Dynamic analysis of a floating hybrid spar tension leg platform concept for wind monitoring applications in deep sea

This study presents an investigation to assess the motions experienced by a floating hybrid spar-tension leg platform structure when supporting a wind-monitoring lattice tower in deep water conditions of the Central Mediterranean. The numerical study is based on the software package ANSYS® AQWA™. The structure supports a 30 m wind-monitoring tower as well as a LiDAR system. A parametric analysis was carried out for different geometrical and met-ocean conditions, and the simulations were restricted to regular (single frequency) wave and constant wind speed conditions only. The Morison formulation was used to resolve the hydrodynamic loads in a time domain. The study shows how the natural periods of the floating wind-monitoring mast structure decrease with increasing buoyancy-to-weight ratios. From the time-series simulations, it was evident that slender spars experience smaller displacements. This is a favourable result as it results in more reliable wind measurements taken by the cup-type anemometers. Finally, a sensitivity analysis was carried out to examine the variations of surge motion predictions resulting from deviations in the hydrodynamic coefficients. It was observed that the platform surge motion is more sensitive to deviations in the added mass coefficient than the drag coefficient.