Algorithm Research Based on the PDE Sensitivity Filter北大核心CSCD

采用PDE灵敏度滤波器可以消除连续体结构拓扑优化结果存在的棋盘格现象、数值不稳定等问题,且PDE灵敏度滤波器的实质是具有Neumann边界条件的Helmholtz偏微分方程.针对大规模PDE灵敏度滤波器的求解问题,有限元分析得到其代数方程,分别采用共轭梯度算法、多重网格算法和多重网格预处理共轭梯度算法对代数方程进行求解,并且研究精度、过滤半径以及网格数量对拓扑优化效率的影响.结果表明：与共轭梯度算法和多重网格算法相比,多重网格预处理共轭梯度算法迭代次数最少,运行时间最短,极大地提高了拓扑优化效率.     

LHCD系统微波激励源性能优化设计

使用数字锁相环技术实现一定带宽内高精度可调节的频率输出,解决了速调管长期工作后响应频率发生偏移,模拟锁相环无法工作在系统最佳频率的问题;在移相器后增加功率幅度控制电路,保证了线性放大器的输出功率不会受到相位调节的影响;设计了一种基于数模转换(D/A)技术与微波电调技术相结合的波形控制单元,解决了激励源输出波形不可控的问题。通过以上三方面的改进,完成了HL-2M装置LHCD系统微波激励源的性能优化设计。     

Colour Adaptation in Three Fringe Photoelasticity

Three fringe photoelasticity (TFP) can give the total fringe order from a single colour isochromatic fringe field by suitably comparing the colour with a calibration specimen. The fringe order evaluation can be erroneous when the materials for the calibration specimen and the application specimen are different. This is because of the colour variation between the two materials. This is conventionally handled by preparing individual calibration tables for each application. A new methodology to tune the calibration table obtained for a single material to accommodate the tint variation in TFP is proposed for the use of different specimen materials. Discontinuities in fringe order variation are smoothed using the refined TFP (RTFP) procedure. The elegance of the new methodology for solving a multi-material system is bought out by solving the problem of a bi-material Brazilian disc. The results obtained are compared with the phase shifting technique.     

四旋翼无人机速度控制系统设计

微小型多旋翼无人机在气象监测、低空侦查、灾区救援等领域中具有广泛的应用。在无人机姿态控制的基础上设计速度控制系统,该速度控制系统采用加速度计、角速率陀螺仪和GPS测量数据,并设计卡尔曼滤波器来抑制传感器噪声,同时估计无法测得的状态变量。为了减小无人机的建模误差并提高控制系统鲁棒性,采用了模型参考滑模控制理论(Model Reference Sliding Mode Control,MRSMC)设计速度控制器。     

小波网络辅助卡尔曼滤波的捷联惯导传递对准

初始对准精度是捷联惯导系统的主要误差来源之一。针对舰载机捷联惯导的传递对准模型准确建模困难,且测量噪声和过程噪声随舰船动态而变化,这样就会降低滤波的精度,卡尔曼滤波有一定的局限性,提出了将小波神经网络辅助卡尔曼滤波器用于惯导系统的传递对准。把能直接影响卡尔曼滤波估计误差的参数作为网络的输入,进过样本训练后,把网络的输出与经过卡尔曼滤波得到的结果相加,实现了捷联惯导的传递对准的滤波功能。这种新算法在实际应用中的非线性情况下优于传统卡尔曼滤波方法。仿真结果表明了其实用性和有效性。     

基于扩展卡尔曼滤波的吊钩姿态估计技术研究 

针对吊钩运动不定且易受大风、雾气等影响其作业效率问题,提出并实现基于MEMS传感器的吊钩姿态估计系统。建立吊钩三维空间运动模型,消除吊钩扭转影响;通过四元数的扩展卡尔曼滤波算法,对MEMS陀螺仪、加速度计与磁强计进行数据融合,解算得到吊钩三维姿态、摆角与摆向;采用基于视觉检测的吊钩空间姿态为参考基准,对起重机吊钩进行姿态估计验证。实验结果表明：该系统能有效融合MEMS传感器数据,获得高精度的吊钩姿态,实现姿态的实时检测。     

基于信号子空间重构的鲁棒子区域Frost波束形成

本文针对一个感兴趣子区域内的宽带波束形成问题, 提出一种基于信号子空间重构的鲁棒Frost波束形成算法. 该算法的基本思想是利用一个矩阵滤波器从所估计的信号加干扰子空间中提取感兴趣信号(SOI)的特征分量; 然后利用该特征分量重构信号子空间; 最后利用重构的信号子空间构造一组线性约束最小方差(LCMV)准则, 来保证SOI近似无失真通过. 与现有的其他鲁棒Frost波束形成算法相比, 本文算法的一个显著优点是在未知SOI实际波达方向与频带等先验信息的情况下, 其导向与带宽均能够自适应地匹配SOI. 因此在整个感兴趣子区域内, 它都能获得接近最优值的输出信干噪比. 理论分析与仿真研究验证了算法的有效性.     

Electrostatic properties and characterization of two-layer paper sheets

The aim of the research is to determine the electrostatic properties of two-layer paper sheets composed of laboratory filter paper and polyethylene. The volume resistivity and conductivity in a filter paper sheet, polyethylene film and a two-layer sheet consisting of them were studied. The experiment was done using two techniques. The investigated samples were exposed to static electric field and the surface and volume conductivity were measured in accordance with ASTM D257 standard. The same samples were also exposed to positive and negative air ion flux that allows a periodical deposition of a dosed amount of charge in order to measure electrostatic properties of the samples, i.e. to measure maximum surface voltage, sheet capacitance, surface voltage decay half time, volume resistivity, et cetera. A study of a two-layer sample consisting of laboratory filter paper and polyethylene film superimposed on the conductive surface in one position when the polyethylene film is on top and in other when the sample is in turned over position shows that the electrostatic properties of the top layer become dominant. The obtained results appear to be useful for more precise understanding of the phenomena occurring in multilayer sheets and to find a way to improve the multilayer sheets features.     

Effects of electrode and filter element shapes on characteristics of charge injection type of electrostatic oil filter

This paper reports on an improvement of the filtration speed of charge injection type of electrostatic oil filter. Numerical simulations of the ion drag flow field and electric field are performed to compare the charge density distribution, ion drag flow pattern, and electric field strength distribution for different electrode and filter element shapes. Filtration experiments are conducted and the experimental results are discussed in relation to the simulation results. It is shown that the numerical simulations used in this study can contribute in predicting a better structure for electrostatic oil filters.