Validation and application of a fully nonlinear numerical wave tank for simulating floating offshore wind turbines

Numerical models are becoming a valid supplement, and even a substitute, to physical model testing for the investigation of fluid-structure interaction due to improved methods and a continuous increase in computational power. This research presents an extensive validation of a fully nonlinear numerical wave tank for the simulation of complex fluid-structure interaction of moored floating structures. The validation is carried out against laboratory measurements including recent and unpublished laboratory measurements of the OC5 floating offshore wind turbine subjected to waves. The numerical wave tank is based on the Navier-Stokes/6-DOF solver, interDyMFoam, provided by the open-source CFD-toolbox OpenFOAM, extended with the wave generation and absorption toolbox, waves2Foam, and an implementation for restraints of floating structures. Two methods are evaluated to address the instability issues of the partitioned Navier-Stokes/6-DOF solver, which are associated with artificial added mass. The model has been shown capable of computing detailed fluid-structure interactions, including dynamic motion response of a rigid structure in waves. However, instabilities due to numerical added mass is observed and discussed and it is concluded that further research is needed in order to establish a efficient yet stable scheme. Overall, good agreement is achieved between the numerical model and the physical model results.