Autonomous
301
Part B | 12.1
12. Autonomous Underwater Gliders
Scott A. Jenkins, Gerald D’Spain
This chapter discusses the characteristics, design
considerations, and performance of autonomous
underwater (UW) gliders. These buoyancypropelled, winged vehicles can be categorized as:
(1) profiling gliders that traverse in bobbing trajectories to collect vertical profiles of ocean properties
and (2) cross-country gliders designed for pointto-point horizontal transport efficiency. Horizontal
transport efficiency is quantified by net transport economy and specific energy consumption.
The latter metric for a glider is equal to its inverse lift-to-drag ratio (also called finesse) and
is equivalent to the glide slope in steady-state,
nonturning glides. Increases in efficiency can be
obtained by:
1. Increasing the loaded mass (with larger buoyancy engines) and increasing the overall size of
the glider, which increases the glider’s speed
and maintain sufficiently high Reynold’s numbers to avoid the drag crisis.
2. Reducing the ratio of the total vehicle wetted
area to wing area, via use of flying wing or
blended wing body shapes, and
3. Increasing the wing aspect ratio, within structural strength and stiffness limitations.
Gliders have an intrinsic advantage in transport efficiency over conventional prop-driven
autonomous underwater vehicles (AUVs) due to the
simpler vortex dynamics of a wing versus a propeller. As a result, gliders can fly cooperatively
12.1 Concept............................................... 301
12.2 Hydrodynamics of Wings
Versus Propellers ................................. 305
12.3 Underwater Glider Attributes
and Limitations ................................... 306
12.3.1 Depth Unlimited Roaming.......... 307
12.3.2 Depth Limited Roaming ............. 307
12.3.3 2-D Station Keeping .................. 307
12.3.4 Payload/Cargo Delivery ............... 307
12.3.5 Level Flight Hybrids ................... 307
12.4 Optimal Size and Shape for Horizontal
Transport Efficiency ............................. 308
12.4.1 Net Transport Economy .............. 308
12.4.2 Size Factors ............................... 310
12.4.3 Shape Factors............................ 311
12.4.4 Glide Polar ............................... 313
12.5 Thermal Glider .................................... 318
12.6 Discussion and Conclusions .................. 319
References................................................... 320
with other winged vehicles or employ multielement wings to further improve transport efficiency.
Although a glider must change depth to move forward, these depth changes not only allow the
collection of vertical profiles of ocean properties,
but also enable the extraction of energy from the
ocean’s vertical temperature gradients (thermal
glider).
12.1 Concept
The underwater (UW) glider is a buoyancy-propelled,
winged vehicle, analogous to a glider in air. The mechanical power of locomotion needed to overcome the
drag on the vehicle as it moves through a fluid medium
is supplied by gravity in the form of net buoyancy (positive or negative). Horizontal motion using the vertical
force of gravity is made possible by the action of lift
produced by a wing that acts perpendicular to the trajectory of the vehicle. Therefore, horizontal translation
only occurs when the flight path is inclined at a glide angle (Fig. 12.1) that deviates from the horizontal plane in
the direction of the vertical net force of gravity (upward
for a positive net buoyancy and downward for negative
net buoyancy). Inclination of the flight path along some
glide angle allows the net hydrodynamic force of lift
and drag to balance the net buoyancy in steady-state
flight. The inclined flight path that produces this force
balance also gives rise to a net vertical motion.
301
Part B | 12.1
12. Autonomous Underwater Gliders
Scott A. Jenkins, Gerald D’Spain
This chapter discusses the characteristics, design
considerations, and performance of autonomous
underwater (UW) gliders. These buoyancypropelled, winged vehicles can be categorized as:
(1) profiling gliders that traverse in bobbing trajectories to collect vertical profiles of ocean properties
and (2) cross-country gliders designed for pointto-point horizontal transport efficiency. Horizontal
transport efficiency is quantified by net transport economy and specific energy consumption.
The latter metric for a glider is equal to its inverse lift-to-drag ratio (also called finesse) and
is equivalent to the glide slope in steady-state,
nonturning glides. Increases in efficiency can be
obtained by:
1. Increasing the loaded mass (with larger buoyancy engines) and increasing the overall size of
the glider, which increases the glider’s speed
and maintain sufficiently high Reynold’s numbers to avoid the drag crisis.
2. Reducing the ratio of the total vehicle wetted
area to wing area, via use of flying wing or
blended wing body shapes, and
3. Increasing the wing aspect ratio, within structural strength and stiffness limitations.
Gliders have an intrinsic advantage in transport efficiency over conventional prop-driven
autonomous underwater vehicles (AUVs) due to the
simpler vortex dynamics of a wing versus a propeller. As a result, gliders can fly cooperatively
12.1 Concept............................................... 301
12.2 Hydrodynamics of Wings
Versus Propellers ................................. 305
12.3 Underwater Glider Attributes
and Limitations ................................... 306
12.3.1 Depth Unlimited Roaming.......... 307
12.3.2 Depth Limited Roaming ............. 307
12.3.3 2-D Station Keeping .................. 307
12.3.4 Payload/Cargo Delivery ............... 307
12.3.5 Level Flight Hybrids ................... 307
12.4 Optimal Size and Shape for Horizontal
Transport Efficiency ............................. 308
12.4.1 Net Transport Economy .............. 308
12.4.2 Size Factors ............................... 310
12.4.3 Shape Factors............................ 311
12.4.4 Glide Polar ............................... 313
12.5 Thermal Glider .................................... 318
12.6 Discussion and Conclusions .................. 319
References................................................... 320
with other winged vehicles or employ multielement wings to further improve transport efficiency.
Although a glider must change depth to move forward, these depth changes not only allow the
collection of vertical profiles of ocean properties,
but also enable the extraction of energy from the
ocean’s vertical temperature gradients (thermal
glider).
12.1 Concept
The underwater (UW) glider is a buoyancy-propelled,
winged vehicle, analogous to a glider in air. The mechanical power of locomotion needed to overcome the
drag on the vehicle as it moves through a fluid medium
is supplied by gravity in the form of net buoyancy (positive or negative). Horizontal motion using the vertical
force of gravity is made possible by the action of lift
produced by a wing that acts perpendicular to the trajectory of the vehicle. Therefore, horizontal translation
only occurs when the flight path is inclined at a glide angle (Fig. 12.1) that deviates from the horizontal plane in
the direction of the vertical net force of gravity (upward
for a positive net buoyancy and downward for negative
net buoyancy). Inclination of the flight path along some
glide angle allows the net hydrodynamic force of lift
and drag to balance the net buoyancy in steady-state
flight. The inclined flight path that produces this force
balance also gives rise to a net vertical motion.