Underwater gliders are becoming popular in ocean exploration. However, the main development limitation of underwater gliders is still around energy. This paper proposes a new-type energy harvesting mechanism and explores its design methodology for the gliders using thermal buoyancy engines. With the temperature difference in the ocean, the thermal buoyancy engine changes the buoyancy of the glider and drives the glider to ascend and descend through the water and drive a turbine behind to harvest energy. Based on this harvesting mechanism, firstly, a new-type thermal engine with high ballast capacity is developed with patent applied. Secondly, a dedicated turbine design and optimization method based on modified Blade Element Momentum (BEM) theory has been developed to maximize the energy harvesting capability.
Recently, the underwater glider has become one of the major workforces in ocean exploration because of its long endurance and low operational cost. The glider of this work is powered by a buoyancy engine, which can generate the buoyancy change to drive the glider to ascend and descend in the water. Horizontal forces are generated through hydrofoils, allowing the underwater glider to move in a sawtooth trajectory, which is shown in Fig.1.
Companies and organizations have already developed several commercial underwater gliders with electrical buoyancy engines, such as Slocum(Jones, Allsup, & DeCollibus, 2014), Seaglider (Eriksen et al., 2001), Spray (Sherman, Davis, Owens, & Valdes, 2001). To make the glider a permanent ocean resident, thermal gliders are proposed to use ocean thermal energy to drive the thermal buoyancy engine and drive the gliders up and down. As a good alternative to the electrical buoyancy engine which relies on battery power, the thermal buoyancy engine can harvest thermal energy of the ocean to increase the voyage of the glider by 3-4 times (Russ E Davis, Eriksen, Jones, & vehicles, 2002). For example, the pioneer Slocum glider with a thermal buoyancy engine developed by the Webb Research Corporation reached 40000km (Webb, Simonetti, & Jones, 2001).
