Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

A Novel Energy Harvesting Mechanism and its Design Methodology for Underwater Gliders Using
Thermal Buoyancy Engines
Hongbo Hou, Weichao Shi, Abel Arredondo Galeana
Naval Architecture, Ocean and Marine Engineering, University of Strathclyde
Glasgow, UKYang SongSchool of Mechanical Engineering, Tianjin University
Tianjin, China

Companies and organizations have already developed several
commercial underwater gliders with electrical buoyancy engines, suchas Slocum(Jones, Allsup, & DeCollibus, 2014), Seaglider (Eriksen et al.,2001), Spray (Sherman, Davis, Owens, & Valdes, 2001). To make theglider a permanent ocean resident, thermal gliders are proposed to use
ocean thermal energy to drive the thermal buoyancy engine and drive thegliders up and down. As a good alternative to the electrical buoyancy
engine which relies on battery power, the thermal buoyancy engine canharvest 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).

ABSTRACT
Underwater gliders are becoming popular in ocean exploration. However,
the main development limitation of underwater gliders is still aroundenergy. This paper proposes a new-type energy harvesting mechanismand explores its design methodology for the gliders using thermalbuoyancy engines. With the temperature difference in the ocean, thethermal 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 withpatent 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.

However, thermal gliders are still limited by the battery power which
provides energy for their onboard payloads and attitude control systems.
On the other hand, both electrical and thermal gliders are limited by theslow speed, maximum 1knot, which often requires additional thrusters if
high-speed cruising is needed. Therefore, conversion between thermalenergy and electrical energy is needed. Current developments focus on
hydraulic-based systems, which use a mini generator in the high-pressure
oil pipeline trying to recover the energy while ballasting and deballasting. In 2016, SOLO-TREC was developed based on this principle(Chao, 2016). The Teledyne Webb Research consortium built theSlocum Thermal E-Twin with a similar power generation system fordeveloping global class gliders (Jones et al., 2014). The advantage of thiskind of power generation system is that it is simple and compact. The
disadvantage is that it is limited in energy output. For example, theenergy yield of the Slocum-TREC glider with 10kg PCM based on thisprinciple is around 6.5KJ per working cycle(Wang, Yang, & Wang,2020). At the same time, the hydraulic generator has to work in highpressure and low volume oil loop which results in low efficiency andhigh failure rate.

KEY WORDS: Underwater gliders; energy harvesting mechanism;
thermal buoyancy engine; turbine; BEMT.

INTRODUCTION
Recently, the underwater glider has become one of the major workforcesin ocean exploration because of its long endurance and low operationalcost. The glider of this work is powered by a buoyancy engine, which
can generate the buoyancy change to drive the glider to ascend anddescend in the water. Horizontal forces are generated through hydrofoils,
allowing the underwater glider to move in a sawtooth trajectory, whichis shown in Fig.1.

This research proposes a new type of energy harvesting mechanism
which can be applied to thermal underwater gliders aiming for highenergy yield. The mechanism uses a thermal buoyancy engine and afoldable power generation turbine. When the glider is in the powergenerating mode, the thermal buoyancy engine can use the thermalenergy to change its buoyancy to drive the glider vertically. During theascend and descend, the foldable turbine behind the hull will open andFig.1 the sawtooth trajectory of underwater glider

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