FIM - flow-induced motions of four-column platforms

Abstract Experiments regarding the FIM – flow-induced motion on an array of four floating cylinders with low aspect ratio, H / L = 1.5 , and three different distances between column centers, or spacing ratio, S / L = 2, 3 and 4, were carried out in a towing tank; where H is the column height below the water area, L is the length of the face dimension of the columns, and S is the distance between center columns. The array of four columns was elastically supported by a set of four linear springs to provide low structural damping to the system. Three different section geometries of the columns were tested, namely circular, square, and diamond. Two different current incident angles were tested, 0 and 45°. These configurations of the four-column arrays were selected to cover the range of the main SS – semi-submersible and TLP – tension leg platforms. The aims were to understand the FIM nature of the four-column systems and to provide knowledge to the designers of offshore systems. The range of Reynolds number covered 10,000 S / L = 3 and 4, were very similar. The four-cylinder array with S / L = 2 acted as a single cylinder or changed the wake interference significantly because of the proximity of the columns. Finally, the presence of pontoons had a significant effect on the motions in the transverse direction, and this presence was responsible for decreasing the amplitudes.