Electromagnetic Field Computation Research Articles

Simulation research on magnetoacoustic B-scan imaging of magnetic nanoparticles

As drug carriers, magnetic nanoparticles can specifically bind to tumors and have the potential for targeted therapy. It is of great significance to explore non-invasive imaging methods that can detect the distribution of magnetic nanoparticles. Based on the mechanism that magnetic nanoparticles can generate ultrasonic waves through the pulsed magnetic field excitation, the sound pressure wave equation containing the concentration information of magnetic nanoparticles was derived. Using the finite element method and the analytical solution, the consistent transient pulsed magnetic field was obtained. A three-dimensional simulation model was constructed for the coupling calculation of electromagnetic field and sound field. The simulation results verified that the sound pressure waveform at the detection point reflected the position of magnetic nanoparticles in biological tissue. Using the sound pressure data detected by the ultrasonic transducer, the B-scan imaging of the magnetic nanoparticles was achieved. The maximum error of the target area position was 1.56%, and the magnetic nanoparticles regions with different concentrations were distinguished by comparing the amplitude of the boundary signals in the image. Studies in this paper indicate that B-scan imaging can quickly and accurately obtain the dimensional and positional information of the target region and is expected to be used for the detection of magnetic nanoparticles in targeted therapy.

Induction heat treatment of large rolls with two independent power sources

The two-inductor heat treatment system for rolls of rolling mills is highly flexible and can improve the quality of heat treatment while solving energy-efficiency and productivity problems. A digital model of induction heat treatment of rolls with the computation of electromagnetic, temperature and stress fields is developed taking into account the characteristics of power supplies and control systems for heat treatment modes. Particular attention is paid to the reliability of frequency converters in the presence of magnetic coupling between inductors. Recommendations on frequency selection and inverter settings are given. A universal method of digital design and control of thermal conditions in induction heat treatment systems is considered.

METHODOLOGY FOR CALCULATING ELECTROMAGNETIC FIELDS GENERATED BY AN AUTOMATED WORKPLACE OF AN OBJECT OF INFORMATIZATION

A methodology for calculating electromagnetic fields generated by an automated workstation of an object of informatization has been developed. Using the presented methodology, it becomes possible to form a complete scheme of electromagnetic radia-tion of the space under study. Based on the output of the calculation of electromagnet-ic fields, the permissible time spent by the operator at each point of his workplace is calculated. For the first time, electromagnetic radiation sources are modeled by a com-bination of elementary electric dipoles powered by various harmonic components. The reliability of the illustrated methodology was carried out by comparing the calculated values of the parameters of electromagnetic fields with the measured values of the lev-els at given frequencies.

Accounting for Magnetic Saturation Effects in Complex Multi-harmonic Model of Induction Machine

Computations of quasi-dynamic electromagnetic field of induction machines using the complex magnetic vector potential require the use of the so-called effective magnetization curves, i.e., such in which the magnetic permeability is proportional to the amplitudes of magnetic flux density B or magnetic field strength H, not their instantaneous values. There are several definitions of that parameter mentioned in the literature provided for the case when B or H are monoharmonic. In this paper, seven different methods of determining the effective magnetization curves are compared in relation to the use of a field-circuit multi-harmonic model of an induction machine. The accuracy of each method was assessed by computing the performance characteristics of a solid-rotor induction machine. One new definition of the effective permeability was also introduced, being a function of multiple variables dependent on amplitudes of all the harmonics considered. The analyses demonstrated that the best practical approach, even for the multi-harmonic case, is to express the effective magnetic permeability as the ratio of the amplitudes of the fundamental harmonics of the magnetic flux density and the magnetic field strength, and assuming the sinusoidal variation of the latter.

Model approach for electromagnetically excited mechanical vibrations in direct-drive wind turbines

In this paper a multi-physical modelling approach for calculating parasitic magnetic force excitations in wind turbine generators is presented. These parasitic excitations are dependent on the magnetic field distribution in the air gap and the air gap geometric shape, which is dependent on the external loads of the wind turbine. With this methodology mechanical multibody simulation is coupled with electromagnetic field calculation by means of finite-element calculation. First the general methodology and the calculation of the air gap width distribution is presented and subsequently the electromagnetic field and force calculation is explained.

Two-dimensional finite element mesh generation algorithm for electromagnetic field calculation* *Project supported by the National Natural Science Foundation of China (Grant Nos. 52077203 and 61701467) and the Natural Science Foundation of Zhejiang Province, China (Grant No. LY19E070003).

Two-dimensional finite element mesh generation algorithm for electromagnetic field calculation is proposed in this paper to improve the efficiency and accuracy of electromagnetic calculation. An image boundary extraction algorithm is developed to map the image on the geometric domain. Identification algorithm for the location of nodes in polygon area is proposed to determine the state of the node. To promote the average quality of the mesh and the efficiency of mesh generation, a novel force-based mesh smoothing algorithm is proposed. One test case and a typical electromagnetic calculation are used to testify the effectiveness and efficiency of the proposed algorithm. The results demonstrate that the proposed algorithm can produce a high-quality mesh with less iteration.

Calculation of electromagnetic field for very fast transient process in GIS

The calculation method of electromagnetic field generated by very fast transient process in GIS is studied. The VFTC is calculated, and the mathematical model of direct wire electromagnetic radiation is established according to the structure of GIS. The space electromagnetic field is calculated with VFTC as excitation source. The non-stationary VFTC simulation waveform is decomposed in combination with Hilbert yellow method. The electromagnetic field intensity of each decomposed waveform is calculated on the basis of mathematical model of direct wire electromagnetic radiation. Then the electromagnetic field intensity of fast transient process is reconstructed. The results show that the intensity of electromagnetic field decreases exponentially with the increase of distance. The method proposed solves the theoretical calculation of complex electromagnetic field for unsteady VFTC waveform that contains complex frequency components with transient characteristics in very fast transient process. That has theoretical guiding significance for the electromagnetic field calculation of very fast transient phenomenon in GIS.

A Macromodeling-Based Hybrid Method for the Computation of Transient Electromagnetic Fields Scattered by Nonlinearly Loaded Metal Structures

In this article, we present a hybrid numerical scheme to compute the transient electromagnetic fields scattered by a metallic structure loaded with lumped nonlinear loads. The proposed scheme is based on three successive steps. First, the field coupling problem to the structure with the nonlinear loads removed is solved in the frequency domain using a method-of-moments (MoM) formulation. The unloaded structure is thus characterized as a generalized multiport Thevenin equivalent, whose components are represented as time-domain operators by performing a set of rational approximations followed by closed-form Laplace transform inversion. Transient port voltages and currents in the presence of nonlinear loads are then computed using a standard circuit solver. As a last step, the substitution theorem is used to solve the radiation problem again in the frequency domain using a MoM solver, the results of which are then translated into the time domain by means of rational approximations and recursive convolution operations. The proposed method enables an accurate and efficient evaluation of the transient nonlinearly scattered fields by the loaded structure, with a good potential for scalability to large-scale high-complexity nonlinear shields. Extensive validations are provided to demonstrate the accuracy of the proposed method, which is here applied to the characterization of energy-selective shielding for protection of sensitive devices from high-intensity radiated fields.

Theoretical and NEC Calculations of Electromagnetic Fields Generated From a Multi-Phase Underground Cable

A generalized formulation of electromagnetic fields generated from a multi-phase underground cable is proposed based on a complete solution of Maxwell equations. The lateral electromagnetic field components, the shielding effect of cables and the phase currents at high frequencies of a three phase underground cable are evaluated by the newly derived formulas. The accuracies of the recently developed extended transmission line approach of underground cables are investigated based on the performance of electromagnetic field components. It is also shown that Numerical Electromagnetics Code verifies the results calculated from the new formulas presented in this article.

Research on the temperature rise characteristics of power transformers based on fluid-solid-thermal coupling

The problems of overheating and insulation are the main influencing factors to the operation status of power transformers. Based on the physical model of a 50MVA/110kV oil-immersed self-cooling transformer, the electromagnetic, temperature and fluid field are introduced to establish a three-dimensional temperature rise model of the transformer in this thesis. The loss obtained from the electromagnetic field calculation model is taken as a heat source and input into the transformer temperature rise model. The results show that the hot spot temperature occurs in the core column and increases with the maximum load current when the single-phase ground fault occurs, and the hot spot temperature in the transformer exceeds the limit value. The temperature distribution trends of the core and high and low voltage windings under rated conditions and overload conditions are similar. In addition, the average temperature rise of the windings under overload conditions exceeds the limit value.

An Efficient Method for Calculating the Lightning Electromagnetic Field Over Perfectly Conducting Ground

In the implementation of the Cooray–Rubinstein formula, the calculation of a lightning electromagnetic field over perfectly conducting ground accounted for most of the computation time. Commonly, evaluating the ideal lightning electromagnetic field is based on the numerical integration method. In practice, only a sufficiently small discretization step is essential to get an accurate result, which leads to a relatively large number of calculations and results in a lengthy computation time. Besides, the programming is relatively complicated because the propagation of the lightning current along the channel must be considered. In order to increase the efficiency and simplify the programming, an improved method is proposed in this paper. In this method, the evaluation of the ideal lightning electromagnetic field is equated with a summation of analytical formulae and a simple integral operation, so it would be more efficient and easily programmed. The validation of the proposed method is demonstrated by some simulation examples.

Parallel Algorithm for Electromagnetic Field Computation Based on Particle Simulation Algorithm

Based on current serial algorithms for electromagnetic field computation, the parallel algorithm concept where the “divide and conquer” approach is adopted has designed and implemented electromagnetic field computation in 3D rectangular coordinates, cylindrical coordinates and polar coordinates of CHIPIC software. The speedup ratio of the parallel algorithm is analyzed. Finally, the correctness and efficiency of the algorithm are verified through case studies.

Preliminary Design of DEMO PF Coils Based on EU DEMO 2018 Baseline

The dimensioning of Winding Packs and allocation of materials in DEMO PF coils is proposed based on the requirements defined by the EUROfusion 2018 DEMO baseline. The coils are pancake-wound and use two types of forced flow cable-in-conduit conductors. The conductor which uses NbTi has a high void fraction but has no separated low-impedance cooling channel. On the other hand, the conductor made using Nb3Sn has a separated low-impedance cooling channel and therefore low void fraction in the remaining cable space. Both the conductors have a rectangular cross-section. The design addresses the dimensioning of the Winding Pack (WP) based on the electromagnetic field calculations and stress analysis. The amount of superconductor, copper, and cable void fraction in the conductor are determined by the coil current, magnetic field and assumed temperature margin. The amount of structural material in the conductor jacket depends mainly on the fatigue stress corresponding to the pulsed operation of these coils. For PF1 and PF6 coils, the comparison of NbTi and Nb3Sn design options suggest a more efficient allocation of structural and superconducting material in the latter case. The WP dimensions do not significantly depend on the winding technique (pancake vs layer winding).

Predicting Multi-Order Magnetic Polaritons Resonance in SiC Slit Arrays by Mutual Inductor–Inductor–Capacitor Circuit Model

Abstract Magnetic polariton (MP) that couples electromagnetic waves with magnetic excitation can be predicted by equivalent inductor–capacitor (LC) circuit model. However, when the resonance frequencies of MP and surface phonon polariton (SPhP) is close, the absorption and transmission peaks predicted by LC circuit model are far different from solving electromagnetic field calculation results. In this work, absorption and transmission enhancements with a SiC slit array are theoretically demonstrated within the SiC phonon absorption band with finite difference time-domain (FDTD) method. The interactions between SPhP and MP are confirmed by electromagnetic field distributions. Mutual inductor–inductor–capacitor (MLC) circuit model is used to predict the multiorder MP resonance conditions, and the coupling between MP and SPhP is treated as a mutual inductor in MLC model. The geometric effects of SiC slit arrays are investigated and MLC circuit model works well. This study may contribute to the design and prediction of thermal radiative properties and micro-/nanostructure metamaterials thermal radiative properties database building.

Coupling analysis of transmission lines excited by space electromagnetic fields based on time domain hybrid method using parallel technique**Project supported by the National Natural Science Foundation of China (Grant No. 61701057) and the Chongqing Research Program of Basic Research and Frontier Technology, China (Grant No. cstc2017jcyjAX0345).

We present a time domain hybrid method to realize the fast coupling analysis of transmission lines excited by space electromagnetic fields, in which parallel finite-difference time-domain (FDTD) method, interpolation scheme, and Agrawal model-based transmission line (TL) equations are organically integrated together. Specifically, the Agrawal model is employed to establish the TL equations to describe the coupling effects of space electromagnetic fields on transmission lines. Then, the excitation fields functioning as distribution sources in TL equations are calculated by the parallel FDTD method through using the message passing interface (MPI) library scheme and interpolation scheme. Finally, the TL equations are discretized by the central difference scheme of FDTD and assigned to multiple processors to obtain the transient responses on the terminal loads of these lines. The significant feature of the presented method is embodied in its parallel and synchronous calculations of the space electromagnetic fields and transient responses on the lines. Numerical simulations of ambient wave acting on multi-conductor transmission lines (MTLs), which are located on the PEC ground and in the shielded cavity respectively, are implemented to verify the accuracy and efficiency of the presented method.

Parameters for calculation of three-dimensional electromagnetic field by asymptotic expansion method

The paper deals with an approximate analytical solution of a three-dimensional problem of the theory of electromagnetic field, which is based on the use of asymptotic expansion under the condition of a strong skin-effect for a field produced by a closed current-carrying loop located near a conducting half-space. It is noted that each member of an asymptotic series is determined with an error, the value of which depends on the value of a small parameter and increases with increasing the index of series member resulting in limited number of its members. It is identified that when using the method of asymptotic expansion, the number of members of a series can be limited by the relatively small number, which is determined by the specified limits of the allowable accuracy of calculation (relative error). The authors determine the optimal number of asymptotic series members, and indicate that calculation accuracy depends on the value of a small parameter, and for a specific conducting material it depends on the field frequency and the minimum distance from external field sources to a conducting body.

Electric Motor for Brakes – Optimal Design

<div class="section abstract"><div class="htmlview paragraph">A multi-objective optimal design of a brushless DC electric motor for a brake system application is presented. Fifteen design variables are considered for the definition of the stator and rotor geometry, pole pieces and permanent magnets included. Target performance indices (peak torque, efficiency, rotor mass and inertia) are defined together with design constraints that refer to components stress levels and temperature thresholds, not to be surpassed after heavy duty cycles. The mathematical models used for optimization refer to electromagnetic field and related currents computation, to thermo-fluid dynamic simulation, to local stress and vibration assessment. An Artificial Neural Network model, trained with an iterative procedure, is employed for global approximation purposes. This allows to reduce the number of simulation runs needed to find the optimal configurations. Some of the Pareto-optimal solutions resulting from the optimal design process are analysed. They show high improvements of the performance indices with respect to a reference solution.</div></div>

K-domain method for the fast calculation of electromagnetic fields propagating in graded-index media.

A conceptually straightforward method for the fast calculation of electromagnetic fields propagating in graded-index media is presented. More specifically, in this method, we convert Maxwell's curl equations into the spatial-frequency domain to obtain an ordinary differential equation (ODE), and subsequently solve the ODE with the 4th-order Runge-Kutta method. Compared to the traditional beam propagation methods, this method deals with vectorial fields accurately, without physical approximations, like the scalar field approximation or the paraxial approximation; numerically, this method takes advantage of the fast Fourier transform and the convolution theorem to achieve an efficient calculation.

HST calculation of a 10 kV oil‐immersed transformer with 3D coupled‐field method

Transformer winding hot-spot temperature (HST) is one of the important factors affecting transformer oil–paper insulation deterioration. This study presents a three-dimensional coupled electromagnetic-fluid-thermal analysis method for HST calculation in a 10 kV oil-immersed distribution transformer, the influence of the transformer internal metal structure parts on the HST of the winding is considered in the simulation. Combining electromagnetic-field calculation with no-load test and load test of the transformer provides a more accurate method to determine internal losses of the transformer. Taking those power losses as heat sources, the transformer fluid-thermal field analysis is conducted with the finite volume method. The variation of physical parameters of transformer oil with temperature is considered in the simulation. On the basis of the equivalent thermal resistance theory, the equivalent thermal conductivities of transformer windings are obtained. The simulation results deduced from the proposed method agree well with the experimental ones, which are obtained with fibre optic temperature sensors during the transformer temperature rise test, the maximum temperature difference is <3°C. The results validated the validity and accuracy of the proposed transformer HST calculation method.

Analysis of Electromechanical Processes in Asynchronous Machines during Tests by the Loading-Back Method with Energy Recovery in the Network

The article discusses the interrelated electromechanical processes in asynchronous machines when testing by the loading-back method with energy recovery in the network. We analyze a system of two asynchronous machines connected by a common shaft, in which one machine operates as an engine with the voltage supply of increased frequency from the frequency converter and the external machine operates as a network generator. Electromechanical processes in machines have an influence on each other. We have carried out the simulation of electromechanical processes in the motors with allowance for several factors—namely, different degrees of saturation of magnetic cores, torque equalization, and the change in parameters of the windings when changing the operating mode with a nonsinusoidal voltage supply to the asynchronous motor from the frequency converter. A modeling technique with mutual matching of the electromagnetic field models of machines through the relationship of torques on the shaft, based on system minimization of the electromagnetic energy functionals has been presented. The results of simultaneous numerical calculations of interrelated electromagnetic fields in machines and electromechanical processes have been presented. The calculations of electromechanical processes and the characteristics of an asynchronous motor–generator system with a common shaft, mutual load and energy recovery in the network have been performed. The results of experimental studies of a two-machine unit are presented, confirming the theoretical results. It is established that the application of the calculation technique with direct computing the interrelated electromagnetic fields in the engine and generator with allowance for the electromagnetic torque on the shaft provides an error of no more than 7% compared with the experiment.