Comparison of Three Modeling Methods for Identifying Unknown Magnetization of Ferromagnetic Thin Plate

Abstract

-This study presents three different magnetization models for identifying unknown magnetization of the ferromagnetic thin plate of a ship. First, the forward problem should be solved to accurately predict outboard magnetic fields due to the magnetization distribution estimated at a certain time. To achieve this, three different modeling methods for representing remanent magnetization (i.e., magnetic charge method, magnetic dipole array method, and magnetic moment method) were utilized. Material sensitivity formulas containing the first-order gradient information of an objective function were then adopted for an efficient search of an optimum magnetization distribution on the hull. The validity of the proposed methods was tested with a scale model ship, and field signals predicted from the three different models were thoroughly investigated with reference to the experimental data.

Evaluation of a numerical model for ship magnetic signature induced by an external field

“…Measurements were performed below the ship's keel, at normal measurement depth [7]. The measurement set denoted Bz_nava is shown in Fig.…”

“…Several methods of modeling the induced magnetic signature have been employed throughout the years, ranging from physical scale models to analytical models [7,13] simple models, such as the dipole array method, or numerical models relying on high computing power calculators [10,15,20]. Modeling the ship complex geometry can predict its magnetic signature, by employing suitable numerical tools, such as the finite element method, which take into account the material properties, and the external magnetic field [5,16,21].…”