Improvement of working pattern for thermal underwater glider

Thermal underwater glider (TUG) is a new trend for the development of autonomous underwater vehicles, it is composed of traditional underwater glider (UG) with thermal engine which is used for harvesting and transforming ocean thermal energy. The main problem of TUG is the mismatch between gliding motion pattern and phase change process. The reason is that low heat conductivity of PCM leads to taking a long time for complete phase change. In this paper, new working pattern for TUG is proposed according to the temperature profile of seawater. Full working depth for TUG is divided into warm water layer and cold water layer by phase transition point of PCM (18.15°C for Hexadecane). For a typical seawater temperature profile, warm water layer, in which temperature is higher than the phase transition temperature of PCM, is the water column above the depth with the phase transition temperature. While the cold water layer, in which temperature is lower than the phase transition temperature of PCM, is the water column below the depth with the phase transition temperature. When the TUG is gliding in warm water layer, it is called melting process of PCM. While in cold water layer, it is solidification process. Working parameter for melting process includes vertical velocity and drifting time on sea surface, while for solidification process, it includes vertical velocity and working depth. These working parameters can be reconfigured for the two working processes respectively. Practical ways to change vertical velocity can be adjusting the net buoyancy or pitch angle. The magnitude of vertical velocity can be varied when TUG glides in different water layers.