## 1 Introduction
To find the optimal configuration, the shape and size of the buoy must be tested, as well as the degrees of freedom of the whole system and the flow field around it. In the absence of expensive wave basin facilities, and at the initial stages of development, the abovementioned goals can be partially attained with numerical simulations. In this regard, computational fluid dynamics (CFD) plays an important role in saving time and costs, as it is an excellent tool for the optimization and improvement of the design, which is created based on a performance analysis. The C++ libraries of the open source field operation and manipulation model, better known as OpenFOAM, are designed to solve several fluid mechanics problems [19]. Therefore, OpenFOAM is a CFD software suitable for analyzing a WEC design. In recent years, OpenFOAM has been widely used to set up numerical wave tanks (NWTs) for the research and development of WECs as compared to other similar tools of its kind [20]. OpenFOAM can be used to model a particular device's geometry with a good degree of accuracy; although, the runtime and high demand for computational resources are disadvantages [21]. During the simulation of WECs in an NWT, the mesh quality can decrease during the time of the simulation, since large distortions can appear due to the mesh design and vertical motion of the body (beyond the limits of the model stability [22]), or due to the presence of multiple floating objects [23]. There are many dynamic mesh motion methodologies to avoid mesh distortion; although, some can lead to numerical instability and, finally, to simulation crashes [20]. Examples are the 'overset grid method' (released in OpenFOAM since version v1706 and already validated [22]) and'mesh morphing method'. These two methods were recently assessed in WEC simulations [24], and although the overset grid method can accommodate large body displacements without mesh topological changes, it was found that it posed very high computational costs compared to the mesh morphing method [25]. The implementation of a CFD model could be a very complex process; hence, experience is required to create a correct numerical simulation. In addition, this may require a demanding mesh adjustment process when the motion of the device is coupled to the interaction with the fluid included in the simulation. In this paper, OpenFOAM simulations are used to analyze the instantaneous power absorption of a cylindrical buoy that has a pivot point as the semi-axis of rotation, i.e., a point-pivoted absorber (PPA). The system is forced with regular waves and tested with a set of different buoy radiuses, where certain coefficients had to be modified to accommodate the correct mesh deformation. The subsequent sections are structured as follows. Section 2 addresses the governing equations applied to the fluid flow in the OpenFOAM model, their tools for the discretization of the domain, and the coefficients that describe the free surface deformation due to rigid body motion; a short description of the InterFoam solver, used for multiphase incompressible, isothermal, and immiscible fluids (water and air, in this study) is also included. Section 3 provides a brief explanation of the wave theory used in the simulations and the approaches for power calculations, along with an overview of the way in which the buoys, associated with WECs, absorb energy. Section 4 presents the numerical results of the model sensitivity analysis, the energy absorption by the different buoy diameters, and the effects that the WEC has on the modification of non-linear wave properties. In this section, discussions on mesh deformation, power absorption, and the potential effects on sediment transport due to the motion of the floating object are also included. Section 5 highlights the conclusions and recommendations.