Application of Various Spectral Fatigue Analysis Methods for Ship Structures

Abstract

The Spectral Fatigue Analysis (SFA) is a comprehensive fatigue life assessment method. The SFA is performed by following a systematic process at the onset of hydrodynamic analysis, structural analysis, and spectral analysis. Hydrodynamic analysis and finite element based structural analysis are numerically intense stages, and require a substantial amount of computational time and resources. In the present paper, some simplifications are imposed on individual stages to perform the SFA analysis in a practical time scale but not compromising on the underlying theoretical assumptions. Three distinct methods (semi-analytical formulation, 2D strip method, and 3D panel method) have been used to compute the wave-induced loads while the structural responses are obtained using the beam theory based formulations (in case of semi-analytical and 2D strip method) and finite element analysis (in case of 3D panel method). Fatigue damages are calculated using these methods at the selected locations of a bulk carrier and results are compared with each other. It has been shown that the first two methods (semi-analytical and 2D strip based methods) are quick and efficient and can be used in initial design assessment or identifying the fatigue prone locations. The third method is realistic and accurate and can be used in case of a comprehensive assessment of the design.