Three numerical approaches using CFD are used to model the PTO damping of an onshore dual chamber OWC tested in a scaled wave flume: In the first case, the PTO is modelled with the same geometrical dimensions of the experimental setup; in the second case, the PTO is modelled as a porous medium, while in the third case, it is modelled by a drag force applied directly to the momentum equation. Measurements of air pressure and free surface elevations inside the chambers of the OWC are compared between CFD approaches and the physical model. They show that the 3 CFD models reproduce with relative accuracy the physical experiments. Results also show that the simulations are faster around 25% up to 40% using numerical damping regions comparing to the PTO real geometry.