Research on Influence of Operating Depth on Motion State of Underwater Gliders

Abstract

Net buoyancy, which drives underwater gliders, accounts for approximately 0.5% of their displacement, and its small change may significantly affect the state of their motion. During the gliding process, the displacement changes dynamically owing to the variation in seawater density and pressure with depth, thus resulting in a change in net buoyancy that would then affect the steady state of gliding. In this study, the effect of the change in net buoyancy on the steady state of the gliding motion was studied based on the dynamic equilibrium equation. By combining the mathematical and dynamical models of displacement change with depth the influence of depth on the gliding motion state was studied through simulations. The results show that: 1) the actual motion of underwater gliders under the influence of depth is dynamically balanced gliding, instead of steady balanced gliding; 2) the displacement-depth variation affects the gliding speed with a marginal effect on gliding attitude; 3) without additional control, gliding speed decreases first and then increases in the diving stage, and increases first and then decreases in the rising stage; and 4) the influence of the change in net buoyancy on gliding attitude could be eliminated by adjusting the position of the internal sliding mass, which requires little power. This study provides a reference for the precise control of underwater gliders used in marine environment monitoring and detection.

Keywords

• underwater glider
• gliding motion
• net buoyancy
• depth