The open-source code DualSPHysics is here applied to simulate the interaction of sea waves with floating and offshore structures, which are typically moored to the sea bottom, such as vessels, boats and wave energy converter (WEC) devices. The goal is to employ DualSPHysics to study their survivability under high energetic sea states, obtaining the optimum mooring layout to increase their lifetime. The moorings are modelled by coupling DualSPHysics with MoorDyn, a lumped-mass mooring dynamics model. MoorDyn represents mooring line behaviour subject to axial elasticity, hydrodynamic forces in quiescent water, and vertical contact forces with the seabed and calculates the tensions of the mooring lines, which are added as external forces in order to compute the resulting response and motions of the floating structures in DualSPHysics. The coupled model has been validated against experimental data generated during the experimental campaigns of the MaRINET2 EsfLOWC project.