## 5 Conclusions  
In this paper, the experimental validation of two coupled aero-hydro-servo-elastic simulation models has been addressed. A 1:35 scaled 5 MW wind turbine on a TLP with individual blade pitch was constructed, denoted the AAUE-TLP. The two simulation models was a FAST model and a theoretical simulation model which was developed in Simulink, which theory has been presented in this paper. The experimental validation was conducted under a series of tests in a wave tank in the offshore laboratory at AAU in Esbjerg. For the validation, the displacement in surge of the TLP and the tower top was measured by an OptiTrack camera system. The first series of tests was conducted with only a hydrodynamic load. The wave series was generated from a scaled down JONSWAP wave spectrum. The experimental PSDs of the displacement in surge of the TLP and tower top showed good agreement with the PSDs obtained from the simulations. Though, deviance was found between the PSDs amplitude at the first natural frequency of the tower. The second series of tests were conducted with only an aerodynamic load, where the response was measured during different mean wind speeds. An initial comparison between the simulation and experiment showed that the periodic rotor loadings from 1P and 3P were effect was not adequately apparent in the simulations. This was taken into account in the simulation models by applying a shift in the angle of attack for each blade, causing an aerodynamic imbalance. This made the 1P and 3P effect more apparent in the simulations, but l large discrepancy between experimental and simulated response was still apparent. The test also indicated that the theoretical aerodynamic performance was higher than the experimental. This was apparent as the simulations tended to have a larger mean displacement of the TLP and tower top. The third  
Figure 14: The PSD of the FOWT displacement when affected by a JONSWAP spectrum as in Figure 8 and a mean wind speed of 7 m/s. (**a**) The PSD of the displacement of the TLP in surge. (**b**) The PSD of the displacement of the tower top in surge. series of tests were conducted with simultaneous wind and wave loading. Different frequencies of monochromatic waves and mean wind speeds were tested. These test also indicated that the calculated aerodynamic thrust was too high, as the displacement in the simulations was higher than experimental. Furthermore, the damping of the TLP seemed to be higher in the experiments, then in the simulations. This leads to a large peak in the PSD at the first natural frequency of the TLP in the simulations compared to the experiments. This indicates that the aerodynamic loads and the damping of the TLP need to be looked further into when the FOWT is exposed to simultaneous wind and wave loading. At last, the FOWT was exposed to a mean wind speed of 7 m/s and a JONSWAP wave spectrum. The dynamics of the TLP under these loading conditions seems to be in good agreement with the simulations. The dynamics of the tower top seems to be underestimated by both simulation models. The excitation at the first natural frequency of the tower was not captured well in the simulation by FAST. Writing--original draft preparation, K.J. ; formal analysis, K.J., S.M.M., J.K.J. and K.L. ; investigation K.J., S.M.M., J.K.J., K.L. ; software K.J., S.M.M., J.K.J., K.L. ; validation S.M.M., J.K.J., K.L. ; Writing--review & editing S.M.S., S.M.M., J.K.J. and K.L. ; Supervision S.M.S. ; Project administration S.M.S. This research received no external funding  
The authors would like to express acknowledgement to Aalborg university the department of energy technology for providing funding for the materials of the scaled FOWT and laboratory facilities for the experiments.