Line element for efficient computation of the magnetic field created by thin iron plates

The problem of computing the magnetic anomaly created by iron ships in the Earth´s field is considered. From a modeling point of view, one of the major characteristics of this problem is the external and uniform magnetic source (the Earth´s field). A good way of taking this into account is to simulate infinity and to use the reduced scalar potential as the state function. The major difficulty in modeling ships is the presence of sophisticated 3-D geometries due to the disproportion between the global size of a ship and the thickness of the iron plates. The modeling of the thin iron plates is examined, and it is shown that an efficient method is to use line elements in 2-D and surface elements in 3-D. The authors present the finite-element formulations used, applied to scalar potentials (reduced or total). The formulations using line elements have been successfully applied, even to a magnetic region with small permeability values. Results in 2-D and comparisons with analytical solutions and actual measurements are presented