## 2 Design of Real-Time Communication Subsurface Mooring System
### Hydrodynamic Analysis of SCB  
The SCB is affected by the marine environment, such as currents, tides, wind, waves, and other elements during the monitoring process, which cause attitude changes such as rotation, pitch, tilt, etc. The SCB integrates the satellite communication module, and the communication effect is directly affected by the attitude. When the swaying angle of the SCB increases, the failure rate of the satellite communication increases, which has a serious impact on the timeliness of the observation data from underwater sensors [14]. At the same time, in order to improve the concealment of the SCB and reduce the risk of its destruction, its size should be minimized. The design of the SCB is shown in Figure 2. Its unique shape structure reduces the impact of ocean currents and waves. At the same time, under the comprehensive action of the gravity, the buoyancy, and the pulling force from the mooring cable, the SCB above water is relatively stable, and the water outlet height is moderate. To verify the design effect, the force analysis and numerical simulation analysis of the SCB under the influence of waves were carried out as follows. Figure 1: Real-time Communication Subsurface Mooring System. According to the hydrostatic posture of the SCB along with numerical analysis, the coordinate system shown in Figure 2 was established. The \(X\) axis is defined as the front and rear direction of the SCB. The \(Y\) axis and the \(X\) axis are in the horizontal plane, and the \(Z\) axis is perpendicular to the \(X\)-\(Y\) plane and pointing upward, as shown in the coordinate system in Figure 2. The origin is the center of gravity of the SCB, the rotation around the \(X\) axis is defined as the inclination angle (also known as the roll), the rotation around the \(Y\) axis is defined as the pitch angle (pitch), and the rotation around the \(Z\) axis is defined as the azimuth angle (also known as the yaw) [15]. The SCB is subjected to gravity G, buoyancy f, steel cable pulling force T, fluid force R, the restoring moment M under the steel cable and the side surface of the SCB when it rotates received resistance F. Since the cross-section is an airfoil, the azimuth change of the SCB is mainly affected by the action of the wind, waves, and ocean currents [16]. Due to the pulling force of the steel cable in the X direction, the pitch angle of the rotation around the \(Y\) axis is small. The change in the azimuth angle hardly affects satellite communication, while the inclination angle around the \(X\) axis changes greatly, which has significant influence on satellite communication. A computed numerical simulation analysis was carried out for the structure of the SCB [17]. The SCB was subjected to a four-level sea state with a wave height of 1.2 m and a period of 5 s; the attitude and motion simulation of the surface velocity required 1.5 m/s to establish a connection with SCB and the current and wave. The simulation model is shown in Figure 3.  
In the initial state, the SCB was suspended on the sea surface and the satellite antenna height from the sea surface was about 0.25 m. Under the influence of ocean currents and waves, the SCB was affected by the external force of the fluid, which leads to a posture and position variation and performed heave and pitch motions with the waves and ocean currents. Figure 4 shows the height changes of the satellite antenna above the sea surface within 50 s. The maximum value was 0.44 m and the minimum was 0.04 m. This shows  
Figure 3: Simulation cloud map of SCB. Figure 2: Coordinate system and coordinate analysis of SCB. that under the action of ocean waves, the SCB will instantly sink under the sea surface for a very short period, and then rise to the sea surface under the action of its buoyancy. Figure 4 shows that under a harsh sea state, the water outlet height of the SCB was above 0.25 m for nearly half of the total time, and the water outlet height was above 0.1 m for more than 90% of the time.