Study on green water prediction for FPSOs by a practical numerical approach

The growing usage of permanently moored floating production storage and offloadings (FPSO) in harsh environment regions increases the frequency and severity of the green water problem. Many numerical researches on green water prediction for FPSOs have been carried out. Most of the past researches chose to neglect or consider only part of the effects by appendages and attachments, such as bilge keel, mooring lines, and risers. The influences of these appendages on green water prediction have not been thoroughly studied. This paper presents a practical numerical approach of green water prediction for FPSOs in irregular waves. The calculation of relative wave elevation is conducted in frequency domain, including linear and nonlinear effects of bilge keels, spread mooring system, and asymmetrically arranged risers. Numerical approach was applied to calculate the statistical distribution of relative wave elevation for an FPSO. Comparison with experimental results showed that the accuracy of relative wave motion prediction is significantly improved by incorporating the linear and nonlinear effects of bilge keels, mooring, and risers. Analysis of the results by different numerical models further indicated that the relative wave elevation at sides of the FPSO in oblique waves was strongly affected by bilge keel, mooring, and risers.