Magnetic Signature Analysis of the Propulsor of a Military Ship

The analysis of magnetic signature and the consequent identification of mitigation strategies are crucial issues in naval applications. The possibility to evaluate the magnetic signature of some essential components and structures during the design phase, represents an interesting opportunity to enhance ship design in terms of stealth capabilities. The current paper focuses on the assessment of the magnetic signature produced by a propulsor from a military ship with a fiberglass hull. The propulsor largest and heaviest components, which contribute most to the MS, were considered in the analysis. The numerical analysis carried out by means of a finite-element method technique was based on a simple theoretical model involving the concepts of averaged magnetization and of averaged permeability. The developed investigation is aimed at comparing the magnetic signature of a traditional propulsor with the one achievable by replacing the original ferromagnetic materials with weakly ferromagnetic ones and with a non-magnetic material, such as Aluminum, in the coating of the electric motor. The magnetic signature produced in the underwater region nearby the propulsor is consistently reduced and it is proved that the effect of Aluminum used in place of Cast iron is remarkable in determining this reduction. Therefore, the selection of suitable materials for the most critical parts in terms of magnetization and permeability, represents an effective yet simple strategy to improve the stealth properties of military ships. The possibility to use a simple model to evaluate the magnetic signature during the design phase is, therefore, essential to support a convenient selection of materials.