Reliability analysis of monopile offshore wind turbine support structures

We probe the reliability of monopile support structures designed to support industrial scale turbines along the coastal United States using stochastic models for the wind and wave loadings, and representations of the uncertainty associated with soil properties. The turbine support structure investigated is that promulgated by the National Renewable Energy Laboratory as typical of a monopile support structure designed for tens of meters of water depth and a characteristic wind/wave environment. We investigate the structural reliability using structural finite element models developed in MATLAB and a commonly used industry tool, FAST, developed and distributed by NREL. Reliability investigations include the effect of spatial correlation of soil properties on reliability with respect to serviceability and the combined effects of loading and soil property uncertainty on structural performance. We also comment on the interaction between the tower/pile design space and the resulting reliability, allowing us to comment on the effect tower geometry may have on reliability. FAST uses reduced order structural models in the pursuit of computational efficiency, and we evaluate the efficacy of these models for structural behaviors which may enter the nonlinear regime. These investigations include the ability of FAST to capture structural model shapes with large curvature gradients, and the effect of mode shape approximation on time-history dynamic analysis.