Abstract

Floating Offshore Multi-Wind Turbines (FOMWTs) are an interesting alternative to the up-scaling of wind turbines. Since being new incoming concepts, there are few numerical tools for its coupled dynamic assessment at the present time. In this work, a numerical framework is implemented for the simulation of multi-rotor systems under environmental excitations. It is capable to analyse a platform with leaning towers handling wind turbines with their own features and control systems. This tool is obtained by coupling the seakeeping hydrodynamics solver SeaFEM with the single wind turbine simulation tool OpenFAST. The coupling of SeaFEM provides a higher fidelity hydrodynamic solution allowing the simulation of any structural design since using the Finite Element Method (FEM). Besides, a methodology is proposed for the extension of the single wind solver, allowing the analysis of multi-rotor configurations. To do so, the solutions of the wind turbines are computed independently by several OpenFAST instances, performing its dynamic interaction through the floater. The method is applied to the single turbine Hywind concept and the twin-turbine W2Power floating platform, supporting NREL 5-MW wind turbines. The rigid-body Response Amplitude Operators (RAOs) are computed and compared with other numerical tools. The results showed consistency in the developed framework. Agreement is also obtained in simulations with aerodynamic loads. This resulting tool is a complete time-domain aero-hydro-servo-elastic solver, able to compute the combined response and power generation performance of multi-rotor systems.