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**Source: **STP27577S

The program EDDYNET solves eddy-current problems by means of an integral-equation approach. The conducting material is represented by a network of current-carrying line elements. Consequently, Maxwell's field equations can be replaced by Kirchhoff's circuit rules.

The loop equations for voltages, supplemented by the node equations for the currents, comprise a set of linear equations that can be solved repeatedly to give the time development of the eddy currents. Currents, magnetic fields, and power are calculated at each step.

A TRIM-like mesh generator and internal indexing of lines, nodes, and loops permit solutions with complex geometries incorporating many elements. Results can appear in the form of movies representing currents, field penetration, and power distribution.

Calculations can now be performed for conducting, curved shells acted upon by an applied magnetic field. Changes in the flux through each mesh loop are determined from the normal component of field (both the applied field and the field from the current in each line element). The matrix representing the flux through each loop due to each line can be inverted and the system stepped through time to provide a time history of the currents. Another matrix facilitates calculating the net field over a specified rectangular grid at each time step. Incorporating appropriate symmetry conditions reduces the size of the problem.

Results are presented for field shielding by a thin-walled toroidal shell and for eddy-current effects on a notched tube in a sinusoidal field.

**Keywords:**

eddy currents, computer simulation, nondestructive evaluation, calculation, theory, transient magnetic field

**Author Information:**

Turner, LR *Physicist, Argonne National Laboratory, Argonne, Ill.*

Lari, RJ *Physicist, Argonne National Laboratory, Argonne, Ill.*

Sandy, GL *Physicist, New College, University of South Florida, Sarasota, Fla.*

**Committee/Subcommittee:** E07.07

**DOI:** 10.1520/STP27577S