International Journal of Applied Electromagnetics and Mechanics

Wound-core transformers are characterized by their economical and efficient design and are therefore widely used in power distribution systems; for this reason it is of paramount importance to determine their electrical characteristics. One of the most important parameters in these transformers is leakage reactance, since this is what largely determines short-circuit currents and voltage regulation. And yet the authors have found a conspicuous gap in the scientific literature concerning analytical formulations for the calculation of leakage reactance in wound-core transformers. In order to fill this gap, the authors propose a formula in terms of leakage areas and the Rogowski’s height of the windings. A geometric model of the active part of the transformer is proposed which allows for the exact calculation of the leakage areas. The results of the proposed formula are compared with simulations with the finite element method in 3D (FEM3D) and with measurements in eight real case studies. It is concluded that although the FEM3D calculates the closest results to measurements, the proposed formula reported sufficiently accurate results for transformer design purposes.

In this paper, the lightning return stroke electromagnetic field at close distance is calculated by the way of transmission line (TL) model and full-wave three-dimensional electromagnetic field simulation software XFDTD, which is based on finite-difference time-domain (FDTD) method. The evolution of distributions of electric field and magnetic field are summarized in the study. Furthermore, the total electromagnetic field and major components are analyzed to clarify the electromagnetic hazard from lightning electromagnetic pulse (LEMP). Then the temporal and spatial distribution characteristic of Poynting vector of the electromagnetic environment is shown to expound the energy distribution of LEMP at close distance. The results based on the analyses of field strength and Poynting vector show that the distribution of electric field, magnetic field and Poynting vector at close distance is akin to multilayered cylinder, and LEMP in the region characterized by large amplitude, transient behavior and high electromagnetic energy is a potential threat to adjacent electronic equipments. Moreover, engineering basis concerning LEMP protection and electromagnetic compatibility (EMC) design in the region closed to the return stroke point can be provided by the synthetical analysis of LEMP.

This paper analyzes the steady boundary layer flow and heat transfer of biomagnetic fluid over a stretching/shrinking sheet with prescribed surface heat flux under the influence of a magnetic dipole. The governing equations are transformed into a set of ordinary differential equations (ODEs) by using similarity transformations. Numerical results are obtained using the boundary value problem solver bvp4c of MATLAB. The effects of various physical parameters on the velocity and temperature profiles as well as skin friction coefficient are discussed. The paper shows that dual solutions exist for certain values of stretching/shrinking sheet and suction parameters. Stability analysis is performed to determine which solution is stable and physically valid. Results of the stability analysis depict that the first solution (upper branch) is stable and physically realizable, while the second solution (lower branch) is unstable.

Free-piston engine coupled with linear generator is a new type of thermoelectric energy converter, which has the advantages of high efficiency and simple structure. In this paper, a novel moving-coil linear generator with dual axial-magnetized stator is proposed for this kind of short-stroke high frequency oscillation generating applications. Finite-element (FE) model of the generator is created, the static and transient characteristics are analyzed, and the losses in different components are compared. A full-bridge power converter is designed to meet the control requirements of reversible operation. A 540 W experimental prototype is developed and tested to validate the FE analysis. According to the tested and simulated results, the generator has advantages of high efficiency and fast response. The generating efficiency of 92% can be obtained at the rated generating power. The average inductance of the proposed generator is about 0.7 mH, which benefits from the low armature effect and ensures a very quick electromagnetic response.

Obtaining the constant force at a given current benefits its applications in diverse fields. However, not depending on displacements, such a force characteristic is not available easily since this force is determined by a specific structure, materials, geometrical parameters and others. Therefore, utilizing the finite element method (FEM), the electro-magnet force of a proportional electro-magnet located at a semi-active damper is calculated considering different parameters, further obtaining better choices of crucial parameters for achieving the constant force and independence of displacements. Finally reflected through the maximum fluctuation of 0.82 N and the maximum error of 0.9 N compared to experimental results, a proportional electro-magnet with force characteristics of relatively high accuracy has been achieved.

In this paper, a high-energy density electromagnetic buffer (EMB) is studied and analysed for the violent acceleration and high velocity of intensive impact loads. First, the design requirements of the EMB are proposed to select reasonable structure and magnetic circuit parameters. The equivalent current model is used to introduce the primary eddy current affected by demagnetization effect and the induced secondary eddy current. The magnetization process is studied by dividing the conductor tube into the approach end and the departure end. Considering the nonlinear damping and eddy current interaction between primary and secondary, a primary-secondary eddy current loss coupled nonlinear time-step finite element model (FEM) is established to obtain the spatiotemporal distribution characteristics of eddy current. Finally, a test experiment with weak impact, medium impact and intensive impact was carried out. The measured displacement, velocity, damping force, and time nodes responses during buffering are consistent with the established time-step FEM results. The proposed high-energy density EMB can effectively complete the impact buffering process. It is reasonable to obtain the eddy current loss and its magnetization law from the established FEM which is suitable for shock buffering with different impulse strength.

Soft-switched wireless power transfer system combines the advantages of both wireless power transfer (WPT) and soft-switching technology. In WPT systems, high-frequency power electronic converters are crucial part for coupling/decoupling to transfer power from sending end to receiving end without any physical contact. Soft-switching of power electronic converters can mitigate conduction losses and increase the efficiency. This paper comprises of the technical review and advancements in the technological developments of soft-switched wireless power transfer systems. This work identifies and validates the trends and challenges related to soft-switched wireless power transfer system in the current scenario. This study establishes that reaping the benefits of this technology will need a few more years of research and development. Characterization of various methods and results found in literature for various application are discussed in detail, which provides an in-depth summary of soft-switched wireless power transfer design aspects.

Permanent magnet machine adopting Halbach array has more sinusoidal air-gap flux density distribution and higher air-gap flux density magnitude. Compared with the equal segmented Halbach array, the fundamental magnitude of air gap flux density can be higher and distortion rate can be lower by reasonably designing each segment width in unequal segmented Halbach array. Thus, in this paper, the permanent magnet machine adopting unequal segmented Halbach array is researched. Firstly, an analytical model is established for PM machine adopting Halbach array to improve the calculation efficiency. This analytical model can be applied to the Halbach array having arbitrary pole pair number, arbitrary number of segments per pole, arbitrary segment width and arbitrary gap width between segments. Further, the calculation results for air gap flux density between analytical model and finite element method are compared to verify the analytical model. In addition, the method to determine each segment width in the unequal segmented Halbach array is proposed firstly in this paper. On this basis, effects of the gap width between segments and each segment width under one pole on air gap flux density are researched. The research conclusions will provide guidance for the design and fabrication of unequal segmented Halbach array.

A linear generator system based on a free-piston engine is expected to be a highly efficient power-generation engine for series hybrid vehicles. However, the engine generator must produce in a limited installation space the very high power required to drive a car. Consequently, considering the car-mounting situation, higher power density is required by means of reduced generator size and higher efficiency. In this paper, a cylindrical double-stator linear synchronous generator with opposing permanent magnets is used for free-piston engine. The double stator realizes smaller size, and using opposing magnets achieves a larger thrust constant than that with a single stator. In a finite-element analysis, the high-efficiency area is expanded compared to a surface-magnet type of the same size. Furthermore, this paper clarifies the effectiveness for improved power density with maximum-generation control in a simulation of a dual-sided engine model.

Unsteady viscous two-dimensional magnetohydrodynamic micropolar flow, heat and mass transfer from an infinite vertical surface with Hall and Ion-slip currents is investigated theoretically and numerically. The simulation presented is motivated by electro-conductive polymer (ECP) materials processing in which multiple electromagnetic effects arise. The primitive boundary layer conservation equations are transformed into a non-similar system of coupled non-dimensional momentum, angular momentum, energy and concentration equations, with appropriate boundary conditions. The resulting two-point boundary value problem is solved numerically by an exceptionally stable and well-tested implicit finite difference technique. A stability analysis is included for restrictions of the implicit finite difference method (FDM) employed. Validation with a Galerkin finite element method (FEM) technique is included. The influence of various parameters is presented graphically on primary and secondary shear stress, Nusselt number, Sherwood number and wall couple stress. Secondary (cross flow) shear stress is strongly enhanced with greater magnetic parameter (Hartmann number) and micropolar wall couple stress is also weakly enhanced for small time values with Hartmann number. Increasing thermo-diffusive Soret number suppresses both Nusselt and Sherwood numbers whereas it elevates both primary and secondary shear stress and at larger time values also increases the couple stress. Secondary shear stress is strongly boosted with Hall parameter. Ion slip effect induces a weak modification in primary and secondary shear stress distributions. The present study is relevant to electroconductive non-Newtonian (magnetic polymer) materials processing systems.

In this paper, the concept of body of revolution (BOR) finite-difference time-domain method time-domain (BOR-FDTD) method is applied to symplectic multi-resolution time-domain (SMRTD) algorithm to propose a BOR-SMRTD method. In order to solve the problem that the obliquely incident pulse wave cannot be directly introduced into BOR-SMRTD method, an efficient one-dimensional time-domain algorithm for propagating obliquely incident pulse plane wave in BOR-SMRTD method is also proposed. The numerical results show that the proposed algorithm runs 51 times faster than the algorithm based on fast Fourier transform (FFT) completely. Moreover, the scattering problem of a perfect electric conductor (PEC) cylinder with finite length is calculated to verify the effectiveness of the algorithm. The surface current density distribution along a generatrix of the cylinder at a giving frequency was extracted, and the results are in good agreement with that obtained with the methods of moment (MoM) and BOR-FDTD. Finally, the radar cross section (RCS) of a PEC sphere was calculated, and the results agree well with the theoretical values.