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Featured researches published by P.J. Leonard.


IEEE Transactions on Magnetics | 1992

Coupling meshes in 3D problems involving movements

H.C. Lai; D. Rodger; P.J. Leonard

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. >


ieee international magnetics conference | 1989

A formaulation for 3D moving conductor eddy current problems

D. Rodger; T. Karaguler; P.J. Leonard

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. >


IEEE Transactions on Magnetics | 1990

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

D. Rodger; P.J. Leonard; T. Karagular

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. >


IEEE Transactions on Magnetics | 1988

Finite element scheme for transient 3D eddy currents

P.J. Leonard; D. Rodger

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. >


IEEE Transactions on Magnetics | 1988

Voltage forced coils for 3D finite-element electromagnetic models

P.J. Leonard; D. Rodger

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. >


IEEE Transactions on Magnetics | 2006

Iron losses under PWM excitation using a dynamic hysteresis model and finite elements

P.J. Leonard; Philip Marketos; Anthony John Moses; M. Lu

A dynamic hysteresis model is used with a 2-D magnetic vector potential finite element formulation. The scheme models traditional eddy current, static BH and anomalous losses. The model is used to predict the BH trajectory and hence the losses for a FeSi lamination with a PWM type excitation. The experimental results show good agreement with the finite element predictions


IEEE Transactions on Magnetics | 1991

Modelling electromagnetic rail launchers at speed using 3D finite elements

D. Rodger; P.J. Leonard; J.F. Eastham

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. >


IEEE Transactions on Magnetics | 1994

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

P.J. Leonard; R.J. Hill-Cottingham; D. Rodger

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. >


IEEE Transactions on Magnetics | 1993

Analysis of the performance of tubular pulsed coil induction launchers

P.J. Leonard; H.C. Lai; G. Hainsworth; D. Rodger; J.F. Eastham

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. >


IEEE Transactions on Magnetics | 2008

Linear Induction Motors with Modular Winding Primaries and Wound Rotor Secondaries

Fred Eastham; Tom Cox; P.J. Leonard; Jeff Proverbs

Linear induction motors commonly use double layer windings, which produce good sinusoidal travelling fields, but have relatively bulky end windings and use either half-filled slots or overhanging coil sides at the ends of the machine. Long stator systems are difficult since it is not possible to butt stator modules against each other. Arguably the simplest and most cost effective winding uses modular construction where the coils are planar and do not overlap. Here the end winding is compact and stator sections can be butted together. However modular windings do not produce high quality travelling fields. Two space harmonics of closely the same magnitude are produced that travel in opposite directions, giving induced currents and opposing forces with little net force in plate rotors. The difficulty can be resolved if a wound secondary with a double layer winding is used instead of a plate. Here a substantial induced emf and current is produced only by the field for which the secondary is wound, so that force is produced only in one direction. The use and properties of modular windings for short rotor machines are explored using finite element analysis and the results are validated by practical tests. It is concluded that inexpensive modular windings can be used with wound secondaries to good effect particularly in long stator situations; for example, for electromagnetic launch and urban transport systems.

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