This paper investigates methods for reaction loads extraction in floating offshore wind turbines (FOWTs) within the modal-based aeroelastic modeling framework. Three methods belonging to two different principles (internal and external loads) are presented, where the two external load principle-based methods (‘AuxDOFs’ and ‘d'Alembert’) are rigorously developed for extracting 6-dimensional reactions loads at different cross sections. Verification and evaluation of the developed methods are performed using three different structural systems, as well as comparison with FAST. It is shown that ‘AuxDOFs’ and ‘d'Alembert’ methods are preferred over the internal load method due to the significantly improved accuracy and the ability to extract reactions in rigid substructures. Finally, the developed methods are applied to evaluate the influence of tower torsional degree of freedom (DOF) on FOWT loads for four different types of foundations, considering different load cases. Extensive simulation results indicate that neglecting the tower torsional DOF in the modal-based simulation tools can lead to underestimation of FOWT loads.
