A CONSISTENT SUBGRIDDING SCHEME FOR THE FINITE DIFFERENCE TIME DOMAIN METHOD

Recently, the simulation of high frequency devices has become of increasing importance due to the demand for faster development processes. The Finite Difference Time Domain (FDTD) method has been proved to be an efficient tool for the simulation of electromagnetic phenomena. In the paper we derive a new consistent three-dimensional subgridding scheme for the Finite Integration Technique. In the time domain the latter method reduces to FDTD when only cubical cells are used. The subgridding extension can help to achieve accurate models of small structure details without heavily decreasing numerical efficiency while the properties of continuous Maxwell equations are still conserved in the grid space. After studying numerical dispersion and stability, the applicability of the method is demonstrated by regarding an example studying scattering at a small post in a rectangular waveguide.     

处理电磁场有限元运动问题的新方法

该文总结了电磁场有限元分析中处理运动问题的现有处理方法，指出现有方法中存在的效率低、通用性不强和时间步长不确定等缺点。通过对现有独立坐标系方法的改进，提出一种新的处理方法。新方法不再受运动边界节点必须始终一一对齐的约束，在计算过程中时间步长可以保持为定常数，而空间步长由计算结果决定，取消了有限元网格单元边长对空间步长的限制。通过对异步电机暂态起动过程的计算，证明了新方法的有效性。新方法可以有效地提高电磁场有限元分析中对运动问题处理的时间效率。     

电磁检测中的开域电磁场数值计算

该文以涡流电缆偏心检测为例，针对电磁检测中开域涡流磁场难于求解这一问题，根据有限元和边界元的特点，对开域电磁场，采用设定虚拟边界的方法将无界场域分割成闭合的内部区域和开放的外部区域，在两个区域分别采用有限元法(FEM)和边界元法(BEM)，在虚拟边界上采用直接耦合方法，使有限元方程和边界元方程得以成功组合，从而获得全域解。该方法避免了利用自然边界划分有限元区和边界元区，使开放的边界元区含有多种媒质及源，造成边界元方程组非对称满阵阶数过高，难于计算的缺点。得出了磁场的分布及其检测对象的涡流损耗。计算结果与偏心量变化的线性关系和实验结果与偏心量变化的线性关系在视在阻抗的物理意义上具有良好的一致性，且磁场分布趋势合理。     

插值小波在差分求解工程电磁场问题中的应用

讨论了利用插值小波压缩非均匀变化函数的方法,以及该方法在求解工程电磁场初边值问题中的算法。该方法不需要采用不等距离散,便能使非均匀变化的初值得到自适应压缩存储,从而在减少存储容量的同时,无需对现有的差分算法进行针对初值的修改,免除了程序设计对初始值的依赖性。     

用边界元法计算永磁体磁场

本文提出用间接边界元法计算任意界面的永久磁铁产生的空间磁场,推导出其磁场计算公式,实际计算了稀土永久磁铁的磁场分布,产与实测值进行了比较。实际计算结果表明这 一种简单而实用的方法。     

电磁场混合有限元边界元法的发展

本文从开域电磁场的计算出发，简要地评述了目前电磁场数值计算的各种方法。在此基础上，着重阐述了一种能够有效解决开域电磁场计算的新方法－混合有限元边界的发展情况与基本原理。     

基于STL格式的三维电磁场有限元自动剖分方法

在分析三维实体造型STL数据结构的基础上,提出了采用分层切片法来进行三维电磁场有限元自动剖分的方法。首先,建立了STL文件的拓扑结构数据,然后结合实体结构及材料特性确定一个垂直于z坐标轴的特征面域,并在此面域形成三角形单元网格,最后对实体在z方向分层切片,通过对面域逐层延拓投影,形成三维有限元单元网格。采用该方法开发了基于STL文件格式的三维网格自动剖分程序,并用于两个STL实体的自动剖分,结果表明,该方法可降低数据量,节省计算时间,实用可行。     

OPTIMIZATION ISSUES IN FINITE ELEMENT CODES FOR SOLVING OPEN DOMAIN 3D ELECTROMAGNETIC SCATTERING AND CONFORMAL ANTENNA PROBLEMS

The first part of the paper presents the implementation and performance of a new absorbing boundary condition (ABC) for truncating finite element meshes. This ABC can be applied conformally to the surface of the structure for scattering and antenna radiation calculations. Consequently, the computational domain is reduced dramatically, thus allowing the simulation of much larger structures, and results are presented for three-dimensional bodies. The latter part of the paper discusses optimization issues relating to the solver's CPU speed on parallel and vector processors. It is shown that a jagged diagonal storage scheme leads to a four-fold increase in the FLOP rate of the code, and a standard matrix profile reduction algorithm substantially reduces the inter-processor communication.     

TURBINE-GENERATOR SHAFT TORQUES AND FATIGUE LIFE EXPENDITURE PREDICTED BY FREQUENCY DOMAIN AND TIME DOMAIN METHODS FOLLOWING SEVERE DISTURBANCES ON THE SYSTEM SUPPLY

ABSTRACT

This paper examines precision of predicting time responses for torque in turbine-generator-exciter shafts together with fatigue life expenditure of shafts by frequency domain analysis not analysed in the literature heretofore following incidence and clearance of worst-case disturbances on the electrical supply system. Effect of both governor and avr action following a range of disturbances is also illustrated. The effect of steam and electrical viscous damping on maximum and minimum shaft torques predicted by frequency domain analysis for a range of disturbances as a function of the fault clearing time is also depicted

The analysis is based on Fourier analysis of generator airgap torque following incidence and clearance of a severe supply network disturbance or following mal-synchronisation to obtain torque excitation which acts on the generator rotor corresponding to each modal vibration. Amplitude and phase of each modal vibration is thereby determined. Using appropriate damping, time responses for shaft torque at each shaft cell is constructed by summing components which correspond to each modal vibration. These time responses are compared with those obtained by solution of more than 50 differential equations which simulate the shaft train, turbine, generator, governor and avr

It is shown that time responses for transient turbine-generator-exciter shaft torques together with maximum shaft torques and fatigue life expenditure of the shaft can be predicted faithfully by frequency domain analysis taking due account of magnitude and phase of each modal vibration, and damping, following (i) worst-case Line-Line-Line, Line-Line, and Line-Ground disturbances from full-load to no-load with clearance, and (ii) mal-synchronisation. Simulation of damping of rotor swing, together with governor action, is important in making precise assessments of transient turbine shaft torque (and fatigue life expenditure of the shaft) at shaft locations which are close to die generator

660 MW, 1000 MW and 1300 MW two-pole Machines are analysed.     

TIME DOMAIN MODELLING FOR ELECTRICAL MACHINES

ABSTRACT

In electrical machine problems the mechanical time constant is usually assumed greater than the electrical time constants. Based upon this assumption and using a numerical formula for the evaluation of the Laplace transform inversion integral, a time domain method is developed for the solution of transient problems of machines. This method provides simple problem formulation, fast solution speed and high accuracy. It is applicable to system problems.     

基于时域仿真的暂态裕度灵敏度分析

结合时域仿真,提出了多机系统中单机加速面积、减速面积计算方法、临界机组单机等面积定则第一摇摆稳定判据、稳定裕度计算方法等。并提出了加速面积、减速面积、减速功率（稳定裕度）对网络节点有功、无功及变压器变比的灵敏度分析方法。临界机组群单机等面积定则第一摇摆稳定判据与时域仿真角度准则精度相同,但具有数值积分时间短的优点;暂态稳定裕度灵敏度能用于暂稳控制装置安装地点的选择、安全校正再调度及系统稳定裕度约束和在线稳定监视。     

TIME DOMAIN ESTIMATION TECHNIQUES FOR HARMONIC LOAD MODELS

ABSTRACT

In this paper we present two novel time domain techniques for load modelling in the presence of harmonics. In the first technique, the harmonic contents of the load voltage and current waveforms are assumed to be known in advance. The second technique uses samples of the load voltage and current waveforms directly. The least errors square parameter estimation algorithm is used to estimate the load resistance, inductance and capacitance. The residual current associated with incomplete extraction of the parameters for all significant signal frequencies is also estimated. We also identify harmonics that are not common between the load voltage and current waveforms. The proposed techniques are applied to synthetic and actual recorded data. The paper's conclusions are based on comparing the results obtained using both techniques.     

开域轴对称静磁场的混合有限元边界元法

本文提出了一种解决开域轴对称静磁场问题的混合有限元边界元法。基于矢量边界元法公式，混合有限元边界法以适合轴对称静磁场问题的ｒＡ与ｖ／ｒ δｒＡ／δｎ作为基本求解量，并进一步改进成仅以ｒＡ作为求解量，这样便降低了混合方程组求解量的数目，节省了所占用的计算机存贮容量。文中给出了三个应用实例。     

用边界元法计算含有电位悬浮导体的静电场问题

本文提出用边界元法计算含有电位悬浮导体静电场边值问题,推导出用边界元法计算这类边值问题的边界元方程,给出计算这类边值问题增列约束方程的方法,理论分析和实例结果表明,用边界元法计算含有电位悬浮导体的静电场问题,是一种非常有效的计算方法,可以方便地应用于静电场工程问题的设计与计算。     

A MODIFIED FINITE DIFFERENCE METHOD FOR MODELLING DIFFUSION PROCESSES

A time domain unconditionally stable explicit method is presented which may be used to model processes governed by the diffusion equation such as transient heat flow. Unlike the explicit finite difference routine, the method models the diffusion process within the time step (MPWT). Being explicit, the method (MPWT) may easily account for non-linear physical parmeters and may be compared with the transmission line matrix (TLM) method of diffusion modelling in terms of its utility. Unlike the TLM model, however, the equivalent circuit does not contain inductive components which have no clear physical meaning. The MPWT method is based on a simple resistive and capacitive circuit model, which for short time steps reduces to the explicit finite difference formulation but is stable for large time steps. Good agreement has been found when results obtained using this algorithm are compared with other numerical methods and analytical results.     

轴对称线圈静磁场的计算与应用

本文研究了包括圆环线圈与螺管线圈在内的轴对称线圈以及圆弧段电流单元所产生的静磁场中矢量磁位与磁通密度的计算，着重讨论了计算中完全椭圆积分与奇点的处理。在此基础上，对０．１５Ｔｅｓｌａ磁共振成像电阻式磁体进行了分析，设计了用于永磁磁共振成像的梯度线圈。     

用矢量磁位计算三维磁场问题的有限元程序自动生成的研究

本文运用最新发展起来的有限元语言和有限元程序自动生成技术生成了解三维磁场问题所需要的ＦＯＲＴＲＡＮ有限元程序系统,在此矢量磁位被用来作为磁场的描述函数。     

同步电机温度场数值计算与分析

应用电机温度场的数值计算方法，对同步电机定、转子中的温度场分布作了分析，给出了额定工况下定子、转子铁心和定子、转子绕组中的温度场分布图。文中还对不同条件下转子区域的温度场分布作了研究，结果表明，采用励磁绕组直接绕在极身上的整圆冲片式转子取代分离式结构转子，对降低电机中的温升是有益的。     

具有最小定时限特性的反时限过电流保护

本文论述一种用集成电路来实现最小定时限的反时限曲线的新方法。阐述了四段曲线拟合法的实现方案及拟合误差分析，而且还讨论了实施电路对减少误差所采取的措施。本方案所采用的曲线拟合法在集成电路保护实现领域内是独特的，尤其是在实用性、可靠性以及准确性上都有较新的突破。     

强磁场永磁机构组装过程的动态有限元分析

提出一种外磁场按任意规律变化时,永磁材料特性的数值模拟方法。该方法将Preisach磁滞模型和有限元法相结合,完成对强磁场永磁机构装配过程的动态磁场分析。所提出的方法将永磁材料包括局部回线在内的磁滞特性包含到数学模型中,在合理的假设下,考虑了计及磁滞效应的"旋转磁化"。该方法只需要利用永磁材料的极限磁滞回线即可完成分析计算,避免了采用大量实验统计方法确定传统Preisach磁滞模型的分布函数。通过与传统简化计算方法(电流片等效法)和实验结果的比较,证明了所提方法的有效性。