Fatigue Analysis of an FPSO Under Operational Sea States With Multimodal Spectra

This paper presents a validation of theoretical formulas for the assessment of fatigue damage induced by a multimodal wave spectrum. Those formulas, denoted Iterative Component Addition (ICA), were set up to provide a conservative estimate and use the individual damages of the components of the spectrum. Their objective and main interest is a drastic reduction of computation time, especially for complex (multimodal) wave loading conditions. They are validated on an actual application, which is the assessment of the fatigue damage induced by the wave bending moment of an FPSO hull girder subjected to wave loading in a West Africa area. That damage is computed according to two different procedures, one with the conventional method, taken as a reference, and the other using the ICAs formulas. The results are compared and discussed. They show that the use of ICA formulas provides a reasonably conservative estimate and allows significant savings of computational time.Copyright © 2009 by ASME