A comparison of fatigue and extreme loads from simulations with full-scale measurements collected over a period of ten months in the offshore test field, Alpha Ventus, is presented in this paper. There are two goals of this study:
to check if the measured range of fatigue and extreme loads can be captured correctly by simulations when the variations of relevant environmental parameters are taken into account; and
to investigate if measured extreme loads can be reproduced by simulations when ten-minute averages of the environmental parameters are used.
The results show a good overall match of loads when the variation of environmental parameters is considered but an insufficient match when the events of maximum load occurrence are compared.
The site-specific design of offshore wind turbines requires the use of simplified assumptions of the environment in order to limit the number and detail of simulations to be performed. Additionally, a set of physical assumptions is implied in the various aero-servo-hydro-elastic models used for the simulation of the loads of offshore wind turbines. These include models for the wind and wave environment and models for the load transfer from the environment to the turbine and between system components.
The use of simplified environmental assumptions is generally justified by the use of conservative estimates for environmental parameters (Türk and Emeis, 2010). The verification and validation of the models used to describe offshore wind turbines involve code-to-code comparisons (Jonkman and Musial, 2010; Popko et al., 2012) and comparisons to scaled experimental data (Müller et al., 2014).
To complete the design process and learn from it, a thorough validation of physical models at full scale and subsequent environmental assumptions are necessary in order to identify shortcomings and highlight the potential for less conservative designs and/or additional simplifications within the process of site-specific project certification.