平面式电容传感器阵列激励模式研究

由于非金属复合材料及其内部不同损伤具有不同介电特性,采用平面式电容传感器阵列可实现无损可视化检测。针对平面式阵列电极结构,研究不同激励模式对复合材料内部缺陷检测效果影响。提出单激励、双激励和奇偶激励3种激励模式,对比分析各种激励模式下传感器信号强度、探测深度等性能差异。结果表明:奇偶激励模式在信号测量和成像质量方面都优于前2种模式。同时也验证了基于电容敏感机理的平面电容传感器阵列对复合材料内部缺陷检测的可行性和有效性。     

网络信息分级过滤系统的研究与实现

通过对网络信息内容进行分析并对信息进行过滤,能够保证信息的安全性。在关键字过滤和IP过滤基础上,采用双向最大匹配和基于内容分析的K-最邻近文本分类算法相结合进行内容过滤,以达到信息系统过滤信息的质量和速度的效果。以准确率和查全率为标准,对本方案进行测定和评估,评估结果表明,本方案的过滤效果比较理想。     

Nonlinear controller design of thyristor controlled series compensation for damping inter-area power oscillation

A design method of nonlinear controllers of thyristor controlled series compensation (TCSC) for damping inter-area power oscillation based on direct feedback linearization (DFL) is presented in this paper. To damp inter-area power oscillation of power systems, the power modulation action of the TCSC is illustrated firstly. Then the nonlinear model of a two-area power system with the TCSC control is constructed, and is linearized by the DFL. Finally, the design of the nonlinear optimal controller of the TCSC has been completed using the criterion of integration for time and absolute error (ITAE). The digital simulation results using NETOMAC program and detail models show that the presented controller of the TCSC can efficiently improve inter-area power oscillation damping of power systems.     

包含静止无功发生器的电力系统逆系统解耦控制

研究包含静止无功发生器SVG(Static VAR Generator)的单机-无穷大电力系统中逆系统方法的应用.首先给出研究对象的数学模型,将静止无功发生器作为一无功电流源来处理.发电机采用二阶简化模型,在此情形下,给出包含SVG的单机-无穷大系统的三阶动态模型.然后论述逆系统方法的基本概念.利用求逆算法,逐步给出系统的逆系统、反馈控制规律、α-阶积分逆系统、伪线性系统(积分解耦系统).对所得解耦系统,应用最优控制方法进行综合.仿真结果显示了此方法的有效性.     

LEO卫星网络TCP拥塞控制算法改进研究

基于Vegas拥塞控制算法提出了一个适合于LEO卫星网络环境的TCP拥塞控制算法(Vegas-AB)，该算法是Vegas算法和Vegas-A算法的调和，可以动态地改变Alpha、Beta，Vegas-AB算法与Vegas-A算法的主要分支大体保持一致。在拥塞避免阶段，Vegas-AB算法更激进、更富有侵略性。仿真结果表明，在TCP吞吐量上，Vegas-AB算法优于Vegas算法和Vegas-A算法。     

动态CT脑灌注影像后处理算法

分析了动态CT脑灌注影像定量测量的相关理论基础。设计实现了实用的医学影像后处理算法,通过量化分析动态CT脑灌注检查所获得的影像序列可测量出脑组织的血流灌注量,绘制出一系列的时间密度曲线,进而分析、计算出相关的脑血流动力学参数,得到具有临床诊断价值的功能影像。临床病例测试表明,该算法的计算机实现对于正确诊断急性脑缺血等早期脑部急性病症,具有十分显著的辅助作用。     

Influences of ZrO<Subscript>2</Subscript> nanoparticles on the microstructure and mechanical behavior of Ce-TZP/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposites

Influences of ZrO₂ nanoparticles on the mechanical properties and microstructure of hot-pressing Ce-TZP/Al₂O₃ ceramics were investigated. Meanwhile, t-ZrO₂ to m-ZrO₂ transformation toughening mechanism was investigated by X-ray diffractometry (XRD) method, and deflection of samples under applied stress were recorded too. The results show that when the percentage of ZrO₂ was 20%, the mechanical properties and microstructures of materials are optimum. Moreover, TEM observation show dislocation structures formation both in the Al₂O₃ and on the grain boundary. Because the dislocation agglomeration and fixation by ZrO₂ nanoparticles could deflect cracking or stop cracking development, a strengthening and toughening effect could be achieved.     

Meshless solutions of 2D contact problems by subdomain variational inequality and MLPG method with radial basis functions

A subdomain variational inequality and its meshless linear complementary formulation are developed in the present paper for solving two-dimensional contact problems. The subdomain variational inequality will be defined in detail. The meshless method is based on a local weighted residual method with the Heaviside step function as the weighting function over a local subdomain and radial basis functions as trial functions for interpolation. Three different radial basis functions (RBFs), i.e. Multiquadrics (MQ), Gaussian (EXP) and Thin Plate Splines (TPS) are examined and the selection of their shape parameters is studied based on 2D solid stress problems with closed-form solutions. The developed meshless/linear complementary method is applied to solve two frictionless contact problems. For the RBFs, it has been found that the TPS shape parameter is not sensitive to nodal distance and a value of 4 is found as a good choice for TPS from this research.     

用混合像元线性模型提取中等植被覆盖区的粘土蚀变信息

基于混合像元线性分解模型,针对中等植被覆盖区提出了一种提取粘土蚀变信息的新方法。主要分3步实现:用混合像元线性分解模型提取植被覆盖丰度;对线性模型进行完善,并依此重构不含有植被信息的新的多波段图像;利用TM5/TM7增强粘土蚀变信息。经验证,提取的植被信息以及粘土类蚀变信息与实际吻合较好,与基于比值-主成分分析的方法相比有明显的优越性。
     

Experimental and finite element studies on hot sizing process for L-shaped composite beams

This work aims at developing a hot sizing process on composite materials to correct the profiles of composite structures during manufacture. Hot sizing experiments were carried out at 150 °C with different sizing loads and hot sizing periods for L-shaped composite beams made of carbon fiber plain-weave fabric and epoxy resin. To predict the springback in hot sizing process, a corresponding finite element simulation method was developed using stress relaxation equations determined at the same temperature. Excellent agreements between the predicted and observed results were obtained. The effects of the component thickness and 45° ply percentage on the springback rate were investigated by simulation. Springback rate in hot sizing process on composite materials ranges from 60% to 95%. In conclusion hot sizing process is proved to be a valid method for compensation for the process-induced deformation (PID) of L-shaped composite beams.