Abstract
Computer modeling is frequently applied to predict the Corrosion Related Electric and Magnetic Fields (UEP and CRM) surrounding naval vessels as it is a design requirement to meet some target for the Electric and Magnetic signatures. Comprehensive modeling systems such as BEASY have been developed to model the corrosion performance, predict the related electric and magnetic fields and optimize the ICCP system performance and have been widely used. The simulation model represents the physics of the system by modeling the electrode kinetics on the metallic surfaces together with the current flow through the surrounding electrolyte. These models are then solved using the Boundary Element Method (BEM) or the Finite Element Method (FEM).
Such studies are normally conducted assuming the vessel is located on the sea surface at an average draft and the modeling mesh developed around that condition. However in reality the wetted hull area varies both with load and as a result of pitch and roll. This directly affects the performance of the ICCP/CP system, and may change the destination and magnitude of current flowing from the anodes. Such effects may result in the generation of a low frequency variation in the electric field (ELFE).
In order to predict the ELFE and other effects caused by vessel motion it is necessary to reposition the ship in the electrolyte and regenerate the mesh for each new location of the waterline. Up to now this was not usually done as it involved significant effort to recreate the model. The recent development of the multilayer solution within the BEM software enables the sea, sea bed and any variations in the sea resistivity to be defined implicitly in the model without having to define elements on the sea surface, seabed etc and without having to change the mesh on the hull to represent the new position of the waterline.
In this paper this new technology is applied to simulate the effects of motion of the vessel on the static and ELFE fields. The background to the study will be described as well as the new technology and an application will be presented showing how modeling can be applied to quantify such effects, using as an example a ship with an impressed current cathodic protection system.
Keywords: CP, Cathodic Protection, Pitch, Roll, UEP.
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