Since a rigorous prediction of fatigue life is needed to ensure structural integrity, spectral fatigue analysis is performed for side longitudinals and hopper knuckle connection where fatigue resistance is anticipated to deteriorate. This paper describes some procedures to deal with fatigue loads and damage so as to be applicable to tankers and/or FPSOs. Wave induced loads are determined using three-dimensional diffraction theory and the loads are automatically mapped on the stress influence factors from FE analyses with reference loads. The analysis result gives the fatigue lives from the calculation program made with a systematic approach. The fatigue lives satisfy the design life for side longitudinal connections. However, the life for hopper knuckle area is estimated to be short. A comparative study for fatigue life is carried out with respect to design factors such as S-N curve, wave spectra and scatter diagrams affecting fatigue resistance.
Studies on fatigue prediction have been made to reflect improved analysis procedures of Classification Societies and Owner's demands. As well, some calculation procedures have been developed to apply the theoretical approach to the ship structures. Through tankers and FPSO design, further examination for DSME fatigue analysis procedure was made as to problems and assumptions. In this paper, hopper structure and side lonigitudinals are focused. Since both of a tanker and an FPSO have similarity in the hull structures, an application to a tanker can be also available for an FPSO. Wave induced loads being sensitive to fatigue damage are determined by 3-D diffraction theory and these loads are automatically mapped on the structural model. The considered dynamic loads as fatigue loads comprise external hydrodynamic pressures, internal dynamic pressures, sectional forces, variation of gravity, and oscillatory hydrostatic pressures and hydrostatic pressure increment.