2D-3D CFD coupling methodology for coastal and offshore engineering

The application of CFD models for coastal and offshore engineering has known an important increase in the past decades. Their use is essential for appropriately deal with both non-linearity and dispersion when studying wave structure interaction (WSI). However, the use of a single 3D model is still unviable for application in large domains (Vandebeek et al., 2018 [1]), which are generally needed to properly reproduce wave transformation. Moreover, in coastal and offshore engineering studies several hydro- dynamic actions (wave conditions) need to be analysed by performing a range of simulations rather than a single one. Therefore, the resulting computational time would always be extremely expensive when using a full 3D model. In this work, two bi-dimensional/three-dimensional (2D-3D) Navier-Stokes (NS) based couplings are presented for studying wave structure interaction. The couplings are specified via one-way or two-way exchange of flow information, thus providing a complete tool to address one or bi-directional processes in which the three-dimensional flow is expected to be confined around the structures. The implementations are based on the OpenFOAM (https://www.openfoam.com/ [2]) while IHFOAM (https://ihfoam.ihcantabria.com/ [3]) has been used to generate and absorb waves. The numerical implementations have been validated and applied to wave interaction with a novel dual wave energy converter (WEC) device integrated in a vertical breakwater (Lara et al., 2019 [4]). The numerical implementations allow to extremely reduce the computational time, and therefore, to consider larger domains for wave propagation and transformation. Experimental tests (100s duration), considering ex- treme hydrodynamics, have been replicated using 8 processors only, and taking approximately two-days for completing the simulations. This demonstrates that the coupling methodology allows to increase the range of use and the incorporation of CFD in real offshore and coastal engineering applications.