Analysis Methodology of Vortex-Induced Motions (VIM) on a Monocolumn Platform Applying the Hilbert-Huang Transform Method

Vortex-Induced Motion (VIM) is a highly non-linear dynamic phenomenon. Usual spectral analysis methods, using the Fourier transform, rely on the hypotheses of linear and stationary dynamics. A method to treat non-stationary signals that emerge from non-linear systems is denoted Hilbert-Huang transform method (HHT). The development of an analysis methodology to study the VIM of a MPSO (Monocolumn Production, Storage and Offloading System) using HHT was presented. The purposes of the analysis methodology are to improve the statistics characteristics of VIM. The results showed to be comparable to results obtained from the traditional analysis (mean of the 10% highest peaks) principally for the motions in the transverse direction, although the difference between the results from the traditional analysis for the motions in the in-line direction showed a difference of around 25%. The results from the HHT analysis are more reliable than the traditional ones, owing to the larger number of points to calculate the statistics characteristics. These results should be used to design the risers and mooring lines, as well as to obtain parameters of the VIM to calibrate numerical predictions.