Dynamic behavior analysis and bio-inspired improvement of underwater glider with passive buoyancy compensation gas

To deal with the buoyancy loss caused by hull deformation and seawater density variation, low-density gases, such as nitrogen, have been adopted in underwater vehicles for passive buoyancy compensation. Therefore, the accurate understanding of passive buoyancy compensation gas (PBCG) is critical to the design and operation of underwater glider. In this paper, a theoretical model for the Petrel-L underwater glider with PBCG is established, which consists of environment model, net buoyancy model and dynamic model. The above models are verified by sea trial, and then the feasibility and long-term reliability of PBCG are demonstrated by a long-range voyage. Co-simulation of Petrel-L with the models shows that pre-charge pressure, distribution and volume of PBCG have significant effects on the motion performance in terms of attitude stability and velocity stability. Besides, to achieve better buoyancy compensation and motion stability, an improvement design of PBCG inspired by swim bladder is proposed. Deviation of pitch angle from its target is less than ±2° over the depth range from 50 m to 950 m by optimizing the improvement design.