The aim of this study is to develop a viscous numerical wave tank using a coupled solver between the wave generation and absorption toolbox waves2Foam, developed by Jacobsen et al.  and the overset method built in the open source CFD software OpenFOAM©. This wave tank can be used to analyze the behavior of Floating Offshore Wind Turbine (FOWT) in nonlinear waves. A mesh convergence analysis is presented on a simple 2D case in order to validate the CFD model. The results are compared to experimental data from the literature and show good agreement. The response of a floater developed for a FOWT is analyzed. The free surface elevation, heave and pitch motions are compared to experimental results from the literature. Comparisons between experimental data and numerical results are discussed.