Coordinated adaptive beamformer over distributed antenna network

The spatial diversity of distributed network demands the individual filter to accommodate the topology of interference environment. In this paper, a type of distributed adaptive beamformer is proposed to mitigate interference over coordinated antenna arrays network. The proposed approach is formulated as generalized sidelobe canceller (GSC) structure to facilitate the convex combination of neighboring nodes’ weights, and then it is solved by unconstrained least mean square (LMS) algorithm due to simplicity. Numerical results show that the robustness and convergence rate of antenna arrays network can be significantly improved in strong interference scenario. And they also clearly illustrate that mixing vector is optimized adaptively and adjusted according to the spatial diversity of the distributed nodes which are placed in different power of received signals to interference ratio (SIR) environments.     

Numerical analysis on noise of rotor with unconventional blade tips based on CFD/Kirchhoff method

A solver is developed aiming at efficiently predicting rotor noise in hover and forward flight. In this solver, the nonlinear near-field solutions are calculated by a hybrid approach which includes the Navier-Stokes and Euler equations based on a moving-embedded grid system and adaptive grid methodology. A combination of the third-order upwind scheme and flux-difference splitting scheme, instead of the second-order center-difference scheme which may cause larger wake dissipation, has been employed in the present computational fluid dynamics (CFD) method. The sound pressure data in the near field can be calculated directly by solving the Navier-Stokes equations, and the sound propagation can be predicted by the Kirchhoff method. A harmonic expansion approach is presented for rotor far-field noise prediction, which gives an analytical expression for the integral function in the Kirchhoff formula. As a result, the interpolation process is simplified and the efficiency and accuracy of the interpolation are improved. Then, the high-speed impulsive (HIS) noise of a helicopter rotor at different tip Mach numbers and on different observers is calculated and analyzed in hover and forward flight, which shows a highly directional characteristic of the rotor HIS noise with a maximum value in the rotor plane, and the HSI noise weakens rapidly with the increasing of the directivity angle. In order to investigate the effects of the rotor blade-tip shape on its aeroacoustic characteristics, four kinds of blade tips are designed and their noise characteristics have been simulated. At last, a new unconventional CLOR-II blade tip has been designed, and the noise characteristics of the presented CLOR-II model rotor have been simulated and measured compared to the reference rotors with a rectangular or swept-back platform blade tip. The results demonstrate that the unconventional CLOR-II blade tip can significantly reduce the HSI noise of a rotor.     

Composite control method for stabilizing spacecraft attitude in terms of Rodrigues parameters

In this paper, the attitude stabilization problem of a rigid spacecraft described by Rodrigues parameters is investigated via a composite control strategy, which combines a feedback control law designed by a finite time control technique with a feedforward compensator based on a linear disturbance observer (DOB) method. By choosing a suitable coordinate transformation, the spacecraft dynamics can be divided into three second-order subsystems. Each subsystem includes a certain part and an uncertain part. By using the finite time control technique, a continuous finite time controller is designed for the certain part. The uncertain part is considered to be a lumped disturbance, which is estimated by a DOB, and a corresponding feedforward design is then implemented to compensate the disturbance. Simulation results are employed to confirm the effectiveness of the proposed approach.     

旋转固体火箭发动机燃烧室内流场分析解

对带壁面质量注入的旋转通道(具有柱形装药旋转固体火箭发动机通道)内流场进行了研究。通过解析方法求解简化后的欧拉方程,获得了无粘情况下的旋转通道解析解。在此基础上,运用摄动法中的渐进展开匹配法求解引入粘性修正的切向动量方程,并获得解析解,表明切向速度分布解具有组合涡特征。分析了涡核半径与注入雷诺数及旋转转数的关系,得到了可压缩修正条件下的组合涡规律。     

空时交织码

提出了一种可在频率选择性信道中获得分集增益的满速率满分集空时码.由于所设计方案在不同的天线上设置不同的随机交织器,因此称之为空时交织码.证明了该码满足准静态频选衰落信道满分集准则,并且无速率损失.由于方案仅在各天线处增加交织器,因此易于推广至多个发射天线的场景.同时交织器还使接收机可通过迭代检测逼近最大似然检测性能,因此分别设计了两种迭代接收结构,一种是直接在卷积关系与相等关系间迭代,另一种是在叠加关系、多路卷积关系与相等关系间进行迭代.这些简化了接收机复杂度,使之随发射天线数线性增长.与频选信道中的其他空时码方案相比,该方案在速率、分集以及复杂度方面做出了有效折中.仿真表明,瑞利块衰落信道中该码性能接近多重分集理论曲线.     

涡轮叶片微小通道气膜新型复合冷却结构设计

利用数值模拟的方法,研究了一种应用于涡轮导向器叶片的微小通道气膜新型复合冷却结构.重点是对微小通道和气膜孔的新型复合冷却方法进行结构设计并进行结构优化,探讨不同的冷却结构形式对流动和换热的影响.研究表明:不同的复合冷却结构对冷却效率和压力损失的影响不同;在所设计的几种复合结构中,分枝小通道结构在平衡冷却效率和压力损失方面有着较好的效果;所计算的几种复合结构的结果都显示,微小通道气膜新型复合冷却结构的冷却效率高于铸冷叶片的冷却效率,冷却效果好,具有巨大的应用前景.     

路由算法在LEO通信星座构型优化中的应用

低轨(LEO,Low Earth Orbit)通信星座的特殊功能决定了其构型优化需要综合考虑成本、覆盖和路由性能等因素.以往的研究往往忽略了路由性能,导致优化得到的构型不能很好的满足要求.首先给出了两个意义明确的星座路由性能的评价指标,然后通过将它们作为目标函数进行仿真,验证了其优化必要性和评价有效性.最后利用多目标遗传算法实现了星座的构型优化.仿真结果显示,将路由算法加入到星座的构型优化中,在仅对星座构型参数进行微调的前提下,不仅满足了成本、覆盖等基本要求,而且星座的路由性能大大提高.     

视觉导航下基于H2/H∞的航迹跟踪

为了从理论上研究视觉导航系统的特性,首先在物理上将视觉导航系统划分为传感器(摄像头、激光测距仪)和视觉处理计算机。针对视觉处理计算机,建立视觉位置测量模型。将视觉位置测量模型的不确定性分为参数不确定性和输入干扰2种。然后通过仿真详细分析了视觉位置估计针对不同模型不确定性的敏感程度。最后在引入视觉位置测量模型不确定性的基础上研究H₂/H_∞混合鲁棒控制在航迹跟踪上的应用,并给出了保证航迹控制系统稳定性和跟踪性能情况下的视觉位置测量模型摄动范围,对计算机视觉算法的研究具有一定的指导意义。     

前置隔板对圆柱绕流影响的实验分析

对经典的圆柱绕流模型,运用前置隔板对流场进行控制。利用粒子图像测速(PIV)方法在自循环水槽中研究了雷诺数为1 800时,柔性和刚性2种不同刚度的前置隔板对圆柱绕流的影响。研究发现:柔性隔板自由端的弯曲增加了对流场的额外扰动,并且柔性隔板弯曲变形会诱导产生脱落涡,导致尾迹流场的主频发生变化。在圆柱下游流场,无隔板工况与柔性隔板工况的回流区长度相当,刚性隔板工况的回流区相较之下则更长。结果显示:前置隔板还能在一定程度上减小圆柱绕流的阻力。      

石英挠性加速度计测量航天器微振动的方法

利用高精度石英挠性加速度计可以测量航天器低频微振动,同时也可实现航天器在轨微角振动的间接测量。针对航天器特点,结合石英挠性加速度计工作特性,提出用高精度石英挠性加速度计测量航天器微振动的方法,给出微振动加速度、角加速度、角速度和角位移的不确定度分析,根据测量原理给出了各影响因素对测量合成不确定度的计算方法和分析结果。针对卫星敏感载荷的刚体平面测试环境,设计8个加速度计测点布局,开展了整星试验。试验数据分析表明:石英挠性加速度计可准确测量航天器的低频微振动(200 Hz以内),其直接测量和间接测量结果满足测量应用需求,线加速度测量分辨率为5μg,角位移测量分辨率为0.015″。