式。与传统的时域有限差分(Finited ifference time-do-main,FDTD)法的结果进行了比较,发现M RTD方法较FDTD方法节省相当的计算空间和时间。     

Fault tolerant small satellite attitude control using adaptive non-singular terminal sliding mode

The Attitude Control System (ACS) plays a pivotal role in the whole performance of the spacecraft on the orbit; therefore, it is vitally important to design the control system with the performance of rapid response, high control precision and insensitive to external perturbations. In the first place, this paper proposes two adaptive nonlinear control algorithms based on the sliding mode control (SMC), which are designed for small satellite attitude control system. The nonlinear dynamics describing the attitude of small satellite is considered in a circle reference orbit, and the stability of the closed-loop system in the presence of external perturbations is investigated. Then, in order to account for accidental or degradation fault in satellite actuators, the fault-tolerant control schemes are presented. Hence, two adaptive fault-tolerant control laws (continuous sliding mode control and non-singular terminal sliding mode control) are developed by adopting the nonlinear analytical model to describe the system, which can guarantee global asymptotic convergence of the attitude control error with the existence of unknown external perturbations. The nonlinear hyperplane based Terminal sliding mode is introduced into the control law design; therefore, the system convergence performance improves and the control error is convergent in “finite time”. As a result, the study on the non-singular terminal sliding mode control is the emphasis and the continuous sliding mode control is used to compare with the non-singular terminal sliding mode control. Meanwhile, an adaptive fuzzy algorithm has been proposed to suppress the chattering phenomenon. Moreover, several numerical examples are presented to demonstrate the efficacy of the proposed controllers by correcting for the external perturbations. Simulation results confirm that the suggested methodologies yield high control precision in control. In addition, actuator degradation, actuator stuck and actuator failure for a period of time are simulated to demonstrate the fault recovery capability of the fault tolerant controllers. The numerical results clearly demonstrate the good performance of the adaptive non-singular terminal control in the event of actuator fault compare with the continuous sliding mode control.     

大方位失准角MIMU空中对准建模及半物理仿真

由于快速性的要求,微小型无人机不经过地面精确初始对准就升空作业,因此MIMU(Micro Inertial Measurement Unit)空中对准在大失准角下进行. 为了提高微小型无人机空中的反应速度和作业精度,把非线性误差部分作为状态变量,建立MIMU在大方位失准角下无需小角度近似的空中对准的线性模型,同时为解决噪声不确定导致滤波器发散的问题,提出将AKF (Adaptive Kalman Filter)应用在GPS(Global Positioning System)辅助MIMU的空中对准中,半物理仿真结果证实其取得了比基于非线性误差模型的EKF(Extended Kalman Filter)精度高且速度快的结果,不仅使MIMU的方位失准角由60° 快速下降到2° 左右,且所需时间仅为EKF的67%.      

降落伞开伞过程的多结点模型仿真

根据降落伞的结构和力学特征,在轴对称假设下创建了伞衣及回收物系统的多结点结构模型.通过考虑应力,重力和气动力的作用效果,建立了用于无气流攻角平面圆形降落伞充气模拟的多结点结构模型动力学方程组.对开伞过程中的流场变化引入准定常假设,利用simple算法数值模拟求解RNG(Renormalization Group)k-ε湍流模型下的雷诺平均N-S(Navier-Stokes)方程以获得选定时刻的伞衣表面压力分布.结合多结点模型动力学方程组的解算代码和计算流体力学程序,采用流固耦合的方法对选定的平面圆形降落伞模型的开伞过程进行了动态仿真,得到了开伞过程中降落伞外形和特性的变化.通过结果分析和比较,证明了多结点模型的可行性,发展出了一种用于降落伞流固耦合计算的新方法.      

矩形微槽乙醇水溶液传热特性数值模拟

由于影响微槽传热特性的因素较多,实验研究结果相互矛盾,使得实验研究和数值仿真相结合成为进一步深入认识微槽传热特性的有效手段.在实验研究的基础上,采用有限体积法对矩形微槽中体积浓度30％的乙醇水溶液传热特性进行了三维数值模拟. 矩形微槽采用两种不同对称结构和热边界条件,进口采用流动完全发展边界条件.对不同对称结构和物性条件(常物性和变物性)的计算结果进行了比较,并与实验结果进行了对比.研究表明,对所研究微槽结构和工质,采用流动完全发展进口条件,以及随温度变化的热物性参数,数值计算结果与实验结果基本吻合.      

Standing Alfvén waves with m ≫ 1 in a dipole magnetosphere with moving plasma and aurorae

The structure of standing Alfvén waves with large azimuthal wave numbers (m ? 1) is studied in a dipole model of the magnetosphere with rotating plasma. In the direction across magnetic shells the structure of such waves is determined by their dispersion associated with curvature of geomagnetic field lines and corresponds to the travelling wave localized between toroidal and poloidal resonant surfaces. In projection into the ionosphere (along geomagnetic field lines) this structure is similar to the structure of a discrete auroral arc. The azimuthal structure of an auroral arc is similar to azimuthal structure of Alfvén waves with m ∼ 100. Possible interaction mechanisms between the Alfvén waves and energetic electron fluxes forming auroral arcs are discussed.