D. Rodger

Coupling meshes in 3D problems involving movements

A technique for use in finite-element models for coupling independent three-dimensional meshes together is presented. The coupling is done at an interface using Lagrange multipliers which can be identified as the normal component of B on the interface. This technique is particularly well suited to the analysis of devices with moving parts where the modeling of the moving parts at different positions is required. The proposed scheme was used to model a switched reluctance motor which has been modeled previously using conventional finite elements. >

A formaulation for 3D moving conductor eddy current problems

A three-dimensional finite element formulation for moving conductor problems is outlined. Upwinding is shown to be important at high values of the Peclet number. The authors consider only the type of moving conductor problem in which the moving member is invariant in the cross section which is normal to the direction of motion. This allows motion to be taken into account using the usual Minkowski transformation, which leads to a steady-state solution for constant speed moving conductor problems. A problem of interest in MAGLEV (magnetic levitation) advanced transport system design is considered as an example. >

An optimal formulation for 3D moving conductor eddy current problems with smooth rotors

A finite-element technique for modeling 3D transient eddy currents in smooth-rotor conductors moving at a constant velocity is described. The method does not require the electric scalar potential inside conducting regions in moving-conductor problems. The interface between moving and stationary conductors requires a jump in magnetic vector potential when the electric scalar is not present. This is handled using a thin-surface element. The method has been implemented in the MEGA software package for modeling 2D and 3D electromagnetic fields. Eddy-current regions are modeled using a magnetic vector potential. Nonconducting regions require magnetic scalar potentials. Validation by comparison with experiment has been carried out. The study of eddy currents in an electromagnetic launcher is considered. >

Finite element scheme for transient 3D eddy currents

A transient 3-D finite-element model is presented. The method is based on the solution of the magnetic scalar potential in nonconducting regions and the magnetic vector potential and an electric scalar potential in eddy-current regions. Multiply connected regions of magnetic scalar can be avoided by extending the region modeled by the magnetic vector potential to fill any holes in the conducting regions. The model was used to simulate the FELIX brick experiment. >

Coupled electromagnetic-thermal modeling of electrical machines

This paper describes some modeling techniques used in computing the heat losses and temperature distribution in some electrical machines. The thermal sources can be eddy currents in conductors and winding I/sup 2/R losses. Since the thermal time constants are relatively very long, the coupled electromagnetic-thermal problem is solved as a weakly coupled system using time-harmonic and time-transient methods for the electromagnetic and thermal systems, respectively. The electrical coil is modeled as a reduced scalar region coupled with the thermal equation. Results are compared with experimental measurements.

Voltage forced coils for 3D finite-element electromagnetic models

A method for modeling 3D voltage forced coils is described. The magnetic vector potential A is used within the coil with an additional equation to ensure EMF balance at the terminals. This approach is useful for nonlinear or transient problems when the terminal voltage is specified. The coil model has been incorporated into the general 3D electromagnetics program MEGA. A simple voltage-forced coil has been simulated on the computer and compared with experimental results. >

Modelling electromagnetic rail launchers at speed using 3D finite elements

A formulation which allows the simulation of railguns and other devices incorporating moving conductors which are of constant cross-section in the direction of motion has been described. The formulation is believed to be as economic in terms of computer resources as possible. One important feature is that the final set of equations which has to be solved appears to be well-conditioned, and can be solved efficiently using the preconditioned biconjugate gradient technique. It is important that the mesh used in the moving region does not contain any large jumps in element size in the direction of motion. The application of the method to railgun launchers is illustrated. >

A formulation for low frequency eddy current solutions

Two finite element methods for calculating power frequency 3-dimensional electromagnetic field distributions are described. The problem region is partitioned into parts which contain eddy currents and parts which do not, in such a way that the dividing surfaces are coincident with the conductor surfaces. Magnetic scalar potentials are then used to describe the field in non-conducting regions while either of the vector fields A or H is used in eddy regions. Simple 3-dimensional test results are presented.

3D finite element models and external circuits using the A/spl psi/ scheme with cuts

Many devices can only be accurately modelled using a combined circuit and finite element model (FEM), This paper describes the coupling of massive conductor circuits modelled using 3D finite elements and the A/spl psi/ scheme with an external circuit model. The massive conductor circuits by their nature lead to the fact that the magnetic scalar region becomes multiply connected. The cuts which are introduced to deal with the multiply connected magnetic scaler regions lead naturally to the current and voltage variables required to couple the field model and lumped circuit model. >

Analysis of the performance of tubular pulsed coil induction launchers

The authors present a scheme for modeling coil guns using finite elements. The relative motion between the coils and the projectile is modeled by using two distinct meshes which are coupled using Lagrange multipliers which depend on the relative position of the two meshes. This scheme allows the inner mesh to slide during the transient simulation without the need to remesh the problem. Results are presented for a simple experiment involving a single coil and aluminum projectile. >