## 1 Introduction
In addition, [PERSON] [32] carried out SPH simulation on the oscillation of the ocean buoy on the free surface and the interaction with the incident sinusoidal wave train, and observed that the buoy would have a long-period oscillation phenomenon under the natural frequency of the surge. [PERSON] [33] carried out model calibration and parametric study on wave fluctuation of a nonlinear underwater mooring structure. It was found that the sphere moves mainly in a two-dimensional fashion [or two degrees of freedom (2 DOF)] of the firm and heave, with negligible pitch. [PERSON] [34] carried out numerical simulation on the mooring ocean buoy system and virtual simulation on the movement of the structure in the X and Y directions. It was found that waves had obvious influence on the oscillation of ocean buoys. The buoy would have periodic motion, which was surge motion and sway motion, respectively. Both the sea state and the initial position of the buoy affected its moving range. In addition, [PERSON] [35] also carried out dynamic analysis on the ocean buoy with mooring rope fastening. Under given conditions of ocean state and arrangement, the X-direction displacement of the cable was affected by both the X-direction wave and the Y-direction wave, while the Y-direction displacement was only affected by the Y-direction wave. In addition, when a quarter of the ocean buoy was immersed in water, there would be a systematic error, which had little impact on the buoy heave motion and cable tension. The core issue of TENG is power generation, so simulation of power generation is of vital importance. Many people have conducted research on this issue. [PERSON] [36] used Inexact Newton method, bi-conjugate stabilized method and FFT technique to simulate the electric field. [PERSON] [37] and [PERSON] [38] studied power generation through dynamic characteristics. The results explained some of the electrical properties of TENGs. [PERSON] [39] used PSPICE to simulate the equivalent circuit of TENG. The results provided a theoretical basis for subsequent TENG's theoretical analysis of generators and development of energy management circuits. In related research of TENG, COMSOL was often used for simulation by people. [PERSON] [40], [PERSON] [41], [PERSON] [42] and [PERSON] [43] used COMSOL to simulate the energy capture properties of TENGs. COMSOL [40; 41; 42] is based on the finite element method, discretizing the continuous physical solution domain into a combination of multiple groups of elements. The finite element software COMSOL is a convenient and effective way for simulation. In this work, we report the structure of a novel built-in cylindrical TENG (C-TENG) powering for a kind of ocean buoy, BUOY-41 (Figure 1). The normal power demand of the buoy in ocean waves is about 10 mW. The C-TENG is based on a lateral sliding mode. Firstly, the C-TENG is designed. Then, the motion of C-TENG is calculated by using the software Star-CCM++, which is used to analyze the hydrodynamic properties in waves. The energy capture properties of C-TENG are studied by COMSOL, obtaining the motion calculated. Under the 0.4 m and 2 s wave condition, it is observed that the maximum vertical displacement and buoyancy of buoy can reach 0.19 m and 13.62 N, respectively. Obtaining these motion conditions, it is observed that the instantaneous power output reaches 1.7 mW and the instantaneous maximum power output density arrives at 30 mW\(/\)m\({}^{2}\). By doing this work, the hydrodynamic properties and energy capture properties of C-TENG are revealed, which is of huge significance for research on the theoretical mechanism of TENGs.