介质谐振器天线研究进展

综述了介质谐振器天线技术三十多年来的主要研究进展.归纳了宽带/超宽带、圆/双极化、高阶模/高增益、毫米波设计及介质谐振器天线阵等方面的技术进展,也介绍了介质谐振器天线的特点与分析方法等.     

基于发电单元完整模型的backstepping控制

针对发电单元高阶非线性完整数学模型(锅炉、汽轮机和发电机模型),结合系统参数的不确定性,采用backstepping动态面控制方法设计了一种鲁棒自适应控制器。在反推设计过程中引入了虚拟控制器和一阶低通滤波器,从而避免了对模型非线性进行多次微分而引起的算法复杂性,使设计方法简化。理论分析和仿真结果均表明,该控制器能够保证闭环系统的半全局渐近稳定性,对系统参数的不确定性具有较强的鲁棒性,在系统发生故障时能够使系统稳定运行。     

基于高频特性的电弧故障识别方法的研究

提出了一种基于高频信号的电弧故障识别方法。通过天线接收电弧故障的高频信号,利用电弧故障发生时产生的高频信号的三阶累积量和四阶累积量发生的变化进行电弧故障识别。试验表明,电弧故障发生时辐射的高频信号的三阶累积量呈现明显的负偏态,四阶累积量呈现明显的正偏态,通过该方法可以很好地对电弧故障进行识别。     

Basic research in the field of thermal infrared remote sensing

A new on-line blind equalization approach is proposed. The approach combines over-sampling technique with independent component analysis (ICA) neural network and can give equalized output on-line employing only the received signal. Based on the fourth-order cumulants and the characteristic of the linear system, the parameters of original channel are also estimated using evolutionary computation (EC). Compared to traditional equalization methods, the proposed algorithm is of simple architecture, does not need learning sequences apart from the observation, and can achieve both blind equalization and system identification. Computer simulations show good performance.     

基于高阶累积量的参数化双谱分析的肺音特征提取

用高阶谱分析方法,对肺音信号进行了特征提取.以非高斯白噪声激励的AR(AutoRegressive)参数模型对肺音信号进行建模,导出了基于三阶累积量的三阶递推方法的非高斯参数化双谱的计算方法,用双谱的互相关估计模型阶次,并对肺音数据进行了参数化的双谱估计,给出了在双频域内从双谱及其切片谱提取肺音特征信息的方法,并利用该方法对正常、哮喘和细罗音3种肺音目标进行了神经网络的识别实验.结果表明:所提出的特征提取方法大大降低了输入特征的维数,具有较高的识别率     

Complex-time-step Newmark methods with controllable numerical dissipation

In this paper, unconditionally stable higher-order accurate time-step integration algorithms with controllable numerical dissipation are presented. The algorithms are based on the Newmark method with complex time steps. The ultimate spectral radius (μ), the sub-step locations (β_j) and the weighting factors (α_j) are the algorithmic parameters. For an algorithm that is (2n−1)th order accurate, the sub-step locations which may be complex, are shown to be the roots of an nth degree polynomial. The polynomial is given explicitly in terms of n and μ. The weighting factors are then obtained by solving a system of n simultaneous equations. It is further shown that the order of accuracy is increased by one for the non-dissipative algorithms with μ=1. The stability properties of the present algorithms are studied. It is shown that if the ultimate spectral radius is set between −1 and 1, the eigenvalues of the numerical amplification matrix are complex with magnitude less than or equal to unity. The algorithms are therefore unconditionally C-stable. When the ultimate spectral radius is set to 0 or 1, the algorithms are found to be equivalent to the first sub-diagonal and diagonal Padé approximations, respectively. The present algorithms are more general as the numerical dissipation is controllable and are very suitable for parallel computers. The accuracy of the excitation responses is found to be enhanced by the present complex-time-step procedure. To maintain high-order accuracy, the excitation may need some modifications. © 1998 John Wiley & Sons, Ltd.     

UNCONDITIONALLY STABLE HIGHER-ORDER ACCURATE HERMITIAN TIME FINITE ELEMENTS

In this paper, single step time finite elements using the cubic Hermitian shape functions to interpolate the solution over a time interval are considered. The second-order differential equations are manipulated directly. Both the effects of modal damping and external excitation are considered. The accuracy of the solutions at the end of the time interval and the interpolated solutions within the time interval is investigated. The weighted residual approach is adopted to derive the time-integration algorithms. Instead of specifying the weighting functions, the weighting parameters are used to control the characteristics of the time finite elements. The weighting parameters are chosen to eliminate the higher-order truncation error terms or to enforce the asymptotic annihilation condition. A one-parameter family of third-order accurate asymptotically annihilating algorithms and another one-parameter family of fourth-order accurate non-dissipative algorithms are presented. The ranges of the weighting parameters for unconditionally stable algorithms are given. It is found that one of the members in each family corresponds to the Padé approximants of the exponential function in solving the first-order differential equations. Some of the existing unconditionally stable higher-order accurate algorithms are re-derived by the present unified approach.     

Transient natural convective heat transfer and fluid flow in an undulated cavity: Effects of localized heat sources

The purpose of this research work is to investigate two-dimensional transient natural convective heat transfer and fluid flows in an undulated cavity by placing solid objects with isolated heated surfaces on the bottom wall. We discretize the coupled nonlinear transport equations using a higher-order compact finite-difference scheme. First, we test our scheme using existing experimental and numerical data. Then, we analyze the transient and steady-state natural convective flow phenomena for distributed heat sources on corrugations on the lower wall for a range of the Rayleigh number $\left(Ra=10^3-10^6\right)$ and Prandtl number $\left(Pr=0.71\right)$. These simulated outcomes are presented in the form of central-line velocity $\left(u,v\right)$, local $(N{u}_h^{*},N{u}_v^{*})$ and averaged $(\overline{N{u}_h^{*}},\overline{N{u}_v^{*}})$ Nusselt numbers, streamlines $\left(\psi \right)$, dispersion of isotherms $\left(T\right)$, and so forth. It is found that the transient fluid flow behavior is more magnificent than the steady-state solutions and shows the dominant behavior of the prominent primary cells over secondary cells, where it influences the heat transfer rates inside the entire enclosure. In steady states, at high Rayleigh numbers; convection dominates, formation of thermal boundary layers, compression of isotherms, and stratification of isotherms are significantly observed. Our results show many interesting flow phenomena that have not been analyzed previously.