挠性卫星大角度机动变结构控制的全物理仿真实验研究

以具有大面积太阳帆板的卫星大角度机动为背景，针对常用的“飞轮－喷气”执行机械模式研究了变结构控制方案，考虑了控制精度和喷气消耗量问题，并成功地进行了国内首次挠性卫星大角度机动控制的全物理仿真实验，取得了显著的效果。     

行波机理对低散射目标支架雷达散射截面的影响研究

针对雷达低散射支架,文中首先采用天线机理分析行波对雷达散射截面(RCS)的贡献,并且使用等效相速度的概念求出双弧线外形目标支架在远区的辐射场,最后分析得出低散射支架行波辐射特性,并讨论行波对目标支架RCS的影响。     

无动力飞行器的制导与控制系统

提出了考虑常值风影响时无动力飞行器的动力学方程。基于变结构控制策略设计了三维的制导律和控制律，以此高度非线性、强耦合、时变的模型为基础进行了六自由度仿真，仿真结果表明这种考虑了风影响的动力学模型更接近实际，制导律和控制律是有效的，具有工程应用价值。     

大气层内动能拦截弹直接力/气动力复合控制

以大气层内拦截弹气动力和力矩式侧向直接力复合控制系统为研究对象,基于参考模型变结构控制理论设计了拦截弹末制导段复合控制系统,并研究了相应的控制力分配算法、脉冲发动机组调度算法。数学仿真结果表明,该复合控制方法可以很好地实现拦截弹姿态控制。与气动力系统相比,复合控制系统具有更好的动态性能。     

卫星远距离伴飞的变结构控制

主要研究卫星远距离稳态伴飞的控制问题。首先,根据线性相对运动方程(C-W方程)设计了能实现稳态伴飞的变结构控制律,并证明了其在有干扰情况下的有效性。然后,推导了适用于远距离相对运动的非线性方程解析解,并在此基础上对伴飞控制律进行了改进,以实现远距离的稳态伴飞。通过仿真,比较了上述控制律的效果,证明了基于非线性相对运动的变结构控制能有效地实现远距离稳态伴飞。     

空间拦截器姿态控制系统变结构控制规律研究

结合空间拦截器的姿态控制问题,本文介绍了一种对系统参数摄动和外在不确定性干扰具有鲁棒性的变结构控制律。在此基础上,研究了当控制信号幅值受限的情况下,非线性系统的变结构控制律的设计问题。此方法考虑了空间拦截器姿控发动机推力幅值受限这一实际情况,提出了基于姿态角双包络线概念的实用姿控方法。因此,更符合系统实际的运行情况。仿真结果证明了此方法的有效性。     

模型组转换算法在机动目标跟踪中的应用

为改进变结构多模(VSMM)估计中模型组转换(MGS)算法对运动规律较复杂目标的跟踪,提出了用于模型组激活的核心模型转移法。该法为每个模型组确定一核心模型,并利用当前时刻滤波结果中的模型概率和似然等先验与后验信息,判断模型组的激活。仿真结果表明,核心模型转移法的滤波结果平稳,为MGS算法提供了一种简单易行且全面利用系统信息的模型组激活方法。     

Numerical analysis for impacts of nozzle end-clearances on aerodynamic performance and forced response in a VNT turbine

It has been well known that nozzle end-clearances in a Variable Nozzle Turbine (VNT) are unfavorable for aerodynamic performance, especially at small openings, and efforts to further decrease size of the clearances are very hard due to thermal expansion. In this paper, both the different sizes of nozzle end-clearances and the various ratios of their distribution at the hub and shroud sides were modelled and investigated by performing 3D Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) simulations with a code of transferring the aerodynamic pressure from the CFD results to the FEA calculations. It was found that increasing the size of the nozzle end-clearances divided equally at the hub and shroud sides deteriorates turbine efficiency and turbine wheel reliability, yet increases turbine flow capacity. And, when the total nozzle end-clearances remain the same, varying nozzle end-clearances’ distribution at the hub and shroud sides not only shifts operation point of a VNT turbine, but also affects the turbine wheel vibration stress. Compared with nozzle hub clearance, the shroud clearance is more sensitive to both aerodynamic performance and reliability of a VNT turbine. Consequently, a possibility is put forward to improve VNT turbine efficiency meanwhile decrease vibration stress by optimizing nozzle end-clearances’ distribution.     

Variable stiffness design of redundantly actuated planar rotational parallel mechanisms

Redundantly actuated planar rotational parallel mechanisms (RAPRPMs) adapt to the requirements of robots under different working conditions by changing the antagonistic internal force to tune their stiffness. The geometrical parameters of the mechanism impact the performances of modulating stiffness. Analytical expressions relating stiffness and geometrical parameters of the mechanism were formulated to obtain the necessary conditions of variable stiffness. A novel method of variable stiffness design was presented to optimize the geometrical parameters of the mechanism. The stiffness variation with the internal force was maximized. The dynamic change of stiffness with the dynamic location of the mechanism was minimized, and the robustness of stiff-ness during the motion of the mechanism was ensured. This new approach to variable stiffness design can enable off-line planning of the internal force to avoid the difficulties of on-line control of the internal force.     

Assimilation of endmember variability in spectral mixture analysis for urban land cover extraction

Variable Endmember Constrained Least Square (VECLS) technique is proposed to account endmember variability in the linear mixture model by incorporating the variance for each class, the signals of which varies from pixel to pixel due to change in urban land cover (LC) structures. VECLS is first tested with a computer simulated three class endmember considering four bands having small, medium and large variability with three different spatial resolutions. The technique is next validated with real datasets of IKONOS, Landsat ETM+ and MODIS. The results show that correlation between actual and estimated proportion is higher by an average of 0.25 for the artificial datasets compared to a situation where variability is not considered. With IKONOS, Landsat ETM+ and MODIS data, the average correlation increased by 0.15 for 2 and 3 classes and by 0.19 for 4 classes, when compared to single endmember per class.