Search results

Eddy currents, being of either positive or negative nature, have recently gained more and more importance in their positive aspects. New devices that may be called “eddy current based” have been worked out in recent years. This paper intends to present a quite new application of eddy currents which is an electromagnetic pump of novel design. The pump can be employed to transport liquid sodium for the Fast Breeder Reactor or other conducting materials, like melted metals. Eddy currents are used here for two pur‐poses: the first one is the typical usage to create electromagnetic force (as in tube‐type linear motors or conventional electromagnetic pumps) while the second one is just newly invented. Normally, in linear motors or conventional electromagnetic pump the air gap is relatively big which makes the leakage flux increase. Then the electromagnetic force is strongly reduced. To overcome this negative influence of the air‐gap, i.e. to minimize the leakage flux a conducting plate of special structure is inserted into the exciting coil. The first idea of it was given by K. Bessho for high magnetic field generation. Although the purpose of the application presented here is different from the initial one the idea is common and it is likely to be used for other purposes too. The basic features of the pump resulting from both numerical and experimental investigations are presented in the paper.

This paper aims to introduce the decomposed harmonic balance finite element method (HBFEM) to decrease the memory requirement in large‐scale computation of the DC‐biasing magnetic field. Harmonic analysis of the flux density and flux distribution was carried out to investigate the DC biased problem in a laminated core model (LCM).

Based on the DC bias test on a LCM, the decomposed HBFEM is applied to accurately calculate the DC‐biasing magnetic field. External electric circuits are coupled with the magnetic field in the harmonic domain. The reluctivity matrix is decomposed and the block Gauss‐Seidel algorithm solves each harmonic solution of magnetic field and exciting current sequentially.

The calculated exciting currents and flux density are compared with that obtained from measurement and time domain finite element analysis, respectively, which demonstrates consistency. The DC bias leads to the significant saturation of the magnetic core and serious distortion of the exciting current. The flux density varies nonlinearly with DC bias excitation.

The harmonic balance method is only applicable in solving the steady state magnetic field. Future improvements in the method are necessary in order to manage the hysteresis effects in magnetic material.

The proposed method to solve the DC biased problem significantly reduces the memory requirement compared to the conventional HBFEM. The decomposed harmonic balance equations are solved efficiently by the block Gauss‐Seidel algorithm combined with the relaxation iterative scheme. An investigation on DC bias phenomena is carried out through the harmonic solution of the magnetic field. The decomposed HBFEM can also be applied to solve 3‐D DC‐biasing magnetic field and eddy current nonlinear problems in a practical power transformer.

The harmonic balanced finite element method offers a valuable alternative to the transient finite element method for the quasi‐static simulation of electromagnetic devices operating at steady‐state. The specially designed iterative solver, the adaptive relaxation of the non‐linear loop and the embedding of the harmonic balanced finite element method within a state‐of‐the‐art finite element package, leads to a solver in the frequency domain that is competitive to time stepping. The benefits of this approach are illustrated by its application to an inductor with a ferromagnetic core.

Discusses the 27 papers in ISEF 1999 Proceedings on the subject of electromagnetisms. States the groups of papers cover such subjects within the discipline as: induction machines; reluctance motors; PM motors; transformers and reactors; and special problems and applications. Debates all of these in great detail and itemizes each with greater in‐depth discussion of the various technical applications and areas. Concludes that the recommendations made should be adhered to.

The simulation of eddy currents in laminated iron cores by the finite element method (FEM) is of great interest in the design of electrical devices. Modeling each laminate by finite elements leads to extremely large nonlinear systems of equations impossible to solve with present computer resources reasonably. The purpose of this study is to show that the multiscale finite element method (MSFEM) overcomes this difficulty.

A new MSFEM approach for eddy currents of laminated nonlinear iron cores in three dimensions based on the magnetic vector potential is presented. How to construct the MSFEM approach in principal is shown. The MSFEM with the Biot–Savart field in the frequency domain, a higher-order approach, the time stepping method and with the harmonic balance method are introduced and studied.

Various simulations demonstrate the feasibility, efficiency and versatility of the new MSFEM.

The novel MSFEM solves true three-dimensional eddy current problems in laminated iron cores taking into account of the edge effect.

This paper deals with the two‐dimensional finite element analysis in the frequency domain of saturated electromagnetic devices coupled to electrical circuits comprising nonlinear resistive and inductive components. The resulting system of nonlinear algebraic equations is solved straightforwardly by means of the Newton‐Raphson method. As an application example we consider a three‐phase transformer feeding a nonlinear RL load through a six‐pulse diode rectifier. The harmonic balance results are compared to those obtained with time‐stepping and the computational cost is briefly discussed.

An original and easy‐to‐implement method to take into account movement (motion) in the 2D harmonic balance finite element modelling of electrical machines is presented. The global harmonic balance system of algebraic equations is derived by applying the Galerkin approach to both the space and time discretisation. The harmonic basis functions, i.e. a cosine and a sine function for each nonzero frequency and a constant function 1 for the DC component, are used for approximating the periodic time variation as well as for weighing the time domain equations in the fundamental period. In practice, this requires some elementary manipulations of the moving band stiffness matrix. Magnetic saturation and electrical circuit coupling are considered in the analysis as well. As an application example, the noload operation of a permanent‐magnet machine is considered. The voltage and induction waveforms obtained with the proposed harmonic balance method are shown to converge well to those obtained with time stepping.

More and more older adults begin to use the mobile internet to obtain information. However, the quality of information obtained through mobile internet by older adults is hard to be guaranteed. The purpose of this paper is to study the role of family support when older adults obtain information from mobile internet.

This study conducted a survey of 263 older adults who owned mobile internet devices such as smartphones or tablet PCs. The theory hypotheses are tested using partial least squares techniques.

For older adults, family support is the influencing factor of mobile internet literacy improvement. Family emotional support has stronger impacts on the improvement both of mobile internet skill literacy and of mobile internet information literacy than family cognitive support has. Furthermore, the improvement of both mobile internet skill literacy and of mobile internet information literacy hs positive impacts on the quality improvement of obtained information by older adults.

This paper gives advice on how family members can support older adults during their obtaining information from mobile internet to improve their mobile internet literacy and quality of obtained information.

This study examines the factors that influence mobile internet literacy and quality of obtained information among older adults from the perspective of family support in the Chinese mobile internet context. The research results enrich the internet literacy theory and the information quality theory.

The purpose of this paper is to analyze the existence of differences in the implementation of environmental practices between companies that possess some form of certified environmental management system (ISO 14001 or EMS) and those that do not have any such system. This study also investigates whether companies with a certified EMS are also making additional environmental demands on their suppliers.

An empirical study utilizing survey data from automotive supplier organizations was completed. A total of 157 in‐person interviews were conducted with managers of Spanish companies which are automotive supplier organizations. Logistic regressions and non‐parametric tests are used to evaluate hypotheses.

A positive relation was found to exist between the possession of certified EMS, specifically ISO 14001 and eco‐management and audit scheme, and the environmental demands that these organizations impose on their suppliers. This finding implies that environmental concern spreads upstream in the supply chain. The environmental demands on suppliers increase with customer organization size, but the degree of internationalization, measured by the rates of imports and exports, does not show a significant relationship to these pressures.

The study is limited to a single (important) industrial sector and cannot be directly extrapolated to other industries.

There is a paucity of research that relates the adoption of certified EMS by companies to the adoption and implementation of environmental practices in their own organizations and in supply chain partners. This is the first such study to be completed for the automotive industry.

The high calculation effort for accurate material loss simulation prevents its observation in most magnetic devices. This paper aims at reducing this effort for time periodic applications and so for the steady state of such devices.

The vectorized Jiles-Atherton hysteresis model is chosen for the accurate material losses calculation. It is transformed in the frequency domain and coupled with a harmonic balanced finite element solver. The beneficial Jacobian matrix of the material model in the frequency domain is assembled based on Fourier transforms of the Jacobian matrix in the time domain. A three-phase transformer is simulated to verify this method and to examine the multi-harmonic coupling.

A fast method to calculate the linearization of non-trivial material models in the frequency domain is shown. The inter-harmonic coupling is moderate, and so, a separated harmonic balanced solver is favored. The additional calculation effort compared to a saturation material model without losses is low. The overall calculation time is much lower than a time-dependent simulation.

A moderate working point is chosen, so highly saturated materials may lead to a worse coupling. A single material model is evaluated. Researchers are encouraged to evaluate the suggested method on different material models. Frequency domain approaches should be in favor for all kinds of periodic steady-state applications.

Because of the reduced calculation effort, the simulation of accurate material losses becomes reasonable. This leads to a more accurate development of magnetic devices.

This paper proposes a new efficient method to calculate complex material models like the Jiles-Atherton hysteresis and their Jacobian matrices in the frequency domain.