Fatigue damage prediction of offshore structures during transportation is today commonly based on long term scatter diagram for the sea route. This gives a mean value for the expected fatigue. The deviation from the mean value may however be significant due to the large variability in metocean conditions for the typical short duration of the transport. The actual fatigue damage experienced during the voyage may therefore be much higher than predicted. Hence, it is recommended to take into account the variability of environmental conditions in the calculation of transportation fatigue.

The aim of this paper is to establish a method for estimating transportation fatigue where the fatigue damage is computed with a specified level of non-exceedance.

The fatigue damage is quantified by a measure as defined in OMAE2017 /1/. The distribution of this measure is obtained through Monte Carlo simulation of around 300 separate sea route scatter diagrams derived from hindcast data. The 90% percentile value (10% probability of exceedance) of the fatigue measure is then taken as target value and used for establishing a limited set of design fatigue sea states to be used in the structural fatigue damage calculations.

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