Abstract: The buoyancy of traditional Underwater Glider (UG) with a rigid hull is aff ected by the changing marine parameters, making 
it diffi cult for the vehicle to dive deeper with good motion characteristics. In the present work, the development of a novel 
UG for neutral buoyancy, which is equipped with a Flexible-Liquid-Rigid (FLR) composite hull, is presented. The innovative hull that imitates the buoyancy regulation mechanism of marine organisms is easily adaptable to the changing marine 
environment. The rigid part of the composite hull withstands hydrostatic pressure for inner function modules of the vehicle. 
The liquid of the composite hull mainly serves as a buoyancy compensation to mitigate the eff ect of buoyancy variation 
caused by the changing marine parameters. The fl exible covering provides a good hydrodynamic shape for the vehicle under 
the internal liquid pressure. The buoyancy variation due to the composite hull compression as well as changes of seawater 
density and temperature was comprehensively considered in the design process and integrated to the dynamic model. In 
addition, sea trials were performed to verify the motion characteristics of the proposed vehicle. The results reveal that the 
Flexible-bodied Underwater Glider (FUG) has a better gliding performance in practice.

Key words: Bio-inspired buoyancy regulation, Flexible-bodied vehicle, Composite hull, Adaptable buoyancy compensation