Numerical modelling has become an essential tool for the design of wave energy converters (WECs). However, regarding complex coupled mechanisms, conventional numerical tools may not be able to capture the required full range of behavior for a comprehensive engineering analysis of such devices. In this work, a multi-physics augmented version of the SPH-based code DualSPHysics is applied to study a full-scale wave energy hyperbaric converter (WEHC) on the south-western coast of Portugal. The newly developed numerical tool provides a more accurate analysis for the coupling of the three different sub-systems of the WEHC: floater, lever arm, and hydraulic power take-off (PTO) mechanism, modelled as a single and double-acting cylinder. The validated numerical tool was then applied to study the effect of several mechanical constraints, PTO damping coefficients and inertia. The results show that the capture width ratio (CWR) of WEHC strongly depends on the unbalanced force of the cylinder, by up to 15%. Optimizing the pressure in the cylinder can increase the CWR by 30%. It was also observed that the CWR is directly affected by the geometry of the seawall.