FIM - Flow-Induced Motion of Three-Column Platforms

摘要

Experiments regarding the flow-induced motion (FIM) on an array of three floating cylinders with low aspect ratio (H/L = 15), and three different distances between column centers (S/L = 2, 3, and 4) were carried out in a towing tank. The array of three cylinders was elastically supported by a set of four linear springs to provide low structural damping on the system. Three different section geometries were tested, namely, circular, square, and diamond. Three different current incident angles were tested: theta = 0, 90, and 180 degrees. These configurations of the three-column arrays were selected to cover the range of the main floating offshore wind turbine (FOWT). The aims were to understand the FIM of the three-column systems and to compare the results of the single column and an array of four cylinders. The range of Reynolds numbers covered 10 1000 Re 110 1000. Concerning the geometry of the column sections, the amplitude results showed larger amplitudes for the three-cylinder array than the single-cylinder case and the four-cylinder array for circular and diamond cases, in which cases the phenomenon was similar to vortex-induced motion (VIM). On the other hand, the amplitudes for the single square case were higher than for the array of cylinders; in this case, the galloping phenomenon was predominant. Concerning the distance between column centers, the amplitude results for the three-cylinder array with S/L = 3 and 4 were very similar. Yet the three-cylinder array with S/L = 2 acted as a single cylinder because the proximity of the cylinders changed the wakes around them. Finally, concerning the incident angle effects, the changes in the angle significantly affected the arrays with S/L = 2; therefore, only the in-line motions were slightly modified for the cases with the larger distances between columns.