Evaluation of the effect of sacrificial anodes on the drag coefficient of tubular elements due to marine currents

Abstract

The structural design of fixed offshore platforms is mainly based on characterizing inertial and drag loads due to waves, currents, and wind. These structures incorporate sacrificial anodes as corrosion protection systems. The sacrificial anodes increase the exposed area of the tubular elements of the jacket. Therefore, designers need to determine hydrodynamic coefficients for tubular elements with anodes to calculate the load increment due the anodes. This work focuses on evaluating the effects of anodes on the drag coefficients for tubular elements, considering current velocities from 0.25 m/s to 2 m/s, in 0.25 m/s increments, tubular element diameters from 0.508 m to 3.048 m, in 0.508 m increments, and three different positions of the anode, back (P1), front (P2), and lateral (P3) to the tubular element, concerning the direction of the current. This work uses CFD analysis, considering RANS and the k-ω model. The results show that the drag coefficient can be calculated as a function of the tubular element's diameter and the anode's position. Correlations were obtained for calculating an equivalent drag coefficient or an equivalent hydrodynamic diameter for any position of the anode as a function of a diameter ratio and the angle of its position in the tubular element concerning the flow direction.