<p>In the field of reliability analysis of structural systems, the treatment of uncertainty has traditionally been addressed by considering three main types: physical uncertainty, statistical uncertainty, and modeling uncertainty. This paper explores the effects of the latter two on the estimation of long-term extrapolated extreme responses in a fixed-bottom wind turbine system. The statistical uncertainty is addressed by studying the effect of the length of stochastic simulations on the statistical extrapolation of short and long term extremes. Simulation lengths of 10, 20, and 30-min are considered and contrasted against the results of 1hr simulations. Modeling uncertainty is explored by evaluating the effects of considering a rigid and flexible foundation. To take into account the flexible behavior of the soil, the improved apparent fixity method is considered. The modified environmental contour method is used for the estimation of 50yr long-term extreme responses.&nbsp;<br>
&nbsp;&nbsp; &nbsp;This paper focuses on the fore-aft shear force (FASF) and bending moment (FABM) at the mudline as they are considered to best capture the combined effects of wind and waves. The results show that using a length of simulation of 10-min, as is usual in the industry, does not provide sufficient accuracy when it is extrapolated to a level of 50yr. It is shown that simulations of at least 30 minutes provide an accuracy of about +/-5% for the FASF. In contrast, 20-min and 30-min simulations provide the same accuracy for FABM reaching deviations up to +20%. Finally, the consideration of a flexible foundation also has an observable effect on the estimation of the extreme long-term response for the case of the bending moment at mudline.</p>

Effects of Simulation Length and Flexible Foundation on Long-Term Response Extrapolation of a Bottom-Fixed Offshore Wind Turbine

Paper Proceedings: https://asmedigitalcollection.asme.org/OMAE/OMAE2021/volume/85116

OMAE 2021

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