## 1 Introduction  
Over the past few decades, numerous studies have been carried out on renewable energy to overcome the limitations/harm of fossil fuels. Among the renewable energies, ocean renewable energy is seriously considered since the ocean covers approximately 70% of the Earth's surface. In particular, ocean wave energy is abundant and has the highest energy density compared with other renewable energy sources [1, 2]. Therefore, numerous studies on the potential of wave energy [1, 2, 3, 4, 5, 6] and wave energy converters (WECs) converting wave energy into electrical energy [7, 8, 9, 10] have been conducted. WEC devices can be classified into three types according to the working principle: oscillating water columns, oscillating body systems, and overtopping systems [7]. The International Renewable Energy Agency (IRENA) reported that the installed capacity of the oscillating water column was the highest of these technologies. On the other hand, oscillating body systems are expected to play an important role in the future. In particular, the point absorber, one of the oscillating body systems, is being studied most actively because it can be scaled from small to large [11]. This study focused on a heaving-point-absorber (HPA) WEC, such as Wavestar [12]. Multiple hemispherical floating bodies were connected to the bottom-fixed main structure through hinged arms to generate electricity using the hydraulic power take-off (PTO) system. Many studies have evaluated the dynamic response and power production of the Wavestar WEC with oscillating hemispherical bodies. [PERSON] et al. [13] performedan experimental study on the Wavestar WEC composed of a single hemispherical float. They compared the experimental results with the BEM (boundary element method)-based numerical results. [PERSON] et al. [14] conducted a numerical analysis of the Wavestar WEC using a CFD-based numerical wave tank. They analyzed the dynamic response of the float and the pressure distribution on the surface of the float. [PERSON] et al. [15] performed a numerical analysis of the point absorber WEC and arm using flexible multi-body dynamics composed of a finite element model and multi-body dynamics. They analyzed the arm stress distribution and the displacement and velocity of the float. [PERSON] et al. [16] conducted an experimental study on a hinged hemispherical WEC. They evaluated the hydrodynamic responses and generated power through a BEM-based numerical wave tank. [PERSON] et al. [17] performed numerical analysis and an experimental study using a CFD-based numerical wave tank for a 1/5 scale Wavestar WEC. They compared the results of the power production and the pressure on the surface of the float. [PERSON] and [PERSON] [18] analyzed the behavior of the two-dimensional Wavestar WECs by performing linear analysis using multi-body dynamics and classical mechanics and calculated the constraint forces acting on the hinge points. [PERSON] and [PERSON] [19] compared the dynamic response and generated power of Wavestar WEC considering the body-nonlinear Froude-Krylov and hydrostatic forces. The above studies focused on the behavior of the Wavestar WEC and assumed that the hinge point did not move as a center of rotation. On the other hand, the hinge point is unlikely to be fixed due to the elastic behavior of the foundation structure, particularly when the water depth was large. In turn, the movements of the floaters and the transmitted forces may affect the elastic responses and the corresponding stresses of the foundation structure significantly. These coupling effects must be analyzed to ensure the safety of the foundation structure. Studies on the combined analysis considering the movement of the hinge point connecting the WEC and the behavior of the foundation structure are very important, but not many studies have been carried out so far. In this regard, the present study focused on the analysis of the full dynamic coupling between two floats, connecting arms with hinge points, and elastic foundation structure.