Numerical and experimental analysis of extreme wave induced vertical bending moments on a FPSO

This paper investigates the vertical motions and bending moments of a FPSO platform in regular waves and also in several design storms with a duration of three hours which correspond to the 100 years return period of the North Sea. An experimental program was carried out with a scaled model in a seakeeping tank. The experimental data is systematically compared with numerical results from a nonlinear time domain strip method in order to assess the capability of the method to estimate extreme vertical responses. The analysis of discrepancies between measurements and predictions indicates how the numerical model can be improved. The experimental results are also compared in terms of maximum responses induced by the design storms and induced by an abnormal wave. The objective is to conclude about the relevance of abnormal waves with regard to extreme bending moments. Finally the maximum bending moments, measured and calculated for the North Sea climate, are compared with the rule minimum requirements.