A new integrated numerical wave tank in OpenFOAM for hydrodynamic modelling of offshore renewables

This paper presents a new integrated hydrodynamic modelling framework for wave–structure interaction problems. It is developed by coupling a finite-volume-based fully nonlinear potential flow (FNPF) solver with the native OpenFOAM incompressible ‘interFoam’ solver in a numerical wave tank (NWT). The coupling procedure for this new model, named IntegratedFoam, follows a domain decomposition approach in which an overlapping relaxation zone is utilised to implement a one-way coupling. Consequently, the method for transferring information is made simple and the coupling stable due to the primary advantage that each constituent solver has been developed in the same framework of OpenFOAM, and therefore, are both also based on the same numerical method, i.e., the finite-volume method (FVM). This means that only a method to calculate the volume fraction from the free-surface elevation needs to be implemented: the velocity and pressure are already calculated as part of the FNPF solution and can be transferred accordingly. In addition, existing advanced OpenFOAM functionalities can be used for the required interpolation—easily addressing the problem of nonconforming meshes. These functionalities then also allow for the easy implementation of an overlapping relaxation zone which is key to a stable coupling because it ensures that there is a smooth transition from the FNPF to interFoam solution whilst also absorbing any reflected waves in the NWT. The accuracy and efficiency of the new IntegratedFoam model are then systematically validated through two complex wave–structure interaction test cases: focused wave interaction with a fixed 3-D cylinder acting as a simplified monopile foundation and focused wave interaction with a 3-D wave energy converter (WEC) device. It is shown to produce accurate numerical solutions that agree well with existing numerical results and experimental data, all whilst significantly improving computational efficiency.