Yasuhito Takahashi

Large-scale and Fast Nonlinear Magnetostatic Field Analysis by the Magnetic Moment Method with the Adaptive Cross Approximation

This paper describes large-scale and fast nonlinear magnetostatic field analyses by the magnetic moment method (MMM) with the adaptive cross approximation. In order to stabilize the convergence characteristic of the Newton-Raphson method, we apply a line search technique to the MMM. Some numerical results that demonstrate the validity of the developed method are also presented

Large-scale analysis of eddy-current problems by the hybrid finite element-boundary element method combined with the fast multipole method

This paper shows large-scale eddy-current analysis by a hybrid finite-element and boundary-element (FE-BE) method. We introduce the fast multipole method (FMM) into the two kinds of hybrid FE-BE formulations developed by ourselves. To achieve more reduction of CPU time, we propose a novel preconditioning technique suitable for the hybrid FE-BE methods with the FMM. Furthermore, we improve the FMM calculation process in the hybrid method using magnetic field intensity. Some numerical results that demonstrate the effectiveness of these approaches are also presented

Convergence Acceleration of Time-Periodic Electromagnetic Field Analysis by the Singularity Decomposition-Explicit Error Correction Method

This paper proposes a novel method for the improvement of the convergence to a steady state in time-periodic transient nonlinear eddy-current analyses. The proposed method, which is based on the time-periodic finite element method and the singularity decomposition-explicit error correction method, can extract poorly converged error components corresponding to the large time constants of an analyzed system. The correction of the extracted error components efficiently accelerates the convergence to a steady state. Numerical results verify the effectiveness of the proposed method.

Large-scale and highly accurate magnetic field analysis of magnetic shield

This paper describes a large-scale and highly accurate magnetostatic field analysis targeting a magnetic shield. The hybrid finite element–boundary element method and the magnetic moment method do not require mesh division for the free space and can easily treat the nonlinearity of magnetic property. Therefore, these methods are considered very effective for the analysis of a magnetic shield which has a high aspect ratio of the size scale to the thickness. However, large memory and computational time have been required due to the dense matrices generated by those integral-based formulations. To overcome the difficulties, we introduce the fast multipole method into the hybrid method and the magnetic moment method. Furthermore, to achieve more reduction of CPU time, we propose an effective preconditioning technique suitable for the hybrid method. Some numerical results that demonstrate the effectiveness of these approaches are also presented.

Algebraic Block Multi-Color Ordering Method for Parallel Multi-Threaded Sparse Triangular Solver in ICCG Method

This paper covers the multi-threaded parallel processing of a sparse triangular solver for a linear system with a sparse coefficient matrix, focusing on its application to a parallel ICCG solver. We propose algebraic block multi-color ordering, which is an enhanced version of block multi-color ordering for general unstructured analysis. We present blocking and coloring strategies that achieve a high cache hit ratio and fast convergence. Five numerical tests on a shared memory parallel computer verify that the computation time of the proposed method is between 1.7 and 2.6 times faster than that of the conventional multi-color ordering method.

Large-Scale Magnetic Field Analysis of Laminated Core by Using the Hybrid Finite Element and Boundary Element Method Combined with the Fast Multipole Method

This paper shows a large-scale and highly accurate nonlinear magnetostatic field analysis of laminated iron core by using the hybrid finite element and boundary element (FE-BE) method. The hybrid FE-BE method is fairly effective to directly deal with the microstructure because no mesh division is required for the free space. In order to obtain the drastic reduction of the computational costs and stabilize the convergence characteristic of the Newton-Raphson method, the fast multipole method and the line search are introduced. Some numerical results that verify the effectiveness of the developed method are also presented

Convergence Acceleration in Steady State Analysis of Synchronous Machines Using Time-Periodic Explicit Error Correction Method

This paper develops the time-periodic explicit error correction (TP-EEC) method for the convergence acceleration to a steady state in transient analysis of synchronous machines. The methods to deal with the movement of the rotor and different time-periodicity in the fixed and moving parts of the mesh are investigated. Furthermore, we propose the novel TP-EEC method based on the polyphase time periodic condition. Numerical results verify the effectiveness of the developed methods.

Parallel Time-Periodic Finite-Element Method for Steady-State Analysis of Rotating Machines

This paper investigates the parallelization of the time-periodic finite-element method in nonlinear magnetic field analyses of rotating machines. The developed method, which can obtain the steady state solutions directly, provides large granularity even in the small-scale problems compared with the ordinary parallel FEM based on the domain decomposition approach. Furthermore, we apply the parallel TPFEM to analyses of induction motors which have different time periodicities in stator and rotor regions due to the slip. Numerical results verify the effectiveness of the developed method.

Time-Domain Parallel Finite-Element Method for Fast Magnetic Field Analysis of Induction Motors

This paper investigates the effectiveness of the time domain parallelization in magnetic field analyses of practical electric machines. We propose an efficient procedure to parallelize transient as well as steady-state analyses by generalizing the formulation of the parallel time-periodic finite element method. The proposed method is called the time domain parallel finite element method (TDPFEM) because it can be applied to both transient and steady-state analyses. Additionally, we derive a special condition of the slip to reduce computational costs for steady-state analyses of induction motors by using a half-cycle polyphase time-periodic condition.

Loss Calculation Method Considering Hysteretic Property With Play Model in Finite Element Magnetic Field Analysis

This paper proposes a novel estimation method for iron loss considering hysteretic property. In the proposed method, iron loss considering hysteretic property is estimated with play model as a postprocessing of usual finite element magnetic field analysis based on ordinary magnetization curve. Numerical results are compared with measured results to demonstrate the effectiveness of the proposed estimation method for iron losses.