Finite Element Method Computer Program Research Articles

Reduction of Computing Time for Steady-State Solutions of Magnetic Field and Circuit Coupled Problems Using Time-Domain Finite-Element Method

Time-stepping finite-element method (FEM) does not just analyze the transient process of magnetic field-electric circuit-mechanical motion coupled problems, it can also be used to find their steady-state solutions. In this paper, four effective measures are proposed to significantly reduce the computing time for finding steady-state solutions. With the first measure, it is proposed that first-order elements be used to replace second-order elements before the solution reaches its steady-state. A simple method is also proposed to allow a computer program of second-order element FEM to be used for first-order element FEM. The second measure is to adjust the error tolerance of nonlinear iteration and, with the permeability of iron materials from the last step being used as the initial values at the beginning of each time step, the nonlinear iterations can either be avoided or the number of iterations reduced. The third measure proposes a modified one-step multistage diagonally-implicit Runge-Kutta (DIRK) algorithm. In the fourth measure, during the transient process in the run-up towards steady-state operation, the time step size of the time integration is gradually reduced to a normal value. Numerical experiment shows that the computing time required to reach steady-state, using the combined four proposed methods, is only about 11% of that required by using conventional method.

Overstrain in flush optimal-chamfered cross-bored cylinders

A three-dimensional finite-element method computer program was developed to establish the elastic—plastic, residual, and service stress distributions in cylinders with flush and non-protruding optimal-chamfered cross-bores under internal pressure. Eight-noded brick and four-noded tetrahedral isoparametric elements and the displacement formulation were used. The incremental theory of plasticity with a 5 per cent yield condition and von Mises yield criterion were assumed. The incipient and 5 per cent overstrain (ov) pressures were established for various thickness ratios and cross-bore to main bore radius ratios. For the optimum chamfer angle geometrical configuration, the stresses were determined for varying ov. The maximum and minimum effective stresses were located 7.5° from the meridional and transverse planes, respectively. Meridional plane through thickness yielding occurred at an ov of 41 per cent. The service stress gradients at the cross-bore chamfer end increased with ov for ovs >30 per cent. Stress reversals were eliminated for overstrain >27 per cent. Alternative autofrettage and yield condition procedures were proposed.

Overstraining of flush plain cross-bored cylinders

A three-dimensional finite element method computer program was developed to establish the elastic-plastic, residual and service stress distributions in thick-walled cylinders with flush and non-protruding plain cross bores under internal pressure. The displacement formulation and eight-noded brick isoparametric elements were used. The incremental theory of plasticity with a 5 per cent yield condition (an element is assumed to have yielded when the effective stress is within 5 per cent of the material yield stress) and von Mises yield criterion were assumed. The frontal solution technique was used. The incipient yield pressure and the pressure resulting in a 0.3 per cent overstrain ratio were established for various cylinder thickness ratios and cross bore-main bore radius ratios. For a thickness ratio of 2.25 and a cross bore-main bore radius ratio of 0.1, the stresses were determined for varying overstrain and an optimum overstrain ratio of 37 per cent was established. To find the accuracy of the results, the more stringent yield condition of 0.5 per cent was also considered. The benefits of autofrettage were presented and alternative autofrettage and yield condition procedures proposed.

Homogenization technique for transient heat transfer in unidirectional composites

AbstractThe article presented is devoted to the homogenization of transient heat transfer problems in unidirectional composites. Mathematical model is based on the effective modules method applied to unidirectional periodic composites—the effective heat conductivity is calculated in the closed form; the effective volumetric heat capacity for the entire composite is obtained by simple spatial averaging. Such a homogenization scheme makes it possible to significantly simplify numerical analysis of transient heat phenomena in various types of unidirectional composites with complicated microgeometry. The comparison of transient heat transfer problem for the composite in real and homogenized configuration is carried out using a specially adopted finite element method computer program. Copyright © 2003 John Wiley & Sons, Ltd.

Fundamental characteristic estimation based on finite element method for magnetic shielding type superconducting fault current limiter

The superconducting fault current limiter is expected to be the first application of high-Tc superconductors (HTSs) in power systems. To develop a magnetic shielding-type superconductor fault current limiter, we have carried out some fundamental experiments on the magnetic shielding characteristics of an HTS bulk cylinder. In this paper, the experimental results of magnetic flux penetration into Bi-2223 cylinders are shown. An ac magnetic field is applied to the sample by a primary winding (copper coil) excited by ac triangular- and sinusoidal-waveform currents in the frequency range from 0.1 Hz to 100 Hz. We also developed a finite element method computer program for evaluation of the dynamic electromagnetic behavior of the HTS cylinder in a time-varying external magnetic field. The results of computer simulations considering the voltage–current (E–J) characteristic are compared with experiments. Next we carried out a current-limiting test with a small limiter model, and the developed finite element method computer program successfully simulated the electromagnetic behavior in current-limiting operation. © 2000 Scripta Technica, Electr Eng Jpn, 134(1): 17–27, 2001

有限要素法による磁気遮へい型超電導限流器の基礎特性評価

The superconducting fault current limiter is expected to be the first application of high-Tc superconductors (HTSs) in power systems. To develop a magnetic shielding-type superconductor fault current limiter, we have carried out some fundamental experiments on the magnetic shielding characteristics of an HTS bulk cylinder. In this paper, the experimental results of magnetic flux penetration into Bi-2223 cylinders are shown. An ac magnetic field is applied to the sample by a primary winding (copper coil) excited by ac triangular- and sinusoidal-waveform currents in the frequency range from 0.1 Hz to 100 Hz. We also developed a finite element method computer program for evaluation of the dynamic electromagnetic behavior of the HTS cylinder in a time-varying external magnetic field. The results of computer simulations considering the voltage–current (E–J) characteristic are compared with experiments. Next we carried out a current-limiting test with a small limiter model, and the developed finite element method computer program successfully simulated the electromagnetic behavior in current-limiting operation. © 2000 Scripta Technica, Electr Eng Jpn, 134(1): 17–27, 2001

Elastic-plastic behaviour of WCCo analysed by continuum mechanics

The purpose of this investigation is to find out if continuum mechanics, in particular the finite element method (FEM), applied to the microstructure, can be used to predict the elastic-plastic behaviour of a two-phase composite material. WCCo alloys are discussed as test object. A FEM computer program for elastic-plastic analysis of two-dimensional problems in plane strain is applied to plate models, obtained from electron micrographs, which have been divided into a pattern of triangular elements. The results show the importance of compatibility (continuity in deformation) for the analysis of heterogeneous materials. Agreement between calculated stress-strain behaviour and experimental results taken from the literature is reasonable. A two-stage mechanism for elastic-plastic deformation in WCCo is proposed and some of the existing theories are discussed in the light of the results obtained.

Determination of Young's modulus and poisson's ratio for WCCo alloys by the finite element method

The purpose of this investigation was to find out if the finite element method (FEM), applied to actual microstructures, can be used for analysis of the elastic properties of an isotropic two-phase composite material, WCCo. An FEM computer program was applied to plate models obtained from replica electron micrographs which had been resolved into networks of triangular elements. The calculated values of Young's modulus and Poisson's ratio exhibit good agreement with experimental results. They also lie within or (in the case of ν) close to the theoretical bounds given by Hashin and Shtrikman. A limited number of grain boundary cracks was found to have only a small influence on Young's modulus.