Comparison of numerical response predictions for a bottom-fixed offshore wind turbine

Numerical simulations are widely used for response calculations on offshore wind turbines. Code-to-code comparisons are frequently used for verification of the codes, as full-scale measurements can be difficult to obtain. However, most code comparisons performed focus on documenting the responses predicted by the different codes, or on the effect of specific differences between the codes. Little insight is provided to how these differences would affect design calculations, such as the fatigue utilization. In this paper, the response predictions of the programs SIMA, vpOne and FAST are compared using the DTU 10 MW reference wind turbine on a monopile foundation. While differences in the models are first highlighted through a number of simplified load cases, a lifetime fatigue evaluation of the model is then performed for the monopile at mudline. In the deterministic load cases the response of all models are quite similar, while some differences become apparent in the stochastic analysis. For the fatigue calculations, a difference of 14 % is found in the damage equivalent bending moment at mudline. This demonstrates how sensitive the fatigue utilization is to small differences is code capabilities and modelling.