ABSTRACT

In this paper, an in-house hybrid CFD model qaleFOAM is developed and extended to investigate the wave interaction with multiple floating buoys. This hybrid model adopts the domain decomposition approach, which combines a two-phase Navier–Stokes (NS) model and the fully nonlinear potential theory (FNPT). In a confined region around the structure (NS domain), the problem is solved by the open-source solver OpenFOAM/interDyMFoam. In the rest of the computational domain (FNPT domain), the quasi arbitrary Lagrangian–Eulerian finite element method (QALE-FEM) is adopted. The proposed model is firstly verified against the experimental data for the motion responses of the CorPower Ocean buoy in regular waves. Then the wave interaction with multiple CorPower buoys is investigated, and the interference between multiple buoys is discussed. The surface elevation field near the buoy and motion responses of each buoy are further analyzed.

INTRODUCTION

Ocean waves are a huge and largely untapped resource of renewable energy, due to the high power density and longtime availability. A wide variety of concepts for wave energy converters (WECs) have been invented to extract energy from ocean waves (Falnes, 2007; Drew et al., 2009; Falcão, 2010). Among the wide variety of WECs, point absorbers have attracted a lot of attention. In order to extract a considerable amount of wave power at a location in a cost-effective way, a large number of point-absorber WECs are usually arranged in arrays using a particular geometrical configuration. The interaction between the individual WECs affects the overall power production of the array. An understanding of the hydrodynamic interactions in such arrays is essential for determining optimum layouts of WECs.

A range of numerical techniques have been proposed to model WECs (Li and Yu, 2012; Wolgamot and Fitzgerald, 2015; Davidson and Costello, 2020). In many cases, the linear potential flow theory based representation (e.g., Babarit et al., 2012) is utilized because of its simplicity and computational efficiency. Although the linear-based theory is expected to be sufficient to describe small motions induced by small amplitude waves, WECs are often subject to many nonlinearities such as those arising from steep incident waves, large-amplitude motions, complex mooring arrangements, power take-off (PTO) systems and viscous drag forces (Tarrant and Meskell, 2016). In this case, the linear-based model may not be able to provide an accurate representation of the actual system dynamics. As an alternative, both FNPT and NS models are used to take into account these nonlinear factors. However, the NS model is quite time-consuming and thus is rarely applied to modelling wave-structure interaction in large spatial– temporal domains, particularly for WEC arrays. In recent years, the hybrid models coupling the FNPT and the NS models (e.g., Li et al., 2018; Yan et al., 2020; Aliyar et al., 2022) have been developed to tackle the challenges. These hybrid models take the advantages of the FNPT in fast modelling the large-scale wave propagations and the advantages of the NS models in resolving small-scale viscous effects, like vortex shedding and turbulent effects. These hybrid models are shown to be more efficient than NS models. Further, the comparison by Ransley et al. (2020) may demonstrate a better practical performance of the hybrid model for wave-structure interaction problems compared with both the potential theory and NS solvers.

This content is only available via PDF.
You can access this article if you purchase or spend a download.