The purpose of this paper is to investigate the effect on estimated fatigue damage of TLP tethers of the method used to model the springing response. In particular, the goal has been to look into the consequence for long-term fatigue calculation of modeling the springing response as a second-order, sum-frequency process as opposed to assuming that the springing response is Gaussian. It is shown that with a standard engineering approach to the calculation of long-term fatigue damage, this effect is in fact marginal. However, the deviation between the numerical estimates of the quadratic transfer function describing the springing response as provided by different computer codes is found to produce estimates of the long-term fatigue that exhibit substantial variability.

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