Flnite Element 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.

LEAST-SQUARES SPECTRAL COLLOCATION PARALLEL METHODS FOR PARABOLIC PROBLEMS

In this paper, we study the flrst-order system least- squares (FOSLS) spectral method for parabolic partial difierential equations. There were lots of least-squares approaches to solve elliptic partial difierential equations using flnite element approxi- mation. Also, some approaches using spectral methods have been studied in recent. In order to solve the parabolic partial difieren- tial equations in parallel, we consider a parallel numerical method based on a hybrid method of the frequency-domain method and flrst-order system least-squares method. First, we transform the parabolic problem in the space-time domain to the elliptic prob- lems in the space-frequency domain. Second, we solve each elliptic problem in parallel for some frequencies using the flrst-order sys- tem least-squares method. And then we take the discrete inverse Fourier transforms in order to obtain the approximate solution in the space-time domain. We will introduce such a hybrid method and then present a numerical experiment.

Electric Field Calculation along the Surface of Composite Insulator Covered with Sand Grains Based on Finite Element Method

This paper aims to discuss the efiect of sand grains covered with composite insulator on the surface electric fleld distribution of insulator in sandstorm condition. Comsol Multiphysics software based on flnite element method, was used for the three-demensional modeling and simulation. Based on the calculation results, the efiects of size, charge quantity, polarity and position of sand grains on electric fleld distribution are discussed. The simulation results show sand grains with difierent sizes have difierent distortion to electric fleld. Electric fleld is severely afiected by charge quantity, polarity and position of sand grains. This study provides theoretical reference for the research of insulator ∞ashover mechanism under the dust environment.

NUMERICAL STUDY OF A TIME-DOMAIN FINITE ELEMENT METHOD FOR NONLINEAR MAGNETIC PROBLEMS IN THREE DIMENSIONS (Invited Paper)

In this work, numerical analysis of nonlinear ferromagnetic problems is presented using the three-dimensional time-domain flnite element method (TDFEM). Formulated with the second- order nonlinear partial difierential equation (PDE) combined with the inverse Jiles-Atherton (J-A) vector hysteresis model, the nonlinear problems are solved in the time domain with the Newton- Raphson method. To solve the ordinary difierential equation (ODE) representing the magnetic hysteresis accurately and e-ciently, several ODE solvers are speciflcally designed and investigated. To improve the computational e-ciency of the Newton-Raphson method, the multi-dimensional secant methods, aka Broyden's methods, are incorporated in the nonlinear TDFEM solver. A nonuniform time-stepping scheme is also developed using the weighted residual approach to remove the requirement of a uniform time-step size during the simulation. The capability and the performance of the proposed methods are demonstrated by various numerical examples.

Numerical Simulation and Study of Local Scour around Submarine Pipeline

A two dimensional vertical mathematical model is proposed for simulating the local scour around submarine pipelines. The change caused by local scour of ∞ow fleld and pressure fleld around submarine pipelines is simulated through solving standard k- turbulence model using flnite element numerical method. Result of simulation compared with experiment result to check reliability of the mathematical model. The equilibrium proflle of local scour around submarine pipelines is accurately simulated through establishing mathematical model. Then the mechanism of seabed erosion under pipelines is revealed.

SIMPLE METHODS TO RAISE THE ROBUSTNESS AND EFFICIENCY OF THE INCOMPLETE CHOLESKY PRECONDITIONERS FOR FEM SIMULATION OF ELECTROMAGNETIC PROBLEMS

In this paper, the flnite element method (FEM) is applied to the analysis of three- dimensional (3D) electromagnetic structures. The incomplete Cholesky (IC) preconditioner based on shifted operators is used to solve the flnite element linear systems. Several strategies are adopted to raise the e-ciency and robustness of the preconditioner. Numerical experiments for several microwave devices demonstrate the superior numerical convergence and robustness of the proposed preocnditioner.

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.

ANALYSIS OF SCATTERING FROM DIELECTRIC ROUGH SURFACES BY HYBRID FEM/BIE

To study electromagnetic scattering from dielectric rough surfaces, a hybrid flnite element method (FEM) combined with boundary integral equations (BIE) is extended to the scattering problem with two half-open regions. Integral boundaries, as truncated boundaries of the FEM region, are employed as artiflcial boundaries of dielectric rough surfaces above and below the rough surface. In the hybrid method, conformal integral boundaries are introduced to reduce the computational region. The validity of our hybrid method is examined by available solutions got from the method of moment (MoM), which indicates the feasibility of our scheme in simulating the scattering from dielectric rough surfaces. Bistatic scattering coe-cient from dielectric rough surfaces is studied in this paper for both polarizations, and functional dependence upon difierent parameters are numerically discussed.

MIXED FINITE ELEMENT METHOD FOR 2D VECTOR MAXWELL'S EIGENVALUE PROBLEM IN ANISOTROPIC MEDIA

It is well known that the conventional edge element method in solving vector Maxwell's eigenvalue problem will lead to the presence of nonphysical zero eigenvalues. This paper uses the mixed flnite element method to suppress the presence of these nonphysical zero eigenvalues for 2D vector Maxwell's eigenvalue problem in anisotropic media. We introduce a Lagrangian multiplier to deal with the constraint of divergence-free condition. Our method is based on employing the flrst-order edge element basis functions to expand the electric fleld and linear nodal element basis functions to expand the Lagrangian multiplier. Our numerical experiments show that this method can successfully remove all nonphysical zero and nonzero eigenvalues. We verify that when the cavity has a connected perfect electric boundary, then there is no physical zero eigenvalue. Otherwise, the number of physical zero eigenvalues is one less than the number of disconnected perfect electric boundaries.

THREE-DIMENSIONAL ANALYTICAL MODEL FOR AN AXIAL-FIELD MAGNETIC COUPLING

In this paper, we propose an analytical method for modeling a permanent magnets axial fleld magnetic coupling. The three-dimensional model takes into account the radial fringing efiects of the coupler. The analytical solution requires resolving the Laplace equation in low permeability subdomains. The magnetic fleld calculation allows the determination of global quantities like axial force and torque. 3D flnite element computations as well as measurements validate the proposed model.

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.

SUBSTRATE INTEGRATED WAVEGUIDE DESIGN USING THE TWO DIMENTIONNAL FINITE ELEMENT METHOD

In this paper, a rigorous and accurate numerical two-dimensional modeling flnite element method 2D-FEM is applied to the analysis and design of substrate integrated waveguide components. The flnite element method represents an excellent tool for the analysis and design since it easily allows taking into account all details of each device. The advantages of this method have been proved with the successful design of two SIW waveguide topologies operating in (8{12)GHz and (10.7{12.75)GHz respectively for X-band and Ku-band applications employed in satellite communications. In order to validate the proposed method, a comparison is made between the FEM method implemented in Matlab and CST Microwave Studio R ∞ software. Agreements between the flnite element method data and the CST software results were achieved. The obtained results show the efiectiveness of this method to analyze such types of guides.

DESIGN AND ANALYSIS OF PERMANENT MAGNET MOTOR WITH MOVABLE STATORS

Permanent-magnet motors are widely used in-wheel motors of electric vehicles and hybrid vehicles. Based on a movable stator design, this paper presents a new type permanent-magnet motor, whose torque can be adjusted in order to meet difierent driving requirements. The stator geometry is varied by means of changing movable stator positions. Accordingly, the air-gap length in permanent- magnet motors is changed so that torque can be adjusted. To derive an analytical model, Fourier series expansions are employed to formulate air-gap geometry variation. The analytical model is validated by flnite element numerical results. Concerning motor torque variation capability achieved in this study, the ratio of the largest vs. the smallest torque is 2.3.

A COMPACT DIPLEXER BASED ON LOW PROFILE MULTILAYER FSS FILTERS FOR ULTRA-HIGH DATA RATE POINT TO POINT WIRELESS COMMUNICATION SYSTEM

In this paper, we propose the design of multilayer frequency selective surfaces (FSS) waveguide band-pass fllters (WBPF). The WBPFs are designed to operate at two difierent frequency channels, respectively 71{76GHz (Rx) and 81{86GHz (Tx). The cross section surface of the FSS is imposed by the WR12 waveguide rectangular section's dimensions. The WBPFs are inserted symmetrically in a T-junction waveguide to design a compact diplexer. This is a basic component developed for an e-cient integration in the future E-band millimeter-wave transceiver. The multilayer FSS structure uses only non-resonant sub-wavelength unit cell elements; metallic patch and slot. To reach high channel isolation (… 70dB) a seven order fllter was required. Hence, each fllter is composed of 13 capacitive and inductive metallic FSS spaced by 12 ultra-thin dielectric substrate layers. The dielectric material is Rogers Ultralam 3850 (Liquid Crystalline Polymer; LCP circuit material). The fllter's overall thickness is < ‚=4. The numerical studies have been performed using flnite element method simulator (HFSS) and CST Studio Suites Tools. The experimental validation has been also done in the X band frequency by developing a flfth order FSS WBPF. Good agreements between simulated and measured results are obtained.

A NOVEL DESIGN OF COMPACT DIPOLE ANTENNA FOR 900 MHZ AND 2.4 GHZ RFID TAG APPLICATIONS

A novel design of fractal dipole antenna has been presented for RFID (Radio Frequency Identiflcation) tag applications, which is based on the fractal theory. The antenna consists of two third iteration triangle fractal arms, and has been designed to work at 900MHz (GSM) and 2.4GHz (ISM), and its size is 89mm£29mm£1:6mm. The simulated results for various characteristics of the antenna have been shown using flnite element technique based commercial software ANSOFT HFSS. The simulated and measured impedance results are in good agreement.

OPTIMIZATION OF A PLASMON-ASSISTED WAVEGUIDE COUPLER USING FEM AND MMP

In this paper, we focus on the problem of optimizing plasmonic structures. A plasmon- assisted waveguide coupler is considered as a test problem, which leads to a flve-dimensional optimization problem carried out by an evolution strategy (ES). The optimization results are verifled by a comparative analysis between difierent solvers, i.e., the flnite element package CONCEPTs and the multiple multipole program (MMP). We also compared with results obtained using a deterministic optimization algorithm, namely the Nedler-Mead method as implemented in the commercial software package COMSOL Multiphysics. Some issues concerning deterministic versus evolutionary optimization, in particular, in the fleld of plasmonics have been discussed.

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.

MODELLING AND ANALYSIS OF PERMANENT MAGNET ELECTRODYNAMIC SUSPENSION SYSTEMS

In this paper, an analytical model of permanent magnet electrodynamic suspension systems (PEDSs) is proposed. Horizontal and vertical magnetic flelds of a permanent magnet (PM) are efiectively approximated by sinusoidal functions. By this means, closed form solutions are obtained for lift and drag forces of PEDSs for the flrst time. The suspension system is then modelled by flnite element method (FEM). The accuracy of the analytical model is validated by FEM and experimental measurements.

A LEAST SQUARES FINITE ELEMENT METHOD FOR THE EXTENDED MAXWELL SYSTEM

A flnite element method based on the flrst order system LL ⁄ (FOSLL ⁄ ) approach is derived for time harmonic Maxwell's equations in three dimensional domains. The flnite element solution is a potential for the original fleld in a sense that the original fleld U is given by U = L ⁄ u. The Maxwellian boundary data appears as natural boundary condition. Homogeneous Dirichlet boundary conditions for the potential must be imposed, and they are circumvented with weak enforcement of boundary conditions and it is proved that the sesquilinear form of the flnite element system is elliptic in the space where the Dirichlet boundary conditions are satisfled weakly.

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.