Wind turbine load monitoring during model-test in a wave basin

For the testing of floating wind turbines in a wave basin, several methods have been developed to include the wind turbine loads acting on the floating foundation. To simplify, there is one main choice for the modelling of the wind turbine loads at the scale of the basin: using a physical rotor in a wind field, or using hybrid methods where the wind turbine loads are computed and applied by actuators to the model. Each approach aims at reproducing the loads that the wind turbine generates at the Froude scale chosen for the construction of the model. Transferring these loads can therefore be seen as a step that is common to all methods. While these loads are essential for the modelling of the wind turbine and its interaction with the floating foundation, they are not yet systematically measured nor reported in all basin tests of a floating wind turbine. Most surprisingly, the benefit of measuring of the wind turbine loads transferred to the floating foundation are not explicitly mentioned in the main guidelines on how to test floating wind turbines [e.g.: ITTC]. This paper gives some examples of diverse test set-ups where these loads are measured and it explains how the wind turbine thrust is analytically retrieved from these measurements. It also emphasizes why monitoring the loads actually transferred to the floater adds up to the quality of the test results and confidence in the experiments.