Wind energy plays an important role in the renewable energy concept. Among many wind energy concepts, offshore renewable energy has gained a lot of attention in recent years because of the vast energy resources. However, the environmental conditions assessment, hydrodynamics, aerodynamics, mooring and structural response analysis are complex and challenging tasks for the offshore wind turbines. Several numerical tools exist for modelling the offshore wind turbines. Most of these tools were initially used for onshore wind turbines, and later on extended for offshore ones by including the hydrodynamic effects. When it comes to the offshore wind turbines, the numerical tools should be able to combine the aero-servo-hydro-elastic effects.
The concept of multi-unit wind turbine, which has multiple wind turbines on a single platform, has been emerging for the last few years. For a large floating structure, the deflections in waves will have significant effects on its structural loads, and the structural deflection will affect the fluid forces in return. So it is important to consider the two way coupling between the fluid and structure interaction. The main objective of this study is to develop a time domain numerical method based on potential flow to perform the hydroelastic analysis of a large FOWT platform that are applicable for practical engineering problems. The fluid-structure coupling will be based on modal superposition method. The Froude-Krylov and hydrostatic forces will be calculated for the exact wetted surface area and the radiation forces will be estimated based on Cummins formulation. The study will focus on a FOWT with spar platform and on another one made of pontoons with multi-unit wind turbines. The developed tool will be coupled with the commercial software ‘FAST’ for aeroelastic analysis. Linear and nonlinear linear mooring forces will be considered. The equation of motion will be solved in time domain and will take account of the nonlinear forces from each component. It is expected that the developed tool will help to estimate the motion and the structural loads acting on large FOWTs in both regular and irregular waves.