Finite Element Electromagnetic Code Research Articles

A Three-Dimensional Electromagnetic Shell Finite Element for Coupled Vector-Scalar Potential Formulations

In many eddy current problems solved by FEM, meshing of the skin depth leads to CAD difficulties and large computing. In order to avoid such problems, one currently use surface impedance conditions: boundary conditions in the case of massive conductors or transmission conditions or shell elements in the case of thin conducting layers. In this paper, we propose a new shell finite element with arbitrary thickness that is compatible with the (A-φ) and (T-Ω) formulations. Both formulations exist in some general purpose finite element electromagnetic codes like Code_Carmel3D. To validate the approach, two elementary numerical tests are treated.

An analysis of the use of magnetic source tomography to measure the spatial distribution of electric current during vacuum arc remelting

Magnetic source tomography is explored to analyse the distribution of electric current during vacuum arc remelting (VAR). The goal is to use sensors outside the process to deduce the behaviour within. VAR systems having non-axisymmetric distributions of arc current were modelled using a commercial finite element electromagnetic code (Opera 3d), and a database was created from the resulting patterns of magnetic flux predicted to occur outside the crucible. A reconstruction algorithm was developed using constrained nonlinear optimization to estimate the arc current distribution within the process from the magnetic field data outside. The capabilities of this algorithm were studied, and it was found that given sufficiently low noise in the measurement data it was possible to accurately deduce important features of the spatial distribution of the arc current.

Integrated identification of RFX-mod active control system from experimental data and finite element model

The RFX-mod system for the active control of MHD instabilities has been operating for more than 2 years contributing to improvements of the discharge quality and length. In the past years a dynamic black-box model of the active coils and saddle probes has been developed to analyze and simulate the system electromagnetic behaviour, which is strongly dependent on the frequency due to the presence of passive conductors. Satisfactory results were achieved in reproducing most of experimental responses and the model was used to select and test the gains of operating PID regulators. However, difficulties have emerged in reproducing some flux distributions such as those corresponding to m = 0, low n current patterns. In view of higher current operation a further increase in control system performance and model accuracy is desirable, if not mandatory. To this purpose, new measures have been recently acquired in order to reassess data of critical magnetic couplings and an activity has been started aimed at the verification and integration of data from a white-box model provided by the 3D finite element electromagnetic code Cariddi. The above verification is also a preliminary step for the validation of the CarMa computational tool adaptation to RFX-mod, which has been undertaken to study the plasma resistive wall modes. The paper describes the results of a comparative analysis carried out on experimental and simulation data obtained with the black-box and white-box models.

Transverse impedance of tapered transitions with elliptical cross section

We study the transverse geometric impedance of elliptical cross-section tapers in the lowfrequency ‘‘inductive regime.’’ We have followed a dual approach: computer simulations have been carried out using the finite element electromagnetic code GDFIDL and analytic results for the dipolar and quadrupolar components of the impedance have been derived extending a perturbation technique introduced by Stupakov. Our work provides new insight into the behavior of the impedance of axially asymmetric tapered structures at low frequency. In particular, we clarify the frequency range characterizing the inductive regime, suggesting new criteria relating the extent of the inductive regime for dipolar and quadrupolar components of the impedance to the dimensions of the minimal cross section of a tapered transition.

Computer Modeling of Electromagnetic Fields and Fluid Flows for Edge Containment in Continuous Casting

A computer model was developed to predict eddy currents and fluid flows in molten steel. The model was verified by comparing predictions with experimental results of liquid-metal containment and fluid flow in electromagnetic (EM) edge dams (EMDs) designed at Inland Steel (Ispat Industries Ltd.) for twin-roll casting. This mathematical model can greatly shorten casting research on the use of EM fields for liquid metal containment and control. It can also optimize the existing casting processes and minimize expensive, time-consuming full-scale testing. The model was verified by comparing predictions with experimental results of liquid metal containment and fluid flow in EM edge dams designed at Inland Steel (Ispat Industries Ltd.) for twin-roll casting. Numerical simulation was performed by coupling a three-dimensional (3D) finite-element EM code (ELEKTRA) and a 3D finite-difference fluids code (CaPS-EM) to solve Maxwell’s equations, Ohm’s law, Navier-Stokes equations, and transport equations of turbulence flow in a casting process that uses EM fields. ELEKTRA is able to predict the eddy-current distribution and EM forces in complex geometry. CaPS-EM is capable of modeling fluid flows with free surfaces and dynamic rollers. The computed 3D magnetic fields and induced eddy currents in ELEKTRA are used as input to flow-field computations in CaPS-EM. Results of the numerical simulation compared well with measurements obtained from both static and dynamic tests.

Parametric study of an augmented railgun

Three different geometries of parallel augmented railguns (circular with one pair of augmenting rails, rectangular with two pairs of augmenting rails, and rectangular with one pair of augmenting rails) have been simulated with the finite-element electromagnetic code MEGA. The mutual inductance gradient M' and the stress on the rails have been calculated as a function of the geometry and compared with M' and the rail stress in a simple railgun. Therefore, constant currents were injected in a three-dimensional railgun model with a fixed projectile. The simulations show that the rectangular geometry with one pair of augmenting rails is the best choice for an experimental railgun: M' is the highest of the three geometries studied and the mechanical structure is the simplest. By investigating the stress on the rails when injecting a pulsed current, we found that a delay between the current injection in the inner circuit and that in the outer circuit can reduce the drag force on the projectile due to the eddy currents induced by the outer circuit current. We show that the outer rails can be attracted or repulsed, depending on the ratio between the current in the inner circuit and that in the outer circuit.

Measurements of Dielectric Properties at Ka-Band Using a Fabry-Perot Hemispherical Open Resonator

A Fabry-Perot hemispherical open resonator is designed and constructed in order to measure dielectric properties of BeO in the Ka-band (26 – 40 GHz) frequency range. Based on both analytic calculations and simulations by a 3-D finite element electromagnetic code, HFSS, the hemispherical open resonator is designed to excite a TEM0,0,17 mode at 28 GHz. The TEM0,0,17 mode is experimentally identified by a field perturbation technique. Dielectric measurements are made by both frequency variation and length variation methods. Measurements show that permittivity and loss tangent of BeO are 6.69 and 6.5 × 10−4 - 7.2× 10−4, respectively, in the frequency range of 26 – 34 GHz.

A Single-Ridged Coaxial Hybrid TE011 Coupler with High Mode Purity

We design a single-ridged coaxial hybrid coupler which excites a TE011 mode of high mode content in a cylindrical cavity, resonating at 28.2GHz. The coupler consists of a WR-28 rectangular waveguide, a coaxial TEn11 cavity, and a cylindrical TE011 cavity. Both TE311 coaxial cavity and TE411 single-ridged coaxial cavity are analyzed to examine the TE011 mode purity in the central cavity. Mode purity analysis is performed by a field expansion method using Fourier-Bessel orthonormal basis functions. Numerical calculations predict that the TE411 single-ridged coaxial cavity excites the TE011 mode with mode purity of 98.6%, which is improved by 3% higher compared with the TE311 coaxial cavity. Measurements on the single-ridged coaxial coupler show a resonant frequency at 28.078GHz and ohmic and external Qs of 1560, 473 respectively, which are in good agreement with the simulated results of a 3-D finite element electromagnetic code.

A nodal analysis approach for 2D and 3D magnetic-circuit coupled problems

This paper presents a unified approach for magnetic-circuit coupled problems in 2D and 3D. The approach is based on the A/spl I.oarr/-V formulation with the Coulomb gauge for low frequency eddy currents, and the modified nodal analysis method for electric circuit simulation. It supports static, time-harmonic and transient analysis types. Both stranded coils without eddy currents and massive conductors with eddy currents are included. Compared to other methods, the present approach can be easily implemented in existing finite element electromagnetic codes. Numerical examples are presented to validate the theory.

3-D plasma armature railgun simulations

A three-dimensional Navier-Stokes code has been extended to provide a simulation for the railgun plasma armature. This code was previously used with an approximate electromagnetic model to provide a two-dimensional simulation of a railgun plasma armature flow in the plane containing the insulators. A new three-dimensional electromagnetic solver has been incorporated into the code to permit full 3-D nonsteady MHD simulations of the plasma armature flow in a railgun. The finite-difference equations for magnetic vector potential and electric potential are solved using the ICCG method. The new electromagnetic solver was validated using 3-D solutions obtained from the finite element electromagnetic code MEGA. A full bore, 3-D simulation of a plasma armature reveals flow patterns significantly different than those of rail or insulator plane 2-D simulations. In particular, the maximum J/spl times/B force occurs off-axis and results in a plasma flow away from the projectile along the axis of symmetry. A zone of high shear flow forms near the rail surfaces which increases the viscous losses. Zones of low current, nearly stagnant flow form near the base of the projectile, consistent with experimental observations of a buffer between the armature and the projectile. >

Magneto-thermal coupled analysis of canned induction motor

The authors present the calculation of the distribution of the transient temperature in the rotor bars of a canned induction motor, during locked rotor conditions, where the phenomena of electromagnetically induced currents and heat transfer are coupled. They have developed a coupled finite element electromagnetic code called WEMAP in which the calculated power loss densities are used as the heat sources for a transient thermal solution in subregions of the original problem geometry. These subregions are enclosed by surfaces on which either temperature or a convection boundary condition is known. In addition, the change in rotor bar resistance as a function of the temperature is included in these calculations. The calculated temperatures are compared with test results, and favorable agreement is obtained.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Magneto-thermal coupled finite element calculations in multiconductor systems

In this paper we present, the calculation of temperature transients in devices where the electromagnetic and heat, transfer processes are coupled. We have extended the finite element electromagnetic code (WEMAP) in such a manner that the calculated power loss densities in a multiconductor system are used as the heat, sources for a transient thermal solution in subregions of the original problem geometry. These subregions are enclosed by surfaces on which either temperature, or a convection boundary condition is known. The implementation of this capability will be shown by way of an example.