Corrosion related electromagnetic signatures measurements and modelling on a 1:40th scaled model

Abstract

The Corrosion Related Magnetic Field (CRM) is a part of the static magnetic signature of ships that cannot be precisely quantified for steel hull ships because of the ferromagnetic signature that is added to the CRM in magnetic measurements. For this reason, the CRM is generally evaluated by computation. Most of CRM models are based on analytical formulas of the magnetic field due to electric dipoles which decrease more slowly with distance than the magnetic signature due to ferromagnetism (spatial decay law in 1/r2 instead of 1/r3). This is the reason for the following assumption usually met in the technical literature: CRM is dominates the ferromagnetic signature at long distance. But theses models dont take into account a significant part of the CRM source: the currents that flow through the metallic structures of the ship. As a result, conclusion on the distance for which the CRM is dominating the ferromagnetic or the distance for which the CRM remains important can be corrupted. CRM measurements have been carried out on a ship mock-up to validate a new Finite Element software for CRM that takes into account all the CRM sources: currents in the sea and currents flowing through the metallic structures of the ship. This paper describes the measurements of low levels of CRM on the mock-up, and the first results of its validation with measurements.