## 5 Conclusions  
This paper aimed to help elucidate whether or not a simplified static-equivalent model can be used to predict major trends in the dynamic structural response of monopile OWTs. To do so, this study presents a comparison between the results of two numerical models of different levels of complexity used to estimate the structural response of an OWT under dynamic loads: an advanced time-domain multi-physics tool, namely OpenFAST, and a simplified static-equivalent model. For this purpose, the manuscript presented a comparison between the results obtained from both models for the dynamic structural response of the IEA-15-240-RWT reference wind turbine [37], including soil-structure interaction effects. More precisely, the two structural models were compared in terms of their fundamental frequencies and through the analysis of shear forces and bending moments under wind-only and combined wave and wind load scenarios. The comparison between the fundamental frequencies yielded by both models showed that the simplified lumped model can effectively represent the system's mass and stiffness characteristics. Furthermore, the reduction in the fundamental frequency derived from the SSI effects is practically the same for the two models. Regarding the wind-only load response, the results showed that turbulence and wind velocity have a significant impact on shear forces and bending moments. Wind velocities near the rated wind speed generated the highest internal forces, particularly at the mudline level. The ability of the simplified model to reproduce the OpenFAST results is directly related to the turbulence level, presenting a better agreement for low-turbulence scenarios. Also, significantly larger discrepancies between the models were found for shear forces compared to bending moments. For the relevant environmental load scenarios considered, similar conclusions were obtained. In general, the simplified model underestimates the shear forces at the mudline level for low-turbulence scenarios, with 25% relative differences, and it overestimates them for high-turbulence scenarios, reaching over 20% relative differences. On the other hand, the bending moments at the mudline level are generally overestimated by the simplified model, reaching relative differences of around 20% or 125% for low- and high-turbulence scenarios. Considering OpenFAST's results, the maximum internal forces were obtained for the E-2 scenario (ETM and EWH-50 yr). For this worst-case scenario, the simplified model was able to estimate the maximum shear forces and bending moments with relative differences of below 15% and 10%, respectively. This study reveals that, as expected, the simplified static-equivalent model does not offer sufficient accuracy for its use in final design stages or for the study of specific load scenarios involving high turbulence. However, its conservative nature, limited errors in relevant scenarios, and practically negligible computational costs make this simplified model a viable and interesting option in preliminary analyses, parametric analyses, and the initial stages of the design process, where a high number of evaluations are needed and a high level of accuracy in each simulation is not yet required. For the same reasons, this model could also be suitable for the generation of large datasets developed to train Machine Learning models. The code of the simplified model can be downloaded at [[https://www.mdpi.com/article/10.3390/app15031633/s1](https://www.mdpi.com/article/10.3390/app15031633/s1)]([https://www.mdpi.com/article/10.3390/app15031633/s1](https://www.mdpi.com/article/10.3390/app15031633/s1)). **Author Contributions:** Conceptualization, A.J.R.-M., C.R.-S., G.M.A. and L.A.P. ; methodology, A.J.R.-M. and G.M.A. ; software, A.J.R.-M. and C.R.-S.; validation, A.J.R.-M. and C.R.-S.; formal analysis, A.J.R.-M.; investigation, A.J.R.-M.; data curation, A.J.R.-M.; writing--original draft preparation, A.J.R.-M.; writing--review and editing, [PERSON], G.M.A. and L.A.P.