On the use of the eigenvalue approach in the prediction of transient eddy current fields

Very complex time dependent three-dimensional eddy-current problems are considered. The use of global spatial basis functions with assumed eigenvalue (exp(-λt)) dependence, which is extremely efficient for many problems, is shown to have embedded in it some serious pitfalls which lead to error. Examination shows that extreme caution should be exercised when using an eigenvalue approach; the association of unique eigenvalues with what would appear to be unique eigenmodal shapes leads to errors that are more severe as the object shape gets more complex. An alternative approach to the problem using the standard space-dependent Green´s function is presented. Both approaches above have been applied to the FELIX cylinder experiments, and the results are discussed