# Numerical Modelling of a Floating Wind Turbine Semi-Submersible Platform
## 1 Introduction
Furthermore, another way to study these structures has been to focus on the aerodynamics of the turbine when having a defined motion in the platform [18; 19; 20]. Moreover, the study of this type of platforms has been extended in recent years, with several studies focused on decay testing for different degrees of freedom [11; 21]. [PERSON] et al. [19; 22] studied the unsteady aerodynamics of a turbine by imposing a sine function onto a spar platform. In recent years, various articles have been focusing on the complex behaviour of these structures. [PERSON] et al. [22] studied the effects of the movement of the OC4 DeepCWind platform on the aerodynamics of the wind turbine and vice versa [23], work that continued with the development of an aero-hydro-mooring elastic fully coupled tool by inducing a combined wind and wave condition. Following their work, [PERSON] and [PERSON] [22] investigated a 5 MW wind turbine over an OC4 DeepCWind semi-submersible platform by comparing the results of the dynamic fluid body interaction methodology with those obtained with the open-source software FAST. The aero-hydrodynamic performance of the system was studied under coupled wind-wave conditions and in decay testing [24]. Study of the IDEOL platform in regular wave tests by applying a coupled simulation of multi-body systems with CFD and comparison of the results with experimental data was done by [PERSON] et al. [25]. An unsteady actuator line model for the aerodynamic simulation coupled with a CFD solver for the hydrodynamic part was studied by [PERSON] et al. [26]. Similar works have been done for floating structures but for different aims. [PERSON] et al. [27] present a work in which they experimentally study the decay testing of a multi-module aquaculture platform where they analysed the motion of the platform while also analysing, apart from calculating the natural periods, the stiffness with the mooring system. Fur thermore, they study the response of the platform when facing regular waves. In relation to the experimental study of mooring systems in this type of structures, [PERSON] et al. [28] carried out deep research on this topic. Finally, joint research of computational and experimental approaches has been done too around this type of structures, focusing on extreme conditions [29]. However, it is important to find a computational mesh that has a good relation between computational cost and accuracy. The latter one is especially important, since a bad mesh can modify the response of the sub-platform analysed. This work presents in the following section a summary of the mathematical treatment used in this type of problems. Furthermore, the procedure followed in order to obtain the results is defined, to give a better understanding of this research. Finally, Section 3 presents the outputs of the simulations for platforms both with and without moorings, validated through the data obtained by Saitec Offshore Technologies in their experiments in the LIR/NOTF laboratory through the ARCHVIND Project (adaptation and implementation of floating wind energy conversion technology for the Atlantic region).