Autonomous Underwater Gliders 12.3 Underwater Glider Attributes and Limitations 307
Part B | 12.3
12.3.1 Depth Unlimited Roaming
In depth unlimited roaming, the glider is not confined to
a particular depth regime while transiting cross-country
in a deep ocean environment. Often such roaming will
require trans-basin round-trip excursions. The Seaglider
and Spray are among this functional class, being designed primarily for the role of gathering ocean vertical
profiles of water mass properties. Design adaptations
for such depth unlimited roaming require some or all
of the following capabilities: long range, cruise speeds
adequate to penetrate large-scale ocean circulation but
otherwise kept to a minimum to conserve onboard
propulsion energy, small-to-moderate payload volume,
minimized hotel loads, and deep dive capability with
neutral hull compressibility.
12.3.2 Depth Limited Roaming
This function requires cross-country capability within
a limited depth regime. This constraint arises when operations are required in the shallow water regimes of
the littoral zone, or when the vehicle must operate in
a prescribed sector of the water column such as a sound
channel or avoid penetration across the thermocline.
The Slocum has design adaptations for this role such
as its piston pump that allows it to rapidly reverse dive
direction in close proximity to the free surface or seabed
in confined shallow water areas. Useful design adaptations for this role include: flat glide slope (high L=D)
which simultaneously maximizes range for a minimum
number of dive cycles, high sprint speed capability to
penetrate strong coastal currents, small to moderate
payload volume, minimized hotel loads, rapid highresolution pitch and roll response to avoid broaching
or grounding in confined depth regimes, adequate flight
control authority for suppressing ocean-surface-wave
induced flight oscillations, and avoidance measures for
fishing trawlers.
12.3.3 2-D Station Keeping
Station keeping requires the ability to maintain position at a prescribed point in the ocean. Other than
the case of free drifting in stagnation flow or grounding on the seabed, underwater gliders must execute
depth excursions in order to maintain station at a fixed
latitude and longitude. Hence, the station keeping ability is two-dimensional (2-D) and is referred to as
2-D station keeping. All three profiling gliders have
demonstrated 2-D station keeping, some within a watch
circle of several meters for several weeks at a time.
Some station keeping roles may require the glider to
profile the water column at a fixed latitude and longitude, which might require maximum sprint and dive
speed. Other station keeping roles may involve the
glider maintaining station in a certain depth regime,
which would benefit from the glider having minimum
sink rate properties. In all cases, the glider needs adequate cruise speed to penetrate and hold station against
ocean currents. In addition, the glider may be required to hold station on the seabed, in which case it
must generate sufficient negative net buoyancy and/or
have provisions in its hull and wing shape for anchoring against currents. Other vehicle qualities for
station keeping would be long on-station capability,
small to moderate payload volume, minimized hotel
loads, rapid high-resolution pitch and roll response to
execute grounding maneuvers or maneuvers near the
seabed, adequate flight control authority when operating near the sea surface, and avoidance measures for
fishing trawlers.
12.3.4 Payload/Cargo Delivery
The stealthy, high endurance (long distance combined
with long duration) capabilities demonstrated by profiling gliders suggest that delivery of payloads and cargo
would be logical function when rapid delivery time is
not required. Among the most important characteristics for this breed of underwater glider would be the
ability to move large payloads/cargo over significant
horizontal distances while minimizing onboard energy
consumption (i. e., using minimal numbers of dive cycles). Winged structures such can fly cooperatively to
improve flight efficiency. Therefore, an UW glider can
be equipped with cargo-carrying exterior compartments
so that the total is more energy efficient in point-to-point
transport than the glider alone, as discussed later in this
chapter. This function may require both deep water and
depth-limited operational capability (high L=D) with
adequate cruise speeds to penetrate both large scale
ocean circulation and coastal currents. In addition, large
payload volume is required along with minimal hotel
loads.
12.3.5 Level Flight Hybrids
This concept is posed to compensate for the major
limitation of underwater gliders: the inability to maintain fixed depth in forward transit. This motor–glider
is a glider with an auxiliary motor-driven screw. Propdriven AUVs typically are ballasted for safety reasons
to be slightly positively buoyant and use either vectored thrust or dive planes to achieve level flight. The
motor–glider is a more efficient means for accomplishing the same force balance, using the lift from a high
aspect ratio wing to provide the compensating trim
Part B | 12.3
12.3.1 Depth Unlimited Roaming
In depth unlimited roaming, the glider is not confined to
a particular depth regime while transiting cross-country
in a deep ocean environment. Often such roaming will
require trans-basin round-trip excursions. The Seaglider
and Spray are among this functional class, being designed primarily for the role of gathering ocean vertical
profiles of water mass properties. Design adaptations
for such depth unlimited roaming require some or all
of the following capabilities: long range, cruise speeds
adequate to penetrate large-scale ocean circulation but
otherwise kept to a minimum to conserve onboard
propulsion energy, small-to-moderate payload volume,
minimized hotel loads, and deep dive capability with
neutral hull compressibility.
12.3.2 Depth Limited Roaming
This function requires cross-country capability within
a limited depth regime. This constraint arises when operations are required in the shallow water regimes of
the littoral zone, or when the vehicle must operate in
a prescribed sector of the water column such as a sound
channel or avoid penetration across the thermocline.
The Slocum has design adaptations for this role such
as its piston pump that allows it to rapidly reverse dive
direction in close proximity to the free surface or seabed
in confined shallow water areas. Useful design adaptations for this role include: flat glide slope (high L=D)
which simultaneously maximizes range for a minimum
number of dive cycles, high sprint speed capability to
penetrate strong coastal currents, small to moderate
payload volume, minimized hotel loads, rapid highresolution pitch and roll response to avoid broaching
or grounding in confined depth regimes, adequate flight
control authority for suppressing ocean-surface-wave
induced flight oscillations, and avoidance measures for
fishing trawlers.
12.3.3 2-D Station Keeping
Station keeping requires the ability to maintain position at a prescribed point in the ocean. Other than
the case of free drifting in stagnation flow or grounding on the seabed, underwater gliders must execute
depth excursions in order to maintain station at a fixed
latitude and longitude. Hence, the station keeping ability is two-dimensional (2-D) and is referred to as
2-D station keeping. All three profiling gliders have
demonstrated 2-D station keeping, some within a watch
circle of several meters for several weeks at a time.
Some station keeping roles may require the glider to
profile the water column at a fixed latitude and longitude, which might require maximum sprint and dive
speed. Other station keeping roles may involve the
glider maintaining station in a certain depth regime,
which would benefit from the glider having minimum
sink rate properties. In all cases, the glider needs adequate cruise speed to penetrate and hold station against
ocean currents. In addition, the glider may be required to hold station on the seabed, in which case it
must generate sufficient negative net buoyancy and/or
have provisions in its hull and wing shape for anchoring against currents. Other vehicle qualities for
station keeping would be long on-station capability,
small to moderate payload volume, minimized hotel
loads, rapid high-resolution pitch and roll response to
execute grounding maneuvers or maneuvers near the
seabed, adequate flight control authority when operating near the sea surface, and avoidance measures for
fishing trawlers.
12.3.4 Payload/Cargo Delivery
The stealthy, high endurance (long distance combined
with long duration) capabilities demonstrated by profiling gliders suggest that delivery of payloads and cargo
would be logical function when rapid delivery time is
not required. Among the most important characteristics for this breed of underwater glider would be the
ability to move large payloads/cargo over significant
horizontal distances while minimizing onboard energy
consumption (i. e., using minimal numbers of dive cycles). Winged structures such can fly cooperatively to
improve flight efficiency. Therefore, an UW glider can
be equipped with cargo-carrying exterior compartments
so that the total is more energy efficient in point-to-point
transport than the glider alone, as discussed later in this
chapter. This function may require both deep water and
depth-limited operational capability (high L=D) with
adequate cruise speeds to penetrate both large scale
ocean circulation and coastal currents. In addition, large
payload volume is required along with minimal hotel
loads.
12.3.5 Level Flight Hybrids
This concept is posed to compensate for the major
limitation of underwater gliders: the inability to maintain fixed depth in forward transit. This motor–glider
is a glider with an auxiliary motor-driven screw. Propdriven AUVs typically are ballasted for safety reasons
to be slightly positively buoyant and use either vectored thrust or dive planes to achieve level flight. The
motor–glider is a more efficient means for accomplishing the same force balance, using the lift from a high
aspect ratio wing to provide the compensating trim