Flnite Element Analysis Research Articles

Fast and robust femur segmentation from computed tomography images for patient-specific hip fracture risk screening

ABSTRACT Osteoporosis is a common bone disease that increases the risk of bone fracture. Hip-fracture risk screening methods based on flnite element analysis depend on segmented computed tomography (CT) images; however, current femur segmentation methods require manual delineations of large data sets. Here we propose a deep neural network for fully automated, accurate, and fast segmentation of the proximal femur from CT. Evaluation on a set of 1147 proximal femurs with ground truth segmentations demonstrates that our method is apt for hip-fracture risk screening, bringing us one step closer to a clinically viable option for screening at-risk patients for hip-fracture susceptibility.

DESIGN AND EXPERIMENT OF A PERMANENT MAGNET TUBULAR LINEAR GENERATOR FOR WAVE ENERGY CONVERSION SYSTEM

In this paper, ∞ux of permanent magnet tubular linear generator (PMTLG) is modeled and analyzed. With the model, air-gap leakage ∞ux coe-cient can be expressed analytically in terms of permanent magnet dimensions and air-gap width. The validity of analytical expression of air-gap leakage ∞ux coe-cient is verifled by flnite element analysis (FEA) with a maximum error of 6.8%. Furthermore, longitudinal end ∞ux's in∞uence on the detent force of PMTLG is analyzed in detail with the model. A detent force minimization technique is deduced from the analysis results, and conflrmed by FEA. Finally, after optimization of air-gap leakage ∞ux coe-cient and detent force, a PMTLG is built and experimented.

IMPROVEMENT OF THE COUPLING FACTOR OF LITZ-WIRE COIL PAIR WITH FERRITE SUBSTRATE FOR TRANSCUTANEOUS ENERGY TRANSFER SYSTEM

This paper presents an optimized design of Litz-wire coil pair with ferrite substrates based on a set of analytical expressions and a 2-D flnite-element analysis (FEA) in a way that the coupling coe-cient is maximized. An investigation is made on key structure parameters of coils (e.g., structure of Litz-wire, number of turns, and number of layers) to determine their in∞uence on self-inductance and mutual inductance respectively. The in∞uence of ferrite substrate (e.g., relative permeability and thickness) is also considered. Difierent types of fabricated coils are used to verify all analytical expressions and optimization methods, and it is found that the theoretical predictions and simulations are in agreement with the measured results.

PULSE COMPRESSION WITH GAUSSIAN WEIGHTED CHIRP MODULATED EXCITATION FOR INFRARED THERMAL WAVE IMAGING

This paper proposes a novel signal processing approach to thermal non-destructive testing by incorporating Gaussian window function onto the linear frequency modulated incident heat ∞ux to achieve better pulse compression properties. The present work highlights a flnite element analysis based modeling and simulation technique in order to test the capabilities of the proposed windowing scheme over the conventional frequency modulated thermal wave imaging method. It is shown that by using Gaussian weighted chirp thermal stimulus, high depth resolution can be achieved.

ROBUST CYLINDRICAL PLASMONIC NANO-ANTENNAS FOR LIGHT-MATTER INTERACTION

A cylindrical metallic plasmonic nano-antenna consisting of a shell supporting a disk, named capped shell, is proposed and studied by frequency domain flnite element analysis. This new topology is shown to be weakly dependent on the radius of the structure and is therefore suitable for fabrication by parallel processes such as island lithography which generates a pseudo-random array with a distribution of diameters. Furthermore, compared to similar resonators such as rods, disks and shells, the capped shell generates a larger volume with high flelds, and is hence useful as a nano-antenna for light-matter interaction.

DESIGN OPTIMIZATION AND ANALYSIS OF AFPM SYNCHRONOUS MACHINE INCORPORATING POWER DENSITY, THERMAL ANALYSIS, AND BACK-EMF THD

This paper presents the design and analysis of an inside-out axial-∞ux permanent-magnet (AFPM) synchronous machine optimized by genetic algorithm (GA) based sizing equation, flnite element analysis (FEA) and flnite volume analysis (FVA). The preliminary design is a 2-pole-pair slotted TORUS AFPM machine. The designed motor comprises sinusoidal back-EMF waveforms, maximum power density and the best heat removal. The GA is used to optimize the dimensions of the machine in order to achieve the highest power density. Electromagnetic fleld analysis of the candidate machines from GA with various dimensions is then put through FEA in order to obtain various motor characteristics. Based on the results from GA and FEA, new candidates are introduced and then put through FVA for thermal behavior evaluation of the designed motors. Techniques like modifying the winding conflguration and skewing the permanent magnets are also investigated to attain the most sinusoidal back-EMF waveform and reduced cogging torque. The performance of the designed 1kW, 3-phase, 50Hz, 4-pole AFPM synchronous machine is tested in simulation using FEA software. It is found that the simulation results fully agree with the designed technical speciflcations. It is also found from FVA results that the motor temperature reaches

TWO SIMPLE ANALYTICAL MODELS, DIRECT AND INVERSE, FOR SWITCHED RELUCTANCE MOTORS

This paper presents two simple analytical models of the switched reluctance motor. The flrst model is constructed on two ∞ux linkage-current characteristics: the aligned position one, calculated via flnite element analysis (FEA), and the unaligned position characteristic calculated by using motor geometry data. The second model is based on three ∞ux linkage-current characteristics: the aligned, unaligned and average one, obtained by employing the FEA. In both cases the direct and inverse models are deflned. The models consider the core nonlinearity and the in∞uence of the rotor position on the motor behavior. The estimated magnetizing and torque characteristics are compared with that calculated via two dimensions FEA for a switched reluctance motor (SRM) sample and with the test bench obtained ones. The merits and the drawbacks of the models are evinced.

FINITE ELEMENT ANALYSIS AND EXPERIMENTAL STUDY OF THE NEAR-MAGNETIC FIELD FOR DETECTION OF ROTOR FAULTS IN INDUCTION MOTORS

This paper deals with the flnite element analysis and experimental study concerning the in∞uence of the broken bar and rotor dynamic eccentricity faults on the magnetic fleld outside a squirrel-cage induction motor. The spatial distribution of the magnetic fleld, the time variation of the magnetic ∞ux density at a point outside the machine and the time variation of the electromotive force delivered by a coil sensor are evaluated based on the flnite element models of the healthy and faulty states of the motor. The increase of amplitude from the healthy to the faulty states of some low frequency harmonics measured in the near-magnetic fleld is emphasized. For broken bar fault, the increase of the amplitudes of speciflc harmonics of the coil sensor electromotive force, with frequency lower than 25Hz, is experimentally conflrmed.

ANALYSIS OF RADIAL 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.

AN EMI INVERSING PROBLEM FOR LANDMINE CHARACTERIZATION BASED ON IMPROVED PARTICLE SWARM OPTIMIZATION AND FINITE ELEMENT ANALYSIS

This paper discusses the characterization of landmine by using the electromagnetic induction technique (EMI). The proposed approach is based on the identiflcation of the physical and geometrical properties of a landmine, from the sensor response. But in such an identiflcation, the inverse problem is unavoidable. At flrst, we begin by simulating the landmine signature by solving a direct problem using the flnite element method which constitutes the direct model. After that, we determine the landmine characteristics by using an inverse model based on a cost function optimization. This model is based on an iterative process which coupling flnite element analysis and Particles Swarm Optimization (PSO). In this step, we apply two PSO techniques: the Standard PSO (SPSO) and the Improved PSO (IPSO), and discuss the problem of local minima of the cost function. The proposed iterative model is applied to determine the conductivity, geometry, and depth of metallic landmine from its signature measured by EMI. The numerical solution gives good results for the identiflcation of landmine.

DIFFERENTIAL FORMS INSPIRED DISCRETIZATION FOR FINITE ELEMENT ANALYSIS OF INHOMOGENEOUS WAVEGUIDES

We present a difierential forms inspired discretization for variational flnite element analysis of inhomogeneous waveguides. The variational expression of the governing equation involves transverse flelds only. The conventional discretization with edge elements yields an unsolvable generalized eigenvalue problem since one of the sparse matrix is singular. Inspired by the difierential forms where the Hodge operator transforms 1-forms to 2-forms, we propose to discretize the electric and magnetic fleld with curl-conforming basis functions on the primal and dual grid, and discretize the magnetic ∞ux density and electric displacement fleld with the divergence-conforming basis functions on the primal and dual grid, respectively. The resultant eigenvalue problem is well-conditioned and easy to solve. The proposed scheme is validated by several numerical examples.

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.

SLOT-LESS TORUS SOLID-ROTOR-RINGED LINE-START AXIAL-FLUX PERMANENT-MAGNET MOTOR

This paper presents the design, analysis, and prototyping of a novel axial-∞ux permanent-magnet (AFPM) motor capable of auto-starting. The preliminary design is a slot-less double-sided solid-rotor line-start AFPM motor with 4 poles for high torque density and stable rotation. One spaced raised ring was added to the inner radii of the rotor disc for smooth line-start motor. The design allows the motor to operate at both starting and synchronous speeds. The basic equations for the solid ring of the rotor of the proposed axial-∞ux permanent-magnet motor are presented. Non- symmetry of the designed motor led to its 3D time-stepping flnite element analysis (FEA) via ANSYS 13.0, which evaluated the design parameters and predicted the transient performance. The designed motor was fabricated and tested, the experimental results showing good agreement with FEA simulation results. The prototype motor showed high starting torque and good synchronization.

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.

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.

INTERACTION OF AN ASYMMETRIC SCANNING NEAR FIELD OPTICAL MICROSCOPY PROBE WITH FLUORESCENT MOLECULES

We present a numerical analysis of the interaction between novel scanning near fleld optical microscopy probes based on an asymmetric structure and a single ∞uorescent molecule. Our flnite element analysis shows how such near fleld probes can be efiectively used for high resolution detection of single molecules, in particular those with a longitudinal dipole moment. At the same time, ∞uorescent molecules can be exploited as point-like probes of the single vectorial components of the near fleld distribution at the probe apex, providing a powerful tool for near fleld probe characterization.

COMPARISON OF TWO TYPES OF DUAL LAYER GENERATOR IN FIELD ASSISTED MODE UTILIZING 3D-FEM AND EXPERIMENTAL VERIFICATION

This paper presents the comparison results between two new generator conflgurations. These generator units are namely a fleld assisted switched reluctance generator (SRG) and a brushless dc (BLDC) generator. No permanent magnets are used in either unit. The fleld assisted SR generator consists of two magnetically dependent stator and rotor sets (layers), where each stator set includes twelve salient poles with windings wrapped around them, while the rotor comprises of eight salient poles without any winding or permanent magnet. There is a stationary reel, which has the fleld coil wrapped around it and is placed between the two-stator sets. The BLDC generator is also made up of two magnetically dependent stator and rotor sets, but each stator set includes nine salient poles with windings wrapped around them while, the rotor comprises of six salient poles without any windings or permanent magnets. There is also a stationary reel between the two layers to produce the magnetic fleld through the motor assembly. This magnetic fleld travels through a guide to the rotor then the stator and flnally completes its path via the generator housing. The generator phase windings for each layer are connect such that all the stator poles in that set can have either north or south pole conflguration while the stator poles in the other layer have the opposite pole arrangement. This type of connection can be used in motoring mode as well. To evaluate the performance of the generators, two types of analysis, namely, numerical technique and experimental study have been utilized. In the numerical analysis, three dimensional flnite element analysis is employed, whereas in the experimental study, proto-types have been built and tested.

THE NOVEL TWO PHASE FIELD-ASSISTED HYBRID SRG: MAGNETIO STATIC FIELD ANALYSIS, SIMULATION, AND EXPERIMENTAL CONFIRMATION

This paper introduces a new conflguration for a two phase fleld assisted hybrid switched reluctance generator, which can operate in motoring mode as well. This concept allows higher output power production compare to standard SRG. The proposed novel generator consists of two magnetically independent stator and rotor sets (layers), where each stator set includes four salient poles with windings wrapped around them, while the rotor comprises of two salient poles with difierent arc lengths and no windings. There is a stationary reel, which has the fleld coils wrapped around it and is placed between the two-stator sets. In this format, the developed magnetic fleld from the stator poles travels to the rotor then to the rotor shaft and flnally completes its path via the generator housing. To evaluate the generator performance, two types of analysis, namely the numerical technique and the experimental study have been utilized. The analysis is carried out for the machine in self exited generator mode as well as fleld assisted mode. In the numerical analysis, the flnite element analysis is employed, whereas in the experimental study, a proto-type generator has been built and tested.

AN IMPROVED ALGORITHM FOR MATRIX BANDWIDTH AND PROFILE REDUCTION IN FINITE ELEMENT ANALYSIS

In flnite element analysis, methods for the solution of sparse linear systems of equations usually start out with reordering the coe-cient matrix to reduce its bandwidth or proflle. The location of pseudo-peripheral nodes is an important factor in the bandwidth and proflle reduction algorithm. This paper presents a heuristic parameter, called the \width-depth ratio and denoted by •. With such a parameter, suitable pseudo-peripheral nodes would be found; the distance between which could be much close to or even to be the diameter of a graph compared with Gibbs-Poole-Stockmeyer (GPS) algorithm. As the new parameter was implemented in GPS algorithm, an improved bandwidth and proflle reduction algorithm is proposed. Simulation results show that with the proposed algorithm, sometimes bandwidth and proflle could be reduced by as great as 33.33% and 11.65%, respectively, compared with the outcomes in GPS algorithm, while the execution time of both algorithms is close. Empirical results show that the proposed algorithm is superior to GPS algorithm in reducing bandwidth or proflle.

MAGNETIO STATIC FIELD ANALYSIS REGARDING THE EFFECTS OF DYNAMIC ECCENTRICITY IN SWITCHED RELUCTANCE MOTOR

In this paper, a novel view of a switched reluctance motor under dynamic eccentricity fault to provide the precise and reliable electromagnetics model is presented. It describes the performance characteristics and comparison results of the 6/4 switched reluctance motor with dynamic rotor eccentricity utilizing three-dimensional flnite element analysis. The results obtained using three-dimensional flnite element analysis of the switched reluctance motor includes ∞ux- linkages, terminal inductance per phase, mutual inductances and static torque for various eccentric motor conditions. In this analysis the end efiects and axial fringing flelds for simulating reliable model are obtained and presented. The paper continues with comparing these results with the ones obtained for the same motor proflle but utilizing two-dimensional flnite element method. Finally, Fourier analysis is carried out to study the variations of torque harmonics.