# Design and Motion Simulation of an Underwater Glider in the Vertical Plane
## 5 Experiment  
To verify the feasibility of the glider structure design, a simple experiment was conducted to investigate the variation in the glider pitch angle with the movable mass block  
Figure 14: Gliding speed during simulation.  
Figure 13: Change in gliding angle with buoyancy and movable mass.  
owing to the limitations of the experimental conditions. Due to the communication needs, the antenna part must be exposed above the water surface, which means that the glider cannot be completely submerged in water, which is why the ballast water mass obtained from the experiment is not the same as the ballast water mass in the aforementioned Table 1. This experiment only tests the change of the pitch angle of the glider after the movable mass block is moved when the glider floats on the water surface. The experiment was conducted in the university swimming pool, and the deepest depth of the pool was 3 m, which does not satisfy the gliding experiment requirements. Figure 15 shows photographs of the experimental site.  
The middle section (yellow sector) shown in the photographs above contained communication cables. The total length of the cables was 2800 mm, their diameter was 10 mm, and the buoyancy of the cables was modeled as an equivalent circle (red model), as shown in Figure 15. The glider was not completely submerged in water, which implies that the antenna housing appeared partially above the water. The buoyancy of the glider is illustrated in Figure 16. The green part represents the ballast water in the buoyancy cylinder whose mass was 1.98 kg.  
Figure 16: Buoyancy of the glider.  
Figure 15: Photographs of the experimental site.  
First, the glider was suspended horizontally in water by the buoyancy adjustment mechanism and the movable mass block; at the end of the experiment, the distance from the surface of the piston to the end face of the buoyancy cylinder in the buoyancy engine was measured so that the mass of ballast water in the buoyancy engine for this experiment could be calculated; subsequently, the buoyancy mechanism was maintained, and the experimental values of the pitch angle under different attitudes were obtained by adjusting the different positions of the movable mass block, in which the movable mass block moved 10 mm each time. During the motion of the movable mass, the pitch angle was recorded at each moment using the built-in sensor on board, and after the experiment, the data were exported and fitted to produce a relationship between the pitch angle and the displacement of the movable mass. Next, the experimental results were compared with the simulation results. Owing to the limitations of the experiment, only the comparative results of the forward motion of the movable mass block are shown herein. The comparison results showed that the simulation and experimental results agreed well, with a maximum error of less than 1\({}^{\circ}\). By comparing the model with the physical glider, the analysis concluded that this error should be caused by the distribution of the cables inside the fuselage. We can only measure the mass and the approximate location distribution of the cables, but we cannot easily reproduce the distribution of the cables inside the fuselage with the modeling software. More detailed results will be described in a future paper. The comparative results of the experimental and simulation results are shown below Figure 17.