地震作用下重力坝动水压力的高精度时域公式

提出一种计算直立坝面上地震动水压力的高精度时域公式,与坝体有限元模型结合用于考虑坝-水动力相互作用,避免半无限库水区域的数值模拟。在频域内,基于库水区域分离变量解析解和坝-水交界面条件推导精确的坝面动水力-坝面绝对水平运动关系,之后利用作者已经提出的时间卷积局部化方法将该关系转化为含有辅助变量的高阶精度时域公式。该公式的时空离散形式与坝体有限元模型的耦合方程,可以采用显式时间积分方法求解。为了能够利用商用有限元平台分析非线性坝体-库水动力相互作用问题,在ABAQUS有限元软件中通过UEL用户单元子程序二次开发实现了提出的动水力公式,公式用户单元在有限元建模阶段与坝体有限元模型无缝结合,后续动力计算过程中无须重启动等任何特别处理。刚性坝面地震动水压力分析表明,提出公式的计算结果稳定,并与解析解较好吻合;之后将该公式应用于Koyna重力坝地震反应分析。     

基于精确子域模型的双定子磁通反向电机磁场解析计算

双定子磁通反向电机是一种基于磁场调制原理的新型永磁电机,适用于船舶推进、风力发电等低速大转矩的应用场合.相较于传统的磁通反向电机,双定子拓扑能够解除单定子磁通反向电机永磁体和绕组的空间冲突问题,但同时也会增加其边界条件的复杂度.准确计算双定子磁通反向电机的磁场分布是设计、优化电磁性能的关键,而建立精确的数学模型则是求解...     

计算非线性时变涡流场的有限元方程频域算洁

本文提出了一种计算时变非线性涡流场的有限元方程频域算法，该方法在时域内确定非线性单元各时刻的磁阻率，利用离散付立叶变换在频域内求解有限元方程，并用直接解法与逐次松驰因子迭代法相结合的方法处理频域方程组的非线性问题。文中还用一算例验证了本法的有效性。     

A conformal mapping‐based approach for fast two‐dimensional FEM electrostatic analysis of MEMS devices

In this paper, a methodology is proposed for expediting the coupled electro‐mechanical two‐dimensional finite element modeling of electrostatically actuated MEMS. The proposed methodology eliminates the need for repeated finite element meshing and subsequent electrostatic modeling of the device during mechanical deformation. We achieve this by mapping the deformed electrostatic domain to the reference undeformed domain ‘conformally’. A ‘conformal’ map preserves the form of the Laplace equation and the boundary conditions; thus the electrostatic problem is solved only once in the undeformed electrostatic domain. The conformal map itself is generated through the solution of the same Laplace equation on the undeformed geometry and with displacement boundary conditions dictated by the movement of the mechanical domain. The proposed methodology is demonstrated through its application to the modeling of three MEMS devices with varying length‐to‐gap ratios, multiple dielectrics and complicated geometries. The accuracy of the proposed methodology is confirmed through comparisons of its results with results obtained using the conventional finite element solution. Copyright © 2010 John Wiley & Sons, Ltd.     

Field distribution in cable terminations from a quasi-staticapproximation of the Maxwell equations

A new model for the evaluation of the electric field in a cable termination realized through a nonlinear stress control tube (SCT), is presented in this paper. It is based on the electro-quasistatic approximation of the Maxwell equations: the Laplace equation describes the field in the nonconducting regions whereas a diffusion-like equation gives the field dynamics in the stress control tube. A numerical model is devised by solving the Laplace equation by finite difference and diffusion equations by the Galerkin method. It is shown that even the well-known RC transmission line model can be derived from this general approach. The underlying approximations leading to the circuital model are discussed in detail. The proposed model, in contrast with the circuital one, allows us to take into account properly the nonlinear SCT characteristics and the actual boundary conditions: in this way both spatial and temporal effects of the nonlinearity are-considered. The numerical results obtained by considering the general field approach and by using the transmission line model are compared     

2D time-domain electromagnetic macroscopic numerical modelling on parallel computer: application to the mm-wave silicon DIMPATT diode

A new time-domain two-dimensional (2D) electromagnetic (EM) physical modelling of non-linear distributed semiconductor devices has been developed. It is based on a numerical procedure which solves in a self consistent manner both Maxwell’s equations and a macroscopic transport model based on the drift-diffusion approximation. The software can be run on a parallel computer. It is based on finite-difference time-domain (FDTD) explicit schemes associated to the domain decomposition method. The millimetre-wave travelling-wave IMPATT diode or Distributed IMPact ionisation and Avalanche and Transit Time (DIMPATT) diode is the non linear test structure chosen to validate the model. RF simulations under amplification and CW oscillation operating modes have been performed. The results presented in this paper consist on the one hand of results that can be qualitatively compared to previously published theoretical works and on the other hand of features especially pointed out thanks to the new electromagnetic physical model capabilities.     

Least squares spectral element method for 2D Maxwell equations in the frequency domain

We propose a high order numerical method for the first order Maxwell equations in the frequency domain, defined in media with arbitrary complex shape. Our approach is based on the combination of the least squares approach with the spectral element method. The former frees the solution from spurious modes, that can be found sometimes in classical finite element simulations. Many examples of such non‐physical solutions exist in literature, and elimination of these spurious effects is a subject of great interest. Spectral elements are a numerical technique for solving partial differential equations which can be regarded as an extension of finite elements: they merge the flexibility of finite elements in dealing with complex geometries, and the better accuracy of spectral methods. Convergence to exact solution is improved by increasing (at run time) the polynomial degree, with no changes on the computational grid: this provides a significant advantage in respect to low order finite element, which necessarily have to resort to grid refinement. In the authors opinion this approach can be successfully used for the treatment of large scale electromagnetic problems or, alternatively, for applications where higher precision is required. We present a few numerical experiments which prove the capability of the method in object. Copyright © 2004 John Wiley & Sons, Ltd.     

转子有辅助槽的表贴式永磁电机解析法建模与优化

通过在表贴式永磁电机的的转子上开辅助槽,可间接改善电机的齿槽转矩脉动状况.但目前相关文献大都基于有限元法,需要反复修改模型参数,且尚未得出明确的槽型优化方法.本文选取磁场中的标量磁位为求解变量,在电机的气隙区域、永磁体区域分别建立拉普拉斯和准泊松方程.对于不规则的永磁体形状,采用分块累加方法,提出了一种转子含有半圆形辅...     

An interactive demonstration of electromagnetic wave propagationusing time-domain finite differences

The finite difference time-domain (FDTD) method is one of the most widely used computational methods in electromagnetics. Using FDTF, Maxwell's equations are solved directly in the time domain via finite differences and time stepping. the basic approach is relatively easy to understand and is an alternative to the more usual frequency-domain approaches. In order to take advantage of this, an interactive personal computer program based on FDTD has been developed. The program directly solves Maxwell's equation via finite differences. The solution is for one dimension, corresponding to normal incidence propagation through a planar stratified medium. The program displays an electromagnetic pulse as it propagates through the medium. Since Maxwell's equations are solved directly, the reflected and transmitted pulse amplitudes demonstrate how the reflection and transmission coefficients determine reflected and transmitted wave amplitudes. Since lossy material layers can be included, frequency dispersion can be demonstrated     

Carter's factor calculation using domain transformations and the finite element method

The main purpose of this work is to present a methodology to calculate Carter's factor using the actual air‐gap geometry, that is, without simplifications of the slot geometry. The methodology is based on the finite element method, and its results are compared with some traditional procedures used for Carter's factor calculation and also with a domain transformation technique. It is shown that the finite element method and the domain transformation methodologies present similar results, which are different from the results obtained with traditional procedures. Copyright © 2011 John Wiley & Sons, Ltd.     

基于二元模型的电阻抗成像方法

建立了一种双模型电阻抗成像系统,旨在解决一元模型电阻抗成像系统中耗时较多的问题。基于精细化三维圆柱体模型进行电阻抗正问题分析,采用粗梳三维圆柱体模型进行逆问题求解。在双模型成像系统中,基于稀疏矩阵建立映射公式实现粗疏有限元单元和精细有限元单元的匹配和转换。通过计算机仿真,在该系统中运用基于修正的Laplace Guass‐New ton重建算法可以得到相应的阻抗重建图像,实验结果验证了双模型系统的正确性和可行性。     

基于故障数据的线路分布参数时域辨识方法

针对目前基于故障数据的频域辨识方法难以精确辨识线路分布参数的问题,基于线路分布参数时域模型,提出了一种更精确的分布参数辨识方法。该方法利用线路两端采集的故障电压电流信号,在时域内通过最小二乘搜索法辨识得到线路参数,避免了频域法向量转换导致的误差。并采用瞬时对称分量法提取序分量,实现时域内分别对正序和零序参数的辨识;采用LOWESS方法平滑故障信号中的噪声,以提高算法的抗干扰性。仿真算例的结果表明,所提出的方法能够准确辨识线路的分布参数,并且对各种故障条件均具有良好的适应性。     

基于双标量位与等参元三维静磁场计算及数据前后处理

本文在双标量位法计算三维恒定磁场的理论基础上,引入等参元有限元法。在对两种位建立起来的场方程离散处理过程中,把对应于直角坐标系中的实际单元变换到局部坐标系中的标准单元处理,从而推导出适应场域边界较为复杂的20节点和8节点六面体有限元离散公式,据此编制了易于通用化的计算程序。本文采用与六面体等参元有限元计算完全配套的数据前后处理技术,包括有限元网格自动剖分;全域或局部(分材料区域)网格显示检查;能量、电磁力计算;全标量位域位线显示;场强显示。使上述计算方法便于在工程设计中应用。     

A Contribution to the Frequency Analysis and Transient Response of Power Transformer Windings

Abstract—This article proposes a new approach to study the frequency response and the transient analysis of power transformer windings. For improved accuracy, the suggested model includes, among other equivalent circuit elements, the mutual magnetic couplings between any winding turn and all others. This implies that the equivalent inductance of any considered turn will be a location-dependent parameter. Accordingly, the winding will be analyzed as a non-uniform transmission line. Through the application of a recursive circuit reduction technique, a closed-form Laplace s-domain analytical expression for the winding's input impedance can be obtained for any neutral treatment. The resulting expression can be used to determine the winding's series and parallel resonance frequencies. The s-domain expression for the input impedance, in connection with the numerical inverse Laplace transform, will be utilized for determination of the winding's time-domain transient response for any input voltage or current time waveform. Accuracy increases with the assumed number of winding sections, which can be even increased to the actual number of turns, limited only by the available computation resources. The results of case studies are in good agreement with those available in the literature using the time-domain solution of the simultaneous differential equations in the state variables.     

无限大电极系统的保角变换边界元分析

本文提出用保角变换边界元法计算含有无限大电极系统的二维静电场边值问题，保角变换将无限大电极系统的无穷边界无界场域边值问题变换为有界场域边值问题，再利用具有诸多优点的边界元法进行求角，充分发挥保角变换和边界元法的各自优势，拓宽二者的求解范围。     

SV波斜入射下高拱坝地震反应分析

基于黏弹性人工边界结合显式有限元法的时域波动分析方法,通过三维平面地震波倾斜入射的输入方法,结合小湾拱坝研究了SV波斜入射对拱坝地震反应的影响。结果表明:SV波斜入射角度对拱坝地震反应的影响规律与P波斜入射作用下的情况有着显著的不同,SV波斜入射角度对拱坝抗震安全性起控制作用部位的低频区的幅值放大系数影响显著,顺河向入射时,幅值放大系数随着入射角度的增加而显著减小;横河向入射时,幅值放大系数随着入射角度的增加而显著增大。     

Transient analysis of coupled non‐uniform transmission line using finite element method

This paper presents a finite element time domain model for a numerical solution of a coupled non‐uniform transmission line problem. On the basis of the finite element method, a novel numerical procedure for the solution of a system of the non‐uniform multi‐conductor transmission line equations in the time domain is presented. The results obtained by the proposed method have been compared with the solution obtained using the finite difference time domain method, and an excellent correlation has been demonstrated. Copyright © 2014 John Wiley & Sons, Ltd.     

双渐近透射边界下的隧洞-层状地基时域分析

高阶双渐近透射边界发展于改进比例边界有限单元法和连分式解,实现了时域局部化,获得在全频域范围内快速收敛的动力刚度准确解,兼具高精度和效率。本文将该边界推广应用到复杂层状地基弹性波传播问题,并与有限元耦合构建出一种隧洞-层状地基动力响应的时域耦合模型。耦合模型划分为近场与远场,其中,近场采用有限元单元离散,远场采用高阶双渐近透射边界模拟。通过数值算例分析上述耦合模型,结果表明：耦合模型计算结果稳定,与扩展网格解具有良好的一致性,同时兼顾精度与效率,适用于长时间的地震响应时域研究。该模型为研究地震动下隧洞-层状地基相互作用提供新的思路,可进一步用于实际工程中。     

压阻式硅加速度计固有频率的解析计算

固有频率对硅加速度计的性能影响很大。针对目前硅加速度计的固有频率计算公式误差大的缺点,利用力学原理推导了悬臂梁式和双端梁式硅加速度计固有频率的计算公式。计算结果与有限元软件仿真分析的结果相符。推导的公式能快速准确地计算压阻式硅加速度计的固有频率,并可直接用来编程,避免了有限元仿真分析需要反复建模的复杂过程,简化了优化设计的过程。