## 1 Introduction  
The exploitation and use of renewable energy have become hot topics in recent years because of environmental reasons such as climate change, the greenhouse effect, and the oil crisis. Wave energy is one of the renewable energy sources with potential for exploitation and energy production thanks to the vastness of the ocean. The development of wave energy utilization was reviewed by [PERSON] in [1]. [PERSON] et al. presented the principles of wave energy power in [2], which include the technical principle of wave energy power generation, the realization of WECs, and the performance evaluation of converters. [PERSON] et al. introduced a point-absorber wave energy converter featuring a magnetic tristable mechanism that comprised coaxial inner and outer magnetic rings [3]. There are three main locations for operating a WEC: offshore, nearshore, and onshore [4], each with its unique wave energy characteristics. For the offshore and nearshore areas, the point absorber WEC has more advantages thanks to its size and spherical float, which can exploit many wave directions with many different types of PTO. These include hydraulic PTOs [5; 6; 7; 8], which use the piston's up-and-down movement to make the hydraulic motor rotate; PTO linear generators [9; 10; 11], which use the float's movement to activate the stator and rotor to generate electricity; and mechanical PTOs, which have been successfully used by CorPower Ocean to extract five times more energy per ton [12]. [PERSON] et al. introduced a control method designed to enhance the resonance of a Dual-Port Direct-Drive wave energy converter by fine-tuning both the dual electromagnetic force and electromagnetic spring force [13]. On the other hand, WECs installed onshore need a bigger space to operate. However, the Eco Wave Power company, which uses hydraulic PTO, succeeded in this field when they solved the commercial problems due to low costs implicit in the installation, maintenance, and connection to the electrical grid, but still maintained high reliability for controlling the system in harsh climate conditions [14; 15]. For WECs using a mechanical PTO, the authors et al. have carried out several studies on the point absorber types [16; 17; 18]. These papers show the significant contributions of conceptual design, which can increase the capture width ratio. Here, a conceptual design of the variable inertia hydraulic flywheel (VIHF) was employed to control the natural frequency of the PTO [16]. Moreover, a control stiffness mechanism was proposed in [17], and an optimum control strategy was applied in [18] to investigate the performance of the proposed design under the modeling program. A WEC is composed of a floating buoy and an upper structure placed over the floating buoy connected by a spring and a ball screw with a rotational mass, which converted linear motion to rotational motion, and the ball screw is connected to a rotating generator [19]. Moreover, some important approaches in modeling WEC in the frequency and time domains were presented in [20; 21; 22; 23; 24]. A frequency domain analysis on a generic WEC based on a two-body point absorber was performed in [20]. The hydrodynamic parameters are obtained with ANSYS AQWA, and numerical modeling and simulation in both the frequency and time domains were presented in [21]. Three different geometric shapes of the floating buoy were tested to obtain the hydrodynamic parameters for different sea states in [22]. [PERSON] et al. presented a numerical model of the coupled buoy-generator system. The output power was maximized by adding a submerged object to bring the system into resonance with the incident regular wave frequencies in [23]. An onshore WEC using the ball-screw in the elastohydrodynamic lubrication regime was modeled and simulated in the time domain in [24]. To improve the converted efficiency, the optimal control algorithms have been applied to maximize the harvesting energy [25; 26; 27]. [PERSON] et al.