Many units in the DNV, semi-submersible fleet have now reached such an age that their documented minimum design fatigue life is either already exceeded, or will, in the very near future be exceeded. It is anticipated that these units will continue in their existing mode of operation for some time to come, and further, that some of these units will be considered as candidates for production units with the associated requirements from extended lifetimes. It has been common practice to evaluate the fatigue damage of a semi-submersible by use of simplified fatigue analytical procedures, based on pure Morison formulation. This simplified load calculation procedure is compared to a more advanced procedure based on combined Morison/Potential theory (hybrid) formulation.
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