Study on the vertical motion characteristics of disc-type underwater gliders with zero pitch angle

A disc-type underwater glider (DTUG) is characterized by full-wing body shape, omnidirectional characteristics, and high maneuverability. To further reveal the differences between DTUGs and hybrid-driven underwater gliders (HUGs), the vertical motion of a DTUG with zero pitch angle is simulated. Based on the structural characteristics of DTUGs, the motion control equations with control inputs are derived and solved by the fourth-order Runge-Kutta method. The DTUG's vertical velocity, fixed-depth motion, vertical motion with external disturbance, and stability are mainly analyzed and compared with those of an HUG. The results show that the DTUG's full-wing body shape increases its vertical resistance so that the vertical steady motion velocity is low, which is advantageous for vertical depth control but disadvantageous for fast vertical motion; furthermore, fixed-depth motion control can be easily realized in limited space. The DTUG's vertical motion with external disturbances can quickly return to a stable state within a smaller vertical distance than that of the HUG, which is beneficial for assisting the DTUG in returning to the target position and will improve its movement efficiency in a small body of water with limited depth. The stability analysis shows the DTUG can remain stable within the range of control parameter.