A study on vessel fatigue damage as a criterion for heading selection

Abstract:

Planning and execution of marine operations requires proper estimation of vessel dynamic re-6 sponses and their corresponding operational limits, including considerations of fatigue damage. Cur-7 rent guidelines for marine operations are based on a design wave height without considering the wave 8 energy distribution in frequency and direction. This can be critical for ships operating in open seas 9 where multimodal wave spectra may occur frequently. This study provides criteria for heading selec-10 tion, with the aim of reducing fatigue damage of vessels under action of directional (2D) bimodal and 11 multimodal wave spectra. In addition, some consequences of using analytical 2D JONSWAP spectra 12 are also addressed. Based on a hydrodynamic model of a vessel, stresses at the midships section are 13 computed using a spectral method. For bimodal wave spectra and considering that all dynamic re-14 sponses are acceptable, fatigue damage can be reduced in about 50% when the vessel is heading to the 15 least energetic wave component of 2D wave spectra. Moreover, fatigue damage obtained from actual 16 2D bimodal spectra can be well represented by its corresponding JONSWAP counterpart computed 17 from the spectral parameters of the largest wave component. These findings can be used for vessel 18 heading selection during planning and execution of marine operations. 19

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