基于贝叶斯后验概率和非合作博弈的推荐算法

针对传统协同过滤推荐算法推荐精度较低等问题,提出一种基于贝叶斯后验概率预测和非合作博弈的个性化推荐算法。采用文件主题模型求取用户与其参加过的所有社交活动的主题分布,利用隐含主题概率分布表征用户兴趣度,根据信任传递机制求取用户的直接信任和间接信任,形成用户间的信任度;将用户的兴趣度和信任度等隐式特征赋予合理的先验分布,利用贝叶斯后验概率预测隐式特征后的显式反馈;依据显式反馈将推荐结果转化为非合作博弈中用户效益最大化的纳什均衡求解。仿真对比实验表明,与其他三种推荐算法相比该算法的查准率至少提高了3.13%,查全率至少提高了2.62%。     

未知时变惯量航天器自适应姿态跟踪容错控制

针对存在未知时变惯量不确定性、执行机构衰退故障和外部干扰力矩的非刚体航天器系统,研究了航天器自适应姿态跟踪容错控制问题,结合非线性鲁棒控制方法、自适应方法、容错控制理论和参数估计方法,提出了一种鲁棒自适应姿态跟踪容错控制器。所设计的控制器克服了执行器故障、惯量不确定性以及外界干扰对系统稳定性的影响,保证了航天器姿态及角速度能够跟踪上时变的期望状态,实现了跟踪误差系统最终一致有界稳定。最后通过数字仿真验证了所提方法的有效性,并且与已有方法进行了对比,说明了所提方法的优越性。     

Robust adaptive fixed‐time tracking control of 6‐DOF spacecraft fly‐around mission for noncooperative target

The fixed‐time relative position tracking and attitude synchronization control problem of a spacecraft fly‐around mission for a noncooperative target in the presence of parameter uncertainties and external disturbances is investigated. Firstly, a novel and coupled relative position and attitude motion model for a noncooperative fly‐around mission is established. Subsequently, a novel nonsingular fast terminal sliding mode (NFTSM) surface is developed, and the explicit estimation of the convergence time independent of initial states is provided. Fair and systematic comparisons among several typical terminal sliding modes show that the designed NFTSM has faster convergence performance than the fast terminal sliding mode. Then, a robust integrated adaptive fixed‐time NFTSM control law with no precise knowledge of the mass and inertia matrix and disturbances by combining the nonsingular terminal sliding mode technique with an adaptive methodology is proposed, which can eliminate the chattering phenomenon and guarantee that the relative position and attitude tracking errors can converge into the small regions containing the origin in fixed time. Finally, numerical simulations are performed to demonstrate the effectiveness of the proposed control schemes.     

Nussbaum‐type function–based attitude control of spacecraft with actuator saturation

This paper investigates the attitude stabilization problem of spacecraft subject to external disturbances and actuator saturation. A novel attitude control scheme is technically proposed by incorporating the Nussbaum gain technique into backstepping design. The key idea behind this is to introduce a special Nussbaum‐type function in order to compensate for the time‐varying nonlinear terms arising from input saturation. By exploiting the dynamic surface control technique, the problem of “explosion of terms” inherent in traditional backstepping designs is effectively eliminated and the computational burden is significantly reduced. Additionally, based on the selected Nussbaum‐type function, a constructive analysis methodology is presented, which plays an important role in analyzing the stability properties of the closed‐loop system. It is then proved that the proposed control scheme can guarantee the boundedness of all closed‐loop signals. Furthermore, the unwinding phenomenon is given a simple and effective remedy by resorting to suitable choices of the attitude error variable and the virtual control law. Finally, simulation experiments are carried out to assess the effectiveness and demonstrate the advantages of the proposed control scheme.     

Robust adaptive attitude control for flexible spacecraft in the presence of SGCMG friction nonlinearity

This paper investigates attitude maneuver control issues of a flexible spacecraft with pyramid‐type single gimbaled control moment gyroscopes (SGCMGs) as the actuator. The LuGre friction model is adopted to precisely describe the nonlinearity of the SGCMG gimbal friction. Aiming at restraining the adverse effects of the friction existed in SGCMG on the attitude control performance, a robust adaptive attitude controller is proposed, and projection‐based adaptive laws are presented to estimate the friction parametric uncertainties and the bound of friction nonlinearity. By treating the flexible mode coupling effect and external disturbances as lump disturbances, the inertia uncertainties and the bound of the lump disturbances are also estimated and compensated simultaneously to reduce their adverse effect on the system. With the Lyapunov technique, the states of flexible spacecraft control system are proved to be uniformly ultimately bounded. Numerical simulations demonstrate the effectiveness of the proposed scheme.     

柔性航天器拖拽空间碎片动力学与控制仿真研究

针对地球静止轨道空间碎片清除需求,开展了服务星通过绳索拖拽空间碎片离轨多体动力学与控制仿真研究.分析了在轨拖拽期间系统拓扑构型,采用递推方法推导了考虑地球J2摄动的服务星和空间碎片柔性多体动力学方程组,建立了基于集中参数法的绳索动力学模型,通过约束方程将绳索与服务星和空间碎片相连接,建立了服务星姿态控制力矩方程,最后形成了服务星在轨拖拽空间碎片期间柔性多体系统多体动力学方程.通过悬链线模型与本文采用的集中参数模型的比较验证了本文采用的柔性绳索模型的正确性,然后通过数值仿真分析了与服务星质量接近的空间碎片被拖动期间动力学特性,为这类航天器总体设计及空间碎片清除策略制定提供了参考依据.     

Prediction-based sampled-data H∞ controller design for attitude stabilisation of a rigid spacecraft with disturbances

This paper investigates the H_∞ control problem of the attitude stabilisation of a rigid spacecraft with external disturbances using prediction-based sampled-data control strategy. Aiming to achieve a ‘virtual’ closed-loop system, a type of parameterised sampled-data controller is designed by introducing a prediction mechanism. The resultant closed-loop system is equivalent to a hybrid system featured by a continuous-time and an impulsive differential system. By using a time-varying Lyapunov functional, a generalised bounded real lemma (GBRL) is first established for a kind of impulsive differential system. Based on this GBRL and Lyapunov functional approach, a sufficient condition is derived to guarantee the closed-loop system to be asymptotically stable and to achieve a prescribed H_∞ performance. In addition, the controller parameter tuning is cast into a convex optimisation problem. Simulation and comparative results are provided to illustrate the effectiveness of the developed control scheme.     

航天器中性浮力实验体外形设计与仿真

文章对中性浮力地面实验系统中实验体的外形进行了设计。首先利用Fluent软件求解计算出几种可供选择的实验体外形在各种工况下的水动力系数,同时通过力矩系数给出几种外形的静稳定性;然后在对水阻力系数和静稳定性进行分析和对比的基础上,选择了正方体作为实验体的外形;最后对正方体实验体进行动力学建模及仿真分析,结果表明此外形实验体的水阻力可以被克服。由此说明从阻力能够被克服和具有良好的静稳定性的角度考虑,此外形可以作为较好的实验体外形选择。研究结果可为相关方面的进一步研究和设计提供依据。     

基于MAS的航天器故障诊断系统模型

为了实现航天器故障处理的实时性、智能性,本文构建了基于MAS(Multi-Agent System)的航天器故障诊断系统模型。该结构通过分层实现了系统级诊断、缩小计算空间及加快隔离故障源。诊断智能体根据本系统的领域知识特点,建立自己的智能诊断模型,能够自主处理紧急故障;多个智能体能够协同并行地工作,提高了诊断速度。本文还构建了基于HLA(high level architecture)的故障诊断系统的仿真平台,通过仿真证明了该航天器故障诊断系统模型的优越性,也验证了仿真平台的可行性。     

柔性航天器次优鲁棒调节器设计

本文考虑星载转动部件在工作时,柔性航天器的振动抑制问题。首先对转化后的带两帆板航天器的模型设计反馈调节器;接着借助Sylvester矩阵方程的参数化解法,给出调节器增益矩阵的完全参数化表达;最后以自由参数为自变量,给出调节器增益矩阵梯度方向的次优解,得到次优鲁棒调节器。数值结果证明了本文方法的有效性。