Search

We present a general approach to directly couple finite-element models with arbitrary electric circuits for application to electromagnetic devices. We describe both two-dimensional (2-D) and three-dimensional (3-D) transient finite-element models, with emphasis on 3-D using a T-[OMEGA] formulation. For 3-D transient and circuit coupling, the derivation of the induced voltage is an integral part of the coupling approach, and the induced voltage links the magnetic field and the electrical circuit together. The system of electric circuits is created automatically. Then graph theory is used to deduce the circuit by tree/cotree and loop analysis. The resulting field equations and circuit equations are coupled together and solved simultaneously at each time step in the time domain. We give three examples of applications: a brushless de motor drive, a permanent-magnet synchronous motor drive, and a three-phase power transformer with rectifier and load circuit. Index Terms--Circuits, electric machines, electromagnetic coupling, finite-element analysis, magnetic devices.

We present an approach for directly coupling transient magnetic fields and electric circuits. The circuit can contain arbitrarily connected solid conductors located in the magnetic field region. A systematic procedure suitable for both nodal method and loop method is used to couple fields and circuits. The structures of the system equations of the two methods are analogous. The formulations allow the equations in stranded windings and solid conductors to be unified and the coefficient matrix of the system equations to be symmetrical. In order to reduce the solution domain, the periodic boundary conditions are still applicable when the solid conductors are involved. Our approach has been applied to the simulation of electric machines. We give four examples: 1) calculation of the input phase current and output torque when a single-phase induction motor with shaded rings is in locked-rotor operation; 2) simulation of the sudden short circuit of a synchronous generator with starting cage; 3) study of the phase current waveform of an induction motor when the rotor bars are broken; and 4) investigation of the parasitic capacitive impact of the surge voltage on a winding due to drive switching and cable ring. Index Terms--Circuit, couple, electric machine, finite element, simulation, solid conductor.

The definition of energy/coenergy in permanent magnets (PMs) is still in dispute when virtual work is used to compute magnetic forces using finite-element methods. There is also no current practical method for computing forces when PMs touch objects. These problems are addressed in this paper in terms of a new definition of energy/coenergy in PMs and by using shell elements. The results are verified by analytical computations. Index Terms--Electromagnetic fields, electromagnetic forces, finite-element method, permanent magnets, virtual work.

The National Academy of Engineering's annual meeting focused on the promise and problems of synthetic fuels development. (BB)

A meeting held at the National Bureau of Standards is reported on. Topics included metrology, standardization, quality control, technology transfer, and technical management. (BB)

This paper investigates an approach to passively eliminate subharmonic responses in nonlinear oscillators forced at resonance. A general framework is developed for identifying asymptotic levels where parameter values can be passively tuned to achieve dynamic cancellation of subharmonics. The results apply to oscillators with an arbitrary nonlinear structure. Due to its breadth of application from atomic force microscopy to aeromechanics, the methodology is demonstrated using a reduced-order model for an inextensible cantilevered beam carrying a concentrated mass. The concentrated mass provides a simple opportunity to vary parameters to achieve subharmonic elimination characteristics. Nonlinear simulation results indicate that parameter choices derived from the perturbation scheme are robust for a significant range of forcing amplitudes. Limits of the harmonic elimination and the sensitivity of the result to control parameters are discussed as well. [ABSTRACT FROM AUTHOR]