Directional Wave Partitioning and Its Applications to the Structural Analysis of an FPSO Available to Purchase

A full characterisation of the individual components of a sea-state is key to enabling the response of an offshore structure to be accurately calculated. This paper discusses the partitioning of a time series of directional wave spectra into wind-sea and swell components with distinct frequency and direction characteristics. Once the wave data have been partitioned, JONSWAP or Pierson-Moskowitz parameters can be fitted to each spectrum using ‘best-fit’ techniques. The result of the partitioning and fitting analyses is a time series of wave parameters defining the wave spectrum for each component of the sea state. A 10-year site specific time series of directional wave spectra has been partitioned in this way and used in the analysis of the Triton FPSO, a turret moored FPSO in the central North Sea. The representation of the directionality and magnitude of each environmental force acting simultaneously on the vessel, allows the relative heading of the vessel to be determined and the mooring and hydrodynamic analyses to be performed. These analyses provided input to a structural analysis of the FPSO, which resulted in an inspection plan for monitoring the effects of the metocean conditions on the unit.