The combination of wave and aerodynamic loads acting on Floating Offshore Wind Turbines (FOWT) creates a complex system that must be studied in detail to harness as much energy possible while maintaining structural integrity. Computational fluid dynamics (CFD) is a useful analysis tool, which enables to consider the key parameters (e.g., mooring line forces, wave characteristics, aerodynamic loads) and, thus, help in the design process. However, its computational cost is often prohibitive. For this reason, simplifications must typically be introduced. In this paper, simulations of heave decay tests, with and without moorings, under regular waves were compared with experimental data obtained from previous studies carried out by Saitec Offshore Technologies in the MaREI Centre (Ireland). Future research will focus on the dynamic viscosity behaviour.