# Design and Motion Simulation of an Underwater Glider in the Vertical Plane
## 6 Conclusions  
In this study, a UG that can dive to a depth of 400 m at a cruising speed of 2 knots was investigated. The motion of the UG with respect to the position variation of the internal movable mass and piston cylinder pump was analyzed. The hull profile of the glider was designed using the MYRING equations. The hydrodynamic parameters of the glider were obtained based on computer simulation using SolidWorks. By analyzing the mass distribution of each component in the glider, two reference coordinate systems were established for the underwater glider, different from the motion models of other references, the displacements of the movable mass block (\(d_{\overline{m}1}\)), and the piston assembly (\(d_{p1}\)) in the \(x\)-axis of body coordinate as inputs for the simulation, and the equations of motion of the glider in the vertical plane were derived and simulated using MATLAB and Simulink. An underwater glider was constructed to validate the simulation analysis, and experiments were conducted. Figure 17: Comparative results of experiment and simulation. The simulation results indicated that the AOA changed rapidly with the position change of the movable mass, i.e., the larger the displacement of the movable mass, the smaller the AOA, and the smoother the change in the AOA. In addition, as the displacement of the movable mass increased, the buoyant effect on the AOA diminished gradually. The movable mass significantly affected the pitching angle, where a larger mass and displacement resulted in a more significant change in the pitching angle. The results showed that the pitch angle varied approximately linearly with the displacement of the piston in the glider dive stage and that the pitch angle changed by approximately \(1^{\circ}\) for every 10 mm movement of the piston. However, the displacement of the piston imposed a less significant effect on the pitch angle when the glider was surfacing. In the glider diving or surfacing stage, the pitch angle changed linearly with the displacement of the movable mass, and the pitch angle changed by approximately \(7^{\circ}\) for every 10 mm movement of the movable mass; however, as the displacement of the movable mass block increased, the change in pitch angle decreased slowly. The effects of the displacements of the piston and movable mass block on the glide angle were consistent with the pitch angle results. From the contents of Figures 10 and 11, it can be obtained that under five different conditions, the glider showed different magnitude fluctuations in the angle of attack and pitch angle during the attitude switching; keeping the consistency of the piston and movable mass block can make the glider behave more stably in the attitude transformation; and the simulation results can be used as reference data for the attitude control of the UG. For the pitching experiments involving the adjustments of different positions of the movable mass block, the maximum pitching angle error was less than \(1^{\circ}\), which indicates the excellent modeling of the glider. Conceptualization, H.-S.C. and J.H. ; methodology, [PERSON]; software, [PERSON] and D.-W.J. ; validation, J.H., H.-J.C., J.-H.L., M.-J.K., K.-B.C., D.-W.J. and H.-S.J. ; formal analysis, [PERSON] and H.-S.J. ; investigation, [PERSON]; resources, [PERSON] and H.-S.C.; data curation, [PERSON] and D.-W.J. ; writing--original draft preparation, [PERSON]; writing--review and editing, D.-W.J., H.-J.C., J.-H.L., M.-J.K., K.-B.C., H.-S.J. and H.-S.C.; supervision, H.-S.C.; project administration, H.-S.C.; funding acquisition, H.-S.C. All authors have read and agreed to the published version of the manuscript.