The Davidson method as an alternative to power iterations for criticality calculations

The Davidson method is implemented within the neutron transport core solver parafish to solve k-eigenvalue criticality transport problems. The parafish solver is based on domain decomposition. It uses spherical harmonics (P_N method) for angular discretization, and non-conforming finite elements for spatial discretization. The Davidson method is compared to the traditional power iteration method in this context.     

A Model-trajectory-based Method for Analyzing the Time-varying Oscillation Characteristics of a Fault System

Due to the impossibility for the equilibrium-point eigenvalue method to reflect the oscillation characteristic of the fault system correctly, and the difficulty in choosing the window length using a trajectory eigenvalue method, a model-trajectory method is proposed to analyze the eigenvalue of a fault system. First, the system is equated by the mutual factor after fault clearance. Then the branch current and power of the post-fault system is calculated by the branch current of the original and the fault component network, respectively. Furthermore, the equivalent model of the system is built and linearized at each measuring point. By combining the linearized model with the actual disturbed trajectory, the time series of the eigenvalue of the fault system is calculated. Simulation results of 2-generator system and a 16-generator system illustrate that the model-trajectory method is able to describe the time-varying oscillation characteristic of a fault system effectively and accurately.     

双馈风电机组附加控制对轴系振荡影响的评估方法

为消除绝对特征值灵敏度指标中参数量纲的影响,同时计及风速的概率分布特性对特征值灵敏度排序的影响,提出了一种累积相对特征值灵敏度(CRES)指标及其计算方法,并基于该指标定量评估了双馈风电机组附加控制(有功功率调制、虚拟惯性控制、下降控制、无功功率调制和机端电压控制)对机组本身轴系振荡阻尼的影响。CRES本质上是相对特征值灵敏度的加权和。通过引入相对特征值灵敏度消除了参数量纲的影响;在此基础上,按照转子运行状态将风速划分为若干区间,以平均风速作为该区间的典型风速,以风速落入该区间的概率作为该区间典型风速下计算所得相对特征值灵敏度的权重。时域仿真结果表明:基于CRES指标能有效地确定不同类型附加控制中影响轴系振荡阻尼的关键参数,通过对关键参数的重新整定可显著减小附加控制器对轴系振荡的不利影响和降低其对传动轴系统的转矩冲击。     

逆变型微网状态空间方程的分析与建立

通过对逆变型微网中逆变型分布式电源、滤波环节、等效线路等的惯性时间常数和系统特征值分析,提出了不同电压等级微网可以采用不同状态空间方程进行微网小信号稳定性分析。对400V母线的逆变型微网,其电网络方程应采用稳态方程;对10kV母线及以上电压等级的逆变型微网,其电网络方程应采用微分方程。系统特征值分析和时域仿真证明了该结论的正确性。     

塔河油田奥陶系碳酸盐岩储层预测新进展

经过多年的理论研究与生产实践相结合,在塔河油田奥陶系碳酸盐岩缝洞型储层预测方面取得了丰富的成果,形成了一系列的方法技术。近两年又创新推广了新技术趋势面法的应用,对一些前期成熟技术进行了发展与延伸,如本征值精细相干,并且加强了多方法的联合应用,取得了较好的效果。     

基于动力学修改重分析的圆柱齿轮动力学研究

结构动力学修改是用于结构振动特征值问题的高效重分析方法和结构（修改）重设计技术的理论。通过对一对圆柱齿轮传动的动力学修改重分析的介绍，给出了一种方便的动力学修改重分析方法。     

基于磁弹法的磨削烧伤检测及定标在企业中的应用

描述磨削烧伤及相应检测手段，介绍一种新颖、高效、实用的“磁弹法”的工作原理，以及专用仪器，重点叙述应用磁弹法时的评定指标和仪器的特征值定标，通过实例予以说明。     

Spectral calculations in magnetohydrodynamics using the Jacobi–Davidson method

For the solution of the generalized complex non-Hermitian eigenvalue problems Ax=λBx occurring in the spectral study of linearized resistive magnetohydrodynamics (MHD) a new parallel solver based on the recently developed Jacobi–Davidson [SIAM J. Matrix Anal. Appl. 17 (1996) 401] method has been developed. A brief presentation of the implementation of the solver is given here. The new solver is very well suited for the computation of some selected interior eigenvalues related to the resistive Alfvén wave spectrum and is well parallelizable. All features of the spectrum are easily and accurately computed with only a few target shifts.     

An invariant subspace‐based approach to the random eigenvalue problem of systems with clustered spectrum

The repeated or closely spaced eigenvalues and corresponding eigenvectors of a matrix are usually very sensitive to a perturbation of the matrix, which makes capturing the behavior of these eigenpairs very difficult. Similar difficulty is encountered in solving the random eigenvalue problem when a matrix with random elements has a set of clustered eigenvalues in its mean. In addition, the methods to solve the random eigenvalue problem often differ in characterizing the problem, which leads to different interpretations of the solution. Thus, the solutions obtained from different methods become mathematically incomparable. These two issues, the difficulty of solving and the non‐unique characterization, are addressed here. A different approach is used where instead of tracking a few individual eigenpairs, the corresponding invariant subspace is tracked. The spectral stochastic finite element method is used for analysis, where the polynomial chaos expansion is used to represent the random eigenvalues and eigenvectors. However, the main concept of tracking the invariant subspace remains mostly independent of any such representation. The approach is successfully implemented in response prediction of a system with repeated natural frequencies. It is found that tracking only an invariant subspace could be sufficient to build a modal‐based reduced‐order model of the system. Copyright © 2012 John Wiley & Sons, Ltd.     

CORRESPONDENCE: THE FLUX-BRIDGE MACHINE

ABSTRACT

This note describes a new kind of electromagnetic machine whose action is based on the change of flux linkage between two stationary coils-field and armature coils-when a segmental rotor moves between them. The machine differs from conventional inductor machines in having a dynamic component of emf in addition to the usual pulsation component, and also the windings are disposed on separate machine members. The basic principles are outlined and simple analysis is attempted. Possible modes of application are proposed.