Flnite Element Research Articles

A NEW APPROACH TO ANALYSIS OF INDUCTION MOTORS WITH ROTOR FAULTS DURING STARTUP BASED ON THE FINITE ELEMENT METHOD

The increasing popularity of a so-called transient motor current signature analysis requires the fault diagnostics parameters which could not be exposed to other factors irrelevant to the fault to make a precise assessment of the failure severity level. This challenging task needs a precise modeling of faulty motor behavior in various operating conditions at difierent fault severity levels. This paper introduces a new approach to the flnite element analysis of an induction motor with broken rotor bars during startup. The approach is based on the principle of superposition and contributes to examination of the fault rotor backward rotating magnetic fleld and current components produced by such fleld separating them from stator currents. It gives a new sight on the behavior of a faulty motor during startup for the diagnosis purposes. Further analysis of the simulation data by means of the Extended Park's Vector Approach and the continuous wavelet transform and its experimental validation is also presented in the paper.

GENERAL 2-D TRANSIENT EDDY CURRENT FORCE EQUATIONS FOR A MAGNETIC SOURCE MOVING ABOVE A CONDUCTIVE PLATE

When a magnetic source is moved and/or oscillating above a conductive linear plate a traveling time varying magnetic fleld is created in the airgap. This fleld induces eddy currents in the plate that can simultaneously create normal and tangential forces. The transient flelds and the forces created by the magnetic source are modeled using a novel 2-D analytic based A-` method in which the presence of the source fleld is incorporated into the boundary conditions of the plate. The analytic based solution is obtained by using the spatial Fourier transform and temporal Laplace transform. The performance of the method is compared with a 2-D transient flnite element model with a Halbach rotor source fleld. The derived transient force equations are written in a general form so that they can be applied to any magnetic source.

DESCRIPTION OF MULTIPLY CONNECTED REGIONS WITH INDUCED CURRENTS USING <I>T</I>-<I>T</I><sub>0</sub> METHOD

The paper presents the description of multiply connected conducting regions (MCCR) in the flnite elements space. In order to deflne induced currents distribution in multiply connected regions, an innovative method of combined vector potentials T and T0 has been suggested. The equations of T-T0 method have been presented. The relations describing sources for the fleld of induced currents in the discussed regions have been given. The proposed method has been applied to solve Problem No. 7 of the International TEAM Workshops. The selected results of calculation have been compared with the measurement results.

A NOVEL COMPACT SPLIT RING SLOTTED ELECTROMAGNETIC BANDGAP STRUCTURE FOR MICROSTRIP PATCH ANTENNA PERFORMANCE ENHANCEMENT

A novel design of an electromagnetic bandgap (EBG) structure based on the uniplanar compact EBG (UCEBG) concept is proposed in this paper. The structure is realized by inserting split- ring slots inside two reversely connected rectangular patches, which is known as a split-ring slotted electromagnetic bandgap (SRS-EBG) structure. The bandgap properties of the EBG structure are examined by the suspended microstrip line and flnite element methods (FEM). The achieved bandgaps have widths of 4.3 (59.31%) and 5.16GHz (38.88%), which are centered at 7 and 13GHz, respectively. The SRS-EBG is applied to enhance the performance of a single-element microstrip patch antenna (at 7GHz) and a two-element array (at 13GHz) conflguration. A wider bandwidth is obtained with a better re∞ection coe-cient level for the single element antenna; a reduction in mutual coupling of more than 20.57dB is obtained for the array design. In both cases, the gain and radiation characteristics are improved. The results are verifled by measuring the fabricated lab prototype, and a comparison with the computed results showed good agreement.

SOLVING PERIODIC EIGENPROBLEMS BY SOLVING CORRESPONDING EXCITATION PROBLEMS IN THE DOMAIN OF THE EIGENVALUE

Periodic eigenproblems describing the dispersion behavior of periodically loaded waveguiding structures are considered as resonating systems. In analogy to resonators, their eigenvalues and eigensolutions are determined by solving corresponding excitation problems directly in the domain of the eigenvalue. Arbitrary excitations can be chosen in order to excite the desired modal solutions, where in particular lumped ports and volumetric current distributions are considered. The method is employed together with a doubly periodic hybrid flnite element boundary integral technique, which is able to consider complex propagation constants in the periodic boundary conditions and the Green's functions. Other numerical solvers such as commercial simulation packages can also be employed with the proposed procedure, where complex propagation constants are typically not directly supported. However, for propagating waves with relatively small attenuation, it is shown that the attenuation constant can be determined by perturbation methods. Numerical results for composite right/left-handed waveguides and for the leaky modes of a grounded dielectric slab are presented.

ANALYSIS OF ELECTROMAGNETIC PLANE WAVE SCATTERING FROM 2-D PERIODIC ARRANGEMENTS OF POSTS

In the paper, the analysis of electromagnetic wave scattering from frequency selective surface is presented. The surface is composed of periodically arranged posts. The multimodal scattering matrix of such structure is derived and the transmission and re∞ection characteristic for the structure with arbitrary plane wave illumination are calculated. The exact full-wave theory based on the mode-matching method is applied to develop an e-cient theory to analyze such structures. The validity and accuracy of the approach are verifled by comparing the results with those obtained from alternative methods. The analysis of plane wave scattering form the frequency selective surface (FSS) composed of periodic arrangements of scatterers is conducted in this paper. The constructive elements of this structure are comparable in size to the operation wavelength and are composed of conducting and dielectric material. FSSs when multilayered can be utilized as an electromagnetic band structure (EBG) in microwave wavelength range or photonic band structure (PBG) in optical range. Recently, EBGs and PBGs are of great interest due to their extraordinary properties and potential applications, e.g., fllters, polarizers, substrates for radiating elements, or optical switches (1{14). Many numerical techniques have been utilized to investigate band gap structures. The most popular are the cylindrical-harmonic expansion method (15), the flnite element method (16), the flnite difierence method (17), and Fourier modal method (18). FSSs can also flnd application in polarizers

ELECTROMAGNETIC ANALYSIS OF A MODULAR FLUX-SWITCHING PERMANENT-MAGNET MOTOR USING FINITE-ELEMENT METHOD

This paper proposes a new 3-phase ∞ux-switching permanent-magnet (FSPM) motor termed as modular FSPM (M- FSPM) motor, for high reliability applications. Due to PMs in the stator, the proposed motor ofiers high e-ciency, simple and robust rotor structure, and good thermal dissipation conditions. The key is the new motor topology which incorporates the concept of fault- tolerant teeth to provide the desired decoupling among phases. By using flnite element method, the proposed M-FSPM motor is analyzed as compared with the existing fault-tolerant FSPM (FT-FSPM) motor. The results show that the proposed M-FSPM motor not only retains the merits of high power density, strong mechanical integrity, good immunity from thermal problem and high torque capability, but also ofiers lower torque ripple, higher average torque and lower cost than the existing FT-FSPM motor. A proposed M-FSPM motor is designed and built for exempliflcation. Experimental results of the prototype are given to conflrm the validity of the proposed motor.

RESOLUTION OF MULTIPLE CONCEALED THREAT OBJECTS USING ELECTROMAGNETIC PULSE INDUCTION

The detection and identiflcation of conducting objects using electromagnetic pulses to excite circulating eddy currents within the object is demonstrated by numerical simulation using a flnite element time domain electromagnetic solver. The ability to discriminate between objects is based on the decay rate of the induced currents in the object, typically » 100S. The decay rates are difierent for a wide variety of everyday objects, allowing threat objects such as handguns, grenades and knives to be discriminated from benign objects such as mobile phones handsets, watches, keys, etc.. Crucially, the time constant characterising an object depends only upon the electrical properties of the object (conductivity) and the shape and size of the object; the orientation of the object is irrelevant. This aspect independence of temporal current decay rate forms the basis of a potential object detection and identiflcation system. By application of an algorithm based on the generalized pencil of function method, the authors demonstrate the ability to efiectively count and indentify multiple objects carried in close proximity providing that the objects do not have very similar time constants and that signal to noise ratio is high.

MULTI-PHASE SYNCHRONOUS MOTOR SOLUTION FOR STEERING APPLICATIONS

This paper presents the analysis of a six-phase permanent magnet synchronous machine (PMSM6) dedicated for electrical power steering system applications. The motor design is brie∞y described, as well as the construction of the studied motor. The study is validated by flnite element method and via experimental results. Some simulated results prove the machine's capability to work even in faulty conditions. The operation of the machine was evaluated in generator and motor operation. In motor operation, the PMSM6 was fed based on scalar control.

IMPROVEMENT TO PERFORMANCE OF SOLID-ROTOR-RINGED LINE-START AXIAL-FLUX PERMANENT-MAGNET MOTOR

This paper presents two design-and-analysis cases of a line- start axial-∞ux permanent-magnet motor: with solid rotor and with composite rotor. For a novel structure of the motor, two concentric unilevel spaced raised rings are added to the inner and outer radii of its rotors to enable auto-start capability. The composite rotor was coated by a thin (0.05mm) layer of copper. The basic equations for the solid rotor ring were extracted. The motor's lack of symmetry necessitated 3D time-stepping flnite element analysis, conducted via Vector Field Opera 14.0, which evaluated the design parameters and predicted the motor's transient performance. Results of the FEA show the composite rotor signiflcantly improving both starting torque and synchronization capability over solid rotor.

A THREE DIMENSIONAL ANALYTICAL CALCULATION OF THE AIR-GAP MAGNETIC FIELD AND TORQUE OF COAXIAL MAGNETIC GEARS

In order to solve the defects that the end-efiect of magnetic fleld is ignored in two dimension (2-D) analytical method or 2-D flnite element method (FEM); meanwhile, mass computer resource and time for parametric design or optimization are wasted in three dimension (3-D) FEM, a concise and e-cient 3-D analytical approach is put forward for the calculation of the air-gap magnetic fleld and torque of coaxial magnetic gears. Based on the cylindrical coordinates where a coaxial magnetic gear is in, the equivalent current model and vector magnetic potential equation of permanent magnets in high speed permanent magnetic ring are constituted. By superposed magnetic ∞ux density of every tile permanent magnets on high speed permanent magnetic ring in cylindrical coordinates, a air-gap magnetic fleld 3-D analytical formula is set up without ferromagnetic pole-pieces; in the interest of modulated air-gap magnetic fleld 3-D analytical formula with ferromagnetic pole-pieces, three types boundary conditions using state equations of contact surfaces between ferromagnetic pole-pieces and air-gap are established by a thorough analysis of the modulate mechanism of ferromagnetic pole-pieces. Finally, magnets of the low speed permanent magnetic ring are reduced to a distribution of equivalent current, which experience the Lorentz force in modulated magnetic fleld of high speed permanent magnetic ring for torque calculation. The integrals in all aforementioned calculation are axial, so the end-efiect is embodied in above analytical model and more precise than 2-D analytical method or 2-D FEM. As the calculation results, the formula is accurate but faster than the 3-D FEM. The analytical model is suited for programmable calculation and that will make the structural and parametric design or optimization of coaxial magnetic gears simple and timesaving.

ANALYTICAL FIELD CALCULATION FOR LINEAR TUBULAR MAGNETIC GEARS USING EQUIVALENT ANISOTROPIC MAGNETIC PERMEABILITY

Linear magnetic gears take the deflnite merit of direct force ampliflcation or speed reduction without using any bulky, ine-cient rotary-to-linear mechanism. In this paper, an analytical calculation approach to determine the performance of linear tubular magnetic gears is proposed. The key is to adopt the concept of anisotropic magnetic permeability to handle the fleld-modulation region which consists of iron rings and airspaces in a zebra-striped manner. By solving the Laplace's and Poisson's equations in the linear tubular magnetic gear, the corresponding magnetic fleld distributions can be analytically determined. Finally, the analytical calculation results are compared with the numerical results obtained from the flnite element method, hence verifying the validity of the proposed analytical fleld calculation.

ANALYSIS OF AXIALLY MAGNETIZED PERMANENT MAGNET BEARING CHARACTERISTICS

The use of permanent magnets as bearings has gained attention of researchers nowadays. The characteristics of forces and moments have to be analysed thoroughly for the proper design of permanent magnet bearings. This paper presents a mathematical model of an axially magnetized permanent magnet bearing (ring magnets) using Coulombian model and a vector approach to estimate the force, moment and stifiness. A MATLAB code is developed for evaluating the parameters for flve degrees of freedom (three translational and two rotational) of the rotor. Furthermore, it is extended to analyse stacked ring magnets with alternate axial polarizations. The proposed model is validated with the available literature. Comparison of force and stifiness results of the presented model with the results of three dimensional (3D) flnite element analysis using ANSYS shows good agreement. Finally, the cross coupled stifiness values in addition to the principal stifiness values are presented for elementary structures and also for stacked structures with three ring permanent magnets.

DESIGN OPTIMIZATION OF TWO SYNCHRONOUS RELUCTANCE MACHINE STRUCTURES WITH MAXIMIZED TORQUE AND POWER FACTOR

The subject of this article is to optimize the design of synchronous reluctance machines with massive rotor and multi-∞ux barrier rotor. The optimization procedure, which aims to improve simultaneously the machines' torque and the power factor, uses the cyclic coordinate method coupled with the magnetostatic flnite- element (FE) fleld solutions. The optimization results regarding these two types of machines, which provide the optimized rotor geometrical dimensions and the in∞uence of the current angle, are discussed.

ANALYSIS OF A QUADRUPLE CORNER-CUT RIDGED/VANE-LOADED CIRCULAR WAVEGUIDE USING SCALED BOUNDARY FINITE ELEMENT METHOD

This paper presents an extension of the recently-developed e-cient semi-analytical method, namely scaled boundary flnite element method (SBFEM) to analyze quadruple corner-cut ridged circular waveguide. Owing to its symmetry, only a quarter of its cross- section needs to be considered. The entire computational domain is divided into several sub-domains. Only the boundaries of each sub- domain are discretized with line elements leading to great ∞exibility in mesh generation, and a variational approach is used to derive the scaled boundary flnite element equations. SBFEM solution converges in the flnite element sense in the circumferential direction, and more signiflcantly, is analytical in the radial direction. Consequently, singularities around re-entrant corners can be represented exactly and automatically. By introducing the \dynamic stifiness of waveguide, using the continued fraction solution and introducing auxiliary variables, a generalized eigenvalue equation with respect to wave number is obtained without introducing an internal mesh. Numerical results illustrate the accuracy and e-ciency of the method with very few elements and much less consumed time. In∞uences of corner-cut ridge dimensions on the wave numbers of modes are examined in detail. The single mode bandwidth of the waveguide is also discussed. Therefore, these results provide an extension to the existing design data for ridge waveguide and are considered helpful in practical applications.

A NEW FAST METHOD OF PROFILE AND WAVEFRONT REDUCTION FOR CYLINDRICAL STRUCTURES IN FINITE ELEMENTS METHOD ANALYSIS

We present a new accurate node's renumbering method for minimizing the proflle of stifiness matrix arising in flnite elements problems. This method is suitable for cylindrical structures like electrical rotating machines and is especially intended for movement consideration by the moving band method. The structure is divided into sectors classifled in a special way. The nodes contained in each sector are classifled according to their radius value in regressing order. We show that the performances of the method are better than the most popular ones proposed in the literature. Application for a permanent magnet synchronous machine is presented. Application for flnite elements analysis of a permanent synchronous machine in motion is achieved.

FEM MODELING FOR PERFORMANCE EVALUATION OF AN ELECTROMAGNETIC ONCOLOGY DEEP HYPERTHERMIA APPLICATOR WHEN USING MONOPOLE, INVERTED T, AND PLATE ANTENNAS

This study focuses on the evaluation of the performance of a rectangular waveguide for deep hyperthermia when difierent antennas are used. Although there are several models of hyperthermia applicators, there are no studies of the advantages of employing difierent antennas for waveguides used in deep seated tumor treatments. Monopole antennas are the most used radiating elements inside waveguides. Here, the modeling of a monopole and two new proposed antennas, inverted T and plate, in order to flnd their optimal performance is presented. Parameters like output power, SWR and transmission coe-cient generated for each modeled antenna were calculated by using the flnite element method. The antennas with the best performance were selected in order to model an applicator-phantom system, which was used to calculate the temperature distributions generated inside the muscle phantom. The models were based on Maxwell and bioheat equations. Finally, thermal distributions were obtained and compared. The results indicate that the plate antenna generated a better focusing. The SWR obtained was 1.25, the output power was 54.71W of 66W applied, and the 42 - C isotherm had a size of 2cm £ 2cm.

FETD COMPUTATION OF THE TEMPERATURE DISTRIBUTION INDUCED INTO A HUMAN EYE BY A PULSED LASER

In this paper we present the three-dimensional flnite element time domain model of the human eye exposed to pulsed holmium: YAG laser radiation used in thermokeratoplasty procedure. The model is based on the Pennes' bioheat transfer equation and takes into account the focusing action of the lens. The absorption of laser energy inside the eye tissues is modeled using the Lambert-Beer's law. Model takes into account the pulse temporal proflle. The maximum temperature values obtained from steady state and transient analysis are compared against those reported from other papers. Finally, sensitivity analysis of several parameters on the calculated temperature fleld is carried out.

EFFECT OF THE METAL SHEET THICKNESS ON THE FREQUENCY BLUESHIFT IN SINGLE LAYER COMPOSITE MATERIALS AT KA MICROWAVE FREQUENCY

The frequency shift of the transfer function of single layer composite materials has been analyzed and tested. The efiects are studied by means of planar pseudo-elliptical fllters in Ka waveguide. The fllters, consisting of a frequency selective surface placed perpendicularly to the waveguide axis, have been realized by a high resolution photolithographic technique. Deviations of the experimental transfer functions from the simulation are analyzed with particular emphasis to the efiect of metal thickness. The flnite thickness of the metal constituting the frequency selective surface causes a shift of the transfer function towards high frequencies (blueshift), attributed to dipole-dipole interaction in the metal layer. Such an efiect is only partially predicted by full wave analysis based on flnite element method. The increase of the thickness determines a reduction of the attenuation for thickness values between 10 and 100 skin depths.

TIME-HARMONIC CURRENT DISTRIBUTION ON CONDUCTOR GRID IN HORIZONTALLY STRATIFIED MULTILAYER MEDIUM

This paper presents a novel time-harmonic electromag- netic model for determining the current distribution on conductor grids in horizontally stratifled multilayer medium. This model could be seen as a basis of the wider electromagnetic model for the frequency-domain transient analysis of conductor grids in multilayer medium. The total number of layers and the total number of conductors are completely arbitrary. The model is based on applying the flnite element technique to an integral equation formulation. Each conductor is subdivided into segments with satisfying the thin-wire approximation. Complete elec- tromagnetic coupling between segments is taken into account. The computation of Sommerfeld integrals is avoided through an efiective approximation of the attenuation and phase shift efiects. Computation procedure for the horizontally stratifled multilayer medium is based on the successful application of numerical approximations of two kernel functions of the integral expression for the potential distribution within a single layer, which is caused by a point source of time-harmonic cur- rent. Extension from the point source to a segment of the earthing grid conductors is accomplished through integrating the potential con- tribution due to the line of time-harmonic current source along the segments axis.