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The evaluation of all the magnetic-related contributions to ship signature is not a trivial task, particularly for vessel which doesn’t have a magnetic hull that can shield its internal apparatus effect. Such operating condition requires a detailed magnetic model able to represent each magnetic signature phenomenon for permanent and induced magnetization and stray-field contribution. Based on the equivalent dipole approach a fast analytic magnetic model for the vessel under investigation has been developed where only the most impactful apparatus are included.

Since the model development has been performed during the preliminary stage of vessel design, before the keel laying, the dipole moment intensity and orientation were assumed based on the apparatus size and magnetic specification requirement. Once the equipment onshore magnetic measurement results are available the magnetic contributions decomposition will be performed, updating therefore the initial guess about dipole moment and orientation.

The dipole model was integrated with the degaussing system effect, each coil has been discretized via a series of straight segments on which the Biot-Savart law has been applied to compute the coil field distribution on the reference measurement plane.

Main scope of the overall study is to define the best value for each coil supply current that allows the minimum overall magnetic signature to be achieved over the reference measurement plane.

Marelec 2023, Southampton UK – Spin and Fincantieri

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