Hydrodynamic forces on a cylinder with anode

Jackets are offshore structures which have anodes distributed on them to prevent corrosion of the structure by seawater. The anodes project from the surface of the jacket, altering the drag coefficient and projected area, thereby increasing the wave load. They are distributed according to the surface area contribution of each submerged bay of the jacket and those near the surface will attract more wave loads because of their proximity to surface waves. The orientation of the anode with respect to the direction of wave will also affect the wave load generated. Anodes which project outwards from the jacket members will generate more wave load than an anode shielded by the jacket leg. In the industry, the general practice is to increase the overall wave loading due to presence of anodes by a factor, using thumb-rules and experience. This is a conservative practice and may also be an over-estimation of the loading attributed to anodes. A good understanding and estimation of the increase in wave loads due to anodes will lead to a more economical design of the structure. Existing information in present literature is limited. In this regard, detailed experimental investigations were carried on a vertical cylinder fitted with an anode, as existing information in present literature is found to be lacking. Experiments were conducted on a bare cylinder and a cylinder fitted with an anode to observe the variation in hydrodynamic coefficients and wave load for different angles of wave attack. Regular wave tests were carried out in a wave flume in the Department of Ocean Engineering, Indian Institute of Technology Madras, Chennai, India, capable of simulating intermediate and deep water conditions. From the limited set of experiments, inferences are drawn on the increase in wave load and variation of hydrodynamic coefficients of the cylinder with anode.