时域有限差分中各向异性完全匹配层的实现方法

本文讨论了如何在给定边界层数的条件下,通过调整各介质层吸收层的介质参数来实现入射波的最佳吸收,并利用自适应遗传算法对算法中的边界参数进行优化。     

基于有限差分法的轨道电路时域分析

针对道床环境较恶劣时,在空间域难以区分轨道电路工作状态的问题,提出基于有限差分法的轨道电路时域解求解方法。利用偏微分方程数值解理论对轨道电路偏微分方程组进行离散,建立轨道电路的差分格式,并根据电压、电流在始端、终端的边界条件对调整态受电端时域电压响应进行分析,得到轨道电路的时域解。在不同初始电气参数下,通过算例仿真分析调整态受电端电压的变化情况,结果表明,所得时域解符合轨道电路的传输特性,可为轨道电路暂态分析提供理论依据。     

基于时域有限差分的通信干扰信号广域监测

针对传统通信干扰信号广域监测方法没有变换处理干扰信号,导致方法存在监测稳定性较差等问题,提出基于时域有限差分的通信干扰信号广域监测方法.分析时域有限差分工作原理,引入导数与傅里叶变换方法,实现通信信号的采集与变换,通过支持矢量机构建干扰信号数学模型,根据上述模型识别出干扰信号种类,利用Lagrange函数算法获得干扰信号,完成通信干扰信号广域监测.实验结果表明,上述方法有效提升监测稳定性与准确率,综合有效性更好.     

基于GPU的FDTD麦克斯韦方程快速求解

采用图形处理器(GPU)为主计算核心,应用时域有限差分法(FDTD)实现电磁学中麦克斯韦方程组的快速求解。通过对FDTD求解麦克斯韦旋度方程的直接时间域的分析,给出FDTD的仿真算法。根据GPU能高效地提高FDTD的仿真速度,解决FDTD仿真算法中的计算量庞大问题。利用GPU在FDTD计算中的处理能力,实现了更长的脉冲持续时间和庞大的模型求解与仿真,在适当的时间内完成了超大量的仿真计算。根据在CPU和FDTD上的实际计算结果表明,基于GPU的FDTD仿真算法具有高精度和高效率等特点。     

Finite Volume Element Approximations of Nonlocal in Time One-Dimensional Flows in Porous Media

Various finite volume element schemes for parabolic integro-differential equations in 1-D are derived and studied. These types of equations arise in modeling reactive flows or material with memory effects. Our main goal is to develop a general framework for obtaining finite volume element approximations and to study the error analysis. We consider the lowest-order (linear and L-splines) finite volume elements, although higher-order volume elements can be considered as well under this framework. It is proved that finite volume element approximations are convergent with optimal order in H ¹-norms, suboptimal order in the L ²-norm and super-convergent order in a discrete H ¹-norm. Received August 3, 1998; revised October 11, 1999     

A study of microwave imaging for a metallic cylinder

This article presents the studies of time‐domain inverse scattering for a metallic cylinder which based on the finite‐difference time‐domain (FDTD) method and the dynamic differential evolution (DDE). For this study, the FDTD is used for the analysis of the forward scattering part, while for the DDE is applied for the reconstruction of the two‐dimensional metallic cylinder. For the forward scattering, the FDTD method is used to calculate the scattered E fields. Based on the scattering fields, these inverse scattering problems are transformed into optimization problem. By comparing the simulated scattered fields and the calculated scattered fields, the shape and location of the metallic cylinder are reconstructed. Numerical results demonstrate that, even when the initial guess is far away from the exact one, good reconstruction can be obtained. In addition, the effects of Gaussian noise on the reconstruction results are investigated. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE , 2012.     

Finite element and analytical modelling of a tractor-semitrailer vehicle

A tractor-semitrailer vehicle travelling over a random road surface is modelled using finite element and analytical methods. The vehicle's linear models are constructed in such a way as to describe the bounce and pitch modes of both the tractor and semitrailer, the bounce of each wheel-axle assembly, and also to account for the semitrailer beaming effect. The road surface irregularities are represented as stationary Gaussian random excitations. Spectral analysis technique is employed to analyze the dynamic response of the vehicle.

In this paper, the problem of the interaction of the vehicle with the road is discussed, the proposed mathematical models are presented, and the numerical results showing system eigenvalues, eigenvectors and power spectral densities of the vehicle stochastic response are given and analyzed. The finite element provides a powerful means for the prediction and assessment of the ride motion for this complex structure. The technique of spectral analysis is an effective tool for the analysis of road irregularities and the stochastic response of the road vehicles.     

时间步长对有限容积法数值模拟的影响分析

针对时间步长在CFD商业软件中的选取问题,从迭代收敛性和计算精度两个角度,讨论了时间步长对采用有限容积法的数值模拟的作用和影响.从微分方程的离散化入手,分析了时间步长对稳态问题的欠松弛作用,并指出了拟非稳态项与普通松弛因子的区别;通过误差分析指出了如何选取时间步长来提高计算精度,并用计算实例加以佐证.分析表明,时间步长对稳态及非稳态数值模拟都具有重要作用,合理的时间步长应综合考虑稳定性、收敛性和计算精度.     

Atomistic modelling of crack propagation in a randomly rough nano-scale metallic surface

Molecular dynamics simulations, based on many-body interatomic potentials, are performed to investigate the propagation of a Mode-I (edge) crack in a roughened two-dimensional (2D) (111) plane of a generic lattice for which we adopt the potential parameters pertinent to the elemental Ag. The randomly rough surface is generated with the help of a fractal-based technique referred to as fractional Brownian motion method. We show that fluctuations in the crack velocity, which lead to the phenomenon of crack branching, are also present for crack propagation in rough surfaces. However, as the roughness increases, this phenomenon becomes less pronounced, and another type of velocity fluctuation associated with the roughness of the surface emerges. Furthermore, it is found that as the roughness of the surface increases, the critical stress for the initiation of crack propagation is increased, and the fluctuations in the crack velocity make their appearance sooner.     

Finite element modelling and analysis of a new cemented hip prosthesis

In this study, four different stem shapes for hip prosthesis have been designed to investigate an optimum stem shape. The stem shapes have geometries of varying curvatures. The first stem has standard straight geometry. The other two have notched geometries and the last one has curved geometry. The notched and curved types have been intended to reduce sliding of the implant in the bone–cement. They have been also aimed the implant to stick to the bone–cement securely. The static and dynamic FE analyses of the stems have been conducted using implicit commercial finite element code. The static analyses have been conducted using a load of an average body weight. The dynamic analyses are performed using a load of walking condition of a human. Based on static and dynamic FE analysis results, safety factors for fatigue life of the hip prosthesis have been calculated. Fatigue calculations have been carried out for Ti–6Al–4V, cobalt–chromium alloy materials and bone cement based on Goodman, Soderberg, and Gerber fatigue theories. All calculations have been performed according to the infinite fatigue life criteria. The results obtained have been compared and concluded to the results found by Charnley.     

振动系统的时频域仿真分析研究

将有限自由度振动系统物动力学方程化为系统的状态方程和传递函数，以状态变量分析法和机械阻抗分析法代替振动模态分析法，直接运用MATLAB仿真功能及其控制系统工具箱函数，对振动系统进行了时频域仿真分析，并通过实例进行了说明，为振动系统的分析与设计提供一种工具。     

Modeling and characterization of microwave breakdown at atmospheric pressure in OMUX filters

For output multiplexer (OMUX) filters placed in telecommunication satellites, microwave breakdown happens in an involuntary and undesirable way during tests at atmospheric pressure. This avalanche phenomenon is due to exponential growth of the electronic density caused by thermoelectronic emission under strong electromagnetic field magnitude. In this paper, our objective is to model and characterize experimentally multipole OMUX filters composed with coupled cavities. For identifying the element responsible for the breakdown, the electric field is calculated within each cavity and each iris. In order to characterize the breakdown phenomenon, we proposed an experimental test bench and we measured the power, both at the input and at the output of the filter. The article details the theoretical breakdown prediction and the experimental setup for such a structure. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:46–54, 2014.     

Discovering Similar Patterns for Characterizing Time Series in a Medical Domain

In this article, we describe the process of discovering similar patterns in time series and creating reference models for population groups in a medical domain, and particularly in the field of physiotherapy, using data mining techniques on a set of isokinetic data. The discovered knowledge was evaluated against the expertise of a physician specialized in isokinetic techniques, and applied in the I4 (Intelligent Interpretation of Isokinetic Information) project developed in conjunction with the Spanish National Center for Sports Research and Sciences for muscular diagnosis and rehabilitation, injury prevention, training evaluation and planning, etc., of elite athletes and ordinary people.     

一种时域盲信号分离系统的DSP实现

盲信号分离是当前信号处理研究的热点课题之一,在无线数据通信、医学、语音以及地震信号处理等领域有着广阔的应用前景.本文基于一种可用于真实环境中的盲信号分离算法,采用TI公司的浮点DSP芯片(TMS320C6701)EVM板实现了一个语音信号的盲信号分离系统.经现场验证,该系统不仅达到了实时处理的要求,而且对真实房间中的两路语音信号的盲分离得到了较好的效果.     

Finite element modelling of compartment masonry walls in fire

A finite element model called MasSET has been developed which is capable of predicting the structural behaviour of single leaf masonry walls subject to elevated temperatures. The analysis models a slice through the wall as a column strip in plane stress, and also includes material with geometric non-linearity. The model has been previously validated by comparison with experimental results [1] and is used in this paper to conduct a parametric study investigating the effects of slenderness ratio, load eccentricity and boundary conditions. The results of the investigation are presented by way of failure temperatures for each condition, and show conclusive findings to the effects of each parameter investigated.     

Finite Volume Discretization and Multilevel Methods in Flow Problems

This article is intended as a preliminary report on the implementation of a finite volume multilevel scheme for the discretization of the incompressible Navier–Stokes equations. As is well known the use of staggered grids (e.g. MAC grids, Perić et al. Comput. Fluids, 16(4), 389–403, (1988)) is a serious impediment for the implementation of multilevel schemes in the context of finite differences. This difficulty is circumvented here by the use of a colocated finite volume discretization (Faure et al. (2004a) Submitted, Perić et al. Comput. Fluids, 16(4), 389–403, (1988)), for which the algebra of multilevel methods is much simpler than in the context of MAC type finite differences. The general ideas and the numerical simulations are presented in this article in the simplified context of a two-dimensional Burgers equations; the two-, and three-dimensional Navier–Stokes equations introducing new difficulties related to the incompressibility condition and the time discretization, will be considered elsewhere (see Faure et al. (2004a) Submitted and Faure et al. (2004b), in preparation).     

基于Simulink的AM通信系统时域与频域仿真模型

在Matlab的Simulink仿真环境下,根据AM通信系统的调制和相干解调的原理,结合单频信号的时域和频域特性,建立了一种新的AM通信系统时域与频域仿真模型,同时能够观察和分析信号的波形与频谱。     

一类脉冲切换系统的有限时间稳定性

针对一类具有脉冲现象的非线性切换系统,提出了一种基于有限时间稳定lyapunov函数技术和多Lyapunov函数技术相结合的有限时间稳定性分析方法。该方法首先将非线性系统的有限时间稳定性的概念推广到所考虑的脉冲切换系统。然后,利用有限时间Lyapunov函数技术,确保各个子系统达到有限时间稳定。进一步,给出一个有限时间稳定的非线性比较系统。通过多Lyapunov函数技术,保证原系统的Lyapunov函数值不超过比较系统的状态值,由此得到原脉冲非线性切换系统有限时间稳定的充分条件。最后,一个数值例子说明文中方法的有效性。本文所得的研究结果能应用于生产线控制,交通管理,网络控制等实际系统。     

传感器动态非线性的一种时域分离方法

采用基于Ｖａｎｄｅｒｍｏｎｄｅ矩阵的最小二乘方法分离动态非线性，将传感器的动态非线性系统分解为动态线性环节和非线性即时环节相级联的形式。结果表明，这种非线性分离方法是正确的和有效的。     

Composing Power Series Over a Finite Ring in Essentially Linear Time

Fix a finite commutative ringR. Letuandvbe power series overR, withv(0) = 0. This paper presents an algorithm that computes the firstnterms of the compositionu(v), given the firstnterms ofuandv, inn^1 + o(1)ring operations. The algorithm is very fast in practice whenRhas small characteristic.