In this thesis, the effect of a surging and pitching motion of a floating wind turbine on its wake as well as the effect of a surging, pitching and yawing motion on a stationary downstream turbine are analysed. Two experiments are conducted in order to address both points. The turbine models used are scale models of the DTU 10 MW turbine, and the upstream turbine is placed onto a kinematic robot which can move in all 6 degrees of freedom. The first objective is studied using Particle Tracking Velocimetry and the second objective using load cell measurements. It is found that pitch has a larger effect on the flow field in the wake than surge and that the effects of low frequency motion are more visible than those of high frequency motion. Moreover, it is found that the tracing particles are concentrated in specific areas, affecting the accuracy of the results. In future research, it should be examined why this is the case and how it can be improved. Additionally, low frequency pitch and surge had the greatest effect on the loads. A clear sinusoidal motion is visible and the mean thrust, torque, and power is increased. The effect of the high frequency motions is not visible in the results. In future studies, the wake behind a downstream turbine can also be examined using Particle Tracking Velocimetry. Moreover, the downstream turbine can also be moving rather than standing still and more movements of the turbine can be examined.

Experimental testing of floating offshore wind turbines (FOWT) is essential for understanding the various engineering challenges posed by their dynamic motion. For example, the pitch and surge motion of the FOWT results in unsteady aerodynamic effects caused by wake interaction. In this project, two FOWT models (DTU10MW with TripleSpar and IEA15MW with VolturnUS) were developed for testing with a hybrid hardware-in-loop (HIL) setup. This setup integrates physical wind loading in a wind tunnel with numerically simulated hydrodynamic loading.

The HIL setup comprises a scaled wind turbine model, a hexapod that can actuate the floating motion, an instrumentation system with sensors to measure forces and accelerations, and a numerical model that simulates FOWT dynamics in real-time based on measured data. This work explores the methodology of developing a numerical model that can simulate the dynamics of the scaled FOWT model in real-time with the applied wind loading and numerically simulated hydrodynamic loading. Furthermore, a methodology for correcting the measured forces to obtain external aerodynamic forces is introduced and validated.

The process of developing the numerical model is thoroughly detailed, including its tuning and validation. The challenges encountered during the validation process are discussed in depth, with an emphasis on their underlying causes. Finally, the HIL numerical model was used to test the scaled DTU10MW wind turbine with a simulated TripleSpar floater at the Open Jet Facility (OJF) wind tunnel at TU Delft. This study also presents intriguing results regarding the HIL model's performance and the impact of wind on FOWT dynamics observed during the test campaign.